Value Of Electrical Impedance Tomography In The Assessment Of The Weaning Outcome Of Mechanically Ventilated Patients After Upper Abdominal Surgery

Objective: To investigate the ratio of mean end-expiratory pulmonary impedance variation(Mean delta end-expiratory lung impedance,Mean EELI)to pre-variation tidal volume(tidal volume,vt),the standard deviation of local ventilation delay index((Standard deviation of regional ventilation delay,RVD SD),and the percentage variation of local compliance(increased compliance,decreased Compliance win,CW;compliance,Compliance loss,CL;)in electrical impedance tomography((Electrical impedance tomography,EIT)monitoring.|the value of parameters such as ?(CW-CL)|)and whole lung heterogeneity index((Global Inhomogeneity Index,GI))in predicting the weaning outcome of mechanically ventilated patients after upper abdominal surgery.Methods: this study was an observational study.The subjects were all patients who received mechanical ventilation for more than 24 hours after upper abdominal surgery in the intensive Care Center of Sichuan Provincial People's Hospital from January 1,2018 to August 31,2019.The patients underwent weaning screening test at a fixed time every morning,and autonomous breathing test was carried out after weaning screening.Patients were enrolled in the group before SBT(spontaneous breathing trial)screening.At the same time,the ventilator mode and parameters were set to pressure support ventilation((Pressure support ventilation:,PSV).The parameters were set to positive end-respiratory pressure(Positiveend-expiratory pressure,PEEP)of 5cmH2 O and pressure support(Pressure support,PS)of 810cmH2 O.The oxygen concentration((Fraction of inspiration oxygen,FiO2)is 40%,the pulse oxygen saturation((pulse oxygen saturation,SPO2)is greater than or equal to 90%,and the ventilation time is more than 30 minutes.Then 30 min SBT test(T tube mode 30 min)was carried out.The starting point of EIT monitoring was 5minutes before SBT and the end point was the end of SBT test.General data were collected: patient's name,sex,age,etiology,mode of operation,time of mechanical ventilation(hours),acute physiology and chronic health score II(Acute physiology and chronic health Evaluation ? score,APACHE II on the day of withdrawal,and 48-hour re-intubation rate.The blood gas indexes of pre-SBT 5min and at the end of SBT were collected: arterial pH(pondus hydrogenii,pH),arterial partial pressure of oxygen(Partial pressure of arterial oxygen(PaO2),arterial partial pressure of carbon dioxide((Partial pressure of arterial carbon dioxide,PaCO2),lactic acid(Lactic acid,Lac)and oxygenation index(Oxygenation index,OI)were calculated.Basic vital signs: heart rate(Heart rate,HR),respiratory rate(Respiratory rate,RR0,mean arterial pressure(Mean arterial pressure,MAP)were recorded before 5min,SBT 5min,SBT15 min and SBT30 min before SBT.If the SBT terminates ahead of time,record the HR,RR and MAP at the time of termination.Failure of weaning was defined as failure of SBT(mechanical ventilation should be restored during SBT),re-intubation or non-invasive ventilation within 48 hours after extubation,and death within 48 hours after extubation.According to the weaning outcome,the patients were divided into two groups: successful weaning group and failed weaning group.The differences of Mean EELI/VT,RVD SD,| ?(CW-CL)| and GI in pre-SBT 5min and SBT were compared between the two groups,and the predictive value of the above parameters on the weaning outcome of mechanically ventilated patients after upper abdominal surgery was analyzed.Results:1.General condition: a total of 32 patients with mechanical ventilation after upper abdominal surgery were enrolled in the intensive care center of our hospital from January 1,2018 to August 31,2019,including 22 males and 10 females.There were 23 cases in successful withdrawal group and 9 cases in failure group.There was no significant difference in general conditions,including age,sex,time of mechanical ventilation and APACHEII score between the two groups.2.Basic vital signs:In the failure group,the average values of HR,RR and MAP before and after SBT test were higher than those of the successful group.The average value of SPO2 in the failure group before and after SBT test was lower than that in the success group.3.Comparison of blood gas indexes betweenpre-SBT 5min and SBT30min:At the end of SBT,there was no significant difference in the results of blood