Acute renal failure in six horses resulting from haemodynamic causes

ECEIM consensus statement on equine kidney disease

The aim of this consensus statement is to summarize and appraise scientific evidence and combine this with the clinical experience of a panel of experts to optimize recommendations on how to recognize and manage kidney disease in horses.

Relevant Equine Renal Anatomy, Physiology, and Mechanisms of Acute Kidney Injury: A Review

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 with activation of the juxtaglomerular apparatus. Mechanisms of acute kidney injury 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.

Imaging of the Urinary Tract

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.

Acute Kidney Injury and Renal Failure in Horses

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 drugs treatments have been used in an attempt to increase urine production, but none are consistently effective in converting oliguria to polyuria.

Calculating and selecting fluid therapy and blood product replacements for horses with acute hemorrhage

BACKGROUND

Blood products, crystalloids, and colloid fluids are used in the medical treatment of severe hemorrhage in horses with a goal of providing sufficient blood flow and oxygen delivery to vital organs. The fluid treatments for hemorrhage will vary depending upon severity and duration and whether hemorrhage is controlled or uncontrolled.

DESCRIPTION

With acute and severe controlled hemorrhage, treatment is focused on rapidly increasing perfusion pressure and blood flow to vital organs. This can most easily be accomplished in field cases by the administration of hypertonic saline. If isotonic crystalloids are used for resuscitation, the volume administered should be at least as great as the estimated blood loss. Following crystalloid resuscitation, clinical signs, HCT, and laboratory evidence of tissue hypoxia may help determine the need for a whole blood transfusion. In uncontrolled hemorrhage, crystalloid resuscitation is often more conservative and is referred to as "permissive hypotension." The goal of "permissive hypotension" would be to provide enough perfusion pressure to vital organs such that function is maintained while keeping blood pressure below the normal range in the hope that clot formation will not be disrupted. Whole blood and fresh frozen plasma in addition to aminocaproic acid are indicated in most horses with severe uncontrolled hemorrhage.

SUMMARY

Blood transfusion is a life-saving treatment for severe hemorrhage in horses. No precise HCT serves as a transfusion trigger; however, an HCT < 15%, lack of appropriate clinical response, or significant improvement in plasma lactate following crystalloid resuscitation and loss of 25% or more of blood volume is suggestive of the need for whole blood transfusion. Mathematical formulas may be used to estimate the amount of blood required for transfusion following severe but controlled hemorrhage, but these are not very accurate and, in practice, transfusion volume should be approximately 40% of estimated blood loss.

KEY POINTS

Modest hemorrhage, <15% of blood volume (<12 mL/kg), can be fully compensated by physiological mechanisms and generally does not require fluid or blood product therapy. More severe hemorrhage, >25% of blood volume (> 20 mL/kg), often requires crystalloid or blood product replacement, while acute loss of greater than 30% (>24 mL/kg) of blood volume may result in hemorrhagic shock requiring resuscitation treatments Uncontrolled hemorrhage is a common occurrence in equine practice, and is most commonly associated with abdominal bleeding (eg, uterine artery rupture in mares). If the hemorrhage can be controlled such as by ligation of a bleeding vessel, then initial efforts to resuscitate the horse should focus on increasing perfusion pressure and blood flow to organs as quickly as possible with crystalloids or colloids while assessing need for whole blood transfusion. While fluid therapy is being administered every effort to physically control hemorrhage should be made using ligatures, application of compression, surgical methods, and local hemostatic agents like collagen-, gelatin-, and cellulose-based products, fibrin, yunnan baiyao (YB), and synthetic glues Although some synthetic colloids have been shown to be associated with acute kidney injury in people receiving resuscitation therapy,²⁰ this undesirable effect in horses has not been reported.

Detecting acute kidney injury in horses by measuring the concentration of symmetric dimethylarginine in serum

BACKGROUND

Acute kidney injury (AKI) in horses may develop as a complication of a primary disease or following the administration of nephrotoxic drugs, and may pose a diagnostic challenge. Hence, the main objective of this study was to evaluate the concentrations and diagnostic significance of serum symmetric dimethylarginine (SDMA) and conventional renal dysfunction biomarkers in healthy horses, horses at risk of developing AKI, and horses with clinically evident AKI. A second aim was to assess how gastrointestinal disease and exposure to potentially nephrotoxic drugs affected SDMA levels. Thirty healthy horses, 30 horses with gastrointestinal disease and/or receiving phenylbutazone or gentamicin (risk group) and 11 horses with AKI were included in the study. Serum SDMA levels were measured using commercially available enzyme immunoassay tests.

