High flow or titrated oxygen for obese medical inpatients: a randomised crossover trial.

Objective: 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.

Design: A randomised, crossover trial undertaken between February and September 2015.

Setting: Internal medicine service, Wellington Regional Hospital, New Zealand.

Participants: 22 adult inpatients, aged 16 years or more, with a body mass index exceeding 40 kg/m.

Interventions: 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.

Main Outcome Measure: Ptco2 at 60 minutes, adjusted for baseline.

Results: 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).

Conclusion: 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%.

Clinical Trial Registration: Australian New Zealand Clinical Trials Registry, ACTRN12610000522011.