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INTRODUCTION

Acute kidney injury (AKI) is defined as an acute and potentially reversible decline in the kidney function/glomerular filtration rate (GFR) that occurs over hours to days. It represents a spectrum of kidney injury ranging from mild to more severe forms of injury requiring renal replacement therapy (RRT). While AKI can occur in patients with normal kidney function, patients with a history of chronic kidney disease (CKD) are at higher risk (AKI on CKD). The Kidney Disease: Improving Global Outcomes (KDIGO) criteria are now accepted worldwide as the criteria for defining AKI (Table 40-1).1 Although AKI is more common after cardiac surgery, its incidence after noncardiac surgery is high as well. Even small postoperative increases in creatinine are associated with several adverse outcomes including higher rates of morbidity, mortality, cardiovascular events, longer lengths of stay, cost, and poor surgical outcomes.

TABLE 40-12012 - KDIGO Criteria for Diagnosing Acute Kidney Injury

EPIDEMIOLOGY

The incidence of AKI varies depending on the population studied, definition used, and setting in which AKI occurs. Cardiac and noncardiac surgeries differ in patient demographics and procedural risk factors, so the risk of AKI also differs in these groups. Advanced age, African American race, CKD, preexisting hypertension, and diabetes pose the greatest postoperative risk for AKI.2 In a retrospective study of 161,185 perioperative Veterans Health Administration patients, 11.8% developed AKI. The incidence of AKI was 4–8% in noncardiac surgery and approximately 19% of cardiac surgery patients. In both groups, AKI requiring RRT occurred in 0.1–0.4% of patients.3

DIAGNOSIS OF POSTOPERATIVE AKI

Serum creatinine is the standard laboratory test used to estimate GFR using equations like MDRD or CKD-EPI. Doubling of creatinine reflects a reduction in kidney function by 50%. Small changes at lower creatinine numbers reflect large changes in GFR, so the line graph depicting the relationship between creatinine and GFR is curvilinear. Creatinine levels can be misleading in patients with abnormal body habitus (amputations, paralysis, etc.) and extremes of age, and can vary based on diet (meat, creatine supplements). Formulas used to estimate GFR are based on steady state creatinine concentrations and are not reliable in extreme GFR states. A drawback with using creatinine as a marker of AKI is that the rise in creatinine lags behind the development of AKI and delays AKI detection. The KDIGO criteria thus use a combination of ...

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