Association of exposure below various thresholds of hemodynamic parameters during cardiopulmonary bypass with acute kidney injury

Introduction: This study aimed to investigate the association of exposure below various thresholds of mean arterial pressure (MAP), pump flow rates, and hemoglobin levels during cardiopulmonary bypass (CPB) with cardiac surgery-associated acute kidney injury (CSA-AKI). Methods: Adult patients undergoing cardiac surgery with CPB at a university hospital between April 2015 and August 2023 were included. The primary outcome was CSA-AKI within 7 days postoperatively. The primary exposures were the area under the threshold (AUT) of MAP, pump flow rate, and Hb during CPB. A multivariable logistic regression using covariates selected via Lasso regularization estimated the adjusted odds ratios (aORs) and 95% confidence intervals (CIs). Results: We finally analyzed 333 patients, of which 156 patients (46.8%) developed CSA-AKI. The AUT of hemoglobin, but not those of MAP and pump flow rate, was associated with CSA-AKI. The lower the threshold, the stronger the association (<8 g/dL, aOR = 1.132 per 10 g/dL × min, 95% CI = 1.036–1.243, p = 0.007; <9 g/dL, aOR = 1.048, 95% CI = 1.013–1.086, p = 0.007; and <10 g/dL, aOR = 1.027, 95% CI = 1.007–1.048, p = 0.010). Conclusion: Hemoglobin levels during CPB below 8.0 g/dL were associated with CSA-AKI, while MAP and pump flow rates indicated no such association.