Expansion
Staged by creatinine rise or urine output, classified as pre-renal, renal or post-renal
Expansion
Staging, by whichever criterion is worse
| Stage | Creatinine | Urine output |
|---|---|---|
| 1 | Rise of 26 micromol/l in 48 hours, or 1.5 to 1.9 times baseline | Under 0.5 ml/kg/h for 6 hours |
| 2 | 2 to 2.9 times baseline | Under 0.5 ml/kg/h for 12 hours |
| 3 | 3 times baseline, or over 354 micromol/l, or renal replacement therapy | Under 0.3 ml/kg/h for 24 hours, or anuria for 12 hours |
Causes
- Pre-renal, the commonest: hypovolaemia, sepsis, cardiac failure, hepatorenal syndrome, renal artery stenosis, and drugs that impair autoregulation, being ACE inhibitors, angiotensin receptor blockers and NSAIDs
- Renal: acute tubular necrosis (ischaemia, sepsis, rhabdomyolysis, contrast, nephrotoxins), glomerulonephritis, interstitial nephritis, vasculitis, myeloma, thrombotic microangiopathy
- Post-renal: stones, prostate, tumour, retroperitoneal fibrosis, blocked catheter
Distinguishing pre-renal from acute tubular necrosis
| Pre-renal | ATN | |
|---|---|---|
| Urine sodium | Under 20 | Over 40 |
| Fractional excretion of sodium | Under 1 per cent | Over 2 per cent |
| Urine osmolality | Over 500 | Under 350 |
| Response to fluid | Improves | No improvement |
| Urinalysis | Bland | Muddy brown casts |
Management is to treat the cause, restore perfusion, stop nephrotoxins, relieve obstruction, and identify the indications for dialysis: refractory hyperkalaemia, acidosis, fluid overload, uraemic encephalopathy or pericarditis, and certain poisonings.