Chapter 74: Acute Kidney Injury

INTRODUCTION

Acute kidney injury (AKI) is a clinical syndrome generally defined by an abrupt reduction in kidney function as evidenced by changes in serum creatinine (Scr), blood urea nitrogen (BUN), and urine output.
RIFLE (Risk, Injury, Failure, Loss of Kidney Function, and End-Stage Renal Disease), AKIN (Acute Kidney Injury Network), and the Kidney Disease: Improving Global Outcomes (KDIGO) clinical practice guidelines are three criteria-based classification systems developed to define and stage AKI in different patient populations (Table 74-1).
All three staging systems have been validated across different patient populations, and their staging correlates closely with hospital mortality, cost, and length of stay.
Scr and urine output are the main diagnostic criteria for each staging system.

TABLE 74-1RIFLE, AKIN, and KDIGO Classification Schemes for AKI^a

View Table||Download (.pdf)

TABLE 74-1 RIFLE, AKIN, and KDIGO Classification Schemes for AKI^a

RIFLE Category

Scr and GFR^b Criteria

Urine Output Criteria

Risk

Scr increase to 1.5-fold or GFR decrease >25% from baseline

<0.5 mL/kg/hr for ≥6 hr

Injury

Scr increase to 2-fold or GFR decrease >50% from baseline

<0.5 mL/kg/hr for ≥12 hr

Failure

Scr increase to 3-fold or GFR decrease >75% from baseline, or Scr ≥4 mg/dL (354 μmol/L) with an acute increase of at least 0.5 mg/dL (44 μmol/L)

Anuria for ≥12 hr

Loss

Complete loss of function (RRT) for >4 weeks

ESKD

RRT >3 months

AKIN Criteria

Scr Criteria

Urine Output Criteria

Stage 1

Scr increase ≥0.3 mg/dL (27 μmol/L) or 1.5- to 2-fold from baseline

<0.5 mL/kg/hr for ≥6 hr

Stage 2

Scr increase >2- to 3-fold from baseline

<0.5 mL/kg/hr for ≥12 hr

Stage 3

Scr increase >3-fold from baseline, or Scr ≥4 mg/dL (354 μmol/L) with an acute increase of at least 0.5 mg/dL (44 μmol/L), or need for RRT

<0.3 mL/kg/hr for ≥24 hr or anuria for ≥12 hr

KDIGO Criteria

Scr Criteria

Urine Output Criteria

Stage 1

Scr increase ≥0.3 mg/dL (27 μmol/L) or 1.5–1.9 times from baseline

<0.5 mL/kg/hr for 6–12 hr

Stage 2

Scr increase 2–2.9 times from baseline

<0.5 mL/kg/hr for ≥12 hr

Stage 3

Scr increase three times from baseline, or Scr ≥4 mg/dL (354 μmol/L), or need for RRT, or eGFR^c <35 mL/min/1.73 m² (0.34 mL/sec/m²) in patients <18 years

Anuria for ≥12 hr

^aFor all staging systems, the criterion that leads to worst possible diagnosis should be used.

^bGFR calculated using the Modification of Diet in Renal Disease (MDRD) equation.

^cGFR calculated using the Schwartz formula.

AKI, acute kidney injury; AKIN, Acute Kidney Injury Network; ESKD, end-stage kidney disease; eGFR, estimated glomerular filtration rate; h, hours; KDIGO, Kidney Disease: Improving Global Outcomes; RIFLE, Risk, Injury, Failure, Loss of Kidney Function, and End-Stage Kidney Disease; RRT, renal replacement therapy; Scr, serum creatinine.

PATHOPHYSIOLOGY

AKI can be categorized as prerenal (resulting from decreased renal perfusion ...

GET ACCESS TO THIS RESOURCE

Your MyAccess profile is currently affiliated with '[InstitutionA]' and is in the process of switching affiliations to '[InstitutionB]'. Please click ‘Continue’ to continue the affiliation switch, otherwise click ‘Cancel’ to cancel signing in.