Acute kidney injury in patients with acute lung injury: Impact of fluid accumulation on classification of acute kidney injury and associated outcomes

Objective: It has been suggested that fluid accumulation may delay recognition of acute kidney injury. We sought to determine the impact of fluid balance on the incidence of nondialysis requiring acute kidney injury in patients with acute lung injury and to describe associated outcomes, including mortality. Design: Analysis of the Fluid and Catheter Treatment Trial, a factorial randomized clinical trial of conservative vs. liberal fluid management and of management guided by a central venous vs. pulmonary artery catheter. Setting: Acute Respiratory Distress Syndrome Network hospitals. Patients: One thousand patients. Interventions: None. Measurements and Main Results: The incidence of acute kidney injury, defined as an absolute rise in creatinine of >= 0.3 mg/dL or a relative change of >50% over 48 hrs, was examined before and after adjustment of serum creatinine for fluid balance. The incidence of acute kidney injury before adjustment for fluid balance was greater in those managed with the conservative fluid protocol (57% vs. 51%, p = .04). After adjustment for fluid balance, the incidence of acute kidney injury was greater in those managed with the liberal fluid protocol (66% vs. 58%, p = .007). Patients who met acute kidney injury criteria after adjustment of creatinine for fluid balance (but not before) had a mortality rate that was significantly greater than those who did not meet acute kidney injury criteria both before and after adjustment for fluid balance (31% vs. 12%, p < .001) and those who had acute kidney injury before but not after adjustment for fluid balance (31% vs. 11%, p = .005). The mortality of those patients meeting acute kidney injury criteria after but not before adjustment for fluid balance was similar to patients with acute kidney injury both before and after adjustment for fluid balance (31% vs. 38%, p = .18). Conclusions: Fluid management influences serum creatinine and therefore the diagnosis of acute kidney injury using creatinine-based definitions. Patients with "unrecognized" acute kidney injury that is identified after adjusting for positive fluid balance have higher mortality rates, and patients who have acute kidney injury before but not after adjusting for fluid balance have lower mortality rates. Future studies of acute kidney injury should consider potential differences in serum creatinine caused by changes in fluid balance and the impact of these differences on diagnosis and prognosis. (Crit Care Med 2011; 39:2665-2671)