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

PURPOSE

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

METHODS

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

RESULTS

Of 4,710 patients, 1,374 (29%) had low EtCO 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 EtCO 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 EtCO 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 EtCO < 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).

CONCLUSION

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