Acute Kidney Injury
Summary
Acute kidney injury (AKI) is an abrupt decline in kidney function characterised by rising creatinine and/or decreased urine output. It is classified using KDIGO staging. AKI is categorised as pre-renal (hypoperfusion), intrinsic (parenchymal damage - ATN, GN), or post-renal (obstruction). Management involves identifying and treating the underlying cause, stopping nephrotoxins, and initiating dialysis when indicated.
Key Facts
- Definition: Acute decline in kidney function (KDIGO criteria)
- Incidence: 5-7% of hospital admissions
- Peak Demographics: Elderly, critically ill
- Pathognomonic: Rising creatinine + decreased urine output
- Gold Standard Investigation: Creatinine trend, urine output, USS
- First-line Treatment: Address underlying cause, stop nephrotoxins
- Prognosis: Variable; hospital mortality 10-30%
Clinical Pearls
Pre-renal Pearl: FeNa less than 1% suggests pre-renal; greater than 2% suggests ATN.
Nephrotoxin Pearl: Stop NSAIDs, ACEi/ARBs, aminoglycosides acutely.
Dialysis Pearl: AEIOU - Acidosis, Electrolytes (K), Intoxication, Overload, Uraemia.
| Stage | Creatinine | Urine Output |
|---|---|---|
| 1 | 1.5-1.9x baseline or rise 26+ | Less than 0.5ml/kg/hr x6-12h |
| 2 | 2-2.9x baseline | Less than 0.5ml/kg/hr x12h+ |
| 3 | 3x baseline or greater than 354 | Less than 0.3ml/kg/hr x24h or anuria 12h |
| Type | Cause | FeNa |
|---|---|---|
| Pre-renal | Hypovolaemia, sepsis, HF | Less than 1% |
| Intrinsic | ATN, GN, AIN | Greater than 2% |
| Post-renal | Obstruction | Variable |
Algorithm
Initial Steps
- Stop nephrotoxins
- Fluid resuscitation if pre-renal
- Relieve obstruction if post-renal
- Treat underlying cause
Dialysis Indications (AEIOU)
- Refractory Acidosis
- Refractory hyperkalaemia (Electrolytes)
- Intoxication (dialysable toxins)
- Fluid Overload
- Uraemic complications
-
KDIGO AKI Work Group. KDIGO Clinical Practice Guideline for Acute Kidney Injury. Kidney Int Suppl. 2012;2(1):1-138.
-
NHS England. NHS England AKI Programme. 2015.
Viva Points
"AKI: KDIGO staging by creatinine and urine output. Pre-renal (FeNa less than 1), intrinsic (ATN, GN), post-renal (obstruction). Stop nephrotoxins, treat cause. Dialysis: AEIOU."
Last Reviewed: 2026-01-01 | MedVellum Editorial Team