Correlating oxygen delivery on cardiopulmonary bypass with Society of Thoracic Surgeons outcomes following cardiac surgery

Background: The relationship between low oxygen delivery (DO₂) on cardiopulmonary bypass and morbidity and mortality following cardiac surgery remains unexamined.

Methods: We reviewed patients undergoing Society of Thoracic Surgeons index procedures from March 2019 to July 2020, coincident with implementation of a new electronic perfusion record that provides for continuous recording of DO₂ and flow parameters. Continuous perfusion variables were analyzed using area-over-the-curve (AOC) calculations below predefined thresholds (DO₂ <280 mL O₂/min/m², cardiac index <2.2 L/min, hemoglobin < baseline, and mean arterial pressure <65 mm Hg) to quantify depth and duration of potentially harmful exposures. Multivariable logistic regression adjusted by Society of Thoracic Surgeons predicted-risk scores were used to assess for relationship of perfusion variables with the primary composite outcome of any Society of Thoracic Surgeons index procedure, as well as individual Society of Thoracic Surgeons secondary outcomes (eg, mortality, renal failure, prolonged ventilation >24 hours, stroke, sternal wound infection, and reoperation).

Results: Eight hundred thirty-four patients were included; 42.7% (356) underwent isolated coronary artery bypass grafting (CABG), whereas 57.3% underwent nonisolated CABG (eg, valvular or combined CABG/valvular operations). DO₂ <280-AOC trended toward association with the primary outcome across all cases (P = .07), and was significantly associated for all nonisolated CABG cases (P = .02)-more strongly than for cardiac index <2.2-AOC (P = .04), hemoglobin <7-AOC (P = .51), or mean arterial pressure <65-AOC (P = .11). Considering all procedures, DO₂ <280-AOC was independently associated prolonged ventilation >24 hours (P = .04), an effect again most pronounced in nonisolated-CABG cases (P = .002), as well as acute kidney injury <72 hours (P = .04). Patients with glomerular filtration rate <65 mL/min and baseline hemoglobin <12.5 g/dL appeared especially vulnerable.

Conclusions: Low DO₂ on bypass may be associated with morbidity/mortality following cardiac surgery, particularly in patients undergoing nonisolated CABG. These results underscore the importance of goal-directed perfusion strategies.