Effects of recruitment maneuver and PEEP on respiratory mechanics and transpulmonary pressure during laparoscopic surgery

Background: We tested the hypothesis that during laparoscopic surgery, Trendelenburg position and pneumoperitoneum (PnP) may worsen chest wall elastance (ECW), concomitantly decreasing transpulmonary pressure (PL) and that a protective ventilator strategy applied after PnP induction, by increasing PL would result in alveolar recruitment and improvement in respiratory mechanics and gas exchange. Methods: In twenty-nine consecutive patients an open lung strategy (OLS) consisting in a recruiting manoeuvre (RM) followed by PEEP 5cmH20 maintained until the end of surgery was applied after PnP induction. Respiratory mechanics, gas exchange, blood pressure (BP) and cardiac index (CI) were measured before (TBSL) and after PnP with zero PEEP (TpreOLS), after RM with PEEP (TpostOLS), after peritoneum desufflation with PEEP (Tend). Results: Esophageal pressure was used for partitioning respiratory mechanics between lung and chest wall (data are mean +-standard deviation, SD): on TpreOLS, ECW and the elastance of the lung (EL) increased (respectively 8.2±0.9cmH2O/L vs 6.2±1.2cmH2O/L on TBSL, p=0.00016; and 11.69±1.68cmH2O/L vs 9.61±1.52cmH2O/L on TBSL; p=0.0007). After OLS both ECW and EL decreased (5.2±1.2cmH2O/L and 8.62±1.03cmH2O/L respectively; both p=0.00015 vs TpreOLS ), and PaO2/FiO2 improved (491+107 vs 425±97 on TpreOLS; p=0.008) remaining stable thereafter. Recruited volume (computed as the difference in lung volume for the same static airway pressure), was 194±80ml. PplatRS remained stable while inspiratory transpulmonary pressure (PplatL) increased (11.65+1.37 cmH2O vs 9.21+2.03 on TpreOLS; p=0.007). All respiratory mechanics parameters remained stable after abdominal desufflation. Hemodynamic parameters remained stable throughout the study. Conclusions: In patients submitted to laparoscopic surgery in Trendelenburg position, an OLS applied after PnP induction increased PL and led to alveolar recruitment and improvement of ECW, EL and gas exchange