Difference between arterial and end-tidal carbon dioxide and adverse events after non-cardiac surgery: a historical cohort study

PURPOSE: The difference between arterial and end-tidal partial pressure of carbon dioxide (ΔCO(2)) is a measure of alveolar dead space, commonly evaluated intraoperatively. Given its relationship to ventilation and perfusion, ΔCO(2) may provide prognostic information and guide clinical decisions. We hypothesized that higher ΔCO(2) values are associated with occurrence of a composite outcome of re-intubation, postoperative mechanical ventilation, or 30-day mortality in patients undergoing non-cardiac surgery. METHODS: We conducted a historical cohort study of adult patients undergoing non-cardiac surgery with an arterial line at a single tertiary care medical centre. The composite outcome, identified from electronic health records, was re-intubation, postoperative mechanical ventilation, or 30-day mortality. Student’s t test and Chi-squared test were used for univariable analysis. Logistic regression was used for multivariable analysis of the relationship of ΔCO(2) with the composite outcome. RESULTS: A total of 19,425 patients were included in the final study population. Univariable analysis showed an association between higher mean (standard deviation [SD]) intraoperative ΔCO(2) values and the composite outcome (6.1 [5.3] vs 5.7 [4.5] mm Hg; P = 0.002). After adjusting for baseline subject characteristics, every 5-mm Hg increase in the ΔCO(2) was associated with a nearly 20% increased odds of the composite outcome (odds ratio, 1.20; 95% confidence interval, 1.12 to 1.28; P < 0.001). CONCLUSIONS: In this patient population, increased intraoperative ΔCO(2) was associated with an increased odds of the composite outcome of postoperative mechanical ventilation, re-intubation, or 30-day mortality that was independent of its relationship with pre-existing pulmonary disease. Future studies are needed to determine if ΔCO(2) can be used to guide patient management and improve patient outcomes.