Oxygen Delivery Thresholds During Cardiopulmonary Bypass and Risk for Acute Kidney Injury

Background Postoperative acute kidney injury (AKI) in cardiac surgery patients is multifactorial and associated with low oxygen delivery (DO2) during cardiopulmonary bypass. Methods Cardiac surgical patients undergoing full cardiopulmonary bypass between May 1, 2016 and December 31, 2021 were included, whereas those on preoperative dialysis, undergoing circulatory arrest procedures, or lacking minute-to-minute physiologic data were excluded. A 5-minute running average of indexed DO2 (DO2i, mL/min/m2) was calculated ([pump flow] × [hemoglobin] × 1.36 [hemoglobin saturation] + 0.003 [arterial oxygen tension]/body surface area). AKI was defined using established Kidney Disease: Improving Global Outcomes criteria. The threshold of nadir DO2i on the effect of AKI was estimated using risk-adjusted Constrained Broken-Stick models. Results Postoperative AKI occurred among 1155 patients (29.4%), with 276 (7.0%) having stage 2 to 3 AKI. The median nadir DO2i was lower for those with (vs without) AKI (197.9 mL/min/m2 [interquartile range {IQR}, 166.3-233.2] vs 217.2 mL/min/m2 [IQR, 184.5-252.2], P < .001) and stage 2 to 3 AKI relative to stage 1 or none (186.9 mL/min/m2 [IQR, 160.1-220.5] vs 213.8 mL/min/m2 [IQR, 180.4-249.4]). In risk-adjusted analyses the estimated threshold for nadir DO2i was 231.2 mL/min/m2 (95% CI, 173.6-288.8) for any AKI and 103.3 (95% CI, 68.4-138.3) for stage 2 to 3 AKI. Conclusions Decreasing nadir DO2i was associated with an increased risk of AKI. The identified nadir DO2i thresholds suggest management and treatment of nadir DO2i during cardiopulmonary bypass may decrease a patient’s postoperative AKI risk.