Predicting postoperative complications with the respiratory exchange ratio after high-risk noncardiac surgery: A prospective cohort study. Issue 11 (November 2020) - Bar, Stéphane
Abstract : BACKGROUND: The respiratory exchange ratio (RER), defined as the ratio of CO2 production (VCO2 ) to O2 consumption (VO2 ), is reported to be a noninvasive marker of anaerobic metabolism. The intubated, ventilated patient's inspired and expired fractions of O2 and CO2 (FiO2, FeO2, FiCO2 and FeCO2 ) are monitored in the operating room and can be used to calculate RER. OBJECTIVE: To investigating the ability of the RER to predict postoperative complications. DESIGN: An observational, prospective study. SETTING: Two French university hospitals between March 2017 and September 2018. PATIENTS: A total of 110 patients undergoing noncardiac high-risk surgery. MAIN OUTCOME MEASURES: The RER was calculated as (FeCO2 − FiCO2 )/(FiO2 − FeO2 ) at five time points during the operation. The primary endpoint was at the end of the surgery. The secondary endpoints were systemic oxygenation indices (pCO2 gap, pCO2 gap/arteriovenous difference in O2 ratio, central venous oxygen saturation) and the arterial lactate level at the end of the surgery. Complications were classified according to the European Peri-operative Clinical Outcome definitions. RESULTS: Postoperative complications occurred in 35 patients (34%). The median [interquartile range] RER at the end of surgery was significantly greater in the subgroup with complications, 1.06 [0.84 to 1.35] than in the subgroup without complications, 0.81 [0.75 to 0.91], and correlated significantly with the arterial lactate ( r = 0.31, P < 0.001) and VO2 ( r = −0.23, P = 0.001). Analysis of the area under the receiver operating characteristic curve for the predictive value of RER for postoperative complications revealed a value of 0.77 [95% confidence interval (CI) 0.69 to 0.88, P = 0.001]. The best cut-off for the RER was 0.94, with a sensitivity of 71% (95% CI 54 to 85) and a specificity of 79% (95% CI 68 to 88). CONCLUSION: As a putative noninvasive marker of tissue hypoperfusion and anaerobic metabolism, the RER can be used to predict complications following high-risk surgery. TRIAL REGISTRATION: ClinicalTrials.gov identifier: NCT03471962. Abstract : Supplemental Digital Content is available in the text