RESULTS

SDMA levels in healthy horses, horses at risk of AKI and horses with AKI were 12 µg/dL (11-14), 12 µg/dL (11-13) and 20 µg/dL (20-37), respectively (all results presented as a median (quartile 1-quartile 3)). There was a significant difference in SDMA concentration between the healthy horses and those with AKI, whereas the SDMA levels in healthy horses and those at risk of AKI were comparable. A SDMA cut-off value of 19 µg/dL was established. Horses from the risk group had higher urine protein concentration and urine protein to creatinine ratio compared with healthy horses. Furthermore, horses with colic from the risk group presented with elevated urine γ-glutamyl transpeptidase to creatinine ratio.

CONCLUSION

The SDMA cut-off value established in healthy horses was higher than previously reported. The SDMA level correlated with the azotaemia levels. Horses from the AKI risk group had normal SDMA levels but single urine parameters was abnormal indicating their higher sensitivity in assessing subclinical kidney dysfunction.

Evaluation of podocin in urine in horses using qualitative and quantitative methods

No sensitive method for diagnosing early kidney dysfunction in horses has been identified so far. Many studies carried out in humans and small animals show that podocin can be useful to diagnose various kidney diseases, mainly affecting the glomeruli. The aim of this study was to perform a qualitative and quantitative analysis of podocin in urine samples obtained from healthy horses, horses with clinical kidney dysfunction and horses at risk of acute kidney injury. The study objectives aimed to assess: (1) whether the selected podocin tryptic peptide for LC-MS-MRM allows for podocin detection in horse; and (2) whether the species-specific ELISA test makes this detection possible as well;, (3) whether the chosen methods are sensitive enough to detect kidney dysfunction and glomerular injury, (4) whether the results of the tests applying both methods correspond with one another, (5) whether the results correlate with the hematological and biochemical data. The signals that may indicate the presence of trypsin fragments of podocin were found in three healthy horses, all the horses diagnosed with kidney dysfunction and half of the animals at risk for acute kidney injury. The concentration of podocin, diagnosed with the ELISA test was as follows: from 0.19 to 1.2 ng/ml in healthy animals, from 0.19 to 20.0 ng/ml in AKI horses, from 0.29 to 5.71 ng/ml in horses at risk for acute kidney injury. The results of both methods corresponded significantly. Podocin may be a potential biomarker of clinical kidney disease in horses and may be used in the detection of glomerular injury. However, its use is limited by the possibility of physiological podocyturia. LC-MS-MRM seems to be a more sensitive method to evaluate the presence of podocin than the ELISA test, whilst selected tryptic peptides of podocin appear to apply to horses. The ELISA test showed greater effectiveness in excluding the disease than in confirming it.

The Sick Adult Horse: Renal Clinical Pathologic Testing and Urinalysis

Clinicopathologic evaluation of renal function and renal disease in sick adult horses remains grounded in detection of azotemia, assessment of serum and urine electrolyte concentrations, and evaluation of urinalysis findings, including specific gravity, reagent strip analysis, and sediment examination. Because increases in serum or plasma urea nitrogen and creatinine concentrations are insensitive indicators of a decreased glomerular filtration rate, there is considerable interest in identifying novel biomarkers of renal function or injury in blood and urine, with serum symmetric dimethylarginine concentration being the most recent addition to the commercial market.

Prevalence of acute kidney injury in a population of hospitalized horses

BACKGROUND

Hospital-acquired acute kidney injury (AKI) in humans and dogs increases morbidity and nonsurvival. Azotemia at presentation has been associated with a poor outcome in horses; however, prevalence and consequences of hospital-acquired AKI are unreported.

