Optimize The Positive End-expiratory Pressure During Perioperative Period Of Thoracoscopic Surgery In Elderly Patients

Background:Surgical treatment is the preferred treatment for lung cancer.Elderly patients often have reduced pulmonary function and high risk of postoperative pulmonary complications.Age is reported to be one of the independent risk factors for postoperative pulmonary complications.Although the application of video-assisted thoracoscopic surgery and other technologies reduces the incidence of pulmonary complications,however the incidence remains relatively high（28%）in the elderly patients,including pneumonia,atelectasis,acute respiratory distress syndrome.Intraoperative anesthesia and ventilation management may be the key to reduce postoperative pulmonary complications,in which pulmonary protective ventilation strategies have received considerable attention.Currently,the protective ventilation strategy included small tidal volume,appropriate positive end-expiratory pressure（PEEP）and lung recruitment maneuver,which prevents alveolar overexpansion and keeps the alveoli open so as to increase alveolar gas-exchange and reduces ventilation-associated lung injury.Considering that the closed volume of elderly patients usually exceeds the functional residual volume,the proper PEEP is to maintain alveolar dilatation,increasing oxygen sum and reducing lung injury.At present,the common PEEP is set at 5cm H₂O,however it may not suit for all kinds of condition,such as single lung ventilation.There still lacks of study about individual setting of PEEP for lung surgery.In this study,elderly patients with thoracoscopic surgery aged more than 65 years were enrolled.The objective of the current study includes that:1.Does individualized PEEP improve oxygenation and lung mechanics during perioperative mechanical ventilation in elderly patients?2.Effects of individualized PEEP ventilation on the plasma inflammatory factors in elderly patients and to explore whether pulmonary protective ventilation can reduce the incidence of pulmonary complications during hospitalization.3.To evaluate the reliability PEEP individualized titration by EIT and whether it can be used as an auxiliary tool for rapid determination of protective ventilation parameters.Methods:This is a randomized,controlled trial study,including nested study（Page21）.1.Two hundred and ninety-four elderly patients over 65 years who scheduled for elective thoracoscopic surgery were randomly allocated into two groups（n=147）:PEEP 5 cm H₂O group and PEEP_IND group.Each group underwent low tidal volume（6m L/PBW）volume-controlled ventilation combined with a PEEP either by a fixed5cm H₂O PEEP or individualized PEEP titration determined by the EIT.The PEEP value was titrated from 15 cm H₂O to 1 cm H₂O,at intervals of 2 cm H₂O.The intersection of lung hyperinflation and lung collapse in the EIT monitoring chart was taken as the optimal PEEP value.The outcomes were driving pressure（ΔP）,dynamic pulmonary compliance（Cdyn）,oxygenation index（PaO₂/FiO₂）,peak airway pressure(P_peak),plateau pressure(P_plat),mean airway pressure(P_MEAN),mean arterial pressure（MAP）,vasopressin drug dosage,partial pressure of carbon dioxide（Pa CO₂）and PH at the time points of two lung ventilation（T1）,one lung ventilation 0.5 h（T2）,one lung ventilation1 h（T3）and the end of operation（T4）.2.The elderly patients after lobectomy were sent into the post-anesthesia care unit（PACU）after the operation（Routine observation 1 h）.Double lung ventilation was performed by the same method.Subgroup criteria refer to Part I.Each group underwent low tidal volume（8m L/PBW）synchronized intermittent mandatory ventilation with a PEEP set at 5 cm H₂O or individualized set by PEEP titration by the EIT.The outcomes were oxygenation index（PaO₂/FiO₂）at the time points of entering the PACU（T1）,mechanical ventilation 0.5 h（T2）,out of the PACU（T3）,driving pressure（ΔP）,dynamic pulmonary compliance（Cdyn）,peak airway pressure(P_peak),mean airway pressure(P_MEAN)and at T1 and T2,incidence of hypoxiaand and extubation time.3.To detect the heparin sulfate and glycosaminoglycan levels after induction,1 h and 2 h after operation;statistics of the incidence of pulmonary complications during postoperative hospitalization.Results:1.Two hundred and sixty patients were analyzed.The study showed that the PEEP titration time of individualized titration of EIT was about 13 minutes;The optimal PEEP set by EIT（median 11 cm H₂O）was significantly higher than that of fixed ventilation group（5 cm H₂O）.Compared with PEEP 5 group,the PEEP_IND group had higher oxygenation index（P<0.05）and better pulmonary dynamic compliance（P<0.05）and lower driving pressure（P<0.05）at T2,T3.However,the P_peak was significantly higher than that of PEEP 5 group at T2 and T3（P<0.05）.At T2,T3 and T4,the P_plat,P_MEAN was significantly higher in PEEP 5 group（P<0.05）.There was no significant difference in MAP between the two groups（P>0.05）.2.Based on the results of the previous studies,109 patients were analyzed.The optimal PEEP set by EIT（median 9 cm H₂O）was significantly higher than that of fixed ventilation group（5 cm H₂O）.Compared with PEEP 5 group,the PEEP_IND group had higher oxygenation index（P<0.05）and better pulmonary dynamic compliance（P<0.05）and lower driving pressure（P<0.05）at T2;there was no significant difference in the incidence of hypoxia,MAP and extubation time between the two groups.The dosage of vasoactive drugs in PEEP_IND ventilation group was higher than that in fixed PEEP ventilation group and there was no significant difference in the incidence of hypoxemia between the two groups.3.The third part showed that there was no significant difference in the concentration of heparin sulfate and glycosaminoglycan between the two groups at 1and 2 h of operation.There was no significant difference in the incidence of pulmonary complications between the two groups.Conclusions:1.The method of EIT titration PEEP is feasible in clinical application.2.During the period of one lung ventilation and postanesthesia care unit（PACU）in elderly patients,the use of small tidal volume combined with EIT individualized PEEP titration can effectively improve the oxygenation index,breathing mechanics and play a protective role in lung ventilation,but has no significant effect on the incidence of hypoxemia and extubation time.3.Lung protective ventilation had no significant effect on the expression of inflammatory factors in elderly patients undergoing thoracoscopic surgery,nor on the incidence of postoperative complications.