Assessing fitness to fly

Contributed by Dr Raymond Johnston, head of Aviation Health Unit, Civil Aviation Authority, Gatwick.

Section 1: Fitness to travel
Commercial air travel is an extremely safe, convenient and relatively inexpensive mode of transport. The global increase in travel as well as an increasingly aged population means that there may well be a significant increase in older passengers and in those with illnesses who wish to fly.

GPs can play a pivotal role by understanding some key issues in the assessment of fitness to fly, in order that the journey is completed without any untoward events.

There are very few contraindications to flying in a commercial jet aircraft and many passengers who have medical conditions travel regularly without incident.

But there are some passengers whose fitness may be borderline or who may be severely ill and still need to travel.

The main concerns in assessing passengers' fitness to fly are, first, will the in-flight environment have an adverse effect on the medical condition; and will this result in delay to or diversion of the aircraft?

For this to work effectively, the passenger must declare to their treating physician that they intend to fly, and the health professional should be familiar with the aviation environment and any potential interaction with the patient's condition.

The frequency of medical conditions causing an in-flight incident has been documented. Respiratory disorders were reported as the cause in 10 per cent of incidents in 19921 and this was unchanged at 10 per cent in more recent figures published in 1996.2

In this study, the most common causes of incidents were GI (22.3 per cent) and cardiovascular (21.8 per cent). Deaths in flight are rare, reported at 0.29-0.31 per million passengers.1,2

Pressurised cabin
An understanding of the environment in the aircraft cabin is important in allowing medical practitioners to achieve an objective conclusion about a passenger's fitness to fly.

The first consequence of the pressurised aircraft cabin is that the alveolar oxygen tension falls from 103mmHg (13.7kPa) at sea level to approximately 70mmHg (9.3kPa) at cabin altitude.

However, as shown by the figure, the sigmoid shape of the haemoglobin dissociation curve only results in an arterial oxygen saturation fall of 3 per cent at 6,000 feet and approximately 9 per cent at 8,000 feet cabin altitude.

This is of no consequence for a fit individual, but might be of more concern for a passenger with a significant medical condition.

The second consequence of the reduction in cabin pressure, as determined by the gas laws, is an expansion of gas in body cavities of some 30 per cent.3

The alteration in pressure during descent is a common cause of pain in the ears and sinuses in passengers with URTIs. This effect during the climb has obvious implications for gas introduced into body cavities during surgical procedures.

Humidity
It is normal practice for 50 per cent of the cabin air to be recirculated by passing it through high efficiency particulate filters, which remove micro-organisms.

Air humidity in the cabin is below the levels for maximum comfort and may cause symptoms of nasal dryness.

However, the symptoms can be alleviated by increasing intake of non-alcoholic liquids.

Section 2: Respiratory diseases
The main respiratory conditions to consider when assessing fitness to fly are asthma, COPD, emphysema and pneumothorax.

In general, it is accepted that a patient can walk 50 metres on the level or climb 10 steps without dyspnoea, they will be able to tolerate the relative hypoxia of the aircraft cabin.

If the patient's PaO2 is less than 70mmHg, additional oxygen should be requested.4 Those with a PaO2 of less than 50mmHg should probably use surface transport.

As an alternative to the walking test, some respiratory physicians may carry out assessments in a laboratory using oxygen-nitrogen mixes to simulate the cabin environment, which is equivalent to an oxygen concentration of approximately 17 per cent at sea level. If this test results in a PaO2 of less than 55mmHg, the patient should request supplementary oxygen from their airline. It is not permissible for the passenger to use their own oxygen system in flight, as all equipment used on board the aircraft must meet specific regulatory standards.

The specification for aviation oxygen is higher than that for normal medical oxygen in terms of permissible water content to prevent freezing of valves at high altitude.

Most patients with asthma travel without problems but it is important that all medication is carried in hand baggage.

Patients with asthma, other than the mildest cases, should take a course of oral steroids with them on a trip, in order to intervene early if there is any deterioration of their condition.

Infection
Patients with active or contagious respiratory infection should not travel until there is documented control of the infection. Those recovering from acute bacterial infection, for example pneumonia, should be clinically improved with no residual infection. Patients with viral respiratory infections, such as influenza, may infect those sitting adjacent to them and they should postpone air travel until the infection has resolved.

Pneumothorax
A patient with a spontaneous pneumothorax should postpone flying for 10-14 days after full inflation. If there is a need to travel earlier, use a one-way Heimlich valve. It is advised that a patient should not fly for 10-14 days after thoracic surgery.

Section 3: Cardiovascular diseases
Relative hypoxia may cause problems for patients with myocardial ischaemia and cardiac failure. Most patients with uncomplicated myocardial infarction should be fit to fly within 10 days.

