Efficacy of preoxygenation with end-tidal oxygen when using different oxygen concentrations in patients undergoing general surgery: a single-center retrospective observational study

Background: Preoxygenation is a simple but very important procedure for preventing arterial desaturation. A higher fraction of inspired oxygen (FiO2) increases atelectasis and 80% oxygen results in significantly less atelectasis than 100% oxygen. We investigated whether there was a difference in the duration of adequate preoxygenation when using 100% and 80% oxygen. The proportion of patients for whom >3 min was required to achieve adequate preoxygenation was also investigated.Methods: The VitalDB database of patients underwent general surgery between February 1, 2021 and November 12, 2021 was reviewed. The time between the start of preoxygenation and the point where a 10% difference between FiO2 and end-tidal oxygen (EtO2) was defined as the preoxygenation time. The patients were classified into 100% and 80% groups according to the oxygen concentration. Propensity score matching (PSM) was performed to control for potential confounding factors.Results: Only 330 of the 1,377 patients had sufficient data for analysis: 179 in the 80% group and 151 in the 100% group. After PSM, 143 patients in each group were analyzed. The median preoxygenation time was 143 s [interquartile range (IQR): 120.5-181.5 s] and 144 s (IQR: 109.75-186.25 s) in the 80% and 100% groups, respectively [P=0.605; median difference =-1 s; 95% confidence interval (CI): -13 to 10]. Of the patients, 27% required >3 min for adequate preoxygenation.Conclusions: No difference in preoxygenation time was found between the 80% and 100% groups. For some patients, breathing for 3 min is not sufficient for adequate preoxygenation. EtO2 monitoring aids evaluation of whether preoxygenation was adequate.