acute renal failure (ARF)

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Acute kidney injury

acute kidney injury (AKI) has replaced the term acute renal failure and an universal definition and staging system has been proposed to allow earlier detection and management of AK. Clinically AKI is characterised by a rapid reduction in kidney function resulting in a failure to maintain fluid, electrolyte and acid-base homoeostasis.

Acute kidney injury is common in hospitalised patients and also has a poor prognosis with the mortality ranging from 10%-80% dependent upon the patient population studied

Patients who present with uncomplicated AKI, have a mortality rate of up to 10%

in contrast, patients presenting with AKI and multiorgan failure have been reported to have mortality rates of over 50%. If renal replacement therapy is required the mortality rate rises further to as high as 80%

Definition of AKI

Acute kidney injury is defined when one of the following criteria is met

serum creatinine rises by >= 26 µmol/L within 48 hours or
serum creatinine rises >= 1.5 fold from the reference value, which is known or presumed to have occurred within one week or
oliguria (urine output is < 0.5ml/kg/hr for >6 consecutive hours) or
a 25% or greater fall in eGFR in children and young people within the past 7 days (3)

The reference serum creatinine should be the lowest creatinine value recorded within 3 months of the event

If a reference serum creatinine value is not available within 3 months and AKI is suspected

repeat serum creatinine within 24 hours
a reference serum creatinine value can be estimated from the nadir serum creatinine value if patient recovers from AKI

Staging of AKI

Stage of AKI	Serum creatinine (SCr) criteria	Urine output criteria
1	increase >=26 µmol/L within 48hrs or increase >= 1.5 to 1.9 X reference SCr	<0.5 mL/kg/hr for > 6 consecutive hrs
2	increase >= 2 to 2.9 X reference SCr	<0.5 mL/kg/ hr for > 12 hrs
3	increase >=3 X reference SCr or increase >=354 µmol/L or commenced on renal replacement therapy (RRT) irrespective of stage	<0.3 mL/kg/ hr for > 24 hrs or anuria for 12 hrs

Notes:

formula-based estimated GFR should be interpreted with caution in AKI - this is because the formulae rely on a stable serum creatinine concentration
is a clinical syndrome characterised by a rapid decline in excretory function occurring over a period of hours or day
if a patient has suspected AKI the s/he should be referred to a nephrologist
acute on chronic renal failure
- if there has been a fall in estimated GFR of >25% since the last measurement of kidney function in a patient with CKD should prompt a repeat measurement of kidney function, assessment as for AKI and referral if the deterioration is confirmed

Reference:

Last edited 04/2019 and last reviewed 01/2020

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