If complications exist, an individual risk assessment should be carried out. Patients who have undergone angioplasty with or without stenting should be fit to fly after three to five days, but after open cardiac surgery the thoracic surgery guidelines should be followed.

Deep vein thrombosis
DVT has been associated with travel by car, bus and sea as well as by air and so the term 'traveller's thrombosis' is the most appropriate term to use, rather than 'economy class syndrome'.

Although there has been considerable interest in the popular press, it is important to emphasise that it is a relatively rare condition bearing in mind the number of passengers who travel.

The WHO's Research into the Global Hazards of Travel study has shown the absolute risk to be one in 4,656 flights of more than four hours duration.5

In order to counteract the effects of prolonged sitting, it is sensible to carry out lower limb exercises, which are illustrated in many aircraft in-flight magazines and videos.

In addition, it is important to remain mobile within the aircraft cabin.

For those with multiple risk factors, anti-embolism stockings, low molecular weight heparin or oral anticoagulation should be considered, in discussion with the patient's consultant.

Anaemia
Haemoglobin of less than 7.5g/dl usually precludes travel and haemoglobin between 7.5 and 10g/dl needs individual assessment.

Section 4: Other medical conditions
Outlined below are general guidelines for a number of medical condition, but specific advice about individual cases should be sought from the airline carrying the passenger.6

Most airlines base their guidelines on those of the Aerospace Medical Association.7 It may be helpful in more complex cases to use the Medical Information Form recommended by the International Air Transport Association (see Resources).

Neurology
Patients recovering from a stroke should not usually travel within 10 days, although with individual assessment travel may be possible after three days with the use of supplemental oxygen. Following neurosurgery, the cranium should be free of air and this usually takes about seven days. Passengers who suffer from epilepsy should pack medication in their hand baggage and should not travel within 24 hours of a grand mal seizure.

Pregnancy
The advisability of flying while pregnant is a frequently asked question. The commercial aircraft environment is not generally considered hazardous to a normal pregnancy.

At a normal cabin altitude, the maternal haemoglobin remains 90 per cent saturated and because of the favourable properties of fetal haemoglobin, including increased oxygen carrying potential together with a high fetal hematocrit and the Bohr effect, fetal PaO2 changes very little. A woman with an uncomplicated single pregnancy might fly with most airlines up to the 36th week of pregnancy; a woman with a multiple pregnancy is usually accepted up to the 32nd week.

For short duration flights individual assessment may allow some discretion.

Surgical procedures
Patients will require individual assessment depending on the nature of the surgical procedure, but most patients are fit to fly 10 days after general surgery. Laparoscopic surgery or investigation usually precludes air travel for 24 hours to ensure all gas is absorbed.

Similarly in eye surgery, air travel is possible after 7-10 days but if there is gas in the globe, total absorption may take six weeks.

Orthopaedic conditions
Patients in plaster should not fly for 24 hours on flights of less than two hours and for 48 hours on longer flights. If there is an urgent need for travel, this may be possible if the plaster is bi-valved. Limited space in the cabin may be a problem on some flights and passengers with mobility problems should not be seated at emergency exit rows.

Psychiatric disorders
With psychiatric disorders, the main problem is the potential effect on other passengers and the safety of the aircraft.

If the patient is well controlled medically and accompanied by an escort capable of administering appropriate medication, they are usually fit to fly.

Managing risk
Commercial air travel is available to the public and is a safe and effective mode of transport.

For some passengers with medical problems, however, flying means exposure to potential additional risk.

If this risk is to be managed effectively, it is essential that pre-planning is undertaken in conjunction with a physician who has an understanding of the aviation environment and its potential interaction with the patient's medical condition.

Resources

References

1. Cummins R O et al. In-flight deaths during commercial air travel: how big is the problem? JAMA 1988; 259: 1,983-8.

2. Bagshaw M. Telemedicine in British Airways. J Telemed Telecare 1996; 36-8.

3. Fitness to travel by air. In: Harding R, Mills F eds. Aviation Medicine. 3rd Edition. BMA Publishing, London, 1993.

4. Gong H. Air travel and oxygen therapy in cardiopulmonary patients. Chest 1992; 101: 1,104-13.

5. Kuipers S, Cannegieter S C, Middeldorp S et al. The absolute risk of venous thrombosis after air travel: a cohort study of 8,755 employees of international organisations. PLoS Med 2007: Vol. 4, No. 9, e290.

6. Bagshaw M, Byrne N. La sante des passagers. Urgence Practique 1999; 36: 37-43.

7. Medical guidelines for air travel. Medical Guidelines Task Force Aerospace Medical Association Aviat Space Environ Med 2003; 74: A1-19.

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