Volume-Controlled Inverse Ratio Ventilation Improves Safe Apnea Time in Obese Patients During Induction of General Anesthesia: A Randomized Controlled Trial

Yonghai Zhang ¹ Bin Li ² Chang Xu ¹ Yan Wu ¹ Ling Ma ¹ Fan Yang ¹ Hanxiang Ma ^1* Xinli Ni ^1*

• ¹ General Hospital of Ningxia Medical University, Yinchuan, China
• ² People’s Hospital of Ningxia Hui Autonomous Region, Yinchuan, China

Background: Inverse ratio ventilation theoretically increases oxygenation in obese patients. However, it is unknown whether the use of inverse ratio ventilation prolongs the safe apnea time during induction of anesthesia. The primary objective of our study was to compare the safe apnea time in obese surgical patients receiving either inverse ratio ventilation or conventional ratio ventilation during induction of anesthesia.Methods: This study is a prospective, randomized controlled trial. Forty obese patients who underwent elective operation under general anesthesia with endotracheal intubation were randomly allocated into CRV group, (n=20) and IRV group, (n=20).After the patients preoxygenated through a face mask for 3 minutes, anesthesia induction was performed. When the patients lost consciousness and spontaneous breathing, non-invasive positive pressure ventilation was performed for 5min, and the inspiratory-to-expiratory (I:E) ratio was set as 1:2 in CRV group and 2:1 in IRV group.Heart rate, systolic blood pressure, diastolic blood pressure and pulse oxygen saturation were recorded at four time points before preoxygenation (T0), preoxygenation for 3 minutes (T1), noninvasive positive pressure ventilation for 3 minutes (T2) and noninvasive positive pressure ventilation for 5 minutes (T3). Arterial blood was collected at T0, T1 and T3 for arterial blood gas analysis, and arterial oxygen partial pressure and carbon dioxide partial pressure were recorded. The patient's expiratory oxygen fraction at T1, T2 and T3 were recorded. Peak airway pressure, plateau pressure and mean airway pressure were record at T2 and T3. The safe apnea time was recorded in both groups.Results: Forty patients completed the study. Baseline parameters were comparable between groups. Safe apnea time was significantly longer (210.40±47.47 vs 153.80±41.54 seconds, mean difference [95% CI], 56.55 [28.00 to 85.10], P=0.0003) and the expired O2 fraction was higher (87.60±2.39 vs 91.60±1.79, mean difference [95% CI],4.00 [2.65 to 5.35], P <0.0001) at T3 in the IRV group compared to the CRV group.Conclusions: Volume-controlled inverse ratio ventilation of I:E ratio 2:1, compared to conventional ratio ventilation, provided a longer safe apnea time and higher expired O2 fraction in obese patients during anesthesia induction.