Association between Intraoperative End-Tidal Carbon Dioxide and Postoperative Organ Dysfunction in Major Abdominal Surgery: A Retrospective Cohort Study

Background Data on the effects of intraoperative end-tidal carbon dioxide (EtCO 2 ) levels on postoperative organ dysfunction are limited. Thus, this study was designed to investigate the relationship between the intraoperative EtCO 2 level and postoperative organ dysfunction in patients who underwent major abdominal surgery under general anesthesia. Methods We conducted a retrospective cohort study involving patients who underwent major abdominal surgery under general anesthesia at Kyoto University Hospital. We classified those with a mean EtCO 2 of less than 35 mmHg as low EtCO 2 . The time effect was determined as the minutes when the EtCO 2 value was below 35 mmHg, whereas the cumulative effect was evaluated by measuring the area below the 35-mmHg threshold. The outcome was postoperative organ dysfunction, defined as a composite of at least one organ dysfunction among acute renal injury, circulatory dysfunction, respiratory dysfunction, coagulation dysfunction, and liver dysfunction within 7 days after surgery. Results Of the 4,171 patients, 1,195 (28%) had low EtCO 2 , and 1,428 (34%) had postoperative organ dysfunction. An association was found between low EtCO 2 and increased postoperative organ dysfunction (adjusted risk ratio, 1.11; 95% confidence interval [CI], 1.03–1.20; p = 0.006). Additionally, long-term exposure to EtCO 2 values of less than 35 mmHg (≥224 min) was associated with postoperative organ dysfunction (adjusted risk ratio, 1.18; 95% CI, 1.06–1.32; p = 0.003) and low EtCO 2 severity (area under the threshold) (adjusted risk ratio, 1.13; 95% CI, 1.02–1.26; p = 0.018). Conclusions Intraoperative low EtCO 2 of below 35 mmHg was associated with increased postoperative organ dysfunction.