Pre-flight assessment in patients with obesity hypoventilation syndrome

Reduced atmospheric pressure during air travel can cause significant hypoxaemia in some patients with respiratory disease. Our aims were to investigate the degree of hypoxaemia in patients with obesity hypoventilation syndrome (OHS) during hypoxic challenge test (HCT), and to identify any predictors of a positive HCT.

Thirteen patients underwent assessment, including HCT, lung function and incremental shuttle walk test. All had OHS well controlled with long-term nocturnal non-invasive ventilation (NIV). Patients with chronic obstructive pulmonary disease were excluded. A positive HCT was defined according to the British Thoracic Society (BTS) recommendation as arterial oxygen tension (PaO₂) <6.6 kPa and/or oxygen saturation <85%.

Mean age was 57 (± 11) years. Mean body mass index was 51.7 (± 12) kg/m(2) . Mean baseline PaO₂ and arterial carbon dioxide tension (PaCO₂) were 10.2 (9.5-11.3) kPa and 5.2 (3.7-6.8) kPa, respectively. Seven patients (54%) had a positive HCT. The correlation between baseline PaO₂ and PaO₂ at the end of the HCT was not statistically significant (r = 0.433, P = 0.184). A negative correlation was observed between baseline PaCO₂ and PaO₂ at the end of the HCT (r = -0.793, P = 0.004). A positive correlation was observed between the distance walked and the PaO₂ at the end of the HCT (r = 0.608, P = 0.047).

OHS is a risk factor for severe hypoxaemia during air travel even if the ventilatory failure is well controlled. An HCT before air travel is advisable in all OHS patients. Those with positive HCT may use NIV or have oxygen on-board as per BTS recommendation.