Introduction The Ventimask method of HCT is widely used in clinical practice however; a major limitation of this method is that the gas concentration administered during testing cannot be verified. The Reduced Oxygen Breathing Device (ROBD) is a flight simulator developed by the US military and the inspired fraction of oxygen (FiO2) can be accurately determined.
Aim The aim of this study was to compare the results obtained during HCT, in patients with chronic respiratory disease, using the ROBD compared to the Ventimask method. The relationship of PaO2 and SpO2 by both methods was compared to in-flight oxygen saturations.
Methods Patients with chronic respiratory disease undertook a HCT by the ROBD and Ventimask methods. The FiO2 was 15.1% to simulate 8,000 ft which is equivalent to the maximum cabin altitude patients are likely to encounter during commercial air travel.
Results 60 patients, (45 males) with stable chronic obstructive or restrictive respiratory disease participated in the study; age mean (SD) 57 (15) years, FEV1 66 (27)%, FVC 66 (27)%, FEV1/FVC ratio 60 (18). There was no significant difference between PaO2 pre-ROBD HCT 9.74 (1.19) and pre-Ventimask HCT 9.72 (1.05) paired t-test p>0.05. PaO2 measured post-ROBD HCT (7.36 (0.93)) was significantly lower compared to PaO2 post-Ventimask HCT (7.96 (0.97)) (p<0.01). There was no significant difference in the mean decrease in SpO2 in-flight mean (SD) 6 (3) compared to the mean decrease in SpO2 post-ROBD HCT 5 (3) (p 0.334). In contrast, there was a significant difference in the mean decrease in SpO2 post-Ventimask HCT 3 (2) compared to the mean decrease in SpO2 in-flight and post-ROBD HCT (p<0.01)
Conclusion The ROBD HCT results in a lower PaO2 compared to a Ventimask HCT at a FiO2 of 15.1%. The ROBD assessment more accurately reflected actual changes in SpO2 in-flight and may be a better method of assessment for in-flight oxygen.
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