INTERNATIONAL TRAVEL AND HEALTH 2005

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CHAPTER 2

Travel by air:

health considerations

This chapter was prepared in collaboration with the International Civil Aviation

Organization and the International Air Transport Association. To facilitate use

by a wide readership, technical terms have been used sparingly. Medical

professionals needing more detailed information are referred to the website of

the Aerospace Medical Association.

The volume of air traffic has risen steeply in recent years and the number of long

distance flights has greatly increased. With modern long range aircraft the need

for stop-overs has been reduced so the duration of flights has also increased.

The passenger capacity of long distance aircraft is also increasing, so larger

numbers of people travel aboard a single aircraft. Frequent flyers now form a

substantial proportion of the travelling public. According to the International

Civil Aviation Organization, the annual number of flight passengers exceeded

1647 million in 2000 and although the numbers dropped the following years

because of security concerns and the outbreak of severe acute respiratory

syndrome (SARS), numbers are again rising and are forecasted to grow by 4.4 per

cent annually until 2015.

Air travel, in particular over long distances, exposes passengers to a number of

factors that may have an effect on their health and well-being. Passengers with

pre-existing health problems are more likely to be affected and should consult

their doctor or a travel medicine clinic in good time before travelling. Those

receiving medical care and intending to travel by air in the near future should

tell their medical adviser. Health risks associated with air travel can be minimized

if the traveller plans carefully and takes some simple precautions before, during,

and after the flight. An explanation of the various factors that may affect the

health and well-being of air travellers follows.

Cabin air pressure

Although aircraft cabins are pressurized, cabin air pressure at cruising altitude is

lower than air pressure at sea level. At typical cruising altitudes in the range

11 000-12 200 metres (36 000-40 000 feet) air pressure in the cabin is equivalent

CHAPTER 2.TRAVEL BY AIR: HEALTH CONSIDERATIONS

to the outside air pressure at 1800-2400 metres (6000-8000 feet) above sea level.

As a consequence, less oxygen is taken up by the blood (hypoxia) and gases

within the body expand. The effects of reduced cabin air pressure are usually

well tolerated by healthy passengers.

Oxygen and hypoxia

Cabin air contains ample oxygen for healthy passengers and crew. However,

because cabin air pressure is relatively low, the amount of oxygen carried in the

blood is reduced compared to sea level. Passengers with certain medical

conditions, in particular heart and lung disease, and blood disorders such as

anaemia, may not tolerate this reduced oxygen level (hypoxia) very well. Such

passengers are usually able to travel safely if arrangements are made with the

airline for the provision of an additional oxygen supply during flight.

Gas expansion

As the aircraft climbs, the decreasing cabin air pressure causes gases to expand.

Similarly, as the aircraft descends, the increasing pressure in the cabin causes gases

to contract. These changes may have effects where gas is trapped in the body.

Gas expansion during the climb causes air to escape from the middle ear and the

sinuses, usually without causing problems. This airflow can sometimes be

perceived as a popping sensation in the ears. As the aircraft descends, air must

flow back into the middle ear and sinuses in order to equalize pressure differences.

If this does not take place, the ears or sinuses may feel as if they were blocked

and, if the pressure is not relieved, pain can result. Swallowing, chewing, or

yawning (‘clearing the ears’) will usually relieve any discomfort. If the problem

persists, a short forceful expiration against a pinched nose and closed mouth

(Valsalva manœuvre) will usually help. For infants, feeding or giving a pacifier

(dummy) to stimulate swallowing may reduce the symptoms.

Individuals with ear, nose, and sinus infections should avoid flying because pain

and injury may result from the inability to equalize pressure differences. If travel

cannot be avoided, the use of decongestant nasal drops shortly before the flight

and again before descent may be helpful.

As the aircraft climbs, expansion of gas in the abdomen can cause discomfort,

although this is usually mild.

Some forms of surgery, other medical treatments, or diagnostic tests, may

introduce air or other gas into a body cavity. Examples include abdominal surgery

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or eye treatment for a detached retina. Passengers who have recently undergone

such a procedure should ask a travel medicine physician or their treating physician

how long they should wait before undertaking air travel.

