Individualized positive end-expiratory pressure in obese patients during general anaesthesia: a randomized controlled clinical trial using electrical impedance tomography

Background. General anaesthesia leads to atelectasis, reduced end-expiratory lung volume (EELV), and diminished arterial oxygenation in obese patients. We hypothesized that a combination of a recruitment manoeuvre (RM) and individualized positive end-expiratory pressure (PEEP) can avoid these effects. Methods. Patients with a BMI a parts per thousand 35 kg m(-2) undergoing elective laparoscopic surgery were randomly allocated to mechanical ventilation with a tidal volume of 8 ml kg(-1) predicted body weight and (i) an RM followed by individualized PEEP titrated using electrical impedance tomography (PEEPIND) or (ii) no RM and PEEP of 5 cm H2O (PEEP5). Gas exchange, regional ventilation distribution, and EELV (multiple breath nitrogen washout method) were determined before, during, and after anaesthesia. The primary end point was the ratio of arterial partial pressure of oxygen to inspiratory oxygen fraction (PaO2/FiO(2)). Results. For PEEPIND (n=25) and PEEP5 (n=25) arms together, PaO2/FiO(2) and EELV decreased by 15 kPa [95% confidence interval (CI) 11-20 kPa, P < 0.001] and 1.2 litres (95% CI 0.9-1.6 litres, P < 0.001), respectively, after intubation. Mean (sd) PEEPIND was 18.5 (5.6) cm H2O. In the PEEPIND arm, PaO2/FiO(2) before extubation was 23 kPa higher (95% CI 16-29 kPa; P < 0.001), EELV was 1.8 litres larger (95% CI 1.5-2.2 litres; P < 0.001), driving pressure was 6.7 cm H2O lower (95% CI 5.4-7.9 cm H2O; P < 0.001), and regional ventilation was more equally distributed than for PEEP5. After extubation, however, these differences between the arms vanished. Conclusions. In obese patients, an RM and higher PEEPIND restored EELV, regional ventilation distribution, and oxygenation during anaesthesia, but these differences did not persist after extubation. Therefore, lung protection strategies should include the postoperative period. Clinical trial registration. German clinical trials register DRKS00004199, www. who. int/ ictrp/ network/ drks2/ en/.