Nadir oxygen delivery on bypass and hypotension increase acute kidney injury risk after cardiac operations

Background Acute kidney injury (AKI) continues to complicate cardiac operations. We sought to determine whether nadir oxygen delivery (DO₂) on cardiopulmonary bypass (CPB) was a risk factor for AKI while also accounting for other postoperative factors. Methods Using propensity scoring, we matched 85 patients who developed AKI after cardiac operations on CPB with 85 control patients who did not. We analyzed the following variables through midnight on postoperative day 1 (POD1): DO₂, antibiotics, blood products and vasopressors (intraoperatively and postoperatively), and hemodynamic variables. Results Univariable analysis revealed AKI patients had lower nadir DO₂ on CPB (208 vs 230 mL O₂/min/m² body surface area, p = 0.03), lower intensive care unit admission blood pressure gradient across the kidney (mean arterial pressure minus central venous pressure; 60 vs 68 mm Hg; p < 0.001), a greater proportion of patients with mean arterial pressure of less than 60 mm Hg for more than 15 minutes in the postoperative period (70% vs 42%, p < 0.001), a greater chance of having a cardiac index of less than 2.2 (74% vs 49%, p = 0.02), and greater total vasopressor use through the end of POD1 (5.2 vs 2.3 mg, p = 0.002). On multivariable analysis, predictors of AKI were a DO₂ on CPB of less than 225 mL O₂/min/m² (odds ratio, 2.46; 95% confidence interval, 1.21 to 5.03; p = 0.01) and postoperative mean arterial pressure of less than 60 mm Hg for more than 15 minutes (odds ratio, 3.96; 95% confidence interval, 1.92 to 8.20; p < 0.001). An average postoperative pressor dose greater than 0.03 μg/kg/min did not reach significance (odds ratio, 1.98; 95% confidence interval, 0.95 to 4.11; p = 0.07). Conclusions Postoperative hypotension on POD0 or POD1 and low DO₂ on CPB both independently increase the AKI risk in cardiac surgical patients.