Cabin humidity and dehydration

The humidity in aircraft cabins is low, usually less than 20% (humidity in the

home is normally over 30%). Low humidity may cause skin dryness and

discomfort of the eyes, mouth, nose and exposed skin but presents no risk to

health. Using a skin moisturizing lotion, saline nasal spray to moisturize the

nasal passages, and wearing spectacles rather than contact lenses can relieve or

prevent discomfort. The low humidity does not cause dehydration and there is

no need to drink extra water.

Ozone

Ozone is a form of oxygen (with three, rather than two, atoms to the molecule)

that occurs in the upper atmosphere and may enter the aircraft cabin together

with the fresh air supply. In older aircraft, it was found that the levels of ozone

in cabin air could sometimes lead to irritation of the lungs, eyes and nasal tissues.

Ozone is broken down by heat and most ozone is removed by the compressors

(in the aircraft engines) that provide pressurized air for the cabin. In addition,

most modern long-haul jet aircraft are fitted with equipment (catalytic converters)

that breaks down any remaining ozone.

Cosmic radiation

Cosmic radiation is made up of radiation that comes from the sun and from

outer space. The earth’s atmosphere and magnetic field are natural shields and

therefore cosmic radiation levels are lower at lower altitudes. Cosmic radiation

is more intense over polar regions than over the equator because of the shape of

the earth’s magnetic field and the flattening of the atmosphere over the poles.

The population is continually exposed to natural background radiation from

soil, rock and building materials as well as from cosmic radiation that reaches

the earth’s surface. Although cosmic radiation levels are higher at aircraft cruising

altitudes than at sea level, research so far has not shown any significant health

effects for either passengers or crew.

Motion sickness

Except in the case of severe turbulence, travellers by air rarely suffer from motion

(travel) sickness. Those who do suffer should request a seat in the mid-section

CHAPTER 2.TRAVEL BY AIR: HEALTH CONSIDERATIONS

of the cabin where movements are less pronounced, and keep the motion sickness

bag, provided at each seat, readily accessible. They should also consult their

doctor or travel medicine physician about medication that can be taken before

flight to help prevent problems.

Immobility, circulatory problems and Deep Vein

Thrombosis (DVT)

Contraction of muscles is an important factor in helping to keep blood flowing

through the veins, particularly in the legs. Prolonged immobility, especially when

seated, can lead to pooling of blood in the legs, which in turn may cause swelling,

stiffness, and discomfort.

It is known that immobility is one of the factors that may lead to the development

of a blood clot in a deep vein, so-called deep vein thrombosis , or DVT. Research

has shown that DVT can occur as a result of prolonged immobility, for instance

during long distance travel, whether by car, bus, train or air. The World Health

Organization (WHO) has set up a major research study to find out if there are

any factors that might lead to the risk of DVT being higher for air travel than for

other causes of immobility.

In most cases of DVT, the clots are small and do not cause any symptoms. The

body is able to gradually break down the clot and there are no long-term effects.

Larger clots may cause symptoms such as swelling of the leg, tenderness, soreness

and pain. Occasionally a piece of the clot may break off and travel with the

bloodstream to become lodged in the lungs. This is known as pulmonary

embolism and may cause chest pain, shortness of breath and, in severe cases,

sudden death. This can occur many hours or even days after the formation of

the clot.

The risk of developing DVT when travelling is very small unless one or more

other risk factors are present. These include:

Previous DVT or pulmonary embolism

History of DVT or pulmonary embolism in a close family member

Use of oestrogen therapy–oral contraceptives ( the Pill ) or hormone

replacement therapy (HRT)

Pregnancy

Recent surgery or trauma, particularly to the abdomen, pelvic region or

legs

Cancer

Some inherited blood-clotting abnormalities.

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It is advisable for people with one or more of these risk factors to seek specific

medical advice from their doctor or a travel medicine clinic in good time before

embarking on a flight of three or more hours.

DVT occurs more commonly in older people. Some researchers have suggested

that there may be a risk from smoking, obesity and varicose veins.

Precautions

The risk of a passenger who does not have any of the risk factors above developing

DVT as a consequence of flying is small and the benefits of most precautionary

measures in such passengers are unproven and some might even result in harm.

