Individualized positive end-expiratory pressure reduces driving pressure in obese patients during laparoscopic surgery under pneumoperitoneum: a randomized clinical trial

Abstract

Introduction: During pneumoperitoneum (PNP), airway driving pressure (ΔP_RS) increases due to the stiffness of the chest wall and cephalic shift of the diaphragm, which favors atelectasis. In addition, depending on the mechanical power (MP) formulas, they may lead to different interpretations.

Methods: Patients >18 years of age with body mass index >35 kg/m² were included in a single-center randomized controlled trial during their admission for bariatric surgery by abdominal laparoscopy. Intra-abdominal pressure was set at 15 mmHg at the pneumoperitoneum time point (PNP). After the recruitment maneuver, the lowest respiratory system elastance (E_RS) was detected during the positive end-expiratory pressure (PEEP) step-wise decrement. Patients were randomized to the 1) CTRL group: ventilated with PEEP of 5 cmH₂O and 2) PEEP_IND group: ventilated with PEEP value associated with E_RS that is 5% higher than its lowest level. Respiratory system mechanics and mean arterial pressure (MAP) were assessed at the PNP, 5 min after randomization (T1), and at the end of the ventilation protocol (T2); arterial blood gas was assessed at PNP and T2. ΔP_RS was the primary outcome. Three MP formulas were used: MP_A, which computes static PEEP × volume, elastic, and resistive components; MP_B, which computes only the elastic component; and MP_C, which computes static PEEP × volume, elastic, and resistive components without inspiratory holds.

Results: Twenty-eight patients were assessed for eligibility: eight were not included and 20 patients were randomized and allocated to CTRL and PEEP_IND groups (n = 10/group). The PEEP_IND ventilator strategy reduced ΔP_RS when compared with the CTRL group (PEEP_IND, 13 ± 2 cmH₂O; CTRL, 22 ± 4 cmH₂O; p < 0.001). Oxygenation improved in the PEEP_IND group when compared with the CTRL group (p = 0.029), whereas MAP was comparable between the PEEP_IND and CTRL groups. At the end of surgery, MP_A and MP_B were correlated in both the CTRL (rho = 0.71, p = 0.019) and PEEP_IND (rho = 0.84, p = 0.020) groups but showed different bias (CTRL, -1.9 J/min; PEEP_IND, +10.0 J/min). At the end of the surgery, MP_A and MP_C were correlated in both the CTRL (rho = 0.71, p = 0.019) and PEEP_IND (rho = 0.84, p = 0.020) groups but showed different bias (CTRL, -1.9 J/min; PEEP_IND, +10.0 J/min).

Conclusion: Individualized PEEP was associated with a reduction in ΔP_RS and an improvement in oxygenation with comparable MAP. The MP, which solely computes the elastic component, better reflected the improvement in ΔP_RS observed in the individualized PEEP group.

Clinical trial registration: The protocol was registered at the Brazilian Registry of Clinical Trials (U1111-1220-7296).

Keywords: laparoscopy; obesity; positive end-expiratory; pressure; respiratory mechanics.