One-year mortality in critically ill patients by severity of kidney dysfunction: A population-based assessment

Background: Kidney dysfunction in the intensive care unit (ICU) results in increased morbidity, mortality, and health care costs; however, long-term mortality has not been described across strata of severity in kidney dysfunction. Methods: The primary objective is to describe and assess factors associated with 1-year mortality in critically ill patients stratified by severity of kidney dysfunction during admission to the ICU. Kidney dysfunction is defined by peak serum creatinine values and stratified by: (1) no dysfunction (creatinine < 1.7 mg/dL [<150 mu mol/L]), (2) mild dysfunction (creatinine, 1.7 to 3.4 mg/dL [150 to 299 mu mol/L])), (3) moderate dysfunction (creatinine >= 3.4 mg/dL [>= 300 mu mol/L]), (4) severe acute dysfunction requiring renal replacement therapy (acute renal failure), or (5) preexisting end-stage kidney disease. Population-based surveillance was of adult residents of the Calgary Health Region (population, I million) admitted to any multidisciplinary ICU and a cardiovascular surgery ICU from May 1, 1999, to April 30,2002. Results: Of 5,693 admissions, 62% were men, median age was 64.9 years (Interquartile range, 50.6 to 74.5 years), and mean Acute Physiology and Chronic Health Evaluation (APACHE) II score was 24.9 +/- 8.7 (SD). Case fatality rates stratified by renal dysfunction were 17% (763 of 4,411), 47% (370 of 790),48% (77 of 160), 64% (153 of 240), and 40% (37 of 92) for no, mild, and moderate dysfunction; severe acute renal failure; and end-stage kidney disease, respectively. By means of multivariate analysis, 1-year mortality was associated independently with advancing age, medical diagnosis, higher APACHE II score, and presence and severity of kidney dysfunction, although no difference was evident comparing those with mild to moderate dysfunction. End-stage kidney disease was not associated independently with 1-year mortality. Conclusion: Severity of kidney dysfunction in patients in the ICU is associated with an incremental increase in long-term mortality. Although patients classified with either mild or moderate kidney dysfunction had an increased risk for death, use of serum creatinine level alone was poor at discriminating long-term outcome, suggesting this measure alone should not be used for defining long-term prognosis.