Outlying End-Tidal Carbon Dioxide During General Anesthesia Is Associated With Postoperative Pulmonary Complications: A Multicenter Retrospective Observational Study From US Hospitals Between 2010 and 2017

BACKGROUND: Postoperative pulmonary complications (PPCs) occur in up to 33% of patients who undergo noncardiothoracic surgery. Emerging evidence suggests that permissive hypercapnia may reduce the risk of lung injury. We hypothesized that higher intraoperative end-tidal carbon dioxide (Etco2) concentrations would be associated with a decreased risk of PPCs.

METHODS: This retrospective, observational, multicenter study included patients undergoing general anesthesia for noncardiothoracic procedures (January 2010-December 2017). The primary outcome was PPC within 30 postoperative days. Secondary outcomes were PPC within 1 week, postoperative length of stay, and inhospital 30-day mortality. The association between these outcomes, median Etco2, and 4 time-weighted average area-under-the-curve (TWA-AUC) thresholds (<28, <35, <45, and >45 mm Hg) was explored using a multivariable mixed-effect model and by plotting associated risks.

RESULTS: Among 143,769 cases across 11 hospitals, 10,276 (7.1%) experienced a PPC. When compared to a baseline median Etco2 of 35 to 40 mm Hg, a median Etco2 >40 mm Hg was associated with an increase in PPCs within 30 days (median Etco2, 40-45 mm Hg; adjusted OR, 1.16 [99% confidence interval {CI}, 1.00-1.33]; P value = .008 and median Etco2, >45 mm Hg; OR, 1.64 [99% CI, 1.33-2.02]; P value < .001). The occurrence of any Etco2 value <28 mm Hg (ie, a positive TWA-AUC < 28 mm Hg) was associated with PPCs (OR, 1.40 [95% CI, 1.33-1.49]; P value < .001), mortality, and length of stay. Any Etco2 value >45 mm Hg (ie, a positive TWA-AUC >45 mm Hg) was also associated with PPCs (OR, 1.24 [95% CI, 1.17-1.31]; P < .001). The Etco2 range with the lowest incidence of PPCs was 35 to 38 mm Hg.

CONCLUSIONS: Both a very low (<28 mm Hg) and a high Etco2 (>45 mm Hg) were associated with PPCs within 30 days. The lowest PPC incidence was found in patients with an Etco2 of 35 to 38 mm Hg. Prospective studies are needed to clarify the relationship between postoperative PPCs and intraoperative Etco2.