Performance of Lactate and CO2-Derived Parameters in Predicting Major Postoperative Complications After Cardiac Surgery With Cardiopulmonary Bypass: Protocol of a Diagnostic Accuracy Study

Background: CO 2 -derived parameters are increasingly used to identify either low-flow status or anaerobic metabolism in shock resuscitation. However, the performance of CO 2 -derived parameters in cardiac surgical patients is poorly understood. This study aims to compare the performance of lactate and CO 2 -derived parameters in predicting major postoperative complications after cardiac surgery with cardiopulmonary bypass. Methods: This is a prospective, single-center, diagnostic accuracy study. All patients who receive elective cardiac surgery involving cardiopulmonary bypass will be screened for study eligibility. Blood samples will be taken for the calculation of CO 2 -derived parameters, including the venous-arterial difference in CO 2 partial pressure (PCO 2 gap), venous-arterial difference in CO 2 content to arterial-venous O 2 content ratio (Cv-aCO 2 /Ca-vO 2 ), and venous-arterial difference in CO 2 partial pressure to arterial-venous O 2 content ratio (Pv-aCO 2 /Ca-vO 2 ) at ICU admission, and 3, 6, and 12 h later. Baseline, perioperative data will be collected daily for 7 days; patients will be followed up for 28 days to collect outcome data. The primary endpoint is the occurrence of major postoperative complications. Receiver-operating characteristics (ROC) curve analysis will be carried out to assess the predictive performance of lactate and CO 2 -derived parameters. The performance of the ROC curves will be compared. Discussion: The performance of lactate and CO 2 -derived parameters in predicting major postoperative complications will be investigated in the non-sepsis population, which has not been extensively investigated. Our study will compare the two surrogates of respiratory quotient directly, which is an important strength. Trial Registration: ChiCTR, ChiCTR2000029365. Registered January 26th, 2020, http://www.chictr.org.cn/showproj.aspx?proj=48744 .