Background and Aim Aircraft travel can worsen hypoxaemia in patients with PAH since pressurised cabins reduce inspired oxygen (FiO2) to the equivalent of breathing 15.1% at sea level. The British Thoracic Society (BTS) recommends assessing these patients for additional oxygen before air travel, but the criteria used are based on studies of people with COPD (Thorax, 2004). New recommendations, in press, suggest that all patients with PAH in WHO Functional Class III and IV have in-flight oxygen (Thorax, In Press). The aim of this study was to determine the impact of current and future recommendations on PAH patients, with the hypothesis that more PAH patients will fail a hypoxic challenge test (HCT) than seen in other respiratory conditions.
Methods Patients with SpO2 >90% on air underwent a HCT using a 40% Venturi mask driven with nitrogen generating an FiO2 of 15.1%. This was stopped after 20 min or if SpO2 <85%. Capillary blood gas (CBG) measurements were made at the start and end of HCT. Current criteria suggest that an arterial partial pressure of oxygen (PaO2) <6.6 kPa or a SpO2 <85% represents failing the test and in-flight oxygen is needed.
Results Thirty-six patients were recruited: 10 failed (28%), 26 passed (72%). The alveolar-arterial oxygen (A-a)O2 gradient significantly fell during the HCT (4.64 vs 1.61 kPa, p<0.0001 [see Abstract P2 figure 1]). Univariate analysis showed pre-test SpO2 (95 vs 92.5, p=0.027), PaO2 (10.63 vs 9.15 kPa, p=0.0021) and (A-a)O2 gradient (4.32 vs 5.48 kPa, p=0.026) to differ significantly between those who passed and failed. Three patients who failed the HCT would be missed by current BTS recommendations and one patient would receive in-flight oxygen despite passing the HCT. According to the new recommendations, 15 people would have been given in-flight oxygen who did not require it according to their HCT result.
Conclusions PAH patients are no more likely to fail a HCT than other respiratory patients. The narrowing of the (A-a)O2 gradient during the test may suggest an improvement in V/Q matching, protecting patients from severe hypoxaemia. Both current and new BTS recommendations missed patients who might require supplementary oxygen, with new recommendations suggesting the need for in-flight oxygen in many patients who do not require it according to the result of their HCT.