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Mares with pariparturient arterial rupture may bleed only into the broad ligament, or the bleeding can rupture the ligament and progress to hemoabdomen. With the former, mares usually manifest signs of colic, and with the latter, signs of hemorrhagic shock are dominant.
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Many cases of dystocia are amenable to intervention in the field, but the veterinarian should have access to a safe area for general anesthesia for controlled vaginal delivery and should follow the time-based guidelines for progressing from assisted delivery to controlled delivery.
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Uterine prolapse is amenable to management in the field but necessitates assistance and aftercare.
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The emergent problems arising in the pregnant mare usually have systemic ramifications and demand skilled monitoring and treatment.
In this second article on reproductive emergencies, conditions arising during parturition and in the periparturient period are discussed.
Uterine artery rupture
Periparturient rupture of arteries supplying the uterus and ovaries is a significant cause of morbidity and fatality in broodmares.
Dolente B, Sullivan E, Lundberg S. Postpartum complications in the mare, in Proceedings: 8th International Veterinary Emergency and Critical Care Society Symposium, San Antonio, 2002:790.
Internal hemorrhage associated with the reproductive tract should be a common rule-out for any periparturient mare with abdominal discomfort. In a 1993 study
of 98 mares that died in the postpartum period, 40 (41%) died of arterial rupture and internal hemorrhage. In a study of postpartum mares admitted to a referral hospital, urogenital tract hemorrhage was diagnosed in 27 of 163 (16.6%) mares, and those mares had a significantly shorter time from parturition to hospital admission, compared with mares referred for other reasons.
Arterial rupture has been diagnosed in younger mares and can affect mares of any parity, but multiparous older mares are most likely to be affected. In 3 retrospective studies,
revealed that 28% of mares older than 15 years died of periparturient artery rupture; when the subject mares were grouped as all mares older than 3 years, the percentage of those dying from arterial rupture was 9.9%. In 73 mares with periparturient hemorrhage that were admitted to a referral clinic, 10 mares (14%) had prepartum hemorrhage, whereas 63 (86%) had postpartum hemorrhage.
21 of 71 (29.6%) mares in a review of necropsy cases had hemorrhaged before parturition, 42 (59.1%) has hemorrhage during parturition, and 8 (11.3%) had hemorrhage after parturition. Arterial rupture is rarely seen at other times besides the periparturient period in mares. Not all cases of periparturient hemorrhage necessitate referral or even treatment: residual hematomas can be detected during routine transrectal palpation and ultrasonography of the reproductive tract in mares that never had signs of colic or hemorrhage after foaling.
Uterine Blood Supply
A review of urogenital tract blood supply is helpful in understanding the vascular injury. Arterial blood supply to the equine uterus is chiefly supplied by the uterine artery, which is a large branch of the external iliac artery, itself a part of the termination of the aorta. From the external iliac, the uterine artery (also called the middle uterine artery) courses toward the uterine horn in the mesometrium, or broad ligament. At the uterine horn, the artery branches cranially and anastomoses with the uterine branch of the ovarian artery, and branches caudally to anastomose with the uterine branch of the vaginal artery. The vaginal artery arises from the internal pudendal artery, which is a branch of the internal iliac artery; the vaginal artery and other branches of the pudendal artery supply the caudal part of the uterus and more distal parts of the tract.
As the uterine artery runs longitudinally along the uterine body and horns in the broad ligament, it diverges into numerous tortuous small branches and anastomoses that meet on the dorsal and ventral aspects of the horn and enable vascular stretching to accommodate uterine engorgement and elongation (Fig. 1).
Fig. 1Diagram of the uterus in situ, suspended by the broad ligaments. Arrow points to uterine artery. Notice how it communicates with the vaginal artery caudally and ovarian artery cranially as it supplies the length of the uterine horn. The small colon is seen suspended by mesocolon and lying dorsal to the uterine horns.
(Modified from: "Equine Reproduction" McKinnon A.O. & Voss J.L., Lea & Febiger, 1993. Used with permission from Lippincott, Williams & Wilkens.)
Serial Doppler monitoring of the uterine arteries has revealed that during the first half of gestation, the vasculature of the pregnant uterus undergoes transition from a high-resistance low-flow circulation to a low-resistance high-flow circulation accommodating large volumes of blood flow.
In combination with degenerative histologic change that develops in arterial walls with age, senescence, and cyclic stretching and shear stress, the situation is set up for arterial wall failure to increase with age and parity.
Upon arterial rupture, the extravasated blood can dissect along planes in the broad ligament, into the uterine or vaginal wall, into the space between the myometrium and serosal surface of the uterus, and occasionally into the uterine lumen. Arterial rupture can involve any of the arterial segments perfusing the reproductive tract, but most commonly involves the proximal segment of the uterine artery.
In a 2010 study of 31 mares with fatal broad ligament hematoma, 24 had uterine artery hemorrhage; in 18 of those the site of rupture was within 15 cm of the vessel’s bifurcation from the external iliac.
Gross lesions in the affected vessels included longitudinal fissuring of the arterial wall or outright transection of the vessels. Detection of the site of arterial wall failure during necropsy can be difficult given the size of the broad ligament and the extensive hemorrhage, but the site of arterial wall failure is typically a partial-circumference tear with jagged dark red edges and covered by blood clot and fibrin.
Toro Mayorga AG, 2015. Uterine artery rupture, an angiopathy of the reproductive system of the mare: occurrence and potential effects. Theses and dissertations – Veterinary Science. 24.
Underlying histologic degenerative changes in the arterial wall include atrophy of the smooth muscle layer, fibrotic change in the tunica media, and disruption or mineralization of the internal elastic lamina.
With the former, it has been postulated that displacement of the uterus to the left by the cecum during gestation causes an added degree of tension on the right broad ligament and its vessels.
Mares that have hemorrhaged can successfully and uneventfully carry foals to term in successive pregnancies.
Clinical Signs
Arterial rupture quickly elicits signs of some combination of colic and hemorrhagic shock. Colic signs can range from mild to severe, including flank-checking, stretching, flehmen, and rolling. Signs of hypovolemic shock include tachycardia, flehmen, muscle fasciculations or trembling, sweating, depression, disorientation, undirected vocalization, and collapse.
The initial extravasation of blood into the broad ligament stretches the ligament and its dorsal attachments and creates tension and pressure within its planes; this usually causes acute colic pain, but the pressure contributes to staunching of the bleeding as long as the ligament remains intact. If the backpressure causes blood loss to cease at this point, signs of colic may persist for several hours but typically respond to analgesics. Depending on the volume of blood pulsing into the broad ligament, the severity of this colic can be mild to moderate. The owner or caretaker will see some combination of the mare pacing or pawing, lying down and getting back up, sweating, splinting the abdomen, flank-checking, and having steam rise from the back and flanks. One feature of pain from broad ligament stretching is raising of the upper lip typical of the flehmen response.
If hemorrhage escapes from the confines of the broad ligament, uncontrolled bleeding into the peritoneal cavity will commence, with rapid deterioration of hemodynamic status and signs of shock predominating over signs of colic. Death may ensue rapidly. If the mare has been observed from the beginning, signs of pain often abate, whereas depression, trembling, agitation, and weakness will progress, with continued sweating, steaming, and lip-lifting. The gingivae become noticeably pallorous, sometimes to the extent that they cannot be blanched with a thumb to check capillary refill. In the words of one experienced clinician, the gums take on the dry sheen of “an old white porcelain sink” (Byars TD, personal communication, April 2007). The pupils are usually dilated. High heart rate (60–80 bpm or higher) is invariably observed, and rectal temperature is usually low or normal. Internal exsanguination can take place rapidly or over a period of hours. The tachycardia, pupillary dilation, and sweating arise autonomically because the acute volume loss leads to activation of the sympathetic nervous system. In many instances, the mare is already in a state of hemodynamic shock at the time the problem is first recognized and a veterinarian summoned; absence of previous colic is not grounds for dismissing arterial rupture and hemorrhage from the top of a list of differential diagnoses in this scenario. It is important to remember that this reproductive emergency can happen days to weeks before parturition.
Diagnosis
Physical examination: Experienced owners can come to quickly recognize the signs of uterine artery rupture: a pawing, sweating postpartum (most frequently) mare with lifted lip. Nevertheless, the veterinarian’s physical examination provides a database of findings that point to diagnosis and also provides the baseline values from which the patient can be seen to improve or worsen during serial monitoring. The examiner and holder should enter the stall with caution and with an assessing eye on the mare’s mental state and physical stability. A mare can be depressed, painful, disoriented, comforted by human presence, agitated by the same, or on the verge of collapse and death. Grasping her foal and removing it from the mare’s sight may cause a spike in anxiety that will upset a fragile stability and renew bleeding. During examination, the newborn foal should be quietly captured and held at the stall door, in close sight of the mare, but in a position to be removed from the stall quickly in the face of terminal excitation or abrupt collapse in the mare.
The examination must often be abbreviated in the interest of efficiency and safety; for instance, although rectal examination is part of full examination of a colicky animal and could confirm a hematoma in a broad ligament, in this situation it may not be advisable or safe for the mare or the examiner. Application of a nose twitch or other physical restraint can induce collapse, and advance of the examiner’s arm into the rectum induces the mare to respond with abdominal press, which can disrupt an early or partial thrombus in the damaged artery. These adverse occurrences are not mere theoretic concerns, and in the authors’ experience, it is possible to diagnose arterial internal hemorrhage without rectal palpation. Obtaining the temperature (often low or normal), heart rate (usually high but occasionally normal), and respiratory rate (usually high) can usually be accomplished. Physical parameters that serve as an index of circulatory status, such as skin turgor (often reduced), capillary refill (usually prolonged), arterial pulse quality (may be bounding but grows increasingly weak and “thready” as hypotension and hypovolemia approach the limits of compensation), jugular refill (usually prolonged), and the cutaneous temperature of the extremities (cool to cold) can usually be assessed quickly and without undue stress to the mare. Persisting tachycardia and the presence of vaginal hemorrhage have been significantly associated with outcome.
Laboratory values: Blood should be collected and submitted for complete blood cell count (CBC) and serum chemistry. If full laboratory services are unavailable in the emergent field setting, a simple packed cell volume (PCV) and total protein analysis and possibly lactate are helpful, even if only for comparison in the ensuing hours to days. In the peracute phase of hemorrhage, PCV and protein values are normal,
as the blood remaining within the circulation to be sampled is unaltered until hemodilution occurs as a result of body mechanisms to preserve blood volume and pressure. Over a period of hours to days, water is pulled from the interstitial and intracellular spaces into the vascular space, plus the thirst response is induced. If the mare survives long enough for these mechanisms to bolster or replace plasma volume, or if veterinary intervention includes administration of intravenous (IV) fluids, serial blood sampling will show increasing hemodilution, with hypoproteinemia and anemia. Hypofibrinogenemia is also common.
Splenic contraction is also stimulated by the sympathetic nervous response to hemorrhage, ejecting erythrocyte mass into the circulation to support oxygen-carrying capacity. This effect may bolster PCV values, and serial blood monitoring may reveal nadir values of protein that are more markedly low than those of PCV. Assuming hemorrhage ceases, the lowest values for PCV and protein are usually seen at about 48 hours after the onset of bleeding.