gas analysis between the failed group and the successful patients(p >0.05).The main indexes of blood gas analysis at the end of SBT in the two groups were not significantly different from those in 5min before SBT(p >0.05).4.Prediction of weaning in mechanically ventilated patients with Mean?EELI/VT parameters during the pre-SBT 5min and SBT tests :Before SBT,there were significant differences in Mean EELI/VT,of 5min,SBT5 min,SBT15min and SBT30 min between the two groups.In SBT30 min,Mean EELI/VT has the highest value in predicting the success of weaning,with an AUC of 0.816.When Mean EELI/VT selected-0.92 as the critical value,the sensitivity and specificity of predicting weaning success were 88.89% and73.91% respectively,the positive predictive value was 57.1%,and the correct prediction rate was 0.63.5.the predictive value of RVDSD before SBT and RVDSD in the process of SBT for mechanically ventilated patients: there was significant difference in RVDSD between the two groups during 5min before SBT.In SBT5 min,there was no significant difference in RVDSD between the two groups(p > 0.05).However,there was a significant difference in RVDSD between SBT5 min and 5min before SBT in the successful weaning group.During SBT15 min and 30 min,there was significant difference in RVDSD between successful weaning group and failure group,and there was also significant difference in RVDSD between RVDSD and pre-SBT 5min at two time points(p < 0.05).In SBT30 min,RVDSD has the highest value for predicting withdrawal,with an AUC of 0.918.When RVDSD > 15.7 was taken as the critical value,the sensitivity and specificity for predicting withdrawal failure were 100% and 78.26% respectively,the positive predictive value was64.3%,and the correct prediction rate was 0.78%.6.During 5min and SBT testbefore SBT,the prediction of ventilator weaning by parameters: in the failure group,the parameters of SBT5 min,15min,30 min | ?(CW-CL)| parameters were significantly different from those of pre-SBT 5min(p < 0.05).| ?(CW-CL)| fluctuates greatly in the failed group,with a fluctuation range of more than 10% compared with the pre-SBT 5min.| ?(CW-CL)| when the parameters are SBT5 min,15min and 30 min,there are significant differences between the two groups.Pre-SBT 5min is used as a baseline and is not included in the prediction model.SBT5 min and 15 min have the highest value in predicting the failure of weaning.When SBT5 min,| ?(CW-CL)| the parameter is 0.981 for the AUC of predicted withdrawal.When RVDSD > 7.7 is taken as the critical value,the sensitivity Se and specificity Sp for predicting withdrawal failure are 88.89% and 100%,respectively,the positive predictive value PV+ is100%,and the prediction accuracy DA is 0.89.When SBT15 min,| ?(CW-CL)|the parameter is 0.981 for the AUC of predicted withdrawal.When the critical value is | ?(CW-CL)| > 7.4,the sensitivity Se and specificity Sp for predicting withdrawal failure are 100% and 95.65%,respectively,the positive predictive value PV+ is 90%,and the prediction accuracy DA is 0.96.7.Prediction of weaning in mechanically ventilated patients with 5min before SBT and GI parameters during SBT test: in the group of weaning failure,the GI index of SBT15 min and 30 min was significantly different from that of 5min before SBT.In the successful weaning group,the GI index of SBT5 min,15min and 30 min was significantly different from that of 5min before SBT.At the same time,there was significant difference in GI index between the two groups at 5min,15 min and 30 min before SBT.SBT5 min and 15 min have the highest value in predicting the failure of weaning.At SBT15 min,the AUC of GI index for predicting withdrawal is 0.908.When the critical value of GI index > 0.97 was taken as the critical value,the sensitivity Se and specificity Sp for predicting withdrawal failure were 77.78% and 91.3%,respectively,the positive predictive value PV+ was 38.1%,and the prediction accuracy DA was 0.69.In the case of SBT30 min,the AUC of the GI parameter for predicting withdrawal is 0.901.When the GI index > 1.02 is taken as the critical value,the sensitivity Se and specificity Sp for predicting withdrawal failure are 88.89% and 73.91%respectively,the positive predictive value PV+ is 57.1%,and the prediction accuracy DA is 0.63.Conclusion: the parameters of Mean EELI/VT,RVD SD,| ?(CW-CL)|and GI in EIT monitoring can predict the weaning outcome of patients with mechanical ventilation after upper abdominal surgery.