Effect Of Nitrous Oxide On The Appearance Time Of The Intersegmental Plane In Thoracoscopic Segmentectomy

Objective:With the popularity of high-resolution computer tomography,anatomical segmentectomy is becoming extensively spread due to removal pulmonary nodules completely and preserve lung function to the maximum extent.The accurate and rapid determination of the intersegmental plane（ISP）is one of the key techniques during this procedure.This study aimed to investigate the effect of the different concentrations of nitrous oxide（N₂O）/oxygen（O₂）inspired mixture gas on the ISP appearance via the modified lung inflation-deflation method.Methods:Sixty-five participants undergoing segmentectomy received general anesthesia were randomly divided into three groups.Patients in 75%N₂O group received a gas mixture of O₂ and N₂O（fraction of inspired oxygen[Fio₂]=0.25,n=24）;those in 50%N₂O group received a gas mixture of O₂ and N₂O（[Fio₂]=0.5,n=23）;and those in 0%N₂O group received 100%O₂（[Fio₂]=1.0,n=18）during lung expansion.Demographic data of sex,age,body mass index and pulmonary function were recorded.The primary outcome was the appearance time of the ISP(T_ISP).Secondary outcomes included arterial blood gas and pulse oxygen saturation（Sp O₂）at breathing room air,one-lung ventilation（OLV）before lung expansion,5 min and 15 min after lung expansion,duration of surgery,the incidence of postoperative complications,total drainage volume,duration of drainage and postoperative hospital stay.Results:There were no significant differences in patient characteristics between each group.The T_ISP was significantly shorter in the 75%N₂O group（320.20±65.89 s）as compared with that of the 50%N₂O group（552.39±88.96 s,P<0.001）and the 0%N₂O group（968.33±85.53 s,P<0.001）,while the 50%N₂O group was shorter than that in the 0%N₂O group（P<0.001）.When the 100%O₂ was provided,arterial oxygenation was significantly improved after lung expansion.At 5 minutes of lung inflation,the average Pa O₂value in the 0%N₂O group （392.06±94.36 mm Hg）was significantly higher than that in the 75%N₂O group（204.71±59.25 mm Hg,P<0.001）and the 50%N₂O group（260.17±86.57 mm Hg,P<0.001）.At15 minutes of lung inflation,the average Pa O2 value in the 0%N₂O group（301.67±67.04mm Hg）was still higher than that in the 75%N₂O group（233.29±81.01 mm Hg,P=0.006）and the 50%N₂O group（251.35±78.16 mm Hg,P=0.042）.While there were no differences in mean Sp O₂values among groups.Additionally,the duration of surgery,incidence of postoperative complications,total thoracic drainage volume,duration of drainage,and postoperative hospital stay did not differ among three groups.Conclusions:Combination of 75%N₂O inspired mixture gas and a modified lung inflation–deflation method is available to quickly identify the ISP without any obvious adverse effect on OLV related arterial oxygenation during segmentectomy.