Findings of leukopenia/neutropenia on the hemogram suggest that the systemic inflammatory response syndrome (SIRS) is in play. Sepsis from translocation of bacteria from the hypoperfused gastrointestinal tract into the lymph nodes, liver, and bloodstream is one sequela of severe hemorrhage and impaired perfusion of the gut mucosa.
Increased values for serum urea nitrogen and/or creatinine are common in mares that are in the stages of surviving hemorrhagic shock. Decreased glomerular filtration and oliguria are common in hypovolemia. Liver values might also be high, reflecting hypoxic damage. Unlike with external hemorrhage, with internal hemorrhage icterus is common during convalescence because of heme recycling.
Normal blood lactate concentration in health is ≤2.0 mmol/L. When values increase in the setting of hemorrhage, it reflects a tissue shift to anaerobic metabolism and hence serves as an index of circulatory sufficiency. In hemorrhaging mares it is helpful to obtain an admission lactate level, and this can be run serially to determine the efficacy of resuscitation and maintenance support. When lactate values increase or remain high in the face of volume replacement with IV fluids, it is a useful indicator for blood transfusion. Mildly elevated values may be tolerated in the face of stabilization of other physical examination parameters.
Abdominocentesis is indicated when other differential diagnoses, such as uterine rupture or gastrointestinal disease, are suspected in place of or in addition to arterial hemorrhage.
Ultrasonography: Transabdominal ultrasonography is the quickest methodology for confirming hemoabdomen. Careful transrectal imaging can be useful when hemorrhage is suspected but confined to a site in the broad ligament. Transabdominal imaging can yield a wealth of information, even with a brief survey of the mare’s abdomen. Whether hemoabdomen is present, whether bleeding is ongoing and active, an approximation of the volume of blood that has been lost to the abdominal third space, whether bleeding has stopped and then resumed, and if resorption of extravasated blood has begun, all can be determined easily and quickly. The best transducer to use for transcutaneous evaluation of the abdomen is a 2.5- to 5.0-MHz macroconvex probe, but nearly any transducer can yield useful images, including a linear rectal probe. The author (K.S.) finds that applying warmed rubbing alcohol (70% isopropyl) to the ventral abdomen and sides precludes the need to clip hair and elicits no signs of resentment from the mares.
The presence of free blood in the peritoneal cavity has a dramatic and unique sonographic appearance, and is not a subtle finding. When bleeding is active, it is usually possible to find an area where the pulsing blood enters the abdomen with smokelike swirling and formation of curlicues in the echogenic fluid (Fig. 2).
Fig. 2Transabdominal sonogram of hemoabdomen in a mare with postpartum uterine artery rupture. Top of the image is ventral. The white curvilinear structures are colon segments buoyed in the free blood. The echogenicity of the gray fluid identifies it as highly cellular; the curlicue swirling pattern in the fluid and swirling motions seen in real time identify the fluid as blood with active arterial spurting.
The sonographic appearance of the abdomen changes with the stage of bleeding. When there is echogenic fluid (blood) accumulated ventrally with viscera floating several to many centimeters above, even in the absence of curliques or swirling appearance, this suggests that there is still active bleeding somewhere in the abdomen as once hemorrhage ceases, the third-space blood is resorbed fairly rapidly. Upon hemostasis, the cavitary blood rapidly separates into plasma and cellular components, and the fluid (serum) in this stage is hypoechoic to anechoic (Fig. 3). The plasma water is reabsorbed back into the circulation, proteins are returned to the liver for catabolism and recycling, and erythrocyte/hemoglobin Fe2+ and protein are also conserved and recycled. Scanning the mare in this stage as frequently as twice a day can reveal significant diminution of the abdominal fluid volume at every examination. After the acute phase of hemorrhage, when a mare has successfully been stabilized with volume replacement and analgesics, and is maintaining a stable if persistently high heart rate, bleeding may continue for several days as seen by persisting swirling in the abdominal blood, but the volume of blood loss will come to be offset by a commensurate rate of resorption, such that the mare’s vital signs and comfort level remain stable. Once active bleeding ceases, resorption commences and is fairly rapid.
Fig. 3Transabdominal sonogram of the abdomen of a mare with postpartum uterine artery rupture and hemoabdomen. Active hemorrhage has ceased, and resorption of the free abdominal blood is in process. The fluid remaining here is chiefly serum, which appears hypoechoic to anechoic. The spleen and several jejunal segments in cross section are seen buoyed in the fluid.
Systemic mean arterial pressure (MAP; 90–120 mm Hg in a healthy adult horse) drives rapid, voluminous extravasation through the ruptured vessel wall, and the drop in pressure is detected by arterial baroreceptors in the aortic arch and carotid bodies. Afferent neurons carry this information to the autonomic control centers in the brainstem, and this elicits a state of sympathetic nervous system outflow.
Fear, pain, exercise, and acute blood loss are all potent activators of the sympathetic fight-or-flight response. For clear reasons it is better to manage uterine hemorrhage at the farm and avoid trailering. However, if provision of the care and monitoring needed to manage this type of emergency is not available at the farm, transporting the mare to a hospital is warranted. Because of the unpredictability and sporadic nature of these cases, much of the information available to guide management of mares with uterine hemorrhage has been derived from retrospective case series involving hospitalized mares rather than from controlled studies.
The first step in providing care to an internally bleeding mare is to provide a quiet, low-stress space in which to work. This step means keeping the foal in immediate view or contact with the mare, yet close enough to the stall exit so that it can be removed if the mare becomes terminally agitated or collapses. Other horses should be kept away to avoid the mare taking up protective maneuvers that will increase blood pressure and disrupt initial coagulation.
The paradigm of intervention for trauma and massive hemorrhage in human medicine consists of would damage-control resuscitation, which consists of permissive hypotension, hemostatic restoration and blood product transfusion, and damage-control surgery. The concept originated in military medicine, and has progressed to also become the current management paradigm for massive bleeding in civilian settings.
Damage control surgery refers to initial laparotomy in a field setting to achieve vascular ligation and hemostasis, with temporary closure techniques used to close the abdomen. The patient undergoes blood transfusion and low-volume crystalloids for physiologic stabilization while being transferred to another location, where the abdomen is reopened and definitive laparotomy is undertaken. These methods yield higher survival rates than in patients in whom definitive laparotomy was the first-line intervention.
Although these measures were developed in human patients with internal hemorrhage from traumatic injury, and these types of studies have not been and likely will not be performed in horses, there is rationale for drawing on these concepts to treat horses with uncontrolled internal hemorrhage.
Arterial ligation during open-abdomen surgery is not feasible in the postpartum mare because of the poor anesthetic candidates represented by anxious, painful, hypovolemic, hypotensive, thousand-pound patients. Even if the mare survived anesthetic induction and the positioning into dorsal recumbency, the sheer volume of free blood in the peritoneal cavity, volume of the broad ligaments, and complex anatomy of the vasculature collectively make detection of the site of rupture difficult and time consuming at best. Therefore, the big picture for the veterinarian undertaking care of the internally bleeding mare is one of being limited to medical management of what is essentially a surgical problem, with an inability to use even the basic first-aid measure of applying pressure to the wound. Understanding this is important in managing client expectations and in implementing and revising interventions as patient status stabilizes or worsens.
Analgesics
For mares in which hemorrhage is contained in the broad ligament or pelvic canal, the treatment aims are to control pain and monitor serially to ensure the situation does not progress to hemoabdomen. In a retrospective study cited earlier in this article,
72 of 73 mares with periparturient hemorrhage required pain management. Providing analgesia and offering a laxative diet to avoid the need for gastric intubation may be all that is required in some mares. Common treatments include flunixin meglumine (1.1 mg/kg, IV), xylazine (0.2–0.5 mg/kg, IV or intramuscular [IM]), and detomidine (0.01–0.02 mg/kg, IV or IM). Alpha-2 agonist drugs have significant cardiac and vasomotor effects, including bradycardia and first- and second-degree atrioventricular block, together with a sustained period of increased peripheral vascular resistance.
These effects decrease cardiac output. These effects are well tolerated by healthy horses, but given the labile, sympathetic-dominated state of a hemorrhaging horse, the author (K.S.) finds it useful to use alpha-2 agonist drugs at lower dosages that may be a fraction of published formulary dosages. Butorphanol, a mixed mu agonist opioid, is also helpful; some twitching may be seen, but in painful horses the analgesic and sedative effects predominate and butorphanol provides significant analgesia when paired with an alpha-2 agonist. Dosage range is 0.01 to 0.03 mg/kg, IV or IM. Similar to the alpha-2 drugs, butorphanol given IM can be helpful in providing analgesia with less noticeable sedation. When opioids are administered several times a day, constipation should be anticipated, and the mare should be given a laxative diet. Restraining a hemorrhaging or newly stabilized mare with a nose twitch for nasogastric intubation should be avoided if possible. A useful approach is to give an initial combination of flunixin plus an alpha-2 agonist and butorphanol IV to gain a level of analgesia, then give additional doses of the latter two drugs IM at intervals thereafter if needed.
Fluids
The aims in stabilizing the mare with hemoabdomen and shock are more complex. The treatment goals are to provide partial volume replacement to a state of permissive hypotension, promote coagulation or impede clot lysis, control pain, and support oxygen-carrying capacity with blood transfusion if necessary and possible. The concept of permissive hypotension means providing sufficient perfusion to support vital functions but not restore normal MAP values and threaten a fragile thrombus at the site of arterial rupture. Volume support can be provided in the form of hypertonic saline, polyionic crystalloid fluids, plasma, and whole blood. Synthetic colloids such as hetastarch are useful in rapid expansion of intravascular volume but should be avoided in this scenario because of its potential negative impact on coagulation and the potential for renal tubular injury in the volume-contracted state. Some practitioners find careful use of synthetic colloids useful, but administration of these fluids have come under scrutiny and questioning recently.
In a mare that is unstable and near collapse from shock at initial evaluation, resuscitation is required. A bolus of hypertonic saline (7.2%; 2–4 mL/kg, IV) can be given, followed by balanced polyionic crystalloids. The optimum volume of fluids to administer in this setting has not been established by evidence-based medicine. With the goal of supporting circulation and critical functions, there is rationale in adopting commonly used resuscitation strategies but stopping short of using full attainment of euvolemia as the targeted endpoint. One method of providing resuscitatory support is to give a 20 mL/kg bolus of IV fluids and assess heart rate and other vital signs. Sequential boluses are given until indices of volume repletion are seen. In an internally hemorrhaging horse that presents in shock, an initial dose of hypertonic saline can be given, followed with an initial slow bolus of polyionic fluids. If the mare’s affect improves, heart rate stabilizes, and perfusion of peripheral tissues improves, this could be followed by no additional fluids, additional slow boluses at scheduled intervals, or a constant infusion of fluids at maintenance or submaintenance volumes. In addition to the risk of restored arterial blood pressure disrupting or dislodging a developing thrombus at the site of vascular rupture, overzealous administration of IV fluids also dilutes clotting factors, platelets, and oxygen-carrying capacity. Constant infusions are not always possible in the field setting, but can be useful for delivering antimicrobials and antifibrinolytic drugs. Indices to monitor for sufficiency of organ perfusion include heart rate, comfort level/affect, blood lactate, and urine output. The maintenance fluid requirement in healthy adult horses is 40 to 60 mL/kg/d,
and water consumption would be taken into account with this calculation.
Once hypertonic saline has been given and crystalloids have been started, if heart rate remains at or near the value before the hypertonic saline was given, there is continued sweating or signs of distress, gums are pallorous, or lactate is high or increasing (reference range, <2.0 mmol/L); these collectively suggest that increased tissue oxygen delivery is needed in addition to volume improvement. In this instance, transfusion of fresh whole blood transfusion (4–8 L, given over 1–4 hours) is warranted. Blood is an effective colloid that not only supplies plasma proteins and oncotic pressure but also erythrocytes and oxygen-carrying capacity. There is no single value for PCV that can be used as a trigger for blood transfusion in all cases. However, a steadily falling value, in conjunction with signs of unabated severe tachycardia, increasing blood lactate, and visual confirmation of continued bleeding on ultrasound, do provide grounds for transfusion. The decision is not a trivial one: fresh whole blood transfusions cost well upward of $1000 in many practices, and the exogenous blood administration can set the mare up for developing antibodies against future fetuses. Sometimes multiple transfusions will be needed over the course of several days. Packed cell volume and protein values usually reach their nadirs in 36 to 48 hours as bleeding slows and ceases while IV fluids and body fluid shifts dilute the remaining intravascular red cell mass and protein. The reader is referred to other texts for details of fresh whole blood transfusion and donor compatibility testing.
Administration of an antifibrinolytic or clot-stabilizing drug is also warranted in the mare with uncontrolled internal hemorrhage. A large meta-analysis of antifibrinolytics in acute severe hemorrhage in human patients revealed that administration of tranexamic acid within 3 hours of onset of bleeding improved overall survival in trauma and postpartum hemorrhage.
Effect of treatment delay on the effectiveness and safety of antifibrinolytics in acute severe hemorrhage: a meta-analysis of individual patient-level data from 40,138 bleeding patients.
The natural balance of procoagulant and anticoagulant processes that are ongoing in the vasculature in health can be tipped toward clot preservation during uncontrolled hemorrhage by administration of tranexamic acid (5–25 mg/kg IV every 12 hours) given as a slow IV bolus or ε-aminocaproic acid (40 mg/kg [20 g for an adult light-breed mare] diluted in 1 L saline and given over 30 to 60 minutes, followed by 20 mg/kg [10 g] given the same way every 6 hours). Both drugs are synthetic lysine analogs that slow fibrinolysis by competitively and reversibly binding to the lysine active site on the plasminogen molecule.
This action prevents activation to plasmin and thwarts the lytic action of plasmin on fibrin, stabilizing a polymerized clot and prolonging its duration. These drugs are usually given for 1 to 2 days, or as indicated by ongoing or resumed hemorrhage. Tranexamic acid has other properties that have been demonstrated experimentally that may have relevance in hemorrhagic shock. In addition to its antifibrinolytic properties, it is also a serine protease inhibitor, one action of which is to inhibit gut epithelial sheddases. Sheddases are activated by shock-mediated hypoxia, and attack syndecan-1, breaking down the mucosal barrier function. In one study,
intraluminal tranexamic acid mitigated intestine and lung injury secondary to hemorrhagic shock in rats. Also interestingly, administration of tranexamic acid is a known cause of nausea and emesis in humans and dogs, and of nausea in experimental rodents such as rats, which, like horses, are nonvomiters.
Prospective, controlled, blinded, randomized crossover trial evaluating the effect of maropitant versus ondansetron on inhibiting tranexamic acid-evoked emesis.
To the authors’ knowledge, this has not been reported in horses, but it is reasonable to observe mares receiving IV infusions of this drug for signs of discomfort or distress.
During the first 24 hours, heart rate and physical status should be frequently monitored. The mare is encouraged to consume a laxative meal and some hay, and analgesics are usually continued. Flunixin, butorphanol or another opioid, and alpha-2 receptor agonists all have a place in controlling pain. In the first one to several hours from the initial evaluation, most mares will respond to these measures with a decreasing heart rate (although usually not to normal range) that remains steady, a state of less distress and controlled pain, and evidence of improving hemodynamic stability. However, it is not unusual for a mare to appear improved for a period of time but then resume signs of decompensation and shock.
Antimicrobials
Antimicrobials are indicated in mares with hemoabdomen and shock. Hemorrhagic shock is an innately inflammatory condition, with cellular hypoxia resulting in accumulation of lactic acid and oxygen radicals and eliciting release of danger-associated molecular proteins (DAMPs). These mediators activate the SIRS response, and multiple organ failure occurs in many tissues, including the intestinal mucosal barrier.
Hypoxia during shock has a quick-onset permissive effect on microbial translocation across the intestinal mucosal barrier. This can manifest in serial blood monitoring as a developing leukopenia/neutropenia, although hemodilution from IV fluids also contributes to this effect. Another reason for antimicrobial support is that hemorrhaging mares cannot be turned out to exercise, depriving them of one of the most important mechanisms supporting uterine clearance and involution: normal physical activity. These mares are also usually not candidates for uterine lavage or administration of oxytocin to help remove luminal blood and residual fluids, at least initially. In select cases, a sterile tube can be inserted into the uterus and used to siphon fluids, but typically this is not resorted to until several days have passed.
Other Treatments
Prednisolone sodium succinate (500–1000 mg per adult mare, IV) is given by some veterinarians to mitigate the effects of shock.
Naloxone is a pure narcotic antagonist that targets all subclasses of opiate receptors (μ, κ, and δ) but has the highest affinity for μ receptors. In studies in both animals and humans, it increased MAP in both endotoxic and hemorrhagic models of shock.
Naloxone application in the shock patient is thought to derive from the assumption that endogenous opiates such as endorphins contribute to the pathophysiology of shock and the antagonizing action of naloxone mitigates these effects.
Scoggin CF, McCue PM. How to assess and stabilize a mare suspected of periparturient hemorrhage in the field. In Proceedings. Am Assoc Equine Pract, Orlando, FL, 2007:342–8.
but it is not thought likely to provide a significant hemodynamic benefit. The interplay between naloxone and butorphanol (which is a mixed μ agonist/antagonist) in horses when given concurrently is unknown.
Yunnan baiyao is a Chinese herbal preparation that is used as an adjunctive treatment of bleeding in veterinary and human medicine. In human and laboratory animal studies, it has been reported to decrease intraoperative blood loss, stimulate platelet function, and quicken clotting times as measured by the buccal mucosa bleeding test. In one study, it decreased template bleeding time in healthy anesthetized ponies.
Graham L, Farnsworth K, Cary J. The effect of yunnan baiyao on the template bleeding time and activated clotting time in healthy halothane anesthetized ponies, in Proceedings. 8th Intl Vet Emer Crit Care Soc Symposium, San Antonio, 2002;790.
The place of this herb in the treatment of uncontrolled hemorrhage in peripartum mares may find rationale in the results of these studies and by anecdotal observations of effect. Recent studies in healthy cats,
in which the hemostatic effects of the herb were evaluated with traditional coagulation tests, tests for von Willebrand factor (vWF) and platelet function, and thromboelastography, revealed no significant differences between treated animals and controls. The herb is purchased in powder form, and the published dosage is 8 mg/kg, given as an oral suspension made by adding water to the powder in which the product is supplied, every 6 to 12 hours.
Formalin has been used as a procoagulant treatment in the setting of uncontrolled peripartum hemorrhage. One controlled study
involving postcastration hemorrhage in one horse reported no benefit from IV formalin administration. Given the lack of evidence for any benefit and the availability of other methods of supporting the hemorrhage patient, it is hard to recommend this treatment, particularly if the hemorrhage is occurring in the prepartum mare. A published dosage is 30 to 150 mL of 10% buffered formalin in 1 L isotonic fluids.
and may be particularly indicated to support oxygen delivery in mares hemorrhaging during the prepartum period.
Summary: mares with life-threatening hemorrhage and shock can be stabilized and managed to survival and a good outcome, including future production of foals, although there may be increased risk of a second hemorrhagic event.
Dystocia
Dystocia is a significant problem at the equine industry level, ranking high on the list of parturition-associated deaths.
but parturition remains an event with a narrow window for successful intervention when it is needed. Normal parturition in the horse is a rapid event, the successful outcome of which results in the fetus exiting the uterus in an orchestrated sequence of events that has been characterized as explosive. Once the chorioallantois ruptures, the allantoic fluid exits and the fetus and amnion move into the birth canal. About 30 minutes is allotted for normal passage and transition of the fetus from residing in an aqueous environment and depending on placentally delivered oxygen to becoming a terrestrial animal dependent on a functioning pulmonary system. At 40 minutes from the time of chorioallantois rupture, the prognosis for survival of the foal decreases sharply.
Thus difficulties in any aspect of this parturitional process, or dystocia, constitutes a bona fide emergency. The emergent nature of dystocia has been underscored many times by the finding that the single most important factor determining whether the foal will survive or be lost is minimizing the duration of stage II labor.
Parturition can be considered as consisting of 3 stages: stage I refers to the premonitory hours to minutes when coordinated uterine contractions are beginning and intensifying, but the mare is not yet recruiting abdominal press in active labor and the chorioallantois has not ruptured. This stage may be recognized by signs of restlessness and mild colic: pawing, pacing, flank-checking, sweating, lying down and standing back up, urinating, and defecating. Some mares may show no signs of restlessness or discomfort. During stage I, the fetus, which has spent much of gestation in a dorsopublic position (foal lying nearly on its back, head toward the mare’s pelvis), is being rotated around on its longitudinal axis by myometrial contractions and the mare’s physical movements into a dorsosacral position commonly called the diver’s position. Getting the body rotated and the limbs extended requires both the myometrial contractions and a requisite level of viability in the fetus.
Once the fetus’ neck and forelimbs are extended so that the foal enters the pelvis and contacts the cervix, contractions are intensified and the chorioallantois ruptures, releasing the light-colored allantoic fluid from the reproductive tract. This water breaking denotes the beginning of stage II. During stage II, the mare usually lies down and begins bearing down with abdominal press to augment the uterine contractions. During passage through the birth canal, the foal is still dependent on the interdigitation between chorionic villi and endometrial crypts for placental oxygenation. The length of the birth canal in mares is only a few feet long, but traversing it can be the most dangerous journey a horse ever takes and the process is unforgiving when there is failure or significant delay at any point. Stage III begins once the foal has been delivered, and is a period of continued uterine contraction that results in expulsion of the chorioallantois and initial uterine involution. A combination of pharmaceuticals for sedation and general anesthesia plus equipment for fetal manipulations and resuscitation should be kept assembled in the veterinarian's toolkit for dystocia (Box 1).
Equipment and pharmaceuticals needed for equine obstetric interventions
obstetric (OB) chains or straps
Foal snare
Stainless-steel buckets
Sterile lubricant
Nonsterile lubricant—carboxymethylcellulose
Pump—sterilized
Sterile nasogastric tube—optimally reserved for obstetric use
Fetotomy wire
Xylazine
Detomidine
Butorphanol
Diazepam or midazolam
Ketamine
Banamine
Epinephrine and/or vasopressin
Ventipulmin oral gel
Self-inflating Ambu-type bag
Cuffed endotracheal tubes for nasotracheal intubation of fetus/foal- keep several sizes, ranging from 7- to 10-mm internal diameter for light horse breeds
Clean towels
Sterile OB sleeves
Optional: E cylinder tank of oxygen with demand valve
Examination of the Mare
When a client first calls with a dystocia, it is helpful to have them make some important observations while the veterinarian is traveling to the site. The clients should make note of the time at which the mare’s water broke and watch for any progress in the foal’s position relative to the vulva and any movement in the foal. Upon arrival, a brief history should be obtained while physical evaluation of the mare is begun. Chemical restraint should be provided if needed (xylazine or detomidine, with or without butorphanol), and the mare is examined with a scrubbed, disinfected, and lubricated bare arm and hand or with a sterile lubricated obstetric sleeve, with the aim of expeditiously determining what is preventing the foal’s progression through the canal. As much chemical restraint needed to facilitate safely working with the mare in the stall should be provided; because of the chance that the mare will abruptly go down during a contraction, the use of stocks is dangerous to the mare and examiner alike and is contraindicated in this situation. The foal’s presentation (normal is anterior longitudinal), position (normal is dorsosacral), and posture (normal is forelimbs, neck, and head extended) should be determined.
