An observational study of end-tidal carbon dioxide trends in general anesthesia

Despite growing evidence supporting the potential benefits of higher end-tidal carbon dioxide (ETCO₂) levels in surgical patients, there is still insufficient data to formulate guidelines for ideal intraoperative ETCO₂ targets. As it is unclear which intraoperative ETCO₂ levels are currently used and whether these levels have changed over time, we investigated the practice pattern using the Multicenter Perioperative Outcomes Group database.

This retrospective, observational, multicentre study included 317,445 adult patients who received general anesthesia for non-cardiothoracic procedures between January 2008 and September 2016. The primary outcome was a time-weighted average area-under-the-curve (TWA-AUC) for four ETCO₂ thresholds (< 28, < 35, < 45, and > 45 mmHg). Additionally, a median ETCO₂ was studied. A Kruskal-Wallis test was used to analyse differences between years. Random-effect multivariable logistic regression models were constructed to study variability.

Both TWA-AUC and median ETCO₂ showed a minimal increase in ETCO₂ over time, with a median [interquartile range] ETCO₂ of 33 [31.0-35.0] mmHg in 2008 and 35 [33.0-38.0] mmHg in 2016 (P <0.001). A large inter-hospital and inter-provider variability in ETCO₂ were observed after adjustment for patient characteristics, ventilation parameters, and intraoperative blood pressure (intraclass correlation coefficient 0.36; 95% confidence interval, 0.18 to 0.58).

Between 2008 and 2016, intraoperative ETCO₂ values did not change in a clinically important manner. Interestingly, we found a large inter-hospital and inter-provider variability in ETCO₂ throughout the study period, possibly indicating a broad range of tolerance for ETCO₂, or a lack of evidence to support a specific targeted range. Clinical outcomes were not assessed in this study and they should be the focus of future research.