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Basics ⬇

Outline

BASICS

Definition!!navigator!!

Both AKI and ARF are a consequence of an abrupt, sustained decrease in GFR, resulting in azotemia and disturbances in fluid, electrolyte, and acid–base homeostasis. The term AKI has been introduced to increase awareness of subclinical renal damage that may accompany many disease processes.

Pathophysiology!!navigator!!

  • Most commonly due to combined hemodynamic and nephrotoxic insults
  • Perpetuated by decreased GFR in damaged glomeruli and tubular obstruction with desquamated tubular epithelial cells and debris

Systems Affected!!navigator!!

  • Renal/urologic—injury/failure
  • Endocrine/metabolic—disturbances in electrolyte and acid–base homeostasis
  • GI—inappetence, possible diarrhea, and increased risk of ulcers
  • Nervous/neuromuscular—occasional ataxia or encephalopathy in severe cases
  • Hemic/lymphatic/immune—altered hemostasis, increased susceptibility to infection
  • Musculoskeletal—acute laminitis in severe cases

Genetics!!navigator!!

N/A

Incidence/Prevalence!!navigator!!

  • Low for ARF
  • AKI may be a common secondary problem with many disease processes

Geographic Distribution!!navigator!!

N/A

Signalment!!navigator!!

Breed Predilections

None

Mean Age and Range

Foals <30 days of age (especially when receiving nephrotoxic medications, or affected with hypoxic–ischemic multiorgan damage or septicemia) may be at greater risk, but all ages can be affected.

Predominant Sex

None

Signs!!navigator!!

Historical Findings

Horse are often presented for concurrent medical problems.

Physical Examination Findings

  • Lethargy, anorexia, dehydration, edema, ulcers, or uremic odor in the oral cavity
  • Severity of lethargy and anorexia often are greater than would be expected for the primary disease process
  • Oliguria/anuria
  • Rectal examination may reveal an enlarged, painful left kidney
  • Markedly azotemic patients may have neurologic deficits—ataxia, hypermetria, and mental obtundation

Causes!!navigator!!

  • Hemorrhagic, hypovolemic, or endotoxic shock
  • Pigmenturia
  • Vasculitis
  • Disseminated intravascular coagulation
  • Use of nephrotoxic medications—aminoglycosides; NSAIDs
  • Other nephrotoxins include heavy metals (e.g. mercury [in counterirritants or blisters], lead, cadmium), vitamins D and K3, and high doses of oxytetracycline, especially when administered to neonates
  • In occasional cases, infectious agents—Actinobacillus equuli in neonates; Leptospira spp. in all age groups

Risk Factors!!navigator!!

  • Renal hypoperfusion
  • Exposure to nephrotoxins or nephrotoxic drugs, particularly in patients with dehydration
  • Colic, diarrhea, pleuritis, peritonitis, prolonged exercise, rhabdomyolysis, hemolysis, or septicemia/endotoxemia

Diagnosis ⬆ ⬇

Outline

DIAGNOSIS

Differential Diagnosis!!navigator!!

  • Uroperitoneum
  • Obstruction of lower urinary tract
  • Chronic kidney disease
  • Heart failure
  • Gastric ulcers

CBC/Biochemistry/Urinalysis!!navigator!!

  • Normal to high PCV, variable leukogram, CBC changes reflect underlying primary disease process
  • AKI may be reflected by minor increases in Cr (0.3 mg/dL or a 50% increase) that often do not exceed the upper limit of the reference range
  • ARF is characterized by progressive increases in BUN (50–150 mg/dL; 18–54 mmol/L) and Cr (2.0–20 mg/dL; 177–1768 μmol/L)
  • Variable hyponatremia, hypochloremia, hyperkalemia, hypocalcemia, and hyperphosphatemia
  • Mild to moderate metabolic acidosis, severity varying with the underlying disease process; development of renal tubular acidosis may complicate recovery
  • Mild to moderate hyperglycemia and hyperlactatemia
  • Urine specific gravity—may remain high (>1.035) with AKI, low (<1.020) with ARF; best assessed during initial patient evaluation (before rehydration)
  • ARF may be accompanied by mild to moderate proteinuria, glucosuria, pigmenturia, and increased RBCs and casts on sediment examination
  • Urine pH—normal to acidic, especially with concurrent depletion of body potassium stores
  • Myoglobinuria or hemoglobinuria/hematuria

Other Laboratory Tests!!navigator!!

  • Increased fractional clearances (i.e. excretions) of sodium and phosphorus; decreased clearance of potassium
  • Enzymuria—urinary GGT:Cr ratio >25
  • Rising titers to Leptospira spp. may be found in horses with ARF attributable to leptospirosis

Imaging!!navigator!!

Transabdominal/Transrectal Ultrasonography

  • Kidneys may be enlarged (diameter >8 cm; length >15 cm), with increased echogenicity of renal cortices
  • Rarely subcapsular/perirenal edema or hemorrhage
  • Variable dilation of renal pelves
  • Nephrolithiasis/ureterolithiasis would indicate underlying chronic kidney disease and possible “acute-on-chronic” exacerbation of renal failure

Other Diagnostic Procedures!!navigator!!

  • Percutaneous renal biopsy with routine histopathologic, immunohistochemical, and electron microscopic evaluation of the sample may provide information regarding cause, severity, and prognosis. Proceed with caution, however, because life-threatening hemorrhage can be a complication
  • CVP >8–10 mmHg indicates fluid overload

Pathologic Findings!!navigator!!

  • Gross—enlargement of kidneys due to nephrosis and subcapsular and interstitial edema, causing tissue to bulge onto cut surfaces
  • Histopathologic—glomeruli may be congested and have a cellular infiltrate; tubules have denuded or flattened epithelium and varying amounts of accumulated eosinophilic debris

Treatment ⬆ ⬇

Outline

TREATMENT

Appropriate Health Care!!navigator!!

Properly recognize and treat all underlying primary disease processes, usually on an inpatient basis for continuous fluid therapy.

Nursing Care!!navigator!!

Fluid Therapy

  • After initial measurement of body weight, judiciously correct estimated dehydration with normal (0.9%) saline or another potassium-poor electrolyte solution over 12–24 h
  • Avoid overzealous fluid replacement (more than twice maintenance rate) unless a higher fluid administration rate is needed for primary disease process
  • Fluids may be supplemented with calcium gluconate or sodium bicarbonate if hyperkalemia or acidosis requires specific correction
  • Additional fluid replacement is no longer necessary once appetite and drinking return to normal (i.e. there is no benefit to continuing fluid therapy until Cr returns to a normal value)

Oral Electrolyte Supplementation

  • Sodium chloride (30 g) can be administered in concentrate feed or as an oral slurry/paste every 6–12 h to encourage increased drinking and urine output
  • Potassium chloride can be supplemented in nonhyperkalemic patients with total body potassium depletion—common with anorexia of ≥ 2 days

Activity!!navigator!!

Stall rest, with limited hand-walking or small paddock for grazing grass if appetite is poor.

Diet!!navigator!!

Encourage intake by offering a variety of concentrate feeds, bran mash, and hay types.

Client Education!!navigator!!

None

Surgical Considerations!!navigator!!

N/A

Medications ⬆ ⬇

Outline

MEDICATIONS

Drug(s) of Choice!!navigator!!

  • Judicious fluid therapy is the mainstay of treatment—see Nursing Care
  • Furosemide—for oliguria/anuria (i.e. lack of urination during first 6 h of fluid therapy or urine output <0.5 mL/kg/h); this diuretic may be administered twice (1–2 mg/kg IV or IM) at 1 h intervals; if effective, urination should be observed within 1 h after the second dose; if ineffective, consider a furosemide constant rate infusion; if ineffective, discontinue treatment
  • Routine use of mannitol and dopamine in patients with ARF is no longer recommended

Contraindications!!navigator!!

Avoid all nephrotoxic medications—gentamicin, tetracyclines, and NSAIDs.

Precautions!!navigator!!

  • As little as 40 mL/kg of IV fluids (20 L per 500 kg horse) may produce increases in CVP and significant pulmonary edema in oliguric/anuric patients
  • Furosemide—at repeated dosages can result in electrolyte derangements
  • Reassess dosage schedule of drugs eliminated by urinary excretion

Possible Interactions!!navigator!!

N/A

Alternative Drugs!!navigator!!

Consider peritoneal dialysis or hemodialysis (foals only) in refractory cases.

Follow-up ⬆ ⬇

Outline

FOLLOW-UP

Patient Monitoring!!navigator!!

  • Assess clinical status (emphasizing hydration), urine output, and body weight at least twice daily during the initial 24 h of treatment and at least daily thereafter
  • Monitor for subcutaneous and pulmonary edema—increased respiratory rate and effort as evidence of overhydration
  • Assess azotemia and electrolyte and acid–basis status at least daily for the initial 3 days of treatment
  • Consider placing a central venous line to maintain CVP <8 cmH2O in more critical patients and neonates

Prevention/Avoidance!!navigator!!

  • Anticipate compromised renal function in patients with other diseases or undergoing prolonged anesthesia and surgery; institute appropriate treatment to minimize dehydration and potential renal damage
  • Ensure adequate hydration status in patients receiving nephrotoxic medications, especially when combined (i.e. aminoglycosides and NSAIDs or tetracyclines)
  • Avoid concurrent use of multiple anti-inflammatory drugs—NSAIDs

Possible Complications!!navigator!!

  • Pulmonary and peripheral edema; conjunctival edema may be dramatic
  • Severe hyperkalemia accompanied by cardiac arrhythmias and death
  • Laminitis—often rapidly progressive and refractory to supportive care
  • Signs of neurologic impairment—ataxia; mental obtundation
  • GI ulceration or bleeding
  • Coagulopathy
  • Sepsis

Expected Course and Prognosis!!navigator!!

  • Prognosis for recovery varies with the underlying primary disease process
  • ARF may complicate recovery, prolong hospitalization and treatment, and increase cost
  • Prognosis for recovery from AKI/ARF usually is favorable if azotemia decreases by 25–50% after the initial 24 h of treatment; extent of recovery of renal function in patients with ARF may require 3–6 weeks to fully assess
  • Guarded prognosis for patients with Cr >10 mg/dL at initial evaluation and when azotemia remains unchanged after the initial 24 h of treatment
  • Poor prognosis for patients that have persistent anuria (>24 h), that have increased magnitude of azotemia after the initial 24 h of treatment, that rapidly develop edema, or that remain oliguric >72 h

Miscellaneous ⬆ ⬇

Outline

MISCELLANEOUS

Associated Conditions!!navigator!!

N/A

Age-Related Factors!!navigator!!

Neonates, especially premature or dysmature foals, may have markedly elevated Cr concentrations (approaching 25 mg/dL) due to placental insufficiency; this azotemia typically resolves in 2–3 days and should not be confused with ARF or uroperitoneum.

Zoonotic Potential!!navigator!!

Leptospirosis has infectious and zoonotic potential; avoid direct contact with infective urine.

Pregnancy/Fertility/Breeding!!navigator!!

N/A

Synonyms!!navigator!!

  • Acute nephrosis
  • Acute tubular necrosis
  • Vasomotor nephropathy

Abbreviations!!navigator!!

  • AKI = acute kidney injury
  • ARF = acute renal failure
  • BUN = blood urea nitrogen
  • Cr = creatinine
  • CVP = central venous pressure
  • GFR = glomerular filtration rate
  • GGT = γ-glutamyltransferase
  • GI = gastrointestinal
  • NSAID = nonsteroidal anti-inflammatory drug
  • PCV = packed cell volume
  • RBC = red blood cell

Suggested Reading ⬆ ⬇

McLeland S. Diseases of the equine urinary system. Vet Clin NA: Equine Pract 2015;31(2):377–387.

Tyner GA, Nolen-Walston RD, Hall T, et al. A multicenter retrospective study of 151 renal biopsies in horses. J Vet Intern Med 2011;25:532–539.

Author(s) ⬆ ⬇

Author: Harold C. Schott II

Consulting Editor: Valérie Picandet

Additional Further Reading ⬆

Click here for Additional Further Reading