Media speculation about the health effects of air travel, including DVTs, has caused unnecessary alarm, says
Dr Ian Perry
Modern aircraft fly quite high, even on journeys of two or three hours, as it is more economical. This means the cabin pressure is reduced to about 5,000-6,000 feet equivalent like being up a mountain. At this altitude, gas bubbles are about twice the size they are at sea level. This is why it is not recommended to drink a lot of fizzy drinks while flying.
The partial pressure of oxygen in the cabin is maintained at about the same as ground level, so no one should suffer from lack of oxygen. It is wise, however, to advise caution for people with respiratory problems. A patient with COPD may require extra oxygen when flying. A few airlines will provide this free of charge, but most do not.
The quality of the air in modern aircraft has to meet certain standards and is probably better than the air in most operating theatres. The exchange rate is certainly higher: 50 per cent of the air is recycled, which means half the air from the cabin is filtered together with the fresh air intake.
It is quite difficult to pass on an infectious disease in an aircraft by breathing, as exhaled air will not normally travel very far. But people sitting next to each other have been infected on the rare occasions that air conditioning has broken down.
Reported cases of TB and other diseases being transmitted on aircraft are unsubstantiated. Although SARS has been transported in aircraft, it was not necessarily spread within them; SARS is now known to be transmitted by touching, kissing and so on. Infected sputum from a SARS case could remain infectious for as long as the specimen remains moist.
Personal hygiene is and always has been the best preventive measure in all disease processes, on the ground and in the air.
Medical assistance in the air
Anyone intending to fly must be capable of travelling for the planned length of time without medical attention.
If medical attention is expected to be necessary in flight, that passenger must have an escort capable of providing it. Airline cabin staff cannot be expected to change urine bags, give tablets or injections, or reapply dressings this is a popular misconception among many of the travelling public.
Airlines will help load and offload anyone who needs help, but the request must be made well in advance of the flight preferably 48 hours before departure. At least the same time is required if the patient needs a stretcher or some other special arrangement, which the airport may not have. This problem occurred recently when a patient had arranged to come to the UK for a spinal operation following a serious car crash. Unfortunately the aircraft arrived without a stretcher. The patient was wheeled to the aircraft on a trolley but then had to be returned to hospital.
Communication is very important in such cases if a patient's air trip is to be made to be as comfortable and trouble-free as possible.
Deep vein thrombosis
There is no medical evidence whatsoever to support the suggestion that flying can actually cause a DVT. A great deal of what has been written on the topic is unsubstantiated.
Anyone who sits still for a long time anywhere, whether in a coach, train, in front of a computer, on a cruise ship or on a plane, is more likely to hasten the onset of the DVT that is already forming. If that person is overweight, smokes, is taking certain medications, has clotting factor irregularities or any one of a number of other factors, then that person is likely to be the one in 30,000 to 300,000 people who is going to get a DVT that day, come what may.
One international airline flies 30,000 people a day, so we know that one of those passengers may get a DVT on the plane or when waiting to get on or off. Recently the Daily Telegraph reported that hospitals around Heathrow admit 2,000 people a year with a DVT. Considering the many millions of people who pass through Heathrow every year, the actual number of DVT cases should be much higher, so this fact merely suggests that flying actually reduces the incidence of DVT.
Just as there is no scientific evidence that flying causes DVT, so there is no evidence that exercise or aspirin when flying prevent it. Some experience suggests that exercise helps well-being. Aspirin has been shown clinically to be of no value and should never be taken other than on medical advice.
Water
Bad advice given by non-professionals is to drink plenty of fluids when flying to prevent the blood from thickening. Any GP knows that this is physiologically impossible.
Aircraft are dry places, so some dehydration does occur during a flight, but not to the extent that people have to drink pints of water.
In one case some years ago, overhydration was a factor in causing
a DVT.
Common sense should always be applied to drinking and eating when flying. Sensible fluid replacement, preferably without lots of gas and alcohol, is the best advice. Heavy meals should be avoided before flying because of gas expansion.
Oedema
People's feet and ankles nearly always swell up because of the reduced cabin pressure. This is normally of no consequence and disappears on landing. It can be reduced by wearing a pair of travel socks or any form of long, firm socks. This sensible type of leg-wear helps those who may have varicose veins and even those with mild heart failure. However, there is no evidence that travel socks prevent DVT.
