Association of the red cell distribution width to total serum calcium ratio with severe AKI in patients undergoing cardiac surgery: a retrospective cohort study using the MIMIC-IV database

BACKGROUND: Acute kidney injury (AKI) is a common complication following cardiac surgery. The RCR (ratio of RDW to total serum calcium (TSC)), which exhibits high predictive value for various perioperative diseases, may also be associated with kidney injury. Therefore, we tested the hypothesis that the postoperative RCR index is associated with kidney injury following major cardiac surgery. METHODS: This was a retrospective observational cohort study. We included 7,872 patients who underwent cardiac surgery from the Medical Information Mart for Intensive Care IV (MIMIC-IV) database. The exposure was the first postoperative measurements of red blood cell distribution width (RDW) and Total serum calcium (TSC). The primary outcome was severe AKI, defined as stage 3 AKI or new-onset dialysis. Secondary outcomes included AKI of any stage, length of hospital stay, and length of intensive care unit (ICU) stay. RESULTS: A total of 5,992 patients (76.1%) developed postoperative AKI, among whom 3,348 (42.5%) had stage 2 AKI, 654 (8.3%) had stage 3 AKI, and 160 (2.0%) required new-onset dialysis. In the multivariate regression model, the RCR index (categorical variable) was significantly associated with severe AKI (adjusted odds ratio [OR], 2.02 [95% CI, 1.54-2.68]) and AKI of any stage (OR, 1.26 [95% CI, 1.05-1.50]). When the RCR index was treated as a continuous variable, this association remained statistically significant. CONCLUSIONS: Elevated postoperative RCR index is associated with postoperative AKI in patients who undergo cardiac surgery.