Definitions
Acute kidney injury (AKI) is a sudden deterioration in renal filtration function. Acute renal failure (ARF) is AKI such that global renal function is no longer capable of excreting body waste products (e.g. urea, creatinine, potassium) that accumulate in the blood. It may be fatal unless treated. Anuria literally means no urine, but is considered to be present when <100 ml/day of urine is passed. Oliguria means that <0.5 ml/kg/hour (<400 ml/day) is passed. Acute tubular necrosis (ATN) is damage to the renal tubular cells caused by ischaemia, hypoxia or nephrotoxins which is usually reversible. Acute cortical necrosis (ACN) is advanced parenchymal destruction secondary to ischaemia, sepsis or toxins.
Key Points
- Oliguria in a surgical patient is an emergency. The cause must be identified and treated promptly.
- Prompt correction of pre-renal causes may prevent the development of established renal failure.
- Ensure the oliguric patient is normovolaemic as far as possible before starting diuretics or other therapies.
- Don’t use blind, large fluid challenges, especially in the elderly – if necessary use a CVP line or transfer to HDU.
- Established renal failure requires specialist support as electrolyte and fluid imbalances can be rapid in onset and difficult to manage.
Common Causes
Pre-Renal Failure (Volume Depletion and Hypotension, Structurally Intact Nephrons)
- Shock from any cause causing reduced renal perfusion (hypovolaemia, haemorrhage, burns, pancreatitis, sepsis, anaphylaxis, heart failure).
- Arteriolar vasoconstriction leading to ARF can occur with hypercalcaemia, radio-contrast agents, NSAIDs, ACE inhibitors, angiotensin receptor blockers and the hepatorenal syndrome.
Intrinsic Renal Failure (Structural and Functional Damage to Kidney)
- Vascular: renal ischaemia (ATN).
- Glomerular: acute glomerulonephritis.
- Tubular (ATN):
