Background Data on the effects of intraoperative end-tidal carbon dioxide (EtCO2) levels on postoperative organ dysfunction are limited. Thus, this study was designed to investigate the relationship between the intraoperative EtCO2 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 EtCO2 of less than 35 mmHg as low EtCO2. The time effect was determined as the minutes when the EtCO2 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 EtCO2, and 1,428 (34%) had postoperative organ dysfunction. An association was found between low EtCO2 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 EtCO2 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 EtCO2 severity (area under the threshold) (adjusted risk ratio, 1.13; 95% CI, 1.02–1.26; p = 0.018).

Conclusions Intraoperative low EtCO2 of below 35 mmHg was associated with increased postoperative organ dysfunction.

The authors have declared no competing interest.

This work was supported in part by the Japan Society for the Promotion of Science KAKENHI program (grant number: 20K09242 principal investigator: Toshiyuki Mizota) and the 2019 Kyoto University ISHIZUE Research Development Program (principal investigator: Toshiyuki Mizota).

I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained.

Not Applicable

The details of the IRB/oversight body that provided approval or exemption for the research described are given below:

The Certified Review Board of Kyoto University(Yoshida-Konoe-cho, Sakyo-ku, Kyoto 606-8501, Japan, Chairperson Prof. Shinji Kosugi) approved the study protocol (approval number: R1272-3 January 23, 2020) and waived the requirement for informed consent because of the retrospective nature of the study.

I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals.

Not Applicable

I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance).

Not Applicable

I have followed all appropriate research reporting guidelines and uploaded the relevant EQUATOR Network research reporting checklist(s) and other pertinent material as supplementary files, if applicable.

Not Applicable

Data cannot be released to the public due to the inclusion of anonymous patient information. Researchers who meet the criteria for access to confidential data may obtain the data from the corresponding author.