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 (Et co 2 ) 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 Et co 2 , 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 Et co 2 of 35 to 40 mm Hg, a median Et co 2 >40 mm Hg was associated with an increase in PPCs within 30 days (median Et co 2 , 40–45 mm Hg; adjusted OR, 1.16 [99% confidence interval {CI}, 1.00–1.33]; P value = .008 and median Et co 2 , >45 mm Hg; OR, 1.64 [99% CI, 1.33–2.02]; P value < .001). The occurrence of any Et co 2 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 Et co 2 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 Et co 2 range with the lowest incidence of PPCs was 35 to 38 mm Hg. CONCLUSIONS: Both a very low (<28 mm Hg) and a high Et co 2 (>45 mm Hg) were associated with PPCs within 30 days. The lowest PPC incidence was found in patients with an Et co 2 of 35 to 38 mm Hg. Prospective studies are needed to clarify the relationship between postoperative PPCs and intraoperative Et co 2 .