Abnormal presentations include posterior presentation and transverse presentation. Posterior presentation of the fetus may result in the hind limbs preceding the fetus into the birth canal. If the hind limbs are extended, the foal can be delivered without complication. However, posterior presentations are often complicated by flexion of the hips at the pelvic inlet, in which case the foal’s buttocks, tail, and possibly the hocks, but no extremities, will be palpated; this is a breech presentation. A transverse ventral presentation will result in an abnormal combination of hooves or extremities in the birth canal, and the fetus’s abdomen may be palpated. With a dorsal transverse presentation, no hooves or limbs will be in the birth canal, and the fetus’ dorsum may be palpated.
Postural abnormalities involve flexion of the limbs (all 4 should be in extension during birth), shoulders, neck, or head. Limbs may be flexed as a result of faulty placement upon entry into the birth canal (Fig. 4), or may be caused by congenital contracture, for instance, of the carpi or hocks. Although large fetal size relative to mare size can cause birthing difficulty, most cases of dystocia confronted by veterinarians at the farm are caused by postural abnormalities: flexion at the carpus or elbow joints, flexion of the shoulder joints, and flexion of the head or neck are all common postural abnormalities that cause dystocia.
Fig. 4Foal with muzzle exiting the vulva unaccompanied by extended forelimbs or front hooves. Palpation of the birth canal revealed both forelimbs in carpal flexion, wedged at the pelvic inlet. After a brief attempt at controlled vaginal delivery, a cesarean delivery was required to deliver the foal.
58 (11.2%) were dystocias, and of those 58 cases, 22.6% had body malpositioning, 41% had malposturing, and 31% had no abnormal positioning but required traction.
Evaluation of Fetal Viability
The next step is to determine whether the fetus is alive. Even if the head is still within the birth canal, this can be done by checking for a corneal reflex, withdrawal reflex of a limb, an anal pinch reflex in a posteriorly presented fetus, detection of peripheral pulses in any available body part, a pulse in the umbilicus, or a heartbeat. The fetal response to hypoxia is to reduce cardiac output and motor activity, an adaptive reflex that minimizes oxygen requirement. A hypoxic fetus may have sluggish pulses and absent reflexes, and in these instances it is not always straightforward to determine whether the fetus is alive or has expired.
Correction of the Dystocia
Once the nature of the problem and the status of the fetus have been established, the options for resolving the dystocia should be explained to the owner. Assisted vaginal delivery, controlled vaginal delivery, and cesarean section surgery are the options by which a viable foal can be delivered; fetotomy and euthanasia of the mare are the remaining options for resolution.
Assisted vaginal delivery refers to manipulation of the fetus to correct abnormal presentation, position, or posture with the mare sedated and standing or lying down. Controlled vaginal delivery refers to inducing general anesthesia and hoisting the hindquarters to facilitate repulsion and manipulations of the fetus (Fig. 5). With either assisted or controlled vaginal delivery, use of obstetric chains or straps will likely be helpful for forced fetal extraction. Taking into account how much time has elapsed since the water broke, the nature of the dystocia, the availability of a safe place for general anesthesia and sufficient equipment and help to hoist the mare, and the likelihood of resolving the malpositioning, the decision must be made whether to undertake correction of the problem on site or refer the mare to a hospital.
The decision should be made promptly, with referral being elected as an early option, not an endgame capitulation.
Fig. 5Controlled vaginal delivery in a mare with dystocia. The mare is hoisted into the Trendelenburg position to facilitate displacement of viscera toward the diaphragm and better enable attempts at fetal repositioning. If the mare has the option of cesarean delivery, personnel will be clipping the abdomen and beginning aseptic skin preparation while the operator is still in the process of attempting to deliver the foal.
Often a timed period of assisted delivery is attempted, followed by either induction of general anesthesia for controlled vaginal delivery or referral. For purposes of managing the case at the farm, if the mare’s hindquarters cannot be hoisted, there is little to no benefit from general anesthesia. If the foal cannot be delivered vaginally, cesarean delivery or fetotomy are the remaining options. Cesarean delivery should be done at a referral center.
For assisted vaginal delivery (AVD), because some degree of repulsion of the fetus back toward the uterus is nearly always necessary to correct limb or body position, preventing straining is helpful. In addition to sedation, 10 mL clenbuterol (Ventipulmin) syrup given orally will provide tocolytic effect. An epidural can also be administered. Administration of a caudal epidural will not terminate uterine contractions, but it induces anesthesia of the perineal region and will reduce the mare’s urge to strain in response to vaginal manipulations.
In addition, administration of epidural anesthesia may complicate recovery from general anesthesia, either at the farm if controlled vaginal delivery (CVD) on site is elected or at the referral hospital if referral is a possibility. Epidural anesthesia can be provided with a combination of lidocaine, carbocaine, or xylazine. Even with these aids, pushing the fetus backward into the tract is inherently risky for contusion, laceration, or rupture of the tract wall. Plenty of lubrication should be used. Carboxymethycellulose-based lubricant is preferred over polyethylene polymer powder, if possible, as leakage of the latter into the peritoneal cavity through tears or lacerations in the tract wall can cause severe peritonitis and death.
Frazer GS, Beard WL, Abrahamson E, et al. Systemic effects of a polyethylene polymer-based obstetrical lubricant in the peritoneal cavity of the horse. In Proceedings. 50th Ann Conv Am Assoc Equine Pract, Denver, 2004;50:484–7.
Once fetal manipulations are underway, a bystander should be tasked with monitoring the time that has passed. If significant progress has not been made after 15 to 20 minutes of effort, controlled vaginal delivery or referral are indicated. It must be kept in mind that survival of the foal is related to the length of stage II labor, and for a mare that has the option of referral the transport time must be figured into the 30 to 40 minutes (from the rupture of the chorioallantoic membrane) inside of which the foal’s chances are optimum. For a farm that is far from a referral center, the superior option is for prompt transport after a few minutes if fetal manipulations do not meet with success.
Hoisting the anesthetized mare’s hindquarters for CVD is helpful in several ways. The myometrial tone and abdominal wall contractions are relaxed by the anesthetic drugs, and the head-down positioning causes the abdominal viscera to fall toward the diaphragm, which creates more room in the abdomen for repulsion of the foal and fetal manipulation. It should be remembered that this positioning is unfavorable for the mare with regard to ventilation, and one person should be tasked with monitoring the mare’s respiratory rate and mucus membrane color while the foal is being extracted.
Posterior presentation dystocias can be very difficult to resolve, and certain types of malpostures are also notoriously difficult to correct. Ventral flexion of the neck, such that the neck and head are beneath the forelimbs; lateral flexion of the neck; and bilateral shoulder flexion can be particularly difficult to resolve without cesarean delivery. If 15 minutes of working to manipulate fetus does not yield progress and referral to a hospital is an option, the mare should be tranquilized and transported.
The reader is referred to detailed guides for correcting specific malpositions or malpostures.
EXIT is an acronym for ex utero intrapartum treatment during a prolonged stage II and refers to supporting the foal in the birth canal with oxygen while efforts are being made to accomplish its delivery. First reported in humans around 1989
In brief, the foal is nasotracheally intubated and ventilated while it remains in the birth canal. Having several sterilized tubes, ranging from 7 to 10 mm in internal diameter and 55 cm in length, will accommodate most light-horse foals. The technique is relatively straightforward if the foal’s head is exteriorized; the extended posture of the head and neck facilitate advancement of a tube into the airway rather than the esophagus, and the upper part of the neck can be palpated during the procedure to help ensure proper placement. The procedure can require technical skill and necessitates cooperation between the person or persons working on fetal mutations and those providing ventilations. Although it is not necessary for support of the fetus, the EXIT technique’s usefulness can be enhanced by inserting a capnograph between the nasotracheal tube and self-inflating bag used to provide breaths. Monitoring end-tidal CO2 (ETCO2) is useful because the first few lung inflations induce conversion of placental circulation to pulmonary circulation,
and CO2 is delivered to the lungs for removal. In a healthy neonate or one that is responding favorably to cardiopulmonary resuscitation, ETCO2 levels are in the range of 40 to 60 torr. Readings in the range of 8 to 20 torr indicate severe compromise and reduced cardiac output, and deceased foals will have no ETCO2. The benefit of supporting the foal with ventilation lies in removing some of the need for haste, and turns an emergent situation into a more controlled event. However, although the procedure provides oxygen across the blood-alveolar interface, placental oxygen transfer is permanently reduced, so ventilation should be continued until the foal is delivered. Attaching the breathing bag to an oxygen line is helpful, but not necessary.
Postdelivery Care
Once the foal has been delivered, resuscitation should be provided as needed. Specifics or neonatal foal resuscitation are beyond the scope of this article. The reader is referred to other publications for details of advanced resuscitation.
The mare should be carefully examined internally and allowed to investigate and bond with the foal. Depending on the rigor of the efforts to reduce the dystocia, the length of time manipulations were being performed, and resulting abrasions or other injury to the reproductive tract, antimicrobials along with a nonsteroidal anti-inflammatory drug (NSAID) for comfort are often warranted. Dystocia is a risk factor for retention of the fetal membranes, and the mare should be monitored for this complication.
Summary
Overview of principles useful in attending the mare with delayed stage II labor:
1.
The situation is emergent: examine mare, determine the problem preventing delivery, assess the premises and assistance available
2.
Explain options to owners: AVD, CVD, or cesarean delivery for a live foal; fetotomy if foal is deceased.
a.
Commence AVD, allow 15 to 20 minutes for successful delivery or significant progress
b.
If AVD unsuccessful, CVD is the next step. If mare has a referral option, refer for CVD at hospital so can proceed to cesarean delivery if unsuccessful. Otherwise commence CV at farm.
c.
If CVD on site is unsuccessful, refer for surgery or perform fetotomy.
3.
Manage expectations, explain the range of possible outcomes and costs, communicate with clinicians at referral facility.
4.
If dystocia resolved and foal delivered at farm, tend to foal resuscitation needs, especially if mare was anesthetized for CVD. Examine mare’s reproductive tract for vaginal and uterine trauma. Prescribe antimicrobials and NSAIDs. Monitor for retained fetal membranes, and plan intervention beginning around 3 hours postpartum if indicated.
5.
Evaluate placenta for completeness once passed.
Uterine prolapse
Prolapse of the uterus following parturition is an infrequent but dramatic emergency that can lead quickly to shock and fatality if movement of the uterus out of the abdominal cavity causes vascular rupture in the broad ligaments. The marked relaxation of the uterus’ supporting structures and all the structures in the pelvis, including the bladder, urinary sphincter, rectum, vulva, and pelvic musculature, is an adaptation for parturition, but facilitates prolapse if there is excessive straining or tension. Reported implicating factors include dystocia, retained fetal membranes, excessive oxytocin administration, abortion, straining because of other causes, colic, and cribbing.
