Acute Kidney Injury: a Very Basic Introduction

Key points

• Acute kidney injury (AKI, formerly acute renal failure) is a rapid fall in renal function; staged by KDIGO on the rise in creatinine or the fall in urine output.
• Pre-renal (commonest): reduced renal perfusion — hypovolaemia (D&V, haemorrhage, burns), hypotension/sepsis, renal artery stenosis, or drugs (ACE-i/ARB, NSAIDs).
• Intrinsic (renal): damage to glomeruli, tubules or interstitium — acute tubular necrosis (ischaemia, nephrotoxins, contrast, rhabdomyolysis), glomerulonephritis, acute interstitial nephritis, vasculitis.
• Post-renal (obstructive): stones, tumour, stricture or prostatic enlargement — exclude with renal tract ultrasound.
• KDIGO staging (creatinine): stage 1 = 1.5-1.9x baseline; stage 2 = 2.0-2.9x; stage 3 = 3.0x or more (or creatinine 354+ micromol/L, or needing dialysis). Manage by treating the cause, optimising fluids/BP, stopping nephrotoxins and treating complications (hyperkalaemia, acidosis, fluid overload, uraemia).