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

Abstract

Purpose: 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.

Methods: 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.

Results: 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).

Conclusions: 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.

Figures

Fig. 1

Flow chart. ASA = American Society of Anesthesiologist; CPT = current procedural terminology; ETCO2 = end-tidal carbon dioxide. LMA = laryngeal mask airway; MPOG = Multicenter Perioperative Outcomes Group. *Blood transfusion > two units was defined as: more than two units of packed cells or whole blood or more than 600 mL of cell saver blood during general anesthesia. †Patients were excluded when they met the inclusion criteria of more than one subgroup: e.g., chronic obstructive pulmonary disease (COPD) and laparoscopic surgery. ‡Only the first case within 30 days was included

Fig. 2

Trend in TWA-AUC ETCO2 for four different thresholds. The trend over time in mean time-weighted average area-under-the-curve (TWA-AUC) per quarter for an end-tidal carbon dioxide levels (ETCO2) of < 28 mmHg, < 35 mmHg, < 45 mmHg, and > 45 mmHg. The TWA-AUC decreased over time for an ETCO2 threshold of < 28, < 35, and < 45 mmHg, whereas the TWA-AUC ETCO2 > 45 mmHg increased over time

Fig. 3

Trend in median ETCO2 over time. The boxplots show an increase in median end-tidal carbon dioxide (ETCO2) values between 2008 and 2016 for the general cohort (A) and the subgroups (B–E). The triangle represents the mean, the whiskers represent the spread between the 10th and 90th percentile. The median ETCO2 was lower for patients presenting for intracranial and carotid artery surgery (B) compared with the general cohort. The median ETCO2 was higher for patients in the (robotic) laparoscopic cohort (C, D) and for patients with chronic obstructive pulmonary disease (COPD) (E) compared with the general cohort (A)