The Ability of Carbon Dioxide-Derived Indices to Predict Adverse Outcome After Cardiac Surgery

Abstract

Objective: The objective of this study was to assess whether the central venous-to-arterial carbon dioxide partial-pressure difference (ΔPCO₂) and the ratio of the ΔPCO₂ to the arterial-venous difference in oxygen content (ΔPCO₂/Ca-vO₂) predict postoperative complications (PC) after cardiac surgery.

Design: Prospective, observational, noninterventional study.

Participants: The study comprised 60 patients undergoing cardiac surgery with cardiopulmonary bypass.

Interventions: The primary endpoint was the occurrence of PC. Data were first analyzed in two groups based on the occurrence of PC. Then, receiver operating characteristic curves of the ΔPCO₂ and the ΔPCO₂/Ca-vO₂ ratio were analyzed for the prediction of PC.

Measurements and main results: Among the study participants, 22 (36.7%) experienced PC. The death rate was 18.3%. The present study found that the ΔPCO₂ and the ΔPCO₂/Ca-vO₂ ratio predicted the occurrence of PC with areas under the curve of 0.702 and 0.666, respectively. The best thresholds of these markers were 8.3 mmHg for the ΔPCO₂ and 2.16 mmHg/mL for the ΔPCO₂/Ca-vO₂ ratio. A significant difference was found for these indicators between the groups with and without PC. The ΔPCO₂ and the ΔPCO₂/Ca-vO₂ ratio were significantly correlated to EuroSCORE II, duration of aortic clamping, majority of prognostic scores the first two days postoperatively, and the lactate level. The ΔPCO₂/Ca-vO₂ ratio is predictive of hyperlactatemia >2 mmol/L, with an area under the curve of 0.787.

Conclusion: The ΔPCO₂ and the ΔPCO₂/Ca-vO₂ ratio predict the occurrence of complications in cardiac surgery.

Keywords: cardiac surgery; cardiopulmonary bypass; central venous-to-arterial carbon dioxide partial- pressure difference; central venous-to-arterial carbon dioxide partial-pressure difference to arterial-venous difference in oxygen content ratio; postoperative complications.