Background: The overall incidence of acute kidney injury (AKI) or mortality after cardiac surgery is low, but mortality in patients with AKI remains high. Effects of factors such as change in comorbid disease burden, intraoperative factors, or postoperative complications on trends in the incidence of AKI and associated mortality after cardiac surgery were not examined.
Study design: Observational cohort study.
Setting & participants: 34,562 cardiac surgeries were performed from 1993 to 2002; only the first surgical procedure was considered (N = 33,217).
Predictor, outcomes, & measurements: AKI was defined as a composite outcome of a 50% or greater decrease in postoperative glomerular filtration rate or requirement of dialysis (AKI-D). Mortality was defined as postoperative hospital mortality. We examined effects of the predictors AKI and year of surgery on mortality after accounting for preoperative risk factors and serious postoperative complications.
Results: Between the first and second halves of the study period (1993 to 2002), the incidence of AKI increased from 5.1% to 6.6%, but the associated mortality rate decreased from 32% to 23% (P < 0.0001). Similarly, the incidence of AKI-D also increased from 1.5% to 2.0%, with a decrease in associated mortality from 61% to 49% (P < 0.01). In a risk-adjusted model, mortality in patients with AKI significantly decreased over time. Patients with AKI-D and with other organ system failures did not show improvement in survival over time. A preoperative history of congestive heart failure was associated significantly with a decrease in mortality risk over time, particularly in patients requiring dialysis.
Limitations: Single-center, retrospective, observational cohort design.
Conclusion: The incidence of AKI after cardiac surgery has increased over time. Although the adjusted risk of mortality decreased in patients with AKI without other postoperative complications, it is unchanged in those with multiorgan system failure.