Phys · renal
Acute Kidney Injury
Also known as AKI · acute renal failure · ARF · acute tubular necrosis · ATN · acute kidney failure · pre-renal AKI · intrinsic AKI · post-renal AKI · contrast-induced nephropathy · contrast-associated AKI · acute interstitial nephritis · AIN · sepsis-associated AKI · SA-AKI
Consultant-physician-depth guide to acute kidney injury — KDIGO definition and staging, pre-renal/intrinsic/post-renal classification, pathophysiology, investigation strategy, management principles, RRT indications, nephrotoxic agents, drug dosing, and prognosis. Structured for FRACP DWE and DCE preparation.
Checked against its sources on 13 Sept 2026
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Target exams
Red flags
- Life-threatening hyperkalaemia (K+ ≥6.5 mmol/L or ECG changes) requiring immediate calcium gluconate
- Severe metabolic acidosis (pH <7.1) refractory to medical therapy
- Pulmonary oedema from volume overload requiring ventilatory support
- Uraemic pericarditis or uraemic encephalopathy — absolute indications for RRT
- Anuria or rapidly rising creatinine suggesting obstruction or catastrophic intrinsic disease
- Rhabdomyolysis with CK >5000 or myoglobinuria requiring aggressive fluid resuscitation
Acute Kidney Injury
The answer first
Acute kidney injury (AKI) is an abrupt reduction in kidney function over hours to days, resulting in retention of nitrogenous waste products (rise in creatinine and urea) and impairment of fluid, electrolyte, and acid-base homeostasis. The KDIGO definition requires one of: creatinine rise of ≥26.5 micromol/L (0.3 mg/dL) within 48 hours; creatinine ≥1.5 times baseline within 7 days; or urine output <0.5 mL/kg/h for ≥6 hours [1].
The management mandate is simple to state, hard to execute well: [1]
- Resuscitate and assess volume status first — is this volume-responsive? Give fluid if depleted, remove fluid if overloaded.
- Treat the underlying cause — sepsis, obstruction, nephrotoxin, hypoperfusion.
- Remove all nephrotoxic agents and adjust every renally-cleared drug dose.
- Manage complications — hyperkalaemia, acidosis, fluid overload.
- Initiate renal replacement therapy (RRT) when absolute indications arise (AEIOU). [1]
The single most important exam principle: AKI is a syndrome, not a diagnosis. Always identify and name the cause. [1]
References8ShowHide
- [1]Ronco C, Bellomo R, Kellum JA. Acute kidney injury Lancet, 2019.PMID 31777389
- [2]Gaudry S, Hajage D, Schortgen F, et al. Initiation Strategies for Renal-Replacement Therapy in the Intensive Care Unit N Engl J Med, 2016.PMID 27181456
- [3]Bagshaw SM, Wald R, Adhikari NKJ, et al. Timing of Initiation of Renal-Replacement Therapy in Acute Kidney Injury N Engl J Med, 2020.PMID 32668114
- [4]Zarbock A, Kellum JA, Schmidt C, et al. Effect of Early vs Delayed Initiation of Renal Replacement Therapy on Mortality in Critically Ill Patients With Acute Kidney Injury: The ELAIN Randomized Clinical Trial JAMA, 2016.PMID 27209269
- [5]Weisbord SD, Gallagher M, Jneid H, et al. Outcomes after Angiography with Sodium Bicarbonate and Acetylcysteine N Engl J Med, 2018.PMID 29130810
- [6]Joannidis M, Forni LG, Klein SJ, et al. Lung-kidney interactions in critically ill patients: consensus report of the Acute Disease Quality Initiative (ADQI) 21 Workgroup Intensive Care Med, 2020.PMID 31820034
- [7]Kaddourah A, Basu RK, Bagshaw SM, Goldstein SL; AWARE Investigators. Epidemiology of Acute Kidney Injury in Critically Ill Children and Young Adults N Engl J Med, 2017.PMID 27959707
- [8]Jaber S, Paugam C, Futier E, et al. Sodium bicarbonate therapy for patients with severe metabolic acidaemia in the intensive care unit (BICAR-ICU): a multicentre, open-label, randomised controlled trial Lancet, 2018.PMID 29910040