Commercial aircraft fly at cruising altitudes of up to 40000 feet above sea level. At cruising altitudes, air pressure in the cabin is equivalent to air pressure 6000-8000 feet above sea level to maintain a safe in-flight environment for passengers. At 8000 feet the partial pressure of oxygen falls to the equivalent of breathing 15.1% oxygen at sea level, therefore less oxygen is taken up by the blood. Healthy passengers can compensate by increasing their minute ventilation, however patients with lung disease may not have the capacity to compensate and become hypoxemic.

To assess the suitability of an at-risk patient to fly, a hypoxic challenge test can be performed.

If there is doubt about a patient’s fitness to fly, and if there are co-morbidities affecting fitness such as cardiovascular disease or immunosuppressant therapy, assessment is advised. Patients with the following conditions should be assessed:

• Previous air travel intolerance with significant respiratory symptoms (dyspnoea, chest pain, confusion or syncope).
• Severe COPD or severe asthma (FEV1<30% predicted).
• Bullous lung disease.
• Severe restrictive lung disease (vital capacity <1 litre) including chest wall and respiratory muscle disease, especially with hypoxaemia and/or hypercapnia.
• Cystic fibrosis.
• Co-morbidity with conditions worsened by hypoxaemia (e.g. cerebrovascular disease, cardiac disease or pulmonary hypertension).
• Pulmonary tuberculosis (non-contagious).
• Within 6 weeks of hospital discharge for an acute respiratory illness.
• Recent pneumothorax.
• Risk of, or previous venous thromboembolism.
• Pre-existing requirement for oxygen or ventilatory support.

The following are contraindications to commercial air travel and therefore testing should not be performed in patients with these conditions:

• Infectious tuberculosis.
• Ongoing pneumothorax with persistent air leak.
• Major haemoptysis.
• Usual oxygen requirement at sea level at a flow rate exceeding 4L/min.
  

• Reason for referral - what is the clinical question to be answered by performing the test?
• Current respiratory medications
• Infectious status

If a specific test result is unable to be obtained due to access, financial, religious, cultural or consent reasons a Clinical Override may be requested. This reason must be clearly articulated in the body of the referral.