Some common-sense advice for such passengers is given below.

Moving around the cabin during long flights will help to reduce any period of

prolonged immobility. However, this may not always be possible and any

potential health benefits must be balanced against the risk of injury that could

occur if the aircraft encounters sudden and unexpected turbulence. A sensible

compromise is to walk around in the cabin, e.g. go to the bathroom, once every

2–3 hours. Many airlines also provide helpful advice on exercises that can be

carried out in the seat during flight. It is thought that exercise of the calf muscles

can stimulate the circulation, reduce discomfort, fatigue and stiffness, and it may

reduce the risk of developing DVT. Hand luggage should not be placed where it

restricts movement of the legs and feet, and clothing should be loose and

comfortable.

Wearing properly fitted graduated compression stockings may be helpful. These

compress the calf muscles and improve the flow of blood in the deep veins. They

may also help prevent the swollen ankles that are quite common on long flights.

However, they need to be the correct size to be effective and passengers should

therefore ask their doctor or a travel medicine clinic which type would be

appropriate for them.

In view of the clear risk of significant side effects and absence of clear evidence

of benefit, passengers are advised not to use aspirin just for the prevention of

travel-related DVT.

Those travellers who are at most risk of developing DVT may be prescribed

specific treatments, such as injections of heparin. Cabin crew are not trained to

give injections and travellers who have been prescribed these must either be taught

to give the injections themselves or make other arrangements to have them given

by a qualified person.

CHAPTER 2.TRAVEL BY AIR: HEALTH CONSIDERATIONS

Diving

Divers should not fly too soon after diving because of the risk that the reduced

cabin pressure may lead to decompression sickness (the bends). It is recommended

that they do not fly until at least 12 hours after their last dive and this period

should be extended to 24 hours after multiple dives or after diving that requires

decompression stops during ascent to the surface. Passengers undertaking

recreational diving before flying should seek specialist advice from diving schools.

Jet lag

Jet lag is the term used for the symptoms caused by the disruption of the body’s

internal clock and the approximate 24-hour (circadian) rhythms it controls.

Disruption occurs when crossing multiple time zones i.e. when flying east to

west or west to east. Jet lag may lead to indigestion and disturbance of bowel

function, general malaise, daytime sleepiness, difficulty in sleeping at night, and

reduced physical and mental performance. Its effects are often combined with

tiredness due to the journey itself. Jet lag symptoms gradually wear off as the

body adapts to the new time zone.

Jet lag cannot be prevented but there are some ways to reduce its effects (see

below). Travellers who take medication according to a strict timetable (e.g. insulin,

oral contraceptives) should seek medical advice from their doctor or a travel

medicine clinic before their journey.

General measures to reduce the effects of jet lag

 

Be as well rested as possible before departure, and rest during the flight. Short

naps can be helpful.

 

Eat light meals and limit consumption of alcohol. Alcohol increases urine

output which can result in disturbed sleep by causing awakenings in order to

urinate. Whilst it can accelerate sleep onset, it reduces sleep quality, making

sleep less recuperative. The after effects of alcohol (hangover) can exacerbate

the effects of jet lag and travel fatigue. Alcohol should therefore be consumed

in moderation, if at all, before and during flight. Caffeine should be limited

to normal amounts and avoided within a few hours of an anticipated period

of sleep.

 

Try to create the right conditions when preparing for sleep. When taking a

nap during the day, eyeshades and earplugs may help. Regular exercise during

the day may help to promote sleep, but avoid strenuous exercise immediately

before sleep.

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At the destination, try to get as much sleep in every 24 hours as normal. A

minimum block of 4 hours sleep during the local night – known as anchor

sleep – is thought to be necessary to allow the body’s internal clock to adapt

to the new time zone. If possible, make up the total sleep time by taking naps

at times when feeling sleepy during the day.

 

The cycle of light and dark is one of the most important factors in setting the

body’s internal clock. Exposure to daylight at the destination will usually

help adaptation.

 

Short-acting sleeping pills may be helpful. They should be used only in accordance

with medical advice and should not normally be taken during the flight, as they

may increase immobility and therefore the risk of developing DVT.