The extent of prolapse can vary: the uterus may evert through the cervix only into the vagina, or may exit the vulva completely (Fig. 6). Rarely, the cervix also prolapses. The greater the degree of prolapse, the greater the tension on the broad ligaments and the chance of vascular rupture. Prolapse of the uterus from the abdominal cavity is occasionally complicated by accompanying prolapse of the bladder. If the uterus had a full-thickness rent in the wall, it is possible that intestinal segments will be exteriorized with the uterus. The relentless straining occasionally everts the bladder through the urethra such that the bladder will be seen in the vestibule or hanging from the vulva along with the uterus.
Fig. 6Prolapsed uterus in a postpartum mare. The organ has everted and exited the vulva, and the endometrial surface is exposed.
(Courtesy of Dr. Peter Morresey, BVSc MVM MACVSc DipACT DipACVIM CVA, Kentucky.)
If appropriate in light of the owners’ or caretakers’ experience level, when the veterinarian is summoned for a prolapse (client photographs sent via text are helpful), he or she can give instructions for a clean sheet or a large plastic bag to be procured and placed underneath the exteriorized tissues, whether the mare is standing or recumbent. The caretakers can start surface irrigation of the uterus with warm water or dilute povidone solution to remove gross contamination while the veterinarian is in transit. Elevating the uterus to the level of the pelvis by placing it on a clean sheet or plastic and supporting it on a cart or table, if the situation allows, removes the tension on the uterus and broad ligaments and will give the mare immediate comfort.
Upon arrival, the physiologic state of the mare should quickly be assessed and analgesia and adequate sedation provided. Antimicrobials should also be given. Taking the time to administer an epidural anesthetic will help reduce straining and facilitate working with the exteriorized tissue. However, anesthesia of the hindquarters is contraindicated if general anesthesia is needed. If there is an option to refer the mare to a surgical facility if standing correction is not successful, sedation and a tocolytic may be given, but the referral surgeon should be consulted before an epidural is given. In addition, securing venous access with a catheter will make it easier to extend the sedation or have an assistant administer other medications at the veterinarian’s direction.
Although time is of essence in replacing the uterus, it is important to examine all the exteriorized tissue for a laceration or rent, and to rule out exteriorization of any extrauterine structures such as the bladder and intestinal segments. The exposed tissues should be lavaged with sterile saline to remove blood and surface contaminants, and this also helps enable identification of the various structures that have prolapsed. The straining can also cause the bladder to evert through the urethra and exit the vulva, with the everted mucosal surface and ureteral openings seen. If the prolapse has been in place long enough for venous congestion and edema to develop, differentiating between the engorged endometrium and rectal prolapse, or identifying eviscerated intestine or bladder, is not always straightforward. A prolapsed bladder should be rinsed with saline and protected from injury during the manipulations to replace the uterus, and carefully replaced through the urethra after the uterus has been replaced. Appearance of the noneverted bladder into the vestibule or outside the vulva indicates extrusion through a full-thickness rent in the vagina or perineum.
Retention of fetal membranes (RFM) is common with uterine prolapse, and the weight of the membranes exacerbates (and may have precipitated) the prolapse and will complicate the efforts to replace the uterus. If they cannot be removed with gentle tension, the bulk of the membranes can be trimmed with a scissor, leaving a long enough tag to enable detection of the stub of retained membranes once the uterus is back in situ. If tears in the uterus are detected, they should be closed with absorbable suture material in a double-layer inverting pattern before beginning reduction of the prolapse.
With the cleansed uterus supported at the level of the pelvis, the tip of the uterus is identified. Using the flat of the fingers or softly rounded fists for even distribution of pressure, the tip of the uterus is pressed into the vagina and through the cervix. As the tip of the uterus reenters the abdominal cavity, the organ’s weight will help retract the remaining portions by gravity. Congestion and edema make the uterine tissue more friable, and great care and patience must be used. Keeping the uterus inside a plastic bag and manipulating it through the bag can help reduce the likelihood of perforating the wall with hands or fingers.
Once the organ is replaced, it is important to ensure that both horns are fully everted; intussusception of a horn tip will lead to renewed straining, colic, and possible reprolapse of the entire uterus. Palpation and ultrasonograohy can be used to appreciate the status of the horn tips, but it can be difficult or impossible to manually evaluate the full extent of the horns, particularly when the uterus is flaccid. Once the uterus is back in place, the mare can be given 3 to 5 L of a crystalloid fluid with 250 to 500 mL of 23% calcium gluconate, and a low dose (10–20 units) of oxytocin IV or IM to promote myometrial tone. If the extent of the horns cannot be palpated to confirm they are fully everted, a well-lubricated sterile speculum can be advanced into each horn and used as an extension of the operator’s arm to gently push against the horn tips. Glass beverage bottles can serve the same function, as can a rectal sleeve, tightly distended with fluid or air and covered with sterile lubricant, and advanced into each horn. Uterine lavage with a high volume (3–10 L) of sterile warmed fluids can also be used to reexpand the uterine body and horns while also diluting and carrying out contaminants; this can be followed with antibiotic infusion into the uterine lumen and serial dosing with oxytocin to help maintain tone and prevent sequestration of fluids. Until it is certain that straining can be controlled, it is advisable to place retaining sutures in the vulva with umbilical tape or heavy suture material; the suture should leave the ventral aspect of the vulva open so as not to impair urination.
If the uterus is found to have a full-thickness laceration or rent, once the prolapse has been reduced, the mare must be evaluated for peritonitis, on site and over the ensuing few days. Similarly, if any intestinal structures are involved with the prolapse and replaced into the peritoneal cavity, once the uterine prolapse has been reduced, the mare is a candidate for referral to a hospital.
Barring complications that warrant referral, the mare’s treatment regimen for the days following prolapse should include NSAIDs, systemic antimicrobials, a laxative diet, and close monitoring. The attending veterinarian should be vigilant for signs of uterine artery hemorrhage and peritonitis following correction of the prolapse. A protocol for retained fetal membranes is necessary if tags of placental tissue were bound to the endometrium. Ultrasonography and palpation of the reproductive tract per rectum enable confirmation that the uterus is involuting, rather than remaining flaccid and sequestering luminal fluid. Uterine lavage should be withheld if the uterine wall was sutured, but luminal fluid can be siphoned. Some veterinarians give intrauterine infusions of antimicrobials. A daily CBC for several days will facilitate monitoring of the white cell count as an indicator of systemic inflammation and the SIRS response that could arise with endometritis, metritis, or peritonitis.
Any of these complications can be anticipated to result in the downstream complications of hypogalactia, laminitis, and founder. Digital pulses should be closely monitored as part of serial daily physical examinations.
Summary: Examine mare to determine physiologic status, and administer sedation, analgesia, an NSAID, and antimicrobials. Elevate the uterus and irrigate with warm water or dilute povidone in saline to remove surface contamination, and inspect the prolapsed tissue to determine whether the bladder or intestine is incorporated. Suture rents in the uterine wall before beginning replacement. Have assistants hold the uterus elevated to the level of the pelvic brim while it is methodically replaced, tip first, through the vagina and cervix. General anesthesia and hoisting the hindquarters as for controlled vaginal delivery will facilitate replacement of the prolapse if standing correction was not successful. Ensure the position of the horn tips by palpation or ultrasonography. Prolapse may cause broad ligament vasculature to rupture, leading to a clinical picture of internal hemorrhage in addition to the prolapse. Peritonitis complicates the convalescent period if a full-thickness rent was found.
Postpartum colic
Signs of colic in a recently foaled mare can be normal and self-limiting, as with third-stage labor contractions or mild postpartum constipation. However, colic in the postpartum period can persist and develop into an emergency clinical entity. Signs of abdominal pain in this setting warrant thorough evaluation of the gastrointestinal tract and the urogenital tract, as the clinical signs can be similar. Moreover, mares with postpartum colic do not infrequently have problems requiring attention in both tracts. Particularly in a mare that had recent dystocia, injuries in the reproductive tract, intestinal tract, or both may manifest in the hours to several days following parturition. The most common serious conditions causing colic in a postpartum mare include uterine artery rupture and bleeding into a broad ligament, bleeding into the abdomen, uterine atony with gross fluid distension, intussuscepted uterine horn tip, metritis-sepsis-SIRS complex, intestinal tract injury, uterine rupture and peritonitis, and intestinal displacement or volvulus.
All of these conditions have a high potential to trigger activation of the systemic inflammatory response and culminate in multisystem tissue injury, particularly laminitis. Therefore, mares with any of these problems merit a full clinicopathologic database, setup of a hospital-level treatment regimen if they will be managed at the farm, and close monitoring for multiple days after the primary problem has been resolved.
The authors approach first evaluation of an uncomfortable postpartum mare with a comprehensive physical examination, including palpation of both the gastrointestinal structures and the urogenital tract per rectum, and speculum examination of the birth canal. If signs of toxemia are observed (any combination of fever, hypothermia, tachycardia, altered mucus membrane color, bounding digital pulses, and indicators of compromised circulatory status such as low skin turgor, poor jugular refill, poor peripheral arterial pulse quality, and cold extremities) in the physical examination, ultrasound imaging and blood work are also performed.
Arterial rupture with hemorrhage into a broad ligament or into the abdomen has been discussed. With the former, diagnosis is based on rectal palpation and detection of the enlarged broad ligament, with ultrasound imaging confirming the problem if helpful. Affected mares can be quite painful. The author (K.S.) finds multimodal analgesia helpful in mares with severe or persistent discomfort, based on a combination of flunixin meglumine, butorphanol, and an alpha-2 agonist at routine dosages given IV initially and followed up with serial doses of butorphanol and the alpha-2 drug given IM afterward to maintain a reasonable level of comfort. Serial monitoring is indicated to ensure that bleeding into the broad ligament does not proceed to uncontrolled bleeding into the abdomen. The mare should be offered a laxative diet for 2 to 3 days to minimize the need for straining to defecate while the hematoma organizes and matures.
Intussusception of the tip of a uterine horn should be considered if the mare has or recently had retained placental membranes. Signs of colic may be accompanied by repeated tenesmus. The straining response to the inverted horn tip can result in prolapse of the uterus, bladder, rectum, or small colon. The uterine lumen should be examined manually and the endometrial surface of each horn palpated. If the extent of the horns can be reached, an inverting horn tip can be felt telescoping into the lumen of the horn. In the immediate postpartum period when the uterus is still dilated, it can be beyond the examiner’s reach to digitally evaluate the full length of the horns. The uterus should also be palpated and imaged transrectally. The sonographic view of an inverted horn is the well-described target lesion or image of 2 concentric circles of tissue as is seen with intestinal intussusception. Retained tags of fetal membranes may also be seen in the inverting horn. If the uterus has not involuted and the horn is too long for the examiner’s fingers to reach to the tip, a well-lubricated glass speculum, glass bottle, or palpation sleeve filled and distended with air or fluid can gently be advanced into each horn and used as an extension of the arm. The uterus can also be lavaged with a moderate volume of sterile saline (3–10 L) to distend and evert the horn tips. Resolution of the intussuscepted tip should be confirmed with palpation and/or ultrasound. Failure to restore the horn tip to its proper everted state elicits continued straining, which can result in consequences that become the new emergency, in particular prolapsed uterus or rectum. Rectal prolapse that progresses to small colon prolapse is usually fatal because of tearing of the mesocolon, abdominal hemorrhage, and disrupted blood supply to the lower small colon (Fig. 7).
