Postoperative acute kidney injury (AKI) in cardiac surgery patients is multifactorial and associated with low oxygen delivery (DO₂) during cardiopulmonary bypass.

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.

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.

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.