Extubation with Reduced Inspiratory Oxygen Concentration or Postoperative Continuous Positive Pressure to Improve Oxygenation after Laparoscopic Bariatric Surgery: A Randomized Controlled Trial

During mechanical ventilation, patients with obesity often experience considerable atelectasis formation with subsequent worsening of oxygenation.1–3 In a previous study from our group, a lung protective strategy based on electrical impedance tomography–guided individualized positive end-expiratory pressure (PEEP; mean, 18.5 cm H2O) combined with repeated recruitment maneuvers improved intraoperative oxygenation and lung mechanics, suggesting lower atelectasis formation compared to a fixed PEEP of 5 cm H2O.1,4 Effects were especially pronounced in a group of patients with obesity (mean body mass index, 51 kg/m²) undergoing bariatric surgery. However, the positive effects were not sustained after extubation, suggesting early atelectasis formation during spontaneous breathing. This may be caused by the sudden PEEP withdrawal, resulting in both compression and absorption atelectasis—especially in patients with obesity.5 We therefore designed a randomized trial to investigate the hypotheses that after intraoperative mechanical ventilation with repeated recruitment maneuvers and individualized PEEP, (1) extubation with reduced fractional inspired oxygen tension (Fio2) to minimize absorption atelectasis or (2) the use of continuous positive airway pressure in the first postoperative hours will improve oxygenation (primary hypothesis) and reduce atelectasis reformation (secondary hypothesis) in patients with obesity.Patients 18 yr or older, with body mass index greater than 35 kg/m2 and intermediate to high risk of postoperative pulmonary complications (Assess Respiratory Risk in Surgical Patients in Catalonia score [ARISCAT-Score] 31 or greater)6 undergoing laparoscopic bariatric surgery were eligible for inclusion. All patients received intraoperative volume-controlled mechanical ventilation with a tidal volume of 8 ml/kg predicted body weight and individualized PEEP, corresponding to the lowest regional ventilation delay index during decremental PEEP titration using electrical impedance tomography as previously described.1 Anesthesia, intraoperative lung protective ventilation, and timing of recruitment maneuvers were also identical to a previously published study by our research group.1Patients were randomized to receive either (1) extubation with an Fio2 of 0.5 (LowFio2 group) or (2) postoperative continuous positive airway pressure (continuous positive airway pressure group) for 2 h after extubation (see also the Supplemental Digital Content for statistical methods, https://links.lww.com/ALN/D168). The LowFio2 group was extubated at an Fio2 of 0.5 and received no continuous positive airway pressure during the first 2 h in the Post Anesthesia Care Unit. The continuous positive airway pressure group was extubated at an Fio2 of 1.0 and received noninvasive continuous positive airway pressure with a PEEP of 12 cm H2O until 2 h postoperatively with an Fio2 of 0.4. All patients received supplemental oxygen via nasal cannula if necessary to maintain an oxygen saturation measured by pulse oximetry of 92% or greater, except the patients in the continuous positive airway pressure group during the continuous positive airway pressure phase (see Supplemental Figure, https://links.lww.com/ALN/D169). Pao2/Fio2 and distribution of tidal ventilation were measured before and 2 and 4 h after extubation, where arterial blood gas analysis was obtained after a 3-min period of breathing 100% oxygen via endotracheal tube (intraoperatively) or tight-fitting face mask (after extubation). The primary endpoint was Pao2/Fio2 at 2 h postextubation. Initially the two randomized arms were also to be compared to a group from a previous trial with Fio2 of 1.0 and without continuous positive airway pressure, but this comparison had to be abandoned because of differences in measurement methods. The trial was approved by our local ethics committee (University of Leipzig, Leipzig, Germany, No. 475/17-ek) and registered in the World Health Organization–listed German trials registry (DRKS00013984).In 41 patients (22 continuous positive airway pressure, 19 Fio2 = 0.5, mean body mass index 46.8 ± 7.9 kg/m2, mean ARISCAT score 34.8 ± 7.1), median individualized PEEP was 18 cm H2O (range, 8 to 24; see Supplemental Table for baseline characteristics, https://links.lww.com/ALN/D170). According to a linear mixed model, Pao2/Fio2 at 2 h after extubation was 77 mmHg lower in the LowFio2 group than in the continuous positive airway pressure group (95% CI, 4 to 149 mmHg; P = 0.040). However, 4 h after extubation meaning 2 h after cessation of continuous positive airway pressure therapy, there were no longer any differences in Pao2/Fio2 (P = 0.51) between groups (fig. 1). Interestingly, this arose through improvement in oxygenation in the LowFio2 group and worsening in the continuous positive airway pressure group, neither of which was statistically significant on its own. Furthermore, there were no significant differences in distribution of tidal ventilation to dependent lung areas between both groups at any time, indicating that the extent of atelectasis formation did not differ between the groups (fig. 2).We conclude that in patients with obesity, continuous positive airway pressure support after mechanical ventilation with individualized PEEP leads to improved oxygenation after extubation, but the positive effects are limited to the duration of continuous positive airway pressure therapy and might be of limited clinical relevance in healthy patients with almost fully recruited lungs. In contrast, extubation with a reduced Fio2 of 0.5 does not appear to be effective in improving oxygenation in patients undergoing bariatric surgery.This trial was funded by the Federal Ministry of Education and Research (Bonn, Germany; Integrated Research and Treatment Center "Adiposity Diseases," FKZ: 01EO1501 IFB K7-80), and by departmental funding.Dr. Wrigge received research funding, lecture fees, and technical support from Dräger Medical (Lübeck, Germany); funding from Pfizer (Investigator Initiated Trial Program; Berlin, Germany); funding and lecture fees from InfectoPharm (Heppenheim, Germany); lecture fees from Getinge (Rastatt, Germany); lecture fees from MSD (Konstanz, Germany); and advisory honoraria from Liberate Medical (Crestwood, Kentucky). Dr. Simon received funding and lecture fees from InfectoPharm. The other authors declare no competing interests.Full protocol available at: felix.girrbach@uk-augsburg.de. Raw data available at: felix.girrbach@uk-augsburg.de.Supplement on statistical methods, https://links.lww.com/ALN/D168Supplemental Figure 1. Experimental protocol timeline, https://links.lww.com/ALN/D169Supplemental Table. Baseline characteristics, https://links.lww.com/ALN/D170