Fig. 7Postpartum mare in which continuous straining led to rectal and small colon prolapse. Sonographic imaging of the mare’s abdomen revealed hemorrhage from mesenteric vessel tearing.
Uterine atony and sequestration of luminal fluid is common following dystocia, hydrops, and in any postpartum scenario when a mare is not allowed free movement following parturition, including mares that are stalled with a hospitalized foal; those with uterine artery hemorrhage, in which restriction of movement is an important part of management; or mares that underwent peripartum surgery. Whatever the cause, mares with accumulation of large volumes of fluid in the uterine lumen usually have signs of vague malaise, mild colic, and lethargy. Rectal palpation or transabdominal ultrasonography easily reveals the fluid-distended uterus, with fluid that is echogenic. Treatment consists of removing the fluid by sterile uterine lavage or careful siphoning. Serial doses of oxytocin (10–20 units, IV or IM, every 6 hours or according to veterinarian preference) will help maintain myometrial tone, which prevents further sequestration of fluid. Some veterinarians administer an antibiotic infusion into the uterine lumen following uterine lavage or siphoning, as adjunctive treatment. Mares will likely already be receiving a broad-spectrum antimicrobial regimen because of dystocia or other problems, and this should be continued until uterine tone improves to a normal postpartum state and the mare can be hand-walked or turned out for exercise. NSAIDs should also be given for the same duration. Digital pulses should be monitored closely during the treatment interval. A CBC performed during this time may reveal leukopenia with neutropenia, a finding that points to activation of the systemic inflammatory response to translocating bacteria. At the authors’ practice, low white blood cell count in a postpartum mare being treated for periparturient complications of any etiology may prompt prophylactic measures for laminitis, including immersion of the front feet in ice boots several times daily and application of sole support pads and bandages between icing treatments, in addition to addressing the source of sepsis.
Metritis/sepsis/SIRS complex is a serious complication of parturition that can lead to life-threatening complications in the affected mare. This complication can arise as an extension of postpartum uterine atony and fluid sequestration as mentioned previously. Colic is not the primary clinical sign, but the inappetance, depression, and vague appearance of abdominal malaise can mimic gastrointestinal colic, and presumed colic may be what prompts the client’s call. One of the most common postpartum diseases,
metritis refers to infection of deep layers of the uterine wall, not just the endometrial surface, and is most frequently seen in the aftermath of dystocia and retained fetal membranes.
Other scenarios that have been reported in mares with metritis are uterine trauma, autolysis of residual placental tissue, uterine inertia, excessive lochial accumulation, abortion, normal foaling in unsanitary conditions, and fetotomy.
Delayed involution and uterine atony allow accumulation of lochial fluid, which, together with autolyzing debris from retained fetal membranes or inflammatory fluid from uterine injury, creates an incubation environment for bacteria. Translocation of bacteria and toxins across the uterine wall leads to sepsis and activation of the SIRS, with the attendant downstream complication of laminitis. Clinical signs of depression, inappetance, and fever show up in the first 7 to 10 days following parturition.
If strands of residual fetal membranes are protruding from the vulva, the association is straightforward. With or without retained tissues, vulvar discharge is often present, may or may not be voluminous, and may have a fetid odor.
Digital pulses may already be abnormally strong at the time of initial examination.
Metritis is diagnosed by physical examination, ultrasound imaging, and culture of uterine fluid. Both transabdominal and transrectal ultrasonography will reveal fluid-filled uterine body and horns, sometimes with edema and thickening in the uterine wall, and careful imaging of the horns may show tags of retained fetal membranes (Fig. 8). A sample of the uterine fluid submitted for aerobic and anaerobic culture will identify organisms present and aid in making antimicrobial selections, but an empirical broad-spectrum regimen with activity against gram-positive and gram-negative bacterial species should be started immediately even before culture and sensitivity results are available. Streptococcus spp and Escherichia coli are frequently isolated, along with the anaerobic species Bacteriodes fragilis and Clostridium spp.
of bacterial isolates from 45 mares with metritis, the most frequent gram-negative pathogens were E coli, Klebsiella spp, and Enterobacter spp, and the most frequent gram-positive pathogens were Streptococcus zooepidemicus, other Streptococcus spp, Enterococcus spp, Citrobacter spp, and Staphylococcus spp. Strains of E coli were the most common pathogen isolated. In that study, there were more (28%; 62%) mixed infections than single-growth infections (17%; 38%). Interestingly, the penicillin + gentamicin combination was only appropriate for 65% of the mares and a trimethoprim-sulfonamide combination was only appropriate for 49%. Given that these are among the most common first-pick empirical treatments, culturing the uterine fluid is probably worthwhile. The pillars of treatment of metritis and the sepsis/SIRS complex are antimicrobials, uterine lavage, NSAIDs, and oxytocin. A parenteral combination of a β-lactam antibiotic with an aminoglycoside usually covers the mixed population of bacteria, and the possibility of anaerobes’ presence merits addition of oral metronidazole to the regimen, at least until culture results are known. Some veterinarians also add intrauterine antibiotic infusions to the parenteral drugs.
Oxytocin is helpful in providing myometrial tone so that luminal fluid is expelled and further accumulation is minimized. It may also help release remaining fetal membrane tags. Other important components of treatment are aimed at the systemic inflammatory response driving organ injury and laminitis. The laminitis associated with metritis and with peritonitis from uterine rupture can be exceptionally rapid and devastating,
with rotation and sinking of the distal phalanx already developed at the time of initial examination. Therefore, many veterinarians include plasma known to contain anti-endotoxin antibodies, IV polymyxin B, IV or oral pentoxifylline, and IV lidocaine infusions as adjunctive anti-inflammatory treatment measures. In addition, the veterinarian should consider incorporating icing of the feet and applying sole-supporting hoof wraps or pads into the management protocol immediately, even prophylactically, if digital pulse quality is normal at the time of examination. Frequent checking of digital pulse quality, hoof wall warmth, and the coronary band area for softening or depression is an important part of the daily physical examination. CBC can be monitored daily during the first part of treatment for ensuring the leukopenia/neutropenia associated with the endotoxemia is responding to treatment. Uterine lavage should continue for as long as retained tissue tags are present, as lavage dilutes and carries out the inflammatory fluid and bacterial load. When retained tissue is no longer evident and peripheral blood white blood cell count returns to reference range, it is usually safe to taper off the laminitis-protective treatments in mares that did not develop digital pain. Mares that did sustain laminar injury as a complication of metritis/sepsis/SIRS are likely to be orthopedic patients and require treatment of laminitis for some time after resolution of the metritis. In some instances rotation and sinking are so rapid and severe that the mare is a euthanasia candidate even if the metritis resolves.
Fig. 8Transabdominal sonogram of a uterine horn in a mare with metritis and uterine atony approximately 60 hours after foaling. The uterine wall is thickened (arrow), and edema can be seen in its layers. The luminal fluid (∗) is echogenic, indicating high cellularity, but is not swirling, indicating that it is not active hemorrhage. The clinical picture was one of lethargy, fever and other signs of systemic inflammation, and abdominal malaise rather than of hemorrhagic hypovolemia and shock.
Uterine laceration and rupture are thought to arise from fetal limb movements, the mare straining against a fetus with impaired movement through the birth canal, or as an accident of manipulations in an assisted birth. It is not surprising when uterine injury is a sequela of dystocia, but uterine rupture or tear also happens in mares that had apparently normal parturitions. In a 2003 retrospective study
Sutter WW, Hopper S, Embertson RM, et al. Diagnosis and surgical treatment of uterine lacerations in mares (33 cases). In Proceedings. 49th Ann Conv Amer Assoc Equine Pract, New Orleans, 2003;357–9.
of 33 mares with postpartum uterine rupture, only 10 had had dystocia or an assisted delivery; the other tears had occurred spontaneously during apparently normal parturitions. History of recent foaling, signs of peritonitis, and results of abdominocentesis are the basis of diagnosis; palpating the uterus per vaginum is unsuccessful at revealing the rent more often that it is successful.
Sutter WW, Hopper S, Embertson RM, et al. Diagnosis and surgical treatment of uterine lacerations in mares (33 cases). In Proceedings. 49th Ann Conv Amer Assoc Equine Pract, New Orleans, 2003;357–9.
Rents in the uterine body are more likely to be detectable by palpation, but rents in the horns are significantly more frequent and are not frequently detected by palpation.
Sutter WW, Hopper S, Embertson RM, et al. Diagnosis and surgical treatment of uterine lacerations in mares (33 cases). In Proceedings. 49th Ann Conv Amer Assoc Equine Pract, New Orleans, 2003;357–9.
Although not borne out by all studies, the 2 recent large retrospective surveys both reported a strong preponderance of tears in the right uterine horn, compared with the left.
Sutter WW, Hopper S, Embertson RM, et al. Diagnosis and surgical treatment of uterine lacerations in mares (33 cases). In Proceedings. 49th Ann Conv Amer Assoc Equine Pract, New Orleans, 2003;357–9.
Diagnosis is typically made on days 1 through 3 following parturition, as the mare develops the clinical features of peritonitis. Depression, tachycardia, and leukopenia on blood work were the most common signs in the 2003 report; across the collection of retrospective reports, the most common presenting signs are some combination of depression, inappetence, reduced borborygmus, ileus, congested or toxic mucus membranes, hypogalactia, mild colic, and fever.
Sutter WW, Hopper S, Embertson RM, et al. Diagnosis and surgical treatment of uterine lacerations in mares (33 cases). In Proceedings. 49th Ann Conv Amer Assoc Equine Pract, New Orleans, 2003;357–9.
A frequent presentation is a mare that appeared clinically normally for an initial period after foaling, and then is presented 24 to 48 hours after foaling with depression, low-grade fever, toxic mucus membranes, mild colic, and a hungry foal. Leukopenia on an admission CBC in mares evaluated at a hospital is common.
In one mare with signs of peritonitis and azotemia, the uterus was perforated by the sharp end of a fetal long bone with a compound fracture, diagnosed on exploratory celiotomy.
The possibility of uterine laceration or perforation should be considered in any peripartum mare with signs of peritonitis. Chronic postpartum uterine rupture has also been reported, in which the clinical signs were referable to infertility rather than peritonitis.
The clinical signs seen in any given postpartum mare with a uterine tear depend on when the mare is being examined. With a large uterine rent, signs of abdominal hemorrhage may be seen initially. Although a perforated uterine wall does not bleed as severely as a ruptured uterine artery, mares may still have significant blood loss, both into the abdomen and into the uterine lumen, and the clinical picture of hemorrhage can mask the signs of uterine wall injury. Transabdominal ultrasound may reveal a pattern consistent with hemorrhage early after the injury, but by days 1 to 3 after foaling, usually reveals nonswirling echogenic (cellular) fluid in the ventral abdomen. A fluid sample obtained by abdominocentesis will reveal hemorrhagic, septic, suppurative characteristics, with high protein, nucleated cell count, and lactate. Bacteria may or may not be seen.
