The Effect Of Different Ventilation Modes On Gastric Volume During Induction Of General Anesthesia In Laparoscopic Surgery

Chapter 1 An exploratory study of the effect of different ventilation modes on gastric volume during induction of general anesthesia in laparoscopic surgeryObjectivesCompare the change of gastric volume before and after manual controlled assisted ventilation,pressure controlled assisted ventilation and non-positive pressure ventilation during induction of general anesthesia in laparoscopic surgery by measuring the cross-sectional area(CSA)of gastric antrum using bedside ultrasound,so as to explore the ventilation mode with the least influence on gastric volume.Methods1.Objects:The study was conducted between July and December 2019 in 30 adult(both male and female)patients aged between 18 and 65 years(excluding 65 years old)of ASA physical status ?-?,Mallampati grade ?-?,BMI<30 kg/m2,presenting for selective laparoscopic surgeries(except gastrectomy,pancreatectomy and duodenectomy)who had fasted more than 8 hours in Our hospital.No drugs affecting gastrointestinal dynamics had been used one day before surgery.The patients were randomly divided into three groups:manual-controlled ventilation group(manualcontrolled group),pressure-controlled ventilation group(pressure-controlled group)and non-positive pressure ventilation group(non-positive pressure group).2.Procedures:All patients were preoxygenated with pure oxygen for 3 minutes at the beginning of induction of general anesthesia,and the oxygen flow rate was 8 L/min.After losing consciousness and intravenous injecting rocuronium,a two-handed jawthrust technique was used to open the airway.Patients in the manual-controlled group were ventilated manually through mask and APL valve was adjusted to 20 cmH2O while the respiratory rate was maintained around 15 breaths/min.The pressurecontrolled group adopted pressure-controlled ventilation mode through mask and the inspiratory pressure was set as 20 cmH2O while the respiratory rate was 15 breaths/min.No positive pressure ventilation was allowed in the non-positive pressure group.Before induction of general anesthesia,all patients were in supine position.The same anesthesiologist used bedside ultrasound to find the cross-section of gastric antrum and measure its area as S1.After successful endotracheal intubation,the anesthesiologist,which didn't know the allocation of the patient,looked for the cross-section of the gastric antrum again at the same superficial location and measured its area as S2.The relevant mathematical model was used to convert the cross-sectional area of gastric antrum into gastric volume,and the gastric volume before general anesthesia induction was recorded as V1 while the gastric volume after endotracheal intubation was recorded as V2.Patients who failed to obtain a clear sonogram of cross-section of the gastric antrum before induction of general anesthesia or after endotracheal intubation,intubation times>1,SpO2<90%or occurrence of reflux or aspiration during the whole process were excluded from the study.3.Indictors:Change of gastric volume per unit body weight((V2-V1)/kg),change of gastric volume(V2-V1),gastric volume per unit body weight before induction of general anesthesia(Vi/kg),gastric volume before induction of general anesthesia(V1),gastric volume per unit body weight after induction of general anesthesia(V2/kg)and gastric volume after induction of general anesthesia(V2),situation of adverse events.4.Statistical analysis:Statistical software IBM SPSS 26.0 was used for data analysis and processing,while Graphpad Prism 5.0 was used for graph.Categorical variables are expressed as counts or percentages while continuous variables are expressed as mean ± standard deviation(x±s).Qualitive data were compared using chi-square test.Paired t-test was used for the comparisons of V1 with V2,V1/kg with V2/kg in each group.One-way ANOVA was used for comparison of V1,V1/kg,V2-V1,(V2-V1)/kg among groups.If the analysis results showed statistical differences among groups,LSD method was used for multiple comparisons.The test level was 0.05,and P<0.05 was considered statistically significant.Results1.A total of 30 patients were included in the analysis,10 in each group.There was no significant difference in the general data among groups.2.Comparison in each group:In manual-controlled group and pressure-controlled group,V2 was significantly greater than V1(P<0.05)and V2/kg was significantly greater than V1/kg(P<0.05).There was no significant difference between V2 and V1,V2/kg and V1/kg in non-positive pressure group(P>0.05).3.Comparison among groups:there was no significant difference in V1,V1/kg and V2-V1 among groups(P>0.05).The difference of(V2-V1)/kg among groups was statistically significant(P<0.05),among which,(V2-V1)/kg of manual-controlled group and pressure-controlled group were both significantly higher than that of nonpositive pressure group(P<0.05),while there was no significant difference between manual-controlled group and pressure-controlled group(P>0.05).4.Adverse events:There were no adverse events such as hypoxemia(SpO2<90%),difficult mask ventilation,difficult endotracheal intubation or reflux or aspiration occurred in each group during the whole study.Conclusions1.During the induction of general anesthesia in laparoscopic surgery,compared with manual controlled assisted ventilation and pressure controlled assisted ventilation which targeted inspiratory pressure was 20 cmH2O,non-positive pressure ventilation had the least effect on gastric volume.2.When targeted inspiratory pressure was 20 cmH2O,both manual controlled assisted ventilation and pressure controlled assisted ventilation resulted in significant gastric insufflation,but there was no significant difference on the effect of gastric volume between them.Chapter 2 A confirmatory study on the effect of positive