Oxygen therapy should be titrated for morbidly obese inpatients to avoid hyperoxaemia and hypoxaemia, New Zealand research finds.

The randomised, crossover trial of 22 morbidly obese adult inpatients found a significantly greater increase in transcutaneous carbon dioxide tension (Ptco₂) following 60 minutes of high concentration oxygen therapy compared with 60 minutes of oxygen titrated to achieve a target peripheral oxygen saturation (Spo₂) of 88–92%.

This effect was regardless of whether hypercapnia was present at baseline or the patient had an acute respiratory disorder.

The mean difference in Ptco₂ between therapies at 60 minutes was 3.2mmHg, researchers reported in the MJA.

Participants, who all had a BMI exceeding 40 kg/m^2, were randomised to the order they received the two therapies. A washout period of at least 30 minutes was ensured between the interventions.

“The increase in Ptco₂ with high concentration oxygen therapy and the difference between the two interventions were evident as early as 10 minutes after commencing the interventions,” researchers wrote.

Co-author Dr Irene Braithwaite, deputy director of the Medical Research Institute of New Zealand, said their research increased the evidence base for British Thoracic Society and Thoracic Society of Australia and New Zealand guidelines recommending titrated oxygen to avoid hyperoxaemia and hypoxaemia in chronic respiratory disease.

“The guidelines are appropriate not only for those with chronic respiratory conditions such as COPD/emphysema and asthma, but also in conditions that may impair respiratory function such as obesity,” she told the limbic.

A number of observational studies have found that despite the guidelines, high concentration oxygen may still be prescribed and administered.

“This research provides an opportunity to reinforce the clinical importance of the guidelines that do exist,” Dr Braithwaite said.

There were a number of other conditions which may place patients at risk of oxygen-induced hypercapnia, such as bronchiectasis, neuromuscular disease and chest wall diseases, she noted.

“Each of these clinical conditions would ideally require randomised controlled trial level evidence to evaluate response to oxygen therapy, but in the interim, clinicians should be aware of the possible risks,” Dr Braithwaite said.