Driving Pressure for Early Postoperative Redistribution of Pulmonary Ventilation in Laparoscopic Surgery : A Prospective Randomized Controlled Trial

After screened for preoperative risk factors, 48 patients undergoing elective laparoscopic surgery and planned to be extubated in the operating room are randomly assigned to two groups: (1) PEEP = 5cmH2O; (2) driving pressure (DP)-guided PEEP. The ventilation protocol consists of volume-controlled mechanical ventilation (Datex Ohmeda S/5 Advance; General Electric Company Healthcare, Helsinki, Finland) at a tidal volume (VT) of 8 ml/kg predicted body weight (PBW), fresh gas of 2 litre /min, inspiratory to expiratory ratio of 1:2, and a respiratory rate adjusted to normocapnia (arterial carbon dioxide partial pressure between 35 and 45 mmHg). For group 2, trial for the lowest DP was started 10 min after pneumoperitoneum and position adjustment by increasing PEEP from 5 to 15 cm H2O incrementally. DP was calculated as "plateau pressure - PEEP". Each PEEP level was maintained for 10 respiratory cycles, with DP in the last cycle recorded. Then the PEEP level producing the lowest DP was identified and maintained intraoperatively. A plateau pressure of no more than 30 cmH2O is targeted in each group.

Early postoperative distribution of regional ventilation as COV (center of ventilation) is the primary endpoint evaluated by EIT (electrical impedance tomography), which was performed by a trained technician who is blinded to randomization. Arterial blood gas is tested, with inflammatory and oxidative mediators from venous sample. Postoperative pulmonary complications within 3 days are also recorded.