Thomas J. Divers
Relevant Equine Renal Anatomy, Physiology, and Mechanisms of Acute Kidney Injury: A Review 1
Thomas J. Divers
Regulation of renal blood flow is by both extrinsic and intrinsic systems. Intrinsic regulation occurs via the afferent and efferent arterioles and tubuloglomerular feedback mechanisms following activation of the juxtaglomerular apparatus. Mechanisms of acute kidney injury in horses are frequently associated with changes in renal blood flow. Acute tubular necrosis and apoptosis are common in horses following ischemic or toxic insults and in sepsis-associated acute kidney injury. Sepsis-associated renal injury often has a complex mechanism of disease involving both functional and obstructive changes in intrarenal circulation. Acute interstitial nephritis may occur following Leptospira sp infection or can be secondary to tubular necrosis.
Acute Kidney Injury and Renal Failure in Horses 13
Thomas J. Divers
Nephrotoxic and hemodynamically mediated disorders are the most common causes of acute renal failure (ARF) in horses and foals. Leptospira spp. is the most common infectious cause of ARF. Initial treatments for ARF include elimination of nephrotoxic drugs, correction of predisposing disorders, and fluid therapy to promote diuresis. Horses and foals with polyuric ARF often have a good prognosis, while those with oliguric or anuric ARF have a guarded to poor prognosis. When fluid therapy is unsuccessful in improving urine production, various drug treatments have been used in an attempt to increase urine production, but none are consistently effective in converting oliguria to polyuria.
Chronic Renal Failure-Causes, Clinical Findings, Treatments and Prognosis 25
Emil Olsen and Gaby van Galen
Chronic kidney disease (CKD) is rare in horses with an overall prevalence reported to be 0.12%. There is often a continuum from Acute Kidney Injury (AKI) to CKD, and patients with CKD may be predisposed to episodes of AKI. The most common clinical signs are non-specific with weight loss, polyuria/polydipsia and ventral edema. Less common clinical signs are poor appetite and performance, dull hair coat, oral ulcerations, gastro-intestinal ulceration, gingivitis, dental tartar and diarrhea. Rarely, horses may develop forebrain signs. Creatinine increases when at least 2/3 of kidney function have been lost and a more accurate assessment of kidney function is an estimated glomerular filtration rate measuring iohexol clearance time combined with protein content in the urine. Tubulointerstitial disease and glomerulonephritis are common causes of chronic kidney disease together with pyelonephritis and nephrolithiasis. Dietary changes and avoiding nephrotoxic drugs are key in slowing down the degenerative process.
Urinary Tract Disorders of Foals 47
SallyAnne L. DeNotta
Urinary disease in the neonatal period can occur with primary congenital renal defects or as a secondary consequence of birth trauma, ischemic injury, nephrotoxic medications, or systemic illness. This article reviews the clinical evaluation of the urinary system in foals and highlights diagnostic and therapeutic features of the most commonly encountered urinary disorders of the equine neonatal patient.
Discolored Urine in Horses and Foals 57
This article describes the most common causes of urine discoloration. The review includes a description of the most common disorders causing hematuria, highlighting clinical presentation, treatments, and pathophysiology. Causes of hemoglobinuria and myoglobinuria together with their mechanisms of renal injury are also reviewed.
Urinary Incontinence and Urinary Tract Infections 73
Urinary incontinence results from disorders of the lower urinary tract or neurologic diseases either of the nerve supply to the bladder/urethra or within the central nervous system. Congenital causes include patent urachus and ectopic ureter. Coordination of lower urinary tract function involves the interaction of both the sympathetic and parasympathetic system as well as somatic branches of the central nervous system. Well-recognized causes of incontinence include equine herpes virus 1 myeloencephalopathy, polyneuritis equi (neuritis of the cauda equina), and sacral/coccygeal trauma. Idiopathic bladder paralysis is characterized by bladder paralysis and sabulous cystitis in the absence of overt neurologic deficits.
Polyuria and Polydipsia in Horses 95
Emily A. Barrell
Polyuria and polydipsia are rare, but significant, manifestations of several different diseases of horses. Causes can be endocrine, iatrogenic, psychogenic, infectious, or toxic in nature and can also be due to primary renal disease or diseases of other organs, such as the liver. Although numerous causes of polyuria and polydipsia in horses exist, the most common conditions include chronic kidney disease, pituitary pars intermedia dysfunction, and psychogenic polydipsia with secondary polyuria. Additional testing is dictated by history, other clinical signs, and the results of blood work and/or urinalysis. Prognosis for horses with polyuria and/or polydipsia varies significantly based on the underlying cause.
Metabolic Disorders Associated with Renal Disease in Horses 109
Kathleen R. Mullen
This article overviews several metabolic disorders associated with renal disease in horses. Included is a discussion of the pathophysiology, clinical signs, and treatment of hyperchloremic metabolic acidosis associated with renal tubular acidosis. Conditions affecting the central nervous system including uremic encephalopathy and hyponatremic encephalopathy secondary to renal disease are presented. Finally, a discussion of the unique features of calcium and phosphorus homeostasis in horses is provided with special emphasis on a recently described syndrome of calcinosis and calciphylaxis of unknown etiology.
Imaging of the Urinary Tract 123
This article provides a comprehensive review of imaging techniques used to evaluate the equine urinary tract. This overview includes officially recognized modalities and new applications reported in the most current literature. Technical aspects and indications for use of endoscopy and ultrasonography are highlighted. Normal endoscopic and ultrasonographic appearance of the upper and lower urinary tract is described, with characterization of common abnormalities found in patients with hematuria, stranguria, and renal failure. Visual examples of several pathologic conditions from clinical cases are provided. An outline of the main features, potentials, and limitations of radiography, nuclear scintigraphy, and computed tomography is provided.
Surgery of the Equine Urinary Tract 141
Susan L. Fubini and Michelle Delco
Urinary surgery in the horse may be challenging. More straightforward procedures, such as urinary bladder or urachal defects, do not usually require specialized equipment or imaging, although laboratory work is helpful. Congenital or acquired conditions of the ureters or kidneys may necessitate advanced diagnostic work-ups including advanced imaging and/or minimally invasive procedures. Some surgery of the lower urinary tract is done in the sedated, standing adult horse. Surgery involving the kidney typically requires general anesthesia. Laparoscopy and associated tools are frequently used. Although many of the surgical procedures discussed are quite involved, they are becoming more commonplace.
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