Respiratory mechanics and mechanical power during low vs. high positive end-expiratory pressure in obese surgical patients - A sub-study of the PROBESE randomized controlled trial

Study objective: We aimed to characterize intra-operative mechanical ventilation with low or high positive end-expiratory pressure (PEEP) and recruitment manoeuvres (RM) regarding intra-tidal recruitment/derecruitment and overdistension using non-linear respiratory mechanics, and mechanical power in obese surgical patients enrolled in the PROBESE trial.Design: Prospective, two-centre substudy of the international, multicentre, two-arm, randomized-controlled PROBESE trial.Setting: Operating rooms of two European University Hospitals.Patients: Forty-eight adult obese patients undergoing abdominal surgery.Interventions: Intra-operative protective ventilation with either PEEP of 12 cmH(2)O and repeated RM (HighPEEP+RM) or 4 cmH(2)O without RM (LowPEEP).Measurements: The index of intra-tidal recruitment/de-recruitment and overdistension (%E-2) as well as airway pressure, tidal volume (V-T), respiratory rate (RR), resistance, elastance, and mechanical power (MP) were calculated from respiratory signals recorded after anesthesia induction, 1 h thereafter, and end of surgery (EOS).Main results: Twenty-four patients were analyzed in each group. PEEP was higher (mean +/- SD, 11.7 +/- 0.4 vs. 3.7 +/- 0.6 cmH(2)O, P < 0.001) and driving pressure lower (12.8 +/- 3.5 vs. 21.7 +/- 6.8 cmH(2)O, P < 0.001) during HighPEEP+RM than LowPEEP, while V-T and RR did not differ significantly (7.3 +/- 0.6 vs. 7.4 +/- 0.8 ml center dot kg(-1), P = 0.835; and 14.6 +/- 2.5 vs. 15.7 +/- 2.0 min(-1), P = 0.150, respectively). %E-2 was higher in HighPEEP+RM than in LowPEEP following induction (-3.1 +/- 7.2 vs. -12.4 +/- 10.2%; P < 0.001) and subsequent timepoints. Total resistance and elastance (13.3 +/- 3.8 vs. 17.7 +/- 6.8 cmH(2)O center dot l center dot s(-2), P = 0.009; and 15.7 +/- 5.5 vs. 28.5 +/- 8.4 cmH(2)O center dot l, P < 0.001, respectively) were lower during HighPEEP+RM than LowPEEP. Additionally, MP was lower in HighPEEP+RM than LowPEEP group (5.0 +/- 2.2 vs. 10.4 +/- 4.7 J center dot min(-1), P < 0.001).Conclusions: In this sub-cohort of PROBESE, intra-operative ventilation with high PEEP and RM reduced intra-tidal recruitment/de-recruitment as well as driving pressure, elastance, resistance, and mechanical power, as compared with low PEEP.