If uterine rupture is suspected, no fluids should be introduced into the uterus. Despite the fact that manual evaluation of the endometrial surface may not reveal a tear, it is part of a complete examination, and tears in the uterine body are amenable to detection. The luminal surface of the body and horns should be examined digitally per vagina. Polyethylene polymer lubricant should not be used.
Frazer G, Beard WL, Abrahamsen E, et al. Systemic effects of peritoneal instillation of a polyethylene polymer based obsteterical lubricant in horses, in Proceedings. Society for Theriogenology Annual Meeting, Lexington, KY, 2004;93–7.
In the immediate postparturient period, the endometrial surface is highly folded and engorged, which contributes to the difficulty in detection. When a perforation is suspected but not found with digital palpation, a technique of transmural palpation has been described
Sutter WW, Hopper S, Embertson RM, et al. Diagnosis and surgical treatment of uterine lacerations in mares (33 cases). In Proceedings. 49th Ann Conv Amer Assoc Equine Pract, New Orleans, 2003;357–9.
is required to locate the injury. A 2010 study comparing outcomes between uterine tears managed medically versus surgically reported a favorable outcome with either approach, with a survival rate of about 75% in both populations.
Medical management involves allowing the injury to heal by secondary intention. Treatment would usually include broad-spectrum antimicrobials including metronidazole, oxytocin at modest doses to maintain uterine tone and prevent sequestration of fluids, placement of a drain and lavage of the peritoneal cavity with warmed crystalloid fluids, NSAIDs, antiendotoxin measures, and prophylaxis for laminitis and founder.
Peritoneal lavage and drainage is an important part of treatment of peritonitis, as mares that do not survive uterine tear frequently are lost to complications of peritonitis, such as extensive adhesions
and founder. Several techniques are used for peritoneal lavage in standing horses. In brief, one technique involves placing a lavage tube in one or both paralumbar fossae and a drainage tube on or to the right side of ventral midline. Warmed crystalloid fluids are infused in the flank tube/s and drain through the ventral tube. Another technique involves placing a single drain, often a ballooned Foley catheter or a chest drain with a trocar, ventrally. With that system, the fluids are infused into and drained from the same drain. Both methods have been used successfully in the treatment of peritonitis. The reader is referred to previously published reports for practical details of inserting abdominal drains.
Lepage OM, Monteiro S, Desmaizieres LM. Peritoneal drainage of fenestrated balloon catheters in standing horse: a comparative study. In Proceedings. 55th Ann Conv Am Assoc Equine Pract, Las Vegas, 2009;487–91.
Many clinicians are of the opinion that larger tears or tears not limited to the dorsal aspect of the tract are best managed with surgical closure, which gives primary closure of the defect and removal of the source of contamination and sepsis. Surgery also enables effective peritoneal lavage and evaluation of surrounding visceral structures. Laminitis associated with uterine rupture and peritonitis can be particularly fulminant and progress rapidly to founder; prophylactic measures for laminitis should be started as soon as uterine rupture is identified or suspected.
Visceral injury or rupture is an occasional cause of postpartum colic. The small intestine, cecum, large colon, small colon, and bladder can all be directly injured by fetal positioning during gestation or fetal movements during parturition.
Segmental ischemic injury from mesenteric tears and disruption of blood supply can also occur, leading to intestinal rupture and fulminant peritonitis.
Clinical signs from this type of injury generally manifest in the 1 to 3 days after parturition and initially start as colic, depression, inappetence, and reduced manure output. With failure of the bowel wall, signs of septic shock predominate: fever or hypothermia, tachypnea, tachycardia, toxic-appearing mucus membranes, hypovolemia, and trembling. The clinical signs seen in any given mare may reflect any of these stages. In the early stages, this cause of colic in a postpartum mare can be difficult to pinpoint, and may be a diagnosis reached by exclusion of other causes of colic or by exploratory laparoscopy
or laparotomy. Blood work usually reveals severe leukopenia and neutropenia. In mares that have signs of peritonitis, the uterus and vagina should be carefully palpated digitally, to search for a rent. Small lacerations or rents can be challenging to find, especially if they are located near the tip of a horn or if the endometrium is edematous and engorged. If no such injury can be identified in the reproductive tract in a mare that has sonographic and clinicopathologic evidence of peritonitis, injury of the intestinal tract should be suspected and investigated.
As seen sonographically, free peritoneal fluid in the ventral aspect of the abdomen or pockets of free fluid at other, more dorsal, areas of the abdomen may reflect a segment of bowel injury. With intestinal wall failure, abdominocentesis will reveal fecal contamination, with intracellular and extracellular bacteria, although these changes may not be seen initially. With laceration or rupture of the bladder wall, the serum biochemistry changes classically associated with uroperitoneum, including high serum urea nitrogen and creatinine, hyperkalemia, hyponatremia, and hypochloremia, will be seen. Free peritoneal fluid can be identified as urine if the creatinine concentration is ≥ 2 times that in peripheral blood. In the early stages of postpartum visceral injury, exploratory laparotomy or laparoscopy may be necessary to identify the site and precise nature of the injury and to resect the injured segment if indicated. If abdominocentesis confirms intestinal rupture, euthanasia is indicated.
Recent studies on the intestinal microbiome have revealed that there are differences in the microbiota of colicky postpartum mares, versus noncolicky postpartum mares.
Large colon volvulus: This strangulating displacement of the large colon is one of the most devastating of all equine diseases. From onset of clinical signs, without intervention it runs a fulminant course of pain and shock and results in death in a matter of hours. This condition accounts for 10% to 20% of colic surgery cases
and is not limited to broodmares, but broodmares accounted for 91% of large colon surgical cases in central Kentucky over a 16-year period in one study.
Moore JN, Dreesen DW, Boudinet DF. Colonic distension, displacement, and torsion in Thoroughbred broodmares: results of a two-year study. In Proceedings. 4th Equine Colic Symposium. Athens: Univ of Georgia, 1991;23–5.
Recent parturition is a known risk factor for this emergency condition in mares, along with recent increase in dietary concentrates and recent exposure to lush pasture. The most common presentation in broodmares is that of a postpartum mare within 90 days of foaling that has acute onset of severe, intractable pain.
Occasionally, mares are presented with a history of having been mildly uncomfortable for the preceding day or two but then becoming acutely more painful.
With either history, once the large colon has become rotated in a strangulating volvulus, the clinical picture is one of intractable pain and rapid systemic deterioration into hypovolemic and septic shock.
Rotation of the large colon along its long axis that involves the mesentery between the ventral and dorsal segments is most correctly termed a volvulus, rather than a torsion, but both terms are commonly used. The site of twisting is most frequently between the right ventral and right dorsal colons, near where the cecocolic ligament ends on the lateral wall of the right ventral colon.
Most commonly the twisting occurs with the right ventral colon migrating medially and dorsally, so that in a 180° twist the large colon segments distal to the volvulus are oriented with the ventral colon lying dorsal to the dorsal colon. The degrees of volvular rotation reported range from 180° to 720°.
The area where the duodenum, cecal base, and origin of the ascending colon are in proximity is tethered to the dorsal body wall by a short mesentery, and this is the only fixed point in the entire large intestine. With the site of fixation restricted to only the beginning of the large colon and the considerable length (around 25 ft) and mobility of the colon segments distal to that point, it is perhaps understandable why gaseous distension or motility alterations can lead to their rotation and migration. Less understood is the predilection of periparturient broodmares for this problem.
It is likely that the main risk factors for volvulus are all in play in the recently foaled mare: in many regions where there are high numbers of broodmares, mares reside in rich pasture during the spring and high-energy concentrate feeds are given to support the dual aims for the professional broodmare—lactation for the present foal and efficiently conceiving and beginning the next gestation—and these could contribute to changes in the microbiome and fermentative environment of the cecum and ventral colons. It has also been conjectured that there is more room for migration of the large colon segments in the abdomen of a recently foaled mare. This migration may play a role, but large colon volvulus is also seen in prepartum mares and nonpregnant horses. Recent studies have shed light on the problem of large colon volvulus by characterizing the fecal microbiome in pregnant and postpartum mares. In one study, the large colon microbiome and metabolome of foaling mares were evaluated by quantifying volatile organic compounds (VOC) produced by the resident microbes. In healthy mares sampled from 3 weeks prepartum through 7 weeks postpartum, there was little change in the fecal microbiota: the microbiome and VOCs were remarkably stable with no significant change associated with parturition.
Acute onset of severe colic pain in a peripartum mare is the hallmark of large colon volvulus and should incite expedited examination and referral if it is an option. Colon volvulus is a surgical disease and not amenable to resolution in the field, but the actions of the veterinarian attending the mare at the farm will play an important role in the mare’s prognosis for survival, as minimizing the length of time to surgery is the single most important determinant of survival.
The time taken for examination in the field and transport to a referral center are the main components of this time interval; therefore it is incumbent on the attending veterinarian to conduct an expedited evaluation that either rules out or confirms large colon volvulus as the chief differential. As would be expected, mares that undergo surgery promptly have fewer complications and a better prognosis for life and future fertility.
Physical examination of a colicky mare in the early stages of volvulus may reveal a normal heart rate, depressed intestinal motility, and few signs of endotoxemia, but within a short period of time increasingly violent pain, hypovolemia, tachycardia, tachypnea, and toxic mucus membranes become prominent. Palpation per rectum reveals progressively severe gas distension of the large colon. Mares may have significant volumes of gastric reflux from occlusion of the duodenum on the right side of the abdomen.
The fluid should be removed, but the gastric decompression will not result in relief as it would in a case of simple obstruction. Ultrasonography of the colon segments on the right side of the abdomen, especially in intercostal spaces 12 to 15, often reveals engorgement of mesenteric vessels and edematous thickening of the large intestinal wall,
(Fig. 9) a result of venous and lymphatic engorgement secondary to the strangulation. Abdominocentesis is usually not needed for diagnosis and can be dangerous to attempt. If peritoneal fluid is obtained well into the course of a volvulus ≥360°, the color is usually serosanguinous and will have high protein, nucleated cell count, and lactate, reflecting colon ischemia and necrosis. Irrespective of the type and location of the intestinal lesion, severe intractable pain is an indication for exploratory celiotomy. If a mare has signs of significant hypovolemia, it may be prudent to place an IV catheter and administer a bolus of resuscitative fluids (hypertonic saline at 4 mL/kg, IV, followed by 3–5 L crystalloid fluids if they can be administered rapidly) before transporting. If gastric reflux was obtained on passage of a nasogastric tube, the tube should be capped, affixed to the halter, and left in place during transit. With severe gaseous distension of the colon segments, the diaphragm’s ventilatory excursions are impaired, which can cause death during transit. Trocarization to decompress the colon segments pressing against the diaphragm should be considered in preparing for transporting a mare with severe abdominal tympany and tachypnea, dyspnea, or cyanotic mucus membranes. All medications and fluids given should be written down and sent with the horse. In addition to the role of conducting an expedited examination and facilitating the decision to refer, the veterinarian is also a critical element in communications between the client and referral center and should play a key role in managing expectations with regard to outcomes and costs. Timely communication with insurance professionals is also an important part of the veterinarian’s service to the client in this emergency scenario.
Fig. 9Transabdominal sonogram of a large colon segment on the right side of the abdomen in a postpartum mare with large colon volvulus. The image was obtained in right intercostal space #14. Notice the grossly increased mural thickness (between the asterisks).
The prognosis for survival and future fertility has improved significantly over the past decade and presently is good for mares that are promptly diagnosed and referred.
