Janine Pilcher, Michael Richards, Leonie Eastlake, Steven J McKinstry, George Bardsley, Sarah Jefferies, Irene Braithwaite, Mark Weatherall, Richard Beasley

To compare the effects on transcutaneous carbon dioxide tension (Ptco2) of high concentration and titrated oxygen therapy in medical inpatients with morbid obesity who were not selected for a pre-existing diagnosis of obesity hypoventilation syndrome. A randomised, crossover trial undertaken between February and September 2015. Internal medicine service, Wellington Regional Hospital, New Zealand. 22 adult inpatients, aged 16 years or more, with a body mass index exceeding 40 kg/m². Participants received in random order two 60-minute interventions, with a minimum 30-minute washout period between treatments: titrated oxygen therapy (oxygen delivered, if required, via nasal prongs to achieve peripheral oxygen saturation [Spo2] of 88-92%), and high concentration oxygen therapy (delivered via Hudson mask at 8 L/min, without regard to Spo2). Ptco2 and Spo2 were recorded at 10-minute intervals. Ptco2 at 60 minutes, adjusted for baseline. Baseline Ptco2 was 45 mmHg or lower for 16 participants with full data (73%). The mean difference in Ptco2 between high concentration and titrated oxygen therapy at 60 minutes was 3.2 mmHg (95% CI, 1.3-5.2 mmHg; P = 0.002). High concentration oxygen therapy increases Ptco2 in morbidly obese patients. Our findings support guidelines that advocate oxygen therapy, if required in patients with morbid obesity, be titrated to achieve a target Spo2 of 88-92%. Australian New Zealand Clinical Trials Registry, ACTRN12610000522011.