pressure assisted ventilation and non-positive pressure ventilation on gastric volume during induction of general anesthesia in laparoscopic surgeryObjectivesTo further validate that non-positive pressure ventilation without has little effect on gastric volume through confirmative test,providing certain clinical basis for the selection of ventilation mode during the induction of general anesthesia for patients undergoing laparoscopic surgery to prevent gastric insufflation.Methods1.Objects:The inclusion,exclusion and elimination criteria were the same as the exploratory study.The patients were randomly divided into manual-controlled ventilation group(manual-controlled group),pressure-controlled ventilation group(pressure-controlled group)and non-positive pressure ventilation group(non-positive pressure group),among which the manual-controlled group and pressure-controlled group formed the positive pressure groups.2.Procedures:The methods of induction and maintenance of general anesthesia,drugs and equipment,detection of CSA by ultrasound,and calculation of gastric volume were same as exploratory study.3.Indictors:(V2-V1)/kg,V2-V1,V1/kg,V1,V1kg,V2,incidence of gastric insufflation,degrees of gastric insufflation,SpO2 before preoxygenation(SpO2(T0)),SpO2(T1)after endotracheal intubation(SpO2(T1)),time of losing consciousness,time of endotracheal intubation,,situation of adverse events.4.Estimation of sample size:This study is a parallel randomized controlled trial.The intervention group was the positive pressure group(including the manualcontrolled group and the pressure-controlled group),while the control group was the non-positive pressure group.(V2-V1)/kg was the main outcome indicator.After estimation with the results from exploratory study,the sample size of the manualcontrolled group and the non-positive pressure group was 20,while that of the pressurecontrolled group and the non-positive pressure group was 13,respectively,so the sample size was set as 20 cases/group.Assuming the rate of elimination of the study object would be 10%,the sample size was 20/0.90=23 cases/group.5.Statistical analysis:Statistical software IBM SPSS 26.0 was used for data analysis and processing,while IBM SPSS 26.0 and Graphpad Prism 5.0 were used for graph.Categorical variables are expressed as counts or percentages.Age,height,body weight and BMI are expressed as mean±standard deviation(x ± s).Duration of fasting and abstinence,time of losing consciousness,time of endotracheal intubation,V1,V2,V1/kg,V2/kg,V2-V1,(V2-V1)/kg,SpO2 are expressed as median[min,max](M[min,max]).Qualitive data were compared using chi-square test.Comparisons between V1 and V2,V1/kg and V2kg,SpO2(T0)and SpO2(T1)in each group.If the difference between the two indictors was normally distributed,the paired t-test was used for analysis,otherwise the paired Wilcoxon rank sum test was used.For the indictors with normal distribution and homogeneous variance in both groups,the independent sample t test was used for analysis,otherwise the Mann-Whitney U test was used.Comparisons of V2-V1,(V2-V1)/kg,incidence of gastric insufflation and degrees of gastric insufflation between positive pressure groups and non-positive pressure group,as well as comparison of V1 with V2,Vi/kg with V2/kg in positive pressure groups were all conducted by unilateral test,with the test level of 0.025.P<0.025 was considered statistically significant.The other indicators were compared by bilateral test.The test level was 0.05,and P<0.05 was considered statistically significant.Results1.A total of 90 patients were included in the analysis,30 in each group.There was no significant difference in the general data between positive pressure groups and nonpositive pressure group.2.Comparisons in each group:(1)Positive pressure groups:V2 was significantly greater than V1(P<0.025)and V2/kg was significantly greater than V1/kg(P<0.025).(2)Non-positive pressure group:There was no significant difference between V2 and V1,V2/kg and V1/kg(P>0.05).3.Comparisons between groups:(1)There was no significant difference in V1 and V1/kg between positive pressure groups and non-positive pressure group(P>0.05).(2)Both V2-V1 and(V2-V1)/kg of positive pressure groups were significantly higher than those of non-positive pressure group(P<0.025).4.The incidence of gastric insufflation of positive pressure groups were significantly higher than that of non-positive pressure group(P<0.025).5.The degrees of gastric insufflation in positive pressure groups were significantly severer than that in non-positive pressure group(P<0.025).6.In each group,comparison between SpO2(T0)and SpO2(T1)showed that SpO2(T1)was significantly higher than SpO2(T0)(P<0.05).There was no significant difference in SpO2(T0)and SpO2(T1)between positive pressure groups and nonpositive pressure group(P>0.05).7.There was no significant difference in the time of losing consciousness and intubation between positive pressure groups and non-positive pressure group(P>0.05).8.Adverse events:There were no adverse events such as hypoxemia(SpO2<90%),difficult mask ventilation,difficult endotracheal intubation or reflux or aspiration occurred in each group during the whole study.Conclusions1.During the induction of general anesthesia in patients undergoing laparoscopic surgery,compared with positive pressure ventilation(including manual-controlled assisted ventilation and pressure-controlled assisted ventilation)whose targeted inspiratory pressure was 20 cmH2O,non-positive pressure ventilation had the less effect on gastric volume,the lower incidence of gastric insufflation and the milder degree of gastric insufflation.2.For ASA physical status I-II,non-obese young and middle-aged patients without difficult airway,induction of general anesthesia using non-positive pressure ventilation won't lead to hypoxemia(SpO2<90%)after 3 minutes of pure oxygen preoxygenation.