(1) Formulate answerable clinical questions

1. (a) In people with dementia does flying affect cognition/behaviour/health/death?

2. (b) For people aged 65 years and over, do long-haul flights affect their mental or physical health?

(2) Literature search

Electronic library searches included Medline, Pubmed, ClinPsyc and the Australian aviation databases Ozemail and Avmedlink, using key search words of DEMENTIA, MENTAL HEALTH, FLYING and TRAVEL. Media articles obtained from the Daily Mail, The Times, and The Independent on Sunday were used for contacts.

The Alzheimer's Society and Aviation Health Institute (both charities) were contacted directly, as was the Civil Aviation Authority at Gatwick.

A number of international airlines were telephoned for advice on passenger health, and Heathrow Occupational Health Department and Terminal Health Control Units were contacted directly.

(3) Critical appraisal

There were no papers specifically answering these clinical questions. The most recognised health risks of flying are deep vein thrombosis and pulmonary embolus. Over a 3-year period, 11 of the 61 deaths of passengers arriving at Heathrow airport were due to pulmonary emboli. These are associated with prolonged sitting in cramped positions and were first noted to occur in people who had spent many hours in air-raid shelters during World War Two (Reference GiangrandeGiangrande, 1999).

However, ‘changes in environment, altitude and time can increase confusion in the mildly demented passenger, and hypoxia at altitude could conceivably precipitate neurological symptoms in patients with cerebral arterial disease. There is a tendency for patients who become confused at night to do so during flight’ (Reference White and AllenWhite & Allen, 1992).

Most long-haul flights cruise at around 500 miles per hour at altitudes of 30 000-40 000 feet above sea level. At sea level, air pressure is approximately 14 pounds per square inch (PSI) and at 40 000 feet it is approximately 2.7 PSI — this is incompatible with life. The cabin environment is artificially controlled and pressurised at 10.8-12.2 PSI, equivalent to 6 000-8 000 feet above sea level. At this controlled altitude there is a reduction of 20-26% in the amount of oxygen available, resulting in haemoxyhaemoglobin saturations of 83-85% of normal. This can cause tachycardia, tachypnoea, headaches, dizziness, impaired coordination, fatigue and confusion (Reference Ernsting, Nicholson and RainfordErnsting et al, 1999).

Reduced air pressure can also cause peripheral oedema and increase in the volume of any air filled spaces, for example sinuses, stomach and guts, and any post-operative or plaster cast air pockets. According to Boyle's law, air spaces will increase by 25-35% at altitudes of 6 000-8 000 feet (Reference Ernsting, Nicholson and RainfordErnsting et al, 1999).

Humidity is also reduced at high altitudes. This can cause dehydration, hypovolaemia and reduced peripheral circulation. The humidity ‘comfort zone’ is 50-65%. A centrally heated room has about 25% humidity. Air cabin humidity is 1-20% depending on the density of passengers, each giving out moisture.

The cabin environment is controlled by air conditioning units that draw air from the plane's jet engines. This is cooled and supplied to the cabin from the front to the rear so the quality of air is best to the flight deck and first class passengers and poorest to the economy passengers at the rear of the plane. Sometimes one of the three air conditioning units is turned off to save fuel, and all units can become clogged by nicotine, reducing their efficiency.

There are no internationally agreed standards for cabin air that may have high levels of carbon dioxide, ozone, nicotine and microbes unacceptable in other artificially controlled environments such as office blocks.

Flying at high altitudes increases exposure to natural radiation. This cannot be artifically controlled and exposure in air crew is carefully monitored.

There is no international organisation with a remit to monitor health and well-being of aircraft passengers and in-flight or post-flight deaths. The International Air Transport Association carried out an 8-year survey of these deaths, but only 39% of the 120 members participated. On a major airline body bags were used once or twice per month (Kahn, 1993).

There is some evidence to suggest that time zone changes may precipitate affective disorders, particularly depression after flying east to west (Reference Jauhur and WellerJauhar & Weller, 1982).

This summarises the findings of the literature search. Critical appraisal pertaining to the clinical questions is not possible given the lack of data.

(4) Implications

There is no good evidence answering the clinical questions, but the information available supports anecdotal observations that flying may pose extra risks for people with dementia. Mrs P.'s family decided that as flying to Cyprus may be difficult and possibly harmful, it was better to leave her in respite while they enjoyed their holiday.

The number of older people is increasing and many of them are fit, rich and have friends and relatives abroad. There seems to be sufficient evidence to suggest that flights with current cabin environments may challenge mental and physical health. It may be that the costs of increasing oxygen concentrations, humidity and leg room are small compared with litigation or losing passengers when they become better informed. Despite the Warsaw Convention (1929) stating that airlines are not responsible for their customer's health (passengers are responsible for their own health), there are sufficient concerns to warrant comprehensive research and monitoring of the welfare of aircraft passengers.