Respiratory Mechanics-oriented Individualized PEEP In Mechanically Ventilation During Surgery For Lung Protection

Objective: To explore the effect of individualized PEEP guided by respiratory mechanics for the prevention of postoperative complications（PPCs）and the influence of tidal volume（VT）and titration indicators on titrated PEEP.Methods: Part 1 Meta analysis about individualized positive end-expiratory pressure guided by respiratory mechanics during anesthesia for the Prevention of PPCs.We searched Pub Med,Embase,and the Cochrane Library to identify randomized controlled trials（RCTs）that compared personalized PEEP based on respiratory mechanics and constant PEEP to prevent PPCs in adults from inception to April 2022.Two researchers independently screened obtained literatures according to the established inclusion and exclusion criteria.And the Cochrane systematic quality assessment tool was used to evaluate the risk of bias of the final included studies.The primary outcome was PPCs.Part 2 Effect of tidal volume and titration indicators on titrated positive endexpiratory pressure in patients undergoing gynecological laparoscopy.Thirty patients undergoing elective gynaecological laparoscopic,aged 18-75 years,with a BMI of 18.5-32 kg/m2,ASA class I or II,and operated in the Trendelenburg position were included.The target VT was set at 6 ml/predictive body weight（kg） and 8 ml/predictive body weight（kg）.PEEP titration was performed sequentially at the target VT and each titration was preceded by two manual recruitment maneuver（airway pressure of 30-40 cm H2 O for 15-20 s）.Airway plateau pressure（Pplat）,peak airway pressure（Ppeak）,respiratory system compliance（Crs）,PEEP and end expiratory carbon dioxide（Pet CO2）were recorded for each patient at all PEEP values.Driving pressure（ΔP）was calculated as ΔPplat = Pplat-PEEP and ΔPpeak = Ppeak-PEEP.After titration,the optimum PEEP was selected based on the lowestΔPplat and the lowest ΔPpeak,respectively.The agreement between the optimum PEEP values was determined by the intra-group correlation coefficient（ICC）,with ICC > 0.75 indicating high agreement.Results: Part 1 Fourteen studies with 1105 patients were included.Compared with those who received constant PEEP,patients who received optimized PEEP exhibited a significant reduction in the incidence of PPCs（RR = 0.54,95% CI = 0.42 to 0.69）.The results of commonly happened PPCs（pulmonary infections,hypoxemia,and atelectasis but not pleural effusion）also supported individualized PEEP group.Moreover,the application of PEEP based on respiratory mechanics improved intraoperative respiratory mechanics（ΔP and Crs）and oxygenation.Part 2 The consistency of the optimum PEEP between different tidal volumes was poor（ICC < 0.75）with the same titration indicator（ΔPplat or ΔPpeak）.The consistency of the optimum PEEP between different titration methods（ΔPplat and ΔPpeak）under the same tidal volume was poor（ICC < 0.75）.At the same tidal volume,the optimum PEEP obtained by ΔPpeak titration method significantly decreased ΔPpeak without increasing ΔPplat compared to the ΔPplat titration method.At the same tidal volume,Pplat and Ppeak increased with increasing PEEP,while Pet CO2 did not change with PEEP.Conclusion:（1）The PEEP titration method based on respiratory mechanics works positively for lung protection in surgical patients undergoing general anesthesia.（2）VT can influence the selection of the optimum PEEP when using ΔP to titrate PEEP.（3）In terms of ΔP,the optimal PEEP obtained by the ΔPpeak method is better than the optimal PEEP obtained by the ΔPplat method at the same VT.（4）while the adjustment of PEEP can affect airway pressure but not PetCO₂ over a short period of time.