At a glance
What is acute kidney failure?
Acute renal failure is the rapid loss of kidney function which causes waste products to build up in the bloodstream as well as electrolyte imbalances as the kidneys lose their ability to concentrate urine.
Each kidney has tiny filtering units called nephrons. Blood passes through the kidney and is filtered by the nephrons. They reabsorb what is needed and the waste is excreted in the urine. The wastes come from the normal breakdown of active muscle from the food the cat eats.
The body uses food for energy and self-repair. After the body has taken what it needs from the food, waste is sent to the blood and transported to the kidneys. The kidneys are an amazing organ and even with the loss of some nephrons, the remaining ones can compensate. Kidney disease becomes apparent when 70% of the kidney function has been lost. Once this happens, the kidneys are unable to remove the waste from the body and therefore these wastes build up in the cat causing poisoning.
Acute renal failure occurs in four phases, the duration of each phase depends on the cause and severity.
- Initial (onset) phase: This is when the kidney injury occurs and can last from hours to days.
- Oliguric (anuric) phase: There is a progressive decline in kidney function. Urine output decreases (oliguria).
- Diuretic (polyuric) phase: Glomerular filtration returns to normal and urine production increases.
- Recovery (convalescent) phase: Kidney function and urine production normalise.
Acute renal failure is a life-threatening condition and a medical emergency which needs immediate veterinary care.
Alternative Names: Renal failure – acute, Kidney failure, Kidney failure – acute, Renal failure, ARF.
What do the kidneys do?
- Control blood pressure by releasing renin (an enzyme). When blood pressure drops and kidneys don’t receive enough blood, renin is released which causes the blood vessels to contract (tighten). When the blood vessels contract, blood pressure goes up.
- Kidneys filter waste products and excess water from the blood. The cleaned blood stays in the body and the waste products leave the body in urine.
- Stimulation of red blood cell production.
- Help maintain the proper balance of acid and minerals, including sodium, calcium, potassium, and magnesium, in the blood.
Acute renal failure occurs as a result of a sudden insult or injury to the kidneys. Damage is split into three types:
- Pre-renal – not enough blood to the kidneys
- Renal – damage to the kidneys
- Post-renal – blockage
Reduced renal perfusion (levels of circulating blood):
- Hypovolemia: Dehydration, blood loss, shock, low blood pressure
- Cardiogenic: Heart disorders that impact the volume of blood flow to the kidneys
- Increased protein catabolism (the breakdown of proteins): Starvation, necrosis, infection, fever
- Arterial thromboembolism: Blood clot which blocks the flow of blood to the kidneys
- Tubular disease: Toxins (anti-freeze or poisonous plants such as lilies), some medications such as NSAIDs (ibuprofen, aspirin), ACE inhibitors, antifungals, gentamicin, chemotherapy agents
- Renal ischaemia (reduced blood supply to the kidneys): Hypovolemia (reduced blood volume), low blood pressure, heart disease
- Infections: Leptospirosis or ascending hematogenous bacterial infections
- Glomerular disease: Immune complex deposition due to infections, immune-mediated diseases, severe inflammation
- Severe hypercalcemia
- Hereditary disease
- Urinary blockage (kidney stones, uroliths, neoplasia)
- Urethral stricture (neoplasia, granulomatous inflammation, fibrosis, or trauma)
- Ruptured bladder
- Decreased urine production (in the first stage during the kidney insult, urine production may be increased, but as the kidneys fail, urination decreases and eventually stops)
- Loss of appetite (anorexia)
- Reduced water intake
- Loss of coordination
- Increased kidney size
- Distended bladder (urinary blockage)
- Fluid in the peritoneal cavity (ruptured bladder)
The veterinarian will perform a physical examination of the cat and require information on the cat’s history, which will include any possible exposure to poisons and medications it may have ingested (either accidental or as a result of medical treatment for a pre-existing condition), and information on previous illnesses.
- Biochemical profile: Elevated blood urea nitrogen (BUN) and creatinine, metabolic acidosis, hyperkalemia (elevated potassium), hyperphosphatemia (elevated phosphate), hypercalcemia (elevated calcium).
- Complete blood count: This test measures several components of the blood including red blood cells, white blood cells, platelets, and be able to provide information on any inflammation or infections your cat may have.
- Urinalysis: A urinalysis is a test of the cat’s urine and may be able to provide additional information on the extent of kidney damage, urine-concentrating ability and if an infection is present in the urinary tract.  Calcium oxalate crystals may be present in the urine of a cat who has ingested antifreeze (ethylene glycol).
- Urine specific gravity to check to see how concentrated the urine is.
- Kidney ultrasound or x-ray to evaluate the size of the kidneys and look for tumours, stones or blockages.
- A kidney biopsy can help determine a definitive underlying cause.
The goal of treatment is to address the underlying cause as well as correct acid-base and electrolyte abnormalities and reverse hydration deficits.
- Fluid therapy and electrolyte correction: To maintain hydration, correct electrolyte imbalances and increase kidney flow and urinary excretion of waste products. Great care must be taken when administering fluids, if the kidneys are not excreting fluids efficiently, they can potentially build up in the body which can lead to pulmonary edema.
- Catheterisation: To restore urination in the blocked cat. Insertion of the catheter will be under sedation.
- Hemodialysis: To remove toxins from the blood.
- Diuretics: Once the cat is rehydrated, diuretics such as furosemide to increase urinary excretion.
- Anti-nausea medications: To control nausea.
During treatment, hydration, kidney function, acid-base and urination will be closely monitored.
- Urinary blockage: Catheterisation or surgery to unblock the cat.
- Toxic medications: Discontinue any medications which may have caused the problem.
- Blood loss: Blood transfusions for cats who have lost a significant amount of blood.
- Poisoning: Induce vomiting or pump the stomach if the ingestion occurred within the previous two hours.
- Activated charcoal: Oral administration of activated charcoal binds to the toxins remaining in the system and prevents further absorption.
- Bacterial infection: Antibiotics.
During treatment, the veterinary staff will closely monitor blood pressure and urine output.
The prognosis is poor for cats who are unable to urinate, despite aggressive therapy.
 The Cornell Book of Cats.