Medical conditions
Some medical conditions, such as myocardial infarction, need to be carefully considered before a GP allows a patient to fly off on a recuperative holiday (see table). A period of at least 10-14 days should elapse before any long journey. This is not because the travel itself may cause any problems but because the destination may not have adequate medical facilities if problems develop.
This also applies to anyone who has had major surgery, hip or knee replacement, or has had any serious form of fracture. After such major trauma fat molecules can get into the bloodstream, which can cause embolism this is an aviation effect and can occur when the cabin pressure is reduced. A satisfactory interval between surgery and travel would be three to four weeks.
Is your patient a pilot?
The National Private Pilots Licence has caused problems for GPs. Any registered patient can ask you to sign a certificate stating that, after a review of their health records, they meet the DVLA driving standards of group 1 or group 2.
If you have not seen the patient before you may consider it necessary to perform some sort of medical examination to make sure that they can see for a distance of up to 25 yards and have normal blood pressure. You may consider it appropriate to charge a fee for this service.
If there is a disease process or some relevant past history that makes you doubt that you can sign the form, telephone one of the national advisers, who will only be too pleased to help you. There have been a large number of queries since the scheme started so the advisers have a good knowledge base.
The best source of this information is the Civil Aviation Authority website www.caa.co.uk
Ian Perry is senior consultant in aviation medicine at the International Aviation Medical Centre, London
Reference
1 Bagshaw M. Aviation medicine. In Zuckerman JN (ed.). Principles and Practice of Travel Medicine. Wiley, 2001
Further information
·Aerospace Medical Association: www.asma.org
·Association of Aviation Medical Examiners: www.aame.co.uk
·British Airways online health and medical information: www.britishairways.com/travel/healthintro/public
·British Airways Passenger Medical Clearance
Unit - free advisory service to doctors: tel 020 8738 5444
·Foreign and Commonwealth Office travel advice: www.fco.gov.uk/travel
·The International Aviation Medical Centre: www.tiamc.com
·US Federal Aviation Administration: www2.faa.gov
·Joint Aviation Authorities: www.jaa.nl
Coping with jetlag
Dr Andrew Herxheimer examines the evidence for different
treatments
Jetlag is likely after any long-haul flight that crosses more than four or five time zones. The sleep and activity cycle is most noticeably disrupted, with reduced physical and mental performance, daytime fatigue, gastrointestinal problems and generalised malaise.
Body rhythms are regulated by internal and external factors, which interact1. For example, the 'body clock' controls melatonin secretion by the pineal gland, an important internal factor, and exposure to light inhibits this secretion. External factors gradually shift the phase of the body clock to coincide with the environment. When the time zone changes rapidly, however, the shift lags behind, so that for some days body and environmental rhythms are out of step.
The severity of the symptoms depends on the number of time zones crossed. Westbound travel generally causes less trouble because it is easier to lengthen than to shorten the natural circadian cycle.
After a flight through six time zones, most travellers take four to six days to get back to a normal sleep pattern and to stop feeling tired during the day. Readjustment occurs at a rate of about one day per one hour's travel eastward and one day per one-and-a-half hours westward.
Can jetlag be prevented?
Speeding up the adaptive phase shift can reduce the severity and duration of jetlag. This can be done by maximising all the relevant outside cues, the most important being bright light.
Others are physical and mental activity, and meals, all taken at times that are normal at the destination. For example, after an eastward flight from Britain to Asia or Australia, avoid bright light and do little until about midday local time, but then walk out of doors, do interesting things, eat (in moderation) when the locals eat, and don't sleep until it gets dark (though a 20-minute nap in the afternoon is unlikely to matter).
Medical treatments
Melatonin The hormone melatonin has been reliably shown to prevent or attenuate jetlag. It is taken about 20 or 30 minutes before the target bedtime at the destination on the day of arrival and on the next two to four days (see box, page 61). The timing is important: if it is taken in the morning it has the opposite effect and hinders adaptation.
Melatonin is a simple, easily synthesised natural substance (N-acetyl-5-methoxytryptamine) which exists in a medicolegal limbo. In many countries, for example the USA, Thailand and Singapore, it is freely sold in health food stores and pharmacies as a 'dietary supplement' (which it clearly is not). No official standards of purity exist. Suppliers present no evidence of how pure their melatonin is3. Four out of six melatonin products bought in the US contained unidentified impurities4. It seems best to buy it from a large reputable pharmacy chain.
In Europe, Australia and many other countries, melatonin is considered a medicine and requires a licence, but no licensed preparation is marketed only the internet offers a grey market.
