In an attempt to guide physicians asked by respiratory patients for advice on flight fitness, the British Thoracic Society (BTS) have published guidelines on fitness to fly. The main potential hazard is hypobaric hypoxia, and efforts have focused on the prediction of hypoxia in individuals. The present study examines 10years’ experience of hypoxic challenge (HC) of respiratory patients to evaluate if the guidelines recommended by the BTS are appropriate.

One hundred and eighteen patients (67 female, mean age 65.6±11.4 (SD) years) were referred for assessment. Patients underwent HC using a 40% Venturi mask supplied with 100% N₂ which lowered the F_iO₂ to 15.1%. A further 13 patients on long-term oxygen therapy also underwent HC whilst receiving supplemental oxygen.

In agreement with the BTS guidelines, all patients with a sea level SpO₂ of over 95% maintained their SpO₂ ≥90% during HC. One third of patients with sea level SpO₂ of 92–95%, but no other risk factor (as defined by the guidelines) also desaturated below 90% during HC. Thirty-two patients were assessed as fit to fly with supplemental oxygen.

Our results support the BTS guidelines for patients with a sea level SpO₂ >95% but suggest that some revision is required for patients with a sea level SpO₂ of 92–95%. It was not possible to predict from either initial SpO₂ or spirometry which individuals were at risk of desaturation below 90% during hypoxic challenge.