HYPOTHESIS/OBJECTIVES

To evaluate the prevalence of AKI in hospitalized horses, risk factors associated with AKI, and the effect of AKI on short-term survival. We hypothesized that the prevalence of AKI in horses is similar to that reported in other domestic mammalian species and would be associated with nonsurvival.

ANIMALS

Adult horses hospitalized for >2 days from which a minimum of 2 measurements of serum creatinine concentration were available.

METHODS

Retrospective cohort study. Clinical records were reviewed and horses grouped according to their baseline serum creatinine concentration and change in serum creatinine concentration from baseline. The associations between signalment, diagnosis, and treatment variables, and the presence of azotemia or AKI were assessed using multinomial logistic regression. The relationship between these conditions and survival to discharge was evaluated.

RESULTS

Three hundred twenty-five horses were included; 4.3% (14/325) had azotemia at baseline and 14.8% (48/325) developed AKI. There were no significant associations between investigated risk factors and development of AKI. The presence of azotemia and AKI did not significantly affect survival to discharge (P = .08 and .81, respectively).

CONCLUSIONS AND CLINICAL IMPORTANCE

The prevalence of AKI in this population of hospitalized horses is similar to that reported in dogs and humans; however, in this study population, there was less impact on morbidity and short-term survival.

Pharmacokinetics and Pharmacodynamics of an Oral Formulation of Apixaban in Horses After Oral and Intravenous Administration

Horses with inflammatory and infectious disorders are often treated with injectable heparin anticoagulants to prevent thrombotic complications. In humans, a new class of direct oral acting anticoagulants (DOAC) appear as effective as heparin, while eliminating the need for daily injections. Our study in horses evaluated apixaban, a newly approved DOAC for human thromboprophylaxis targeting activated factor X (Xa). Our goals were to: (1) Determine pharmacokinetics and pharmacodynamics of apixaban after oral (PO) and intravenous (IV) administration in horses; (2) Detect any inhibitory effects of apixaban on ex vivo Equid herpesvirus type 1 (EHV-1)-induced platelet activation, and (3) Compare an anti-Xa bioactivity assay with ultra-performance liquid chromatography-mass spectrometry (UPLC-MS) for measuring apixaban concentrations. In a blinded placebo-controlled cross-over study, five horses received a single dose (0.2 mg/kg) of apixaban or placebo PO or IV. Blood was collected before and at 3 (IV) or 15 (PO) min, 30 and 45 min, and 1, 2, 3, 4, 6, 8, and 24 h after dosing for measuring apixaban UPLC-MS concentrations and anti-Xa activity. Pharmacodynamic response was measured in a dilute prothrombin time (dPT) assay. Flow cytometric EHV-1-induced platelet P-selectin expression and clinical pathologic safety testing were performed at baseline, 2 and 24 h and baseline and 24 h, respectively. We found no detectable apixaban in plasma PO administration. After IV administration, plasma apixaban levels followed a two-compartment model, with concentrations peaking at 3 min and decreasing to undetectable levels by 8 h. The elimination half-life was 1.3 ± 0.2 h, with high protein binding (92–99%). The dPT showed no relationship to apixaban UPLC-MS concentration and apixaban did not inhibit EHV-1-induced platelet activation after IV dosing. Apixaban anti-Xa activity showed excellent correlation to UPLC-MS (r² = 0.9997). Our results demonstrate that apixaban has no apparent clinical utility as an anticoagulant for horses due to poor oral availability.

Renal replacement therapy in healthy adult horses

BACKGROUND

Renal replacement therapy (RRT) has been implemented extensively in people to facilitate recovery from acute renal failure (ARF). RRT has not been explored in horses, but might provide a further treatment option in horses with ARF.

OBJECTIVE

To investigate efficacy and safety of RRT in horses.

ANIMALS

Five healthy adult horses.

METHODS

A prospective study was performed on horses restrained in stocks and intravenously connected to a commercial RRT machine to allow continuous venovenous hemodiafiltration to be performed for 6 hours. The RRT machine was set at the following flow rates: blood flow rate 250 mL/min; dialysate rate 3,000 mL/h; prefilter replacement pump 3,000 mL/h; and postfilter replacement pump rate 2,000 mL/h. Balanced electrolyte solution was used as dialysate and replacement fluid. Heart rate, respiratory rate, body temperature, direct arterial blood pressure, urine output, and various clinicopathologic parameters were measured over the study period.

RESULTS

Renal replacement therapy was successfully performed in horses, resulting in a mean creatinine clearance of 0.127 mL/kg/min (68.9 mL/min) and urea reduction ratio of 24%. No adverse effects were detected although a significant decrease in rectal temperature was observed (P ≤ .007). A significant increase in serum phosphorus (P ≤ .001) and decrease in BUN (P < .001) were also noted. A significant prolongation of prothrombin (P < .01) and partial thromboplastin time (P < .0001) were observed along with a decrease in platelet count (P ≤ .04).

CONCLUSIONS AND CLINICAL IMPORTANCE

Renal replacement therapy can safely and effectively be used in adult horses.

Risk factors associated with renal insufficiency in horses with primary gastrointestinal disease: 26 cases (2000-2003)

OBJECTIVE

To identify factors associated with renal insufficiency in colic- or colitis-affected horses with high serum creatinine (SCr) concentrations evaluated at a referral hospital.

DESIGN

Retrospective case series.

ANIMALS

167 colic- or colitis-affected horses (88 represented a random sample [hospital population], and 79 had high SCr concentration at initial evaluation [study population]).

PROCEDURE

Medical records were reviewed. Data collected included signalment; physical examination, clinicopathologic, and diagnostic findings; and outcome. The study population was categorized on the basis of whether SCr concentration did (AR group; n = 53) or did not (PA group; 26) normalize within 72 hours of fluid therapy. Characteristics of the study and hospital populations were compared.

RESULTS

Males and Quarter Horses were significantly overrepresented in the study population. Compared with the hospital population, study-population horses were significantly more likely to have colitis, gastric reflux, and diarrhea at initial evaluation. Initial mean SCr concentration in the PA group was significantly higher than the AR group; identification of gastric reflux, abnormal rectal examination findings, and hypochloremia were significantly associated with persistent azotemia after 72 hours of fluid therapy. Compared with the AR group, PA group horses were 3 times as likely to die or be euthanized.

CONCLUSIONS AND CLINICAL RELEVANCE

In colic- or colitis-affected horses, factors associated with renal insufficiency included gastric reflux, abnormal rectal examination findings, or hypochloremia initially; prognosis for horses in which azotemia resolves within 72 hours of treatment appears to be better than for horses with persistent azotemia.

Prevention and treatment of thrombosis, phlebitis, and laminitis in horses with gastrointestinal diseases

Organ thrombosis and laminitis are life-threatening complications in horses with acute gastrointestinal disease, especially those diseases that cause disruption of the protective mucosal barrier. Prevention of these complications should be a high priority when treating horses with gastrointestinal diseases because even with proper and intensive treatments, laminitis or organ thrombosis may not be curative. Preventative therapy should include expedient and appropriate treatment of the primary disease, normalization of tissue perfusion and oxygenation, and inhibition of gut-derived toxins or their systemically activated biologic products along with i.v. replacement of depleted anticoagulant proteins. Additionally, several risk factors for thrombophlebitis in horses with intestinal disease have been identified, and those risk factors should be minimized during the illness.

Use of 99mTc-mercaptoacetyltriglycine to evaluate renal function in horses

Ten healthy horses were injected intravenously with 99mTc-MAG3 and the disappearance of radioactivity from the blood was measured. The total body clearance (Cl(B)) and elimination half-life (t1/2(beta)) were 7.9 +/- 1.5 ml/kg/minute and 32.8 +/- 4.1 minutes, respectively. The disappearance of 99mTc-MAG3 from the blood of 2 horses with compromised renal function was also measured. The data suggest that 99mTc-MAG3 is a useful and clinically applicable radiopharmaceutical for measurement of effective renal blood flow in the horse.

Renal pharmacology

Pharmacologic treatment of diseases of the urinary tract of horses is limited to administration of antibiotics for treatment of urinary tract infections (UTIs), administration of drugs that alter urine pH, administration of drugs that alter bladder smooth muscle function or urethral sphincter tone, and treatment of acute renal failure. The indications, mechanisms of action, pharmacokinetic characteristics, and adverse effects of these agents in each of these groups are discussed in this article. The use of the agents is discussed within the context of the pathophysiology of the disease being treated.

Heparin: a review of its pharmacology and therapeutic use in horses

Heparin is used clinically in horses to treat hemostatic abnormalities associated with severe gastrointestinal disease, septicemia, and endotoxemia. The primary anticoagulant effect of heparin is through the suppression of thrombin-dependent amplification of the coagulation cascade, and inhibition of thrombin-mediated conversion of fibrinogen to fibrin. Heparin may be of benefit in preventing the complications associated with hypercoagulable states such as jugular vein thrombosis, laminitis, and organ failure. Heparin may also be beneficial in the prevention of intraabdominal adhesions after gastrointestinal surgery, and in amelioration of hemodynamic abnormalities associated with endotoxic shock. Because a sequential rise in serum heparin concentration occurs during a uniform dosage regimen, a decreasing dosage regimen is recommended. The initial dose recommended is 150 U heparin/kg body weight subcutaneously, followed by 125 U heparin/kg body weight subcutaneously, every 12 hours for six doses. The dose should be decreased to 100 U heparin/kg body weight subcutaneously, every 12 hours, after the seventh dose. Anemia, hemorrhage, thrombocytopenia, and painful swelling at injection sites are complications of heparin administration in horses.

Pharmacology of furosemide in the horse: a review

Furosemide, a diuretic, is frequently administered to horses for the prophylaxis of exercise-induced pulmonary hemorrhage and the treatment of a number of clinical conditions, including acute renal failure and congestive heart failure. Furosemide increases the rate of urinary sodium, chloride, and hydrogen ion excretion. Plasma potassium concentration decreases after furosemide administration but urinary potassium excretion in horses is minimally affected. Renal blood flow increases after furosemide administration. Systemically, furosemide increases venous compliance and decreases right atrial pressure, pulmonary artery pressure, pulmonary artery wedge pressure, and pulmonary blood volume. The systemic hemodynamic effects of furosemide are only manifest in the presence of a functional kidney, but can occur in the absence of diuresis, emphasizing the importance of the renal-dependent extra-renal effects of furosemide. The renal and systemic hemodynamic effects of furosemide are modified by prior administration of nonsteroidal anti-inflammatory drugs. Furosemide administration attenuates exercise-induced increases in right atrial, aortic, and pulmonary artery pressures in ponies. Furosemide prevents exercise and allergen-induced bronchoconstriction in humans and decreases total pulmonary resistance in ponies with recurrent obstructive airway disease. These pharmacologic effects are frequently used to rationalize its questionable efficacy in the prevention of exercise-induced pulmonary hemorrhage. Neither the effect of furosemide on athletic performance nor its efficacy in the prevention of exercise-induced pulmonary hemorrhage has been convincingly demonstrated.

The nephrotoxic potential of neomycin in the horse

Neomycin was administered intramuscularly to four normal adult horses at a dose rate of 10 mg/kg bodyweight every 12 h for 10 days (21 doses). The pharmacokinetic behaviour of neomycin with multiple dosing was characterised and a range of blood chemical and urinary parameters examined for evidence of nephrotoxicity. There was evidence of physical renal tubular injury (enzymuria and cylindriuria) within four days of neomycin administration but this subsided following cessation of treatment. No significant functional nephrotoxicity was detected. More severe nephrotoxicity might be expected in ill horses and it is recommended that several clinicopathological results be monitored serially in those horses receiving parenteral neomycin.

Laboratory diagnosis and characterization of renal disease in horses

Laboratory evaluation of renal function in horses has advanced dramatically in the last 10 years largely as a result of the interest generated by the creative approach to diagnostic indices taken by Brobst, Traver, Coffman, and others. Some methods of assessing renal function discussed here are clearly outside the scope of a practice environment but are available in referral hospitals for use in difficult or unusual cases. Other methods described, such as calculation of fractional excretions and urine to serum creatinine ratios, are accessible and readily interpreted by the veterinary practitioner. These diagnostic methods should help in the early identification of renal disease in horses and therefore should allow veterinarians the option to treat renal disease before renal failure is advanced. In addition, practitioners may be able to offer more informed prognoses after a more complete evaluation of renal function.