Acute Renal Failure

1.6.07

• Broadly defined as rapid deterioration of renal function resulting in accumulation of waste products such as urea and creatinine.
• Pre-renal, renal, post-renal.

Pre-renal - causes of renal hypoperfusion
• Intravascular volume depletion e.g. through vomiting, diarrhoea.
• Trauma/burns/crash injury.
• Haemorrhage.
• Pancreatitis.
• Diabetic ketoacidosis.
• Addison's disease.

Pre-renal
• Decreased CO2.
• Changes in renal vascular resistance.
• Renovascular obstruction.
• Microvascular obstruction.
• Increased blood viscosity.
• Interference with renal autoregulation.

Intrinsic ARF
• Persistent pre-renal failure of any cause.
• Nephrotoxins.
• Haemoglobinuria/myoglobinuria e.g. from any crush injury.
• Radiological contrast material.
• Acute glomerulonephritis e.g. from Goodpasture's syndrome, Wegener's granulomatosis.
• Acute renal vasculitis.
• Obstetric causes e.g. ATN from severe hypovolaemia.

Obstructive uropathy
• Bilateral urinary tract calculi.
• Single urinary tract calculus.
• Retroperitoneal fibrosis.
• Crystal nephropathy.
• Cancer of bladder/cervix.
• Urethral stone.
• Following pelvic surgery.

Clinical features of urinary tract obstruction
• Anuria.
• Polyuria.
• Alternating anuria and polyuria.
• Pain.
• UTI.
• Uraemia of no apparent cause.

Golden clinical rules
• Assess volume status.
• Search to diagnose urinary tract obstruction:
-History.
-PR.
-Ultrasound.
• If pre-renal, fill up (with saline - isotonic to plasma).
• If renal, remove cause or treat condition.
• If obstructive, relieve obstruction.

Management
• Support renal failure.
-Fluids/CVP.
-Electrolytes e.g. high plasma K+.
-Insulin/dextrose.
-Ca2+ resonium.
-Haemodialysis for uraemia.
• Look for and fight infection.
• Don't forget nutrition - enteral/parenteral.
• Remember dangers of blood-borne agents e.g. HBV, HCV, HIV.
• Renal biopsy, if indicated.
• Treat any underlying treatable condition e.g. arteritis, myeloma, hypercalcaemia.

Acute or acute-on-chronic renal failure?
• Pre-existing renal disease suggested by:
-PMH of proteinuria, Nocturia, renal stones, DM or hypertension.
-Analgesic abuse.
-FH of polycystic kidneys, hereditary nephritis.
-Normochromic normocytic anaemia.
-Secondary hyperparathyroidism.
-Stunting of growth or failure of secondary sexual characteristics.
• Palpable or history of polycystic kidneys.
• Bilaterally small kidneys.

Complications
• Fluid/volume.
• Metabolic.
• Infection.
• Nutritional.
• Related to underlying problem.
• Stressful situation for patient and family.

Prognosis
• ~40% mortality.
• Worse if:
-Post-surgery.
-Infection.
-Catabolic.
-Increase in age and multiple diseases.
-Delay in referral and commencing dialysis.
-Complications.

Survivors
• If patient survives ARF, majority recover renal function to become dialysis independent.