Intraoperative end-tidal carbon dioxide and postoperative mortality in major abdominal surgery: a historical cohort...

There is a paucity of data on the effect of intraoperative end-tidal carbon dioxide (EtCO₂) levels on postoperative mortality. The purpose of this study was to investigate the relationship between intraoperative EtCO₂ and 90-day mortality in patients undergoing major abdominal surgery under general anesthesia.

We conducted a historical cohort study of patients undergoing major abdominal surgery under general anesthesia at Kyoto University Hospital. We measured the intraoperative EtCO₂, and patients with a mean EtCO₂ value < 35 mm Hg were classified as low EtCO₂. The time effect was determined based on minutes below an EtCO₂ of 35 mm Hg, and cumulative effects were evaluated by measuring the area under the threshold of 35 mm Hg for each patient.

Of 4,710 patients, 1,374 (29%) had low EtCO₂ and 55 (1.2%) died within 90 days of surgery. Multivariable Cox regression analysis-adjusted for age, American Society of Anesthesiologists Physical Status classification, sex, laparoscopic surgery, emergency surgery, blood loss, mean arterial pressure, duration of surgery, type of surgery, and chronic obstructive pulmonary disease-revealed an association between low EtCO₂ and 90-day mortality (adjusted hazard ratio, 2.2; 95% confidence interval [CI], 1.2 to 3.8; P = 0.006). In addition, severity of low EtCO₂ was associated with an increased 90-day mortality (area under the threshold; adjusted hazard ratio; 2.9, 95% CI, 1.2 to 7.4; P =0.02); for long-term exposure to an EtCO₂ < 35 mm Hg (≥ 226 min), the adjusted hazard ratio for increased 90-day mortality was 2.3 (95% CI, 0.9 to 6.0; P = 0.08).

A mean intraoperative EtCO₂ < 35 mm Hg was associated with increased postoperative 90-day mortality.