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acute kidney injury (AKI)

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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:

  1. The Renal Association (May 2006).UK CKD Guidelines
  2. UK Renal Association (2011). Acute Kidney Injury
  3. NICE (August 2013). Acute kidney injury - Prevention, detection and management of acute kidney injury up to the point of renal replacement therapy

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