 

Melatonin is available in some countries and can be used to help resynchronize

the body’s internal clock. It is normally sold as a food supplement and therefore

is not subject to the same strict control as medications (for example, it has not

been approved for use as a medication in the United States, but can be sold as a

food supplement). The timing and effective dosage of melatonin have not been

fully evaluated and its side effects, particularly if used long term, are unknown.

In addition, manufacturing methods are not standardised and therefore the dose

in each tablet can be very variable and some harmful compounds maybe present.

For these reasons, melatonin cannot be recommended.

 

It is not always appropriate to adjust to local time for short trips of 2–3 days

or less. If in doubt, seek specialist travel medicine advice.

 

Individuals react in different ways to time zone changes. Frequent flyers

should learn how their own body responds and adopt habits accordingly.

Advice from a travel medicine clinic may be beneficial in determining an

effective coping strategy.

Psychological aspects

Travel by air is not a natural activity for humans and many people experience

some degree of psychological difficulty when flying. The main problems

encountered are stress and fear of flying. These may occur together or separately

at different times before and during the period of travel.

Stress

All forms of travel generate stress. Flying can be particularly stressful because it

often involves a long journey to the airport, curtailed sleep and the need to walk

CHAPTER 2.TRAVEL BY AIR: HEALTH CONSIDERATIONS

long distances in the terminal building. Most passengers find their own ways of

coping, but passengers who find air travel particularly stressful should seek

medical advice in good time. Good planning (passports, tickets, medication, etc)

and allowing plenty of time to get to the airport helps relieve stress.

Flight phobia (fear of flying)

Fear of flying may range from feeling slightly anxious to being unable to travel

by air at all. It can lead to problems at work and leisure.

Travellers who want to travel by air but are unable to do so because of their fear

of flying should seek medical advice before the journey. Medication may be useful

in some cases but the use of alcohol to steady the nerves is not helpful and

may be dangerous if combined with some medicines. For a longer-term solution,

travellers should seek specialized treatment to reduce the psychological difficulties

associated with air travel. There are many courses available that aim to reduce or

cure, fear of flying. These typically include advice on how to cope with the

symptoms of fear, information about how an aircraft flies, how controls are

operated during a flight and, in most cases, a short flight.

Air rage

In recent years, air rage has been recognized as a form of disruptive behaviour

associated with air travel. It appears to be linked to high levels of general stress

but not specifically to flight phobia. It is frequently preceded by excessive

consumption of alcohol.

Travellers with medical conditions or special needs

Airlines have the right to refuse to carry passengers with conditions that may

worsen, or have serious consequences, during the flight. Airlines may require

medical clearance from their medical department/adviser if there is an indication

that a passenger could be suffering from any disease or physical or mental

condition that:

 

May be considered a potential hazard to the safety of the aircraft

 

Adversely affects the welfare and comfort of the other passengers and/or crew

members

 

Requires medical attention and/or special equipment during the flight

 

May be aggravated by the flight.

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If cabin crew suspect before departure that a passenger may be ill, the aircraft’s

captain will be informed and a decision taken as to whether the passenger is fit

to travel, needs medical attention, or presents a danger to other passengers and

crew or to the safety of the aircraft.

Although this chapter provides some general guidelines on conditions that may

require medical clearance in advance, airline policies do vary and the requirements

should always be checked at the time of, or prior to, booking the flight. A good

place to find information is often the airline’s own web site.

Infants

Air travel is not recommended for infants less than seven days old. If travel is

absolutely necessary for babies who are over seven days, but were born

prematurely, medical advice should be sought in each case. Changes in cabin air

pressure may upset infants; this can be helped by feeding or giving a pacifier to

stimulate swallowing.

Pregnant women

Pregnant women can normally travel safely by air, but most airlines restrict travel

in late pregnancy. Typical guidelines for those who have an uncomplicated

pregnancy are:

after the 28th week of pregnancy a letter from a doctor or midwife should

be carried, confirming the expected date of delivery and that the pregnancy

is normal

for single pregnancies, flying is permitted up to the end of the 36th week

for multiple pregnancies, flying is permitted up to the end of the 32nd week.

Pre-existing illness

Most people with medical conditions are able to travel safely by air, