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Chapter 246. Acute Kidney Injury

Kuyilan Karai Subramanian, MD; Ajay K. Singh, MD, MBA, FRCP

  1. How is acute kidney injury defined?

  2. What are the major causes of acute kidney injury?

  3. How is acute kidney injury diagnosed and managed?

  4. What role does renal replacement therapy, such as hemodialysis, have in acute kidney injury?

Acute kidney injury (AKI) is defined as a potentially reversible sudden deterioration in renal function due to prerenal, intrarenal, or postrenal causes. AKI is frequently accompanied by dysregulation of extracellular fluid volume and electrolytes and a marked increase in the retention of nitrogenous and nonnitrogenous waste products over a period of hours to weeks. AKI may be oliguric (< 400 mL/day) or nonoliguric (> 400 mL/day). AKI can also be defined as an acute and sustained increase in serum creatinine of 0.5 mg/dL (44.2 micromol/L), if the baseline is less than 2.5 mg/dL (221 mmol/L), or an increase in serum creatinine more than 20% if the baseline is more than 2.5 mg/dL (221 mmol/L).

There have been several attempts to achieve consensus among intensivists and nephrologists on the definition of AKI. The Acute Dialysis Quality Initiative (ADQI) group published the RIFLE classification of AKI in 2004 based on three severity categories (risk, injury, and failure) and two clinical outcome categories (loss and end-stage renal disease) (Table 246-1). The parameters assessed in the RIFLE classification are changes in serum creatinine level or glomerular filtration rate (GFR) or urine output (UO) from the patient's baseline. The baseline serum creatinine level and GFR may not be readily available. Hence the consensus committee recommends the use of the Modification of Diet in Renal Disease (MDRD) equation to estimate GFR/1.73 m2. The proportional decrease in GFR is calculated from 75 mL/min per 1.73 m2, the agreed-upon lower limit of normal.

Table 246-1 RIFLE Classification for AKI
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Table 246-1 RIFLE Classification for AKI
  • Risk (R)—Increase in serum creatinine level × 1.5 or decrease in GFR by 25%, or UO < 0.5 mL/kg/h for 6 hours
  • Injury (I)—Increase in serum creatinine level × 2.0 or decrease in GFR by 50%, or UO < 0.5 mL/kg/h for 12 hours
  • Failure (F)—Increase in serum creatinine level × 3.0, decrease in GFR by 75%, or serum creatinine level > 4 mg/dL with acute increase of > 0.5 mg/dL; UO < 0.3 mL/kg/h for 24 hours, or anuria for 12 hours
  • Loss (L)—Persistent AKI, complete loss of kidney function > 4 weeks
  • End-stage kidney disease (E)—Loss of kidney function > 3 months

A modified RIFLE criteria schema has been proposed by the Acute Kidney Injury Network (AKIN).The AKIN diagnostic criteria (Table 246-2) and the classification/staging system (Table 246-3) for AKI are an abrupt (within 48 hours) reduction in kidney function currently defined as an absolute increase in serum creatinine of more than or equal to 0.3 mg/dL (≥ 26.4 μmol/L), a percentage increase in serum creatinine of more than or ...

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