Hypnotics Long-haul travellers have long used hypnotics to get some sleep in the hope that they will be less fatigued on arrival. Two randomised trials of hypnotics have been reported. The first had four treatment groups, comparing zolpidem, melatonin, melatonin plus zolpidem, and placebo5. Zolpidem improved sleep quality and jet lag symptoms in comparison with placebo, but the combination of melatonin plus zolpidem was no better than placebo.
The second trial compared zopiclone and placebo; jetlag scores were similar, but zopiclone increased sleep duration compared with placebo6. Hypnotics have been noted to cause headache, dizziness, nausea, confusion, amnesia and hangover.
Diet What difference diet makes to jetlag is not known. As a general principle, one would expect the circadian rhythm of the gut to adapt to a new local time most comfortably and efficiently if meals are of modest size and timed to fit in with the new environment. The same applies to fluid intake.
The stimulant effects of caffeine and the sedative effects of alcohol are difficult to time in a way that is likely to aid circadian adaptation. Furthermore, their diuretic effects are likely to add to the dehydration that occurs during high-altitude flights and they are superimposed on those of the body's own rhythms. Caffeine and alcohol thus seem more likely to hinder and delay adaptation.
Complementary therapies Whether alternative or complementary treatments can help to prevent or alleviate jetlag has not been tested. Massage can facilitate relaxation, which could be useful if done at the right time after sundown at the destination.
Individual differences
People differ greatly in their susceptibility to jetlag, and some don't experience it at all. These differences have hardly been investigated and cannot be reliably predicted we just have to learn from our own experience. The fatigue of long journeys can be difficult to distinguish from symptoms of jetlag; the difference may not become clear until the day after arrival or later.
Very young babies are fully occupied with feeding and sleeping and are probably impervious to jetlag, but they gradually become sensitive to it as their circadian rhythm develops. At the other end of life the normal circadian rhythm may become less marked, and sensitivity to zone change may also diminish.
Frequent fliers
Jetlag is more complicated in pilots and airline stewards. Their body rhythms get very disordered, as in people doing irregular shift work.
They must try to organise their rest, exposure to bright light, meals and exercise in ways that maximise harmony with local time. Doing that in advance for example setting one's watch on departure to the destination time and behaving accordingly seems to help little.
Andrew Herxheimer is emeritus fellow at the UK Cochrane Centre, Oxford
References
1 Waterhouse JM et al. Keeping in time with your body clock. Oxford: Oxford University Press, 2002
2 Herxheimer A, Petrie KJ. Melatonin for the prevention and treatment of jetlag (Cochrane review). In: The Cochrane Library, Issue 4, 2003. Oxford: Update Software
3 Herxheimer A, Waterhouse J. The prevention and treatment of jetlag. BMJ 2003;326:296-7
4 Anon. Melatonin. The Medical Letter 1995; 37:111-2
5 Suhner A et al. Effectiveness and tolerability of melatonin and zolpidem for the alleviation of jetlag. Aviat Space Environ Med 2001;72: 638-46
6 Daurat A et al. Effects of zopiclone on the rest/activity rhythm after a westward flight across five time zones. Psychopharmacology 2000;149:241-5
Effects of melatonin
A systematic review found 10 randomised controlled trials comparing melatonin with placebo; in eight of these, melatonin was clearly more effective2. The other two detected no effect from melatonin, but this seemed to be
due to problems in their design or analysis.
Four of the trials scored global jetlag on a scale from 0 (none) to 100 (extreme jetlag). The combined mean for eastward flights with melatonin was 31, against 51 after placebo; for westward flights (in two randomised controlled trials) the means were 22 and 41 respectively.
The results for individuals reported in two trials suggest that melatonin taken after an eastward flight helps about one person in two. Most trials have used 5mg doses; one using 8mg gave similar results.
One study comparing 5mg and 0.5mg doses found the lower dose almost as effective as the higher, but on the higher dose sleep quality and sleep latency were better. Slow-release melatonin (2mg) is less effective than either 5mg or 0.5mg fast release, so a melatonin pulse seems important for efficacy.
Side-effects of melatonin reported in trials include daytime sleepiness, dizziness,
headache and loss of appetite, but it is uncertain whether these were due to the drug
or part of the jetlag.
'Heavy head', disorientation, nausea and unspecified gastrointestinal problems were also noted. A few reports of adverse events possibly related to use of melatonin outside clinical trials suggest two categories of people should avoid it until more is known anyone taking an oral anticoagulant and those with epilepsy2.
