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

Abstract

The difference between arterial and end-tidal partial pressure of carbon dioxide (DCO 2 ) is a measure of alveolar dead space, commonly evaluated intraoperatively. Given its relationship to ventilation and perfusion, DCO 2 may provide prognostic information and guide clinical decisions. We hypothesized that higher DCO 2 values are associated with occurrence of a composite outcome of reintubation, 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 reintubation, 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 DCO 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 DCO 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 DCO 2 was associated with a