Acute Kidney Injury

Excerpt

Acute kidney injury (AKI), previously called acute renal failure (ARF), denotes a sudden and often reversible reduction in kidney function, as measured by glomerular filtration rate (GFR). However, immediately after a renal insult, blood urea nitrogen (BUN) or creatinine (Cr) levels may be within the normal range, and the only sign of AKI may be a decline in urine output. AKI can lead to the accumulation of water, sodium, and other metabolic products. AKI can also result in other electrolyte disturbances. AKI is a prevalent condition, especially among hospitalized patients, and can be seen in up to 7% of hospital admissions and 30% of ICU admissions. Several criteria have been used to identify AKI, such as RIFLE, AKIN (Acute Kidney Injury Network), and KDIGO (Kidney Disease: Improving Global Outcomes) criteria. Among these, KDIGO is the most recent and most commonly used tool. According to KDIGO, AKI is the presence of any of the following:

1. Increase in serum creatinine by 0.3 mg/dL or more (26.5 μmol/L or more) within 48 hours

2. Increase in serum creatinine to 1.5 times or more than the baseline of the prior 7 days

3. Urine volume less than 0.5 mL/kg/h for at least 6 hours

The RIFLE criteria define 3 categories of impairment—risk, injury, and failure—and 2 categories of long-term renal outcomes—loss and end-stage renal disease (ESRD). Whichever criterion shows the most impairment is used for classification. When baseline Cr is unknown, a baseline GFR between 75 and 100 mL/min is assumed, or the Modification of Diet in Renal Disease (MDRD) equation can be used to calculate an estimated baseline Cr.

1. Risk: Cr ↑ of 1.5x baseline, GFR ↓ of 25%, or urine output <0.5mL/kg/h for 6 h

2. Injury: Cr ↑ of 2x baseline, GFR ↓ of 50%, or urine output <0.5mL/kg/h for 12 h

3. Failure: Cr ↑ of 3x baseline, GFR ↓ of 75 %, Cr ≥4.0, or urine output <0.5mL/kg/h for 12 h

4. Loss: Loss of kidney function for over 4 weeks

5. ESRD: Loss of kidney function for over 3 months

The AKIN criteria are based on the RIFLE criteria and are also called the "modified RIFLE" criteria. While the RIFLE and KDIGO systems have higher sensitivity than AKIN, all 3 have similar predictive abilities for in-hospital mortality.