A quasi-experimental study of fresh oxygen flow on patients’ oxygen reserve during mask-assisted ventilation under general anesthesia induction

BACKGROUND: To compare the effect of different amounts of fresh oxygen flow on oxygen reserve in patients undergoing general anesthesia. METHODS: Seventy-two patients were enrolled in this quasi-experimental study. Patients were randomly divided into experimental groups with a fresh oxygen flow of 1 L/min, 2 L/min, 4 L/min, and 8 L/min (denoted as G1, G2, G3, and G4, respectively) for 2 min of mask-assisted ventilation. Safe apnea time (SAT) was the primary endpoint; SAT was defined as the time from the cessation of ventilation to the time the patient’s pulse oxygen saturation (SpO(2)) decreased to 90%. Ventilation indicators such as end-tidal oxygen concentration (EtO(2)), end-tidal carbon dioxide partial pressure (EtCO(2)), SpO(2,) and carbon dioxide (CO(2)) elimination amount, during mask-assisted ventilation, were the secondary endpoints. RESULTS: The SAT of G1, G2, G3, and G4 were 305.1 ± 97.0 s, 315 ± 112.5 s, 381.3 ± 118.6 s, and 359 ± 104.4 s, respectively (p > 0.05). The EtO(2) after 2 min of mask-assisted ventilation in groups G1, G2, G3, and G4 were 69.7 ± 8.8%, 75.2 ± 5.0%, 82.5 ± 3.3%, and 86.8 ± 1.5%, respectively (p < 0.05). Also, there was a moderate positive correlation between the fresh oxygen flow and EtO(2) (correlation coefficient r = 0.52, 95% CI 0.31–0.67, p < 0.0001). The CO(2) elimination in the G1 and G2 groups was greater than that in the G4 group (p < 0.05). There was no significant difference in other indicators among the groups (all p > 0.05). CONCLUSION: The amount of fresh oxygen flow during mask-assisted ventilation was positively correlated with EtO(2). Also, even though there was no significant difference, the patients’ oxygen reserves increased with the increase in fresh oxygen flow.