Individualized PEEP to optimise respiratory mechanics during abdominal surgery: a pilot randomised controlled trial

Background: Higher intraoperative driving pressures (Delta P) are associated with increased postoperative pulmonary complications (PPC). We hypothesised that dynamic adjustment of PEEP throughout abdominal surgery reduces DP, maintains positive end-expiratory transpulmonary pressures (P-tp_ee) and increases respiratory system static compliance (C-rs) with PEEP levels that are variable between and within patients. Methods: In a prospective multicentre pilot study, adults at moderate/high risk for PPC undergoing elective abdominal surgery were randomised to one of three ventilation protocols: (1) PEEP <= 2 cm H2O, compared with periodic recruitment manoeuvres followed by individualised PEEP to either optimise respiratory system compliance (PEEPmaxCrs) or maintain positive end-expiratory transpulmonary pressure (PEEPPtp_ee). The composite primary outcome included intraoperative Delta P, P-tp_ee, Crs, and PEEP values (median (interquartile range) and coefficients of variation [CVPEEP]). Results: Thirty-seven patients (48.6% female; age range: 47-73 yr) were assigned to control (PEEP <= 2 cm H2O; n=13), PEEPmaxCrs (n=16), or PEEPPtp_ee (n=8) groups. The PEEPPtp_ ee intervention could not be delivered in two patients. Subjects assigned to PEEPmaxCrs had lower DP (median8 cm H2O [7-10]), compared with the control group (12 cm H2O [10-15]; P= 0.006). PEEPmaxCrs was also associated with higher P-tp_ee (2.0 cm H2O [-0.7 to 4.5] vs controls: -8.3 cm H2O [-13.0 to -4.0]; P-.001) and higher Crs (47.7 ml cm H2O [43.2-68.8] vs controls: 39.0 ml cm H2O [32.9-43.4]; P= 0.009). Individualised PEEP (PEEPmaxCrs and PEEPPtp_ee combined) varied widely (median: 10 cm H2O [8-15]; CVPEEP= 0.24 [0.14-0.35]), both between, and within, subjects throughout surgery. Conclusions: This pilot study suggests that individualised PEEP management strategies applied during abdominal surgery reduce driving pressure, maintain positive P-tp_ee and increase static compliance. The wide range of PEEP observed suggests that an individualised approach is required to optimise respiratory mechanics during abdominal surgery. Clinical trial registration: NCT02671721.