Colopexy refers to fixation of the one of the colon segments to the body wall, and the resulting permanent adhesion is a method of preventing colon volvulus in successive pregnancies. Some surgeons recommend colopexy after a single episode of colon volvulus, whereas at other practices colopexy is performed after the second volvulus.
Hunt RJ, Spirito MA. Ventral midline colopexy as a prevention of large colon volvulus. In Proceedings. Am Assoc Equine Pract 41st Ann Conv. Lexington, KY. Dec 2-5, 1995;202.
Colopexy generally resolves the problem of future volvuli but does have known possible complications, some of which can be fatal. Mares that have undergone celiotomy to correct large colon volvulus, either with derotation or colon resection, can survive and bear live foals.
Summary: postpartum mares may have simple constipation and respond to routine administration of an analgesic plus mineral oil and water to ease defecation. However, persistent colic with clinical signs of inflammation and activation of the SIRS should prompt a search for injury to the reproductive tract or GI tract with ultrasound imaging and blood work. Large colon volvulus is a devastating condition of colic in which signs of pain progress along with fulminant hypovolemic and septic shock and should be recognized and the mare referred as quickly as possible. All the conditions causing serious colic in the peripartum mare can cause systemic inflammation and culminate in laminitis, even when the primary condition is addressed.
Retained fetal membranes
RFM is thought to be the most common postpartum problem in mares and may have an incidence as high as 10%.
are associated with higher incidences of retention. An investigation of draft breed mares, in which the incidence of RFM is approximately 50%, has recently revealed a significantly decreased density of oxytocin receptors in placental membranes, explaining the uterine atony and poor response to oxytocin seen in those breeds.
Friesian mares appear to be unique in their response to retained membranes, as they do not frequently develop the sepsis, metritis, and laminitis that affect other mares, and the reproductive performance of Friesian mares that had RFM is not different from those that did not have retained membranes, including likelihood of conceiving on a foal-heat breeding.
Release of the chorioallantois from the endometrium after birth normally takes place during third-stage labor contractions, when the trophoblastic cells of the chorionic villi separate from the endometrial epithelium. When the umbilical cord ruptures following delivery of the foal, it is thought that the fetal placental vessels collapse, causing shrinkage of the chorionic villi and facilitating release of their interdigitations with the endometrial crypts.
The myometrial contractions, which originate at the horn tips and migrate caudally through the uterine body, expel the released membranes. Although one can find a range of published time intervals said to be normal, many practitioners consider membranes still attached after 3 hours to be retained.
Failure of the membranes to be released expelled promptly usually results in a cascade of severe complications, such as metritis, sepsis, endotoxemia, hypogalactia, and laminitis,
The point of retention is usually near the tip of the nongravid horn. Several observations explain this finding. The chorionic microvilli are longer and have more extensive branching in this area, and the endometrial and placental folding is more extensive in the nongravid horn. Uterine involution also takes place more slowly in the nongravid horn.
For these reasons, among others, separation of the chorion from the endometrium may be slower in the nongravid horn.
Clinical signs: diagnosis is straightforward when placental membranes are seen protruding from the vulva. If no retained tissues are seen at the vulva and RFM is not suspected, the first clinical signs may not be seen until a day or more after parturition and will likely be those of lethargy, inappetence, colic, fever, and injected mucus membranes. The uterine interior should be palpated digitally (with the examiner donning a sterile sleeve or using a bare, scrubbed, disinfected, and lubricated arm) for any adherent tags of membrane. If the extent of the horns cannot be reached, common in an atonic, flaccid postpartum uterus, the horns can be imaged sonographically to search for retained tissue. Manual palpation repeated after a dose of oxytocin (10–20 IU, IV or IM) has induced myometrial contraction may improve the examiner’s ability to reach the tips of the horns. Membranes hanging at the level of the mare’s hocks or lower should be tied up to avoid being kicked or stepped on. Stepping on the placenta can evert the horn tip where it is attached or tear it from the endometrium.
By the time a mare has clinical signs of fever and lethargy, bacterial or endotoxin translocation, sepsis, and activation of the SIRS are under way. As discussed previously, the sepsis-associated systemic inflammatory response represents a global, overzealous immune response to a local infection, which proceeds to generalized host tissue injury. The laminae of equidae are a unique site of tissue injury among animals, and laminitis and life-threatening loss of architectural integrity in the horse’s digit is the common end point of severe inflammation incited by a multitude of causes. For this reason, mare owners or farm employees can be instructed on how to evaluate a newly passed placenta for completeness or to make a routine of placing placentas in a clean bucket or plastic bag for veterinary inspection. Retention of even a small portion of fetal membranes can be as lethal as retention of a large mass. A missing horn tip in the chorioallantois alerts to the possibility of RFM, even if no membranes are externally visible. The placenta contains a wealth of information about the gestation and health of the neonate, and the reader is referred to excellent practical articles on evaluation of the placenta.
Treatment of RFM usually begins with oxytocin administration. The doses given and frequency of administration are subject to veterinarian experience and preference, but in brief, a common regimen is to give 10 to 20 units of oxytocin, as an IV or IM bolus, every 1 to 2 hours up to 24 hours.
In many cases, a single dose of oxytocin elicits expulsion of the membranes within minutes. Higher doses have been used, but bolus doses greater than 20 units are associated with colic secondary to excessive uterine cramping that can lead to other complications.
Alternatively, oxytocin can be given as an IV infusion. Most veterinarians who work with broodmares have a preferred protocol, but published doses include adding 80 to 100 units of oxytocin to 500 mL saline and infusing over 30 minutes,
Supplementing calcium by giving 50 units of oxytocin in 450 mL calcium borogluconate solution and infusing over 15 minutes in Friesian mares has also been described.
Serum calcium and magnesium concentrations and the use of a calcium-magnesium-borogluconate solution in the treatment of Friesian mares with retained placenta.
Failure of oxytocin to induce expulsion of the membranes within 12 to 24 hours may be an indication that the retained tissue is not going to be released spontaneously, and the problem will have to be resolved by necrosis of the retained microvilli and cellular clearance mechanisms over a period of time.
Whether retained membranes should be manually removed meets with different opinions among veterinarians. Several methods and techniques for manually separating the chorionic and uterine surfaces at the site of adherence have been described and used with success,
but the decision should be tempered by the known potential complications. Subendometrial hemorrhage, luminal hemorrhage, absorption of bacterial toxins, invagination of the horn tip, pulmonary embolism, delayed involution, and permanent endometrial damage and impaired fertility have all been reported.
Samper J, Plough T. How to deal with dystocia and retained placenta in the field. In: Proceedings. 58th Ann Conv Amer Assoc Equine Pract. Anaheim, CA, 2012;359–61.
Irrespective of the method used, it seems likely that manual shearing of the chorioallantois from its site of retention leaves at least some microvilli embedded in the endometrium, which will be cleared by liquefaction and passage as particulate debris into the uterine lumen. That said, in some instances manual removal is an acceptable management choice, for example, when other methods of resolving RFM have failed
Samper J, Plough T. How to deal with dystocia and retained placenta in the field. In: Proceedings. 58th Ann Conv Amer Assoc Equine Pract. Anaheim, CA, 2012;359–61.
Another method of detaching the membranes involves introducing fluid (water, saline, and povidone iodine in saline have all been used) into an intact allantochorionic space and retaining the fluid by tying off the membranes at the vulva. This technique stretches the uterus, inducing oxytocin release, and causes the chorionic microvilli to release their attachment.
Alternatively, water or saline can be infused into the uterine lumen, between the chorion and uterus, which may aid expulsion by separating the chorionic and endometrial surfaces. Infusion into the uterine space has the added benefit of diluting and carrying out inflammatory debris and bacteria.
Samper J, Plough T. How to deal with dystocia and retained placenta in the field. In: Proceedings. 58th Ann Conv Amer Assoc Equine Pract. Anaheim, CA, 2012;359–61.
If these techniques do not elicit release of the membranes, the mare should be treated with continued oxytocin injections (less frequently than the original 24 hours), systemic antimicrobials, an NSAID drug, daily uterine lavages to remove the source of sepsis, tetanus toxoid, and prophylaxis for laminitis and founder. Intrauterine infusion of antimicrobials is also commonly used.
Retained placenta and metritis are associated with clinical tetanus in cattle; to the authors’ knowledge there are no published reports of tetanus in mares with RFM, but given that anaerobes, including Bacteroides and Clostridium spp, are cultured in some cases,
administering a dose of tetanus toxoid is merited. It is common practice to tie a 250- to 500-mL bag of fluids to the external part of the retained membranes to provide a tonic, mild level of tension.
As normal release of the fetal membranes results from both expulsive actions by smooth muscle contraction and the traction exerted by the weight of the initial portions of placenta to pass,
some believe there is rational for this practice. However, the same caveats pertaining to manual disruption of the connection apply to affixing weights to the placenta, and it should be undertaken carefully. The practice is avoided by some veterinarians.
A technique for intraumbilical injection of a collagenase solution to aid in breaking down the connections between microvilli and endometrium has been used in cows
In that study, 200,000 units of bacterial collagenase diluted in 1 L saline was infused into 2 of the 3 umbilical vessels in 4 mares with RFM. In all cases, retained membranes were passed within 6 hours, with no adverse effects. The procedure would not be feasible in retained membranes that are internal to the vulva or that are shredded and autolyzing. To the authors’ knowledge, this technique is not frequently practiced.
Even in mares in which efforts to remove the retained membranes is not successful, attentive management with a regimen of systemic antimicrobials, daily uterine lavage, oxytocin, intrauterine antimicrobials, NSAIDs, and prophylactic measures for laminitis usually return the mare to health and with the potential to carry a foal in the future. Mares that have had RFM are at risk for the problem in future pregnancies.
Clinics care points
•
Injuries involving reproductive tract tissues are similar to those involving other body areas in that prompt recognition, thorough evaluation, and intervention underlie a favorable outcome
•
Because of the episodic, unpredictable incidence of uterine artery rupture, randomized controlled clinical trials to evaluate treatments are infeasible, and most interventions are based on experience rather than being evidence-based
•
Nevertheless, treatment of mares with internal hemorrhage and shock is justified and often rewarding
•
Controlled reduction of the voluminous fetal fluids in hydropsic conditions necessitates monitoring and support for hypovolemic shock
•
Uterine prolapse can lead to shock and endotoxemia after replacement of the organ
•
Dystocia necessitating anesthesia and controlled vaginal delivery yields 2 postintervention patients in need of monitoring for complications
•
Clear communications and management of client expectations are key skills for veterinarians managing reproductive emergencies
Disclosure
The authors have nothing to disclose.
References
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Sutter WW, Hopper S, Embertson RM, et al. Diagnosis and surgical treatment of uterine lacerations in mares (33 cases). In Proceedings. 49th Ann Conv Amer Assoc Equine Pract, New Orleans, 2003;357–9.
Frazer G, Beard WL, Abrahamsen E, et al. Systemic effects of peritoneal instillation of a polyethylene polymer based obsteterical lubricant in horses, in Proceedings. Society for Theriogenology Annual Meeting, Lexington, KY, 2004;93–7.
Lepage OM, Monteiro S, Desmaizieres LM. Peritoneal drainage of fenestrated balloon catheters in standing horse: a comparative study. In Proceedings. 55th Ann Conv Am Assoc Equine Pract, Las Vegas, 2009;487–91.
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