• Rachel Fulton, Jonathan E Millar, Megan Merza, Helen Johnston, Amanda Corley, Daniel Faulke, Ivan L Rapchuk, Joe Tarpey, Jonathon P Fanning, Philip Lockie, Shirley Lockie, and John F Fraser.
• Department of Anaesthesia and Critical Care, Queen Elizabeth II University Hospital, Glasgow, UK.
• Obes Surg. 2021 Nov 1; 31 (11): 4799-4807.

BackgroundPatients with obesity are predisposed to a reduction in end-expiratory lung volume (EELV) and atelectasis after anaesthesia. High flow nasal oxygen (HFNO) may increase EELV, reducing the likelihood of postoperative pulmonary complications (PPC). We conducted a pilot randomised controlled trial (RCT) of conventional oxygen therapy versus HFNO after bariatric surgery. The aim was to investigate the feasibility of using electrical impedance tomography (EIT) as a means of assessing respiratory mechanics and to inform the design of a definitive RCT.MethodsWe performed a single-centre, parallel-group, pilot RCT. Adult patients with obesity undergoing elective bariatric surgery were eligible for inclusion. We excluded patients with a known contraindication to HFNO or with chronic lung disease.ResultsFifty patients were randomised in equal proportions. One patient crossed over from conventional O2 to HFNO. Delta EELI was higher at 1 hour in patients receiving HFNO (mean difference = 831 Au (95% CI - 1636-3298), p = 0.5). Continuous EIT beyond 1 hour was poorly tolerated. At 6 hours, there were no differences in PaO2/FiO2 ratio or PaCO2. Only one patient developed a PPC (in the HFNO group) by 6 weeks.ConclusionsThese data suggest that a large-scale RCT of HFNO after bariatric surgery in an 'all-comers' population is likely infeasible. While EIT was an effective means of assessing respiratory mechanics, it was impractical over time. Similarly, the infrequency of PPC precludes its use as a primary outcome. Future studies should focus on identifying patients at the greatest risk of PPC.© 2021. The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.

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