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

Abstract

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.