Prophylactic post-operative high flow nasal oxygen versus conventional oxygen therapy in obese patients undergoing bariatric surgery (OXYBAR study): a pilot randomised controlled trial

Obesity has become a global pandemic, as a result surgical intervention for weight loss has increased in popularity. Obese patients undergoing operative intervention pose several challenges in respect of their peri-operative care. A prominent feature is the alteration in respiratory mechanics and physiology evident in the obese. These combine to predispose individuals to a reduction in end expiratory lung volume (EELV) and atelectasis after anaesthesia. Consequently, the incidence of post-operative pulmonary complications (PPC) in this cohort has been reported to be in excess of 35%. High flow nasal oxygen (HFNO) has been suggested as a means of increasing EELV in post-operative patients, reducing the likelihood of PPC. We conducted a single centre, pilot, randomised controlled trial (RCT) of conventional oxygen therapy versus HFNO in patients after bariatric surgery. The aim of the study was to investigate the feasibility of using Electrical Impedance Tomography (EIT) as a means of assessing respiratory mechanics and to inform the design of larger, definitive RCT. Fifty patients were randomised during a 10-month period (conventional O2 n=25 vs. HFNO n = 25). One patient crossed over from conventional O2 to HFNO. There was no loss to follow-up. and analyses were performed on an intention-to-treat basis. 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. ICU and hospital LOS were comparable. Only one patient developed a PPC (in the HFNO group). In a secondary analysis, delta EELI was positively correlated with increasing BMI. These data suggest that a large-scale randomised controlled trial of HFNO after bariatric surgery in an all-comers population is likely infeasible. Furthermore, while EIT is a useful tool for assessing respiratory mechanics in this group it could not be considered a patient-centred outcome in a larger study. Similarly, the infrequency of PPC precludes its use as a primary outcome in a definitive trial. Future studies should focus on identifying patients most at risk for post-operative pulmonary complications and those in whom HFNO is likely to confer greatest benefit.