Pre-existing renal damage with additional insult, eg reduced renal perfusion.
Any cause of reduced renal blood flow.
Anesthesia, especially without appropriate blood pressure monitoring and IV fluid support.
Chemotherapy with cisplatin.
Access to antifreeze (ethylene glycol).
Misuse of NSAIDs, aminoglycosides, diuretics or vasodilators.
Initiation phase (renal insult resulting in damage to renal parenchyma; injury potentially reversible at this stage; hours to 1-2 days).
Extension phase (ongoing cellular injury progressing to cell death, with progressive decline in GFR and loss of urine concentrating ability).
Maintenance phase (elimination of inciting factors at this stage does not alter existing damage or rate of recovery; signs of uremia may be present; a prolonged maintenance phase is associated with slower recovery and increased likelihood of permanently reduced renal function).
Recovery phase (progressive return of renal function).
Reduced renal blood flow → reduced oxygen and energy transport to cells → cell swelling and membrane damage → vasoconstriction and inflammatory mediator release → further vasoconstriction.
Nephrons are damaged at different sites (glomerulus, tubular cell, intercellular junction, basement membrane) depending on etiology → acute decline in glomerular filtration rate → increased urea/creatinine, decrease in urine specific gravity → uremic signs, oliguria (sometimes anuria or polyuria), fluid and electrolyte imbalances, acidosis.
Animals may die acutely, especially if underlying cause is not detected and treated or if oliguric phase persists.
If treated appropriately, animals may recover, but recovery phase can take >3 weeks of intensive care.
Bright (hyperechoic) renal cortex in ethylene glycol cases.
Only indicated if no response to therapy or if prognosis essential. Biopsy may cause hemorrhage resulting in further compromise of renal function.
Renal histopathology may identify underlying cause of acute renal failure and extent of renal damage. Do not biopsy if infectious process is suspected.Do not biopsy if bleeding diathesis is severe; assess with coagulation profile and buccal mucosal bleeding time.
Broad-spectrum antibiotics to prevent infections (animals in ARF are predisposed to infections) but care if indwelling urinary catheter is placed to measure urine output, as more likely to develop resistant urinary tract infection..
Anti-emetics - start with metoclopramide Metoclopramide. If ineffective consider low doses of prochlorperazine.
Nutritional support with high caloric density diet Dietetic diet: for convalescence (animal is in a catabolic state). Consider naso-esophageal, pharyngostomy or percutaneous gastrostomy tube.
Metabolic acidosis (pH <7.1) - consider use of sodium bicarbonate.
Treat underlying cause of ARF (infection, toxins).
Fluid therapy Fluid therapy: overview Hartman's or saline if hyperkalemic to correct dehydration and cause diuresis. Level of fluid therapy needs to be adjusted to urine output to prevent overhydration. Weigh animal before fluid therapy and can safely increase bodyweight by 3-5% with fluids since dehydration up to 5% is not clinically detectable once rehydrated.
If oliguria persists despite rehydration, administer loop diuretics, eg frusemide Furosemide 2-4 mg/kg.
Consider use of low dose dopamine 2-5 microg/kg/min in 5% dextrose Dopamine or mannitol infusion Mannitol (1-2 mg/kg/min), however little evidence to support efficacy.
If oliguria/anuria persists despite these treatments, peritoneal dialysis or hemodialysis is indicated (instill 7.5 ml of 50% dextrose into 250 ml Hartman's and give intraperitoneally and remove 6 hours later).
Fluid replacement should match output. Ideally indwelling urinary catheter should be attached to closed collection system in order that 'ins and outs' can be matched (+ 20 ml /kg/day for insensible losses).
Post-oliguria diuresis may require high fluid levels for 48-72 hours, then fluids should be tapered gradually over several days once patient eating.
Urine output (should be >0.5 ml/kg/h); once patient rehydrated match fluid input to urine output plus insensible losses (20 ml/kg/day).