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Chronic obstructive pulmonary disease - Management
Hypoxic challenge test
- The hypoxic challenge test is the gold standard for pre-flight assessments, and is performed in secondary care.
- It involves measuring the person's response to a simulated aircraft cabin environment.
- In this investigation, the person is exposed to an inspired oxygen tension of 15 kPa, which is the expected worst-case scenario for the aircraft passenger. This can be achieved by two methods:
- Administering 15% oxygen in nitrogen using a face mask and non-rebreathing circuit.
- Filling a body plethysmograph with 15% oxygen — a modification of this technique involves placing a hood over the person's head and shoulders which is ventilated with a constant supply of 15% oxygen. Alternatively, 15% oxygen can be administered by using a 40% Venturi mask with nitrogen as the driving gas (the Venturi mask dilutes the nitrogen with air, producing 15% oxygen).
- During the hypoxic challenge test, the person is monitored continuously with pulse oximetry to prevent severe hypoxaemia. Blood gas tensions are measured before and after the hypoxic exposure.
- Some experts recommend electrocardiographic monitoring to detect asymptomatic arrhythmias.
- A predicted PaO2 of 6.6 kPa is used as the cut-off value below which supplemental oxygen is recommended for air travel.
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