Air travel and respiratory disease

In spite of recent events, air passenger travel is increasing. Globally, over one billion people now fly each year, and the United Kingdom alone had over 180 million air traffic movements in 2001.¹ The increasing availability of lower cost travel also makes such journeys accessible to older or less financially advantaged travellers. It has become common for people with lung disease to wish to travel and in turn seek advice from their medical practitioners about the provision of oxygen and other issues. Surprisingly, reports of serious incidents concerning travellers with lung disease are relatively rare, but a systematic investigation of this area has not yet been conducted. Since respiratory problems are estimated to make up about 11% of in-flight emergencies it is reasonable to assume that the burden of risk surrounding the flight itself and later disruption of the journey is significant.²

Advice about the particular medical hazards of travel for patients with respiratory disease and their necessary assessment has not been easy to obtain. Paradoxically, patients themselves have had greater access to information through charities and the internet. By contrast the information for their medical advisers has been extractable only from clinical guidelines concerning the individual disease or from specialist aviation sources. New evidence based guidelines from the British Thoracic Society have been developed to address this problem by summarising knowledge for adults and children with all respiratory diseases and making recommendations for assessment before travelling. These guidelines are published in a full length version in Thorax, and a primary care summary is available online or from the British Thoracic Society (www.brit-thoracic.org.uk).²,³

Apart from the usual health risks of airline flight, the principal additional challenge for patients with chronic respiratory disease is exposure to hypobaric hypoxia. Modern commercial aeroplanes fly at a height of around 10 700 metres, but the cabin pressure is maintained at the equivalent of 2400 metres in altitude rather than at sea level. The rapid reduction in pressure associated with ascent is accommodated safely by the normal lung. People with abnormal lungs may be vulnerable to the relatively minor pressure changes by enlargement of a pre-existing pneumothorax or rupture of an emphysematous bulla or other spaces containing air.

At cabin altitude even normal people can occasionally desaturate but will generally compensate by increasing alveolar ventilation. People with respiratory disease who use long term oxygen treatment will need to continue using oxygen during a flight. People with borderline hypoxaemia at sea level may also need supplementary oxygen to avoid becoming compromised at altitude. The need for supplementary oxygen can be predicted by careful prior assessment, but this is not widely used.⁴ The new guidelines point out that vulnerable patients can be identified by using a combination of pulse oximetry and identification of predisposing risk factors such as abnormal spirometry. Those patients with a resting oxygen saturation below 92% or 92-95% on air with additional risk factors are recommended to have a formal hypoxic challenge test to identify whether they are able to compensate for the altitude. The normobaric challenge test simply entails the inhalation of 15.1% oxygen for 20 minutes and measurement of arterial blood gases.⁵,⁶ Supplementary oxygen is recommended for those patients whose arterial oxygen pressure remains below 6.6 kPa. In addition to the need for oxygen the guidelines also address issues that may be common to all travellers, including the risks of dehydration, thromboembolism, and cross infection.

The advice from the guidelines may be a welcome start, but unfortunately many of the recommendations are not supported by strong scientific evidence. Insufficient good quality trials exist in many areas and advice stems largely from expert opinion, but the authors do point the way to future research directions. One particular difficulty is that the guidelines are inevitably slanted towards clinicians in secondary care by virtue of the necessary physiological assessment. The primary care version is succinct and clear, but the requirement for assessment by spirometry and pulse oximetry may be beyond the resources of many practices. Nevertheless, as primary care matures it should obtain and understand this relatively basic and inexpensive equipment.

As people with chronic respiratory disease become more adventurous they must also take some responsibility for the safety of their own travel. The British Thoracic Society guidelines will inform clinicians, but some excellent material is also available on leaflets or the web—for example, from the British Lung Foundation, the California Thoracic Society, and the Aerospace Medical Association.^7–9 In addition to informing themselves, travellers must also ensure that proper arrangements are made for travel insurance and the practical issues surrounding the provision of oxygen and equipment on the journey and at the destination.

Although people with chronic lung disease have become more adventurous and informed, an inconsistency remains in the airline industry itself. Airlines may have diverse and arbitrary assessment procedures, and the types of oxygen provision and interface may vary between aircraft. More importantly, the airlines may vary in their willingness to take people with lung disease. Some will charge, and some low cost or charter airlines will not take any passengers requiring oxygen. For people with lung disease the hazards of air travel are now clearer, but it pays for them to be prepared and shop around.