Perioperative fluid balance affects staging of acute kidney injury in postsurgical patients: a retrospective case-control study

BACKGROUND: Although Acute Kidney Injury Network (AKIN) staging is widely used, it has been suggested that classification using serum creatinine levels, which fluctuate because of fluid balance, is not always appropriate for acute kidney injury (AKI) detection. We hypothesized that some patients are misdiagnosed as having no AKI due to dilution resulting from intraoperative infusion, and have worse outcomes than typical patients with no AKI. METHODS: We retrospectively selected patients who did not fulfill the AKI criteria from those who underwent cardiac surgery and remained in an intensive care unit (ICU) for ≥7 days. The patients were divided into two groups: those with AKI (AKI group) and those without AKI (no-AKI group), classified using serum creatinine levels adjusted for fluid balance during the perioperative period. We compared the characteristics and outcomes of the two groups. RESULTS: After adjustment for serum creatinine, 7 of 26 patients were categorized as having AKI. The AKI group had significantly fewer ventilator-free days during a 28-day period and significantly longer ICU stays than the no-AKI group (5.86 ± 10.0 days vs. 15.6 ± 9.71 days, respectively, P = 0.050; 36.4 ± 20.6 days vs. 14.9 ± 10.7 days, respectively, P = 0.033). CONCLUSION: Adjustment of creatinine level for perioperative fluid balance could improve the accuracy of AKI diagnosis after cardiac surgery.