Adjustment of positive end-expiratory pressure based on body mass index during general anaesthesia: a randomised controlled trial.

INTRODUCTION Lung-protective ventilation is essential for preventing postoperative pulmonary complications. While maintaining a low driving pressure and optimising PEEP is of importance, the ideal strategy remains contentious. This study evaluated whether adjusting PEEP based on BMI, compared with standard PEEP, could reduce driving pressure and peri-operative loss of lung aeration. METHODS We conducted a randomised controlled, patient-blinded, single-centre superiority trial with two parallel groups. Adult patients undergoing surgery with general anaesthesia who required tracheal intubation were assigned randomly to either standardised PEEP (PEEP = 5 cmH2O; group PEEP-5) or PEEP set according to BMI (PEEP = BMI/3 cmH2O; group PEEP-BMI/3). Patients' lungs were ventilated using a volume-controlled mode with tidal volumes of 7 ml.kg-1 predicted body weight. Lung aeration scores were assessed using ultrasound pre- and postoperatively. RESULTS Sixty patients were enrolled and allocated randomly. Adjustment of PEEP according to BMI/3 was associated with a significantly lower driving pressure, with a median (IQR [range]) of 8.9 (7.1-10.4 [5.2-14.9]) cmH2O in group PEEP-5 and 7.9 (7.2-8.5 [5.9-14.1]) cmH2O in group PEEP-BMI/3 (p = 0.027) and higher mean (SD) respiratory system compliance (group PEEP-5, 0.83 (0.20) ml cmH2O-1 kg-1 predicted body weight vs. group PEEP-BMI/3, 0.95 (0.17) ml cmH2O-1 kg-1 predicted body weight; p = 0.020). Lung ultrasound revealed a reduced postoperative loss of lung aeration in patients allocated to the BMI/3 group. Patients allocated to the BMI-adjusted group required less supplemental oxygen, had less newly developed atelectasis and had higher oxygen saturations upon arrival in the post-anaesthesia care unit. DISCUSSION In patients without major pulmonary disease who were undergoing non-cardiothoracic surgeries with tracheal intubation, adjusting PEEP based on a calculation of BMI/3 improved lung mechanics and reduced postoperative loss of lung aeration. This approach provides a straightforward and pragmatic method for individualising PEEP in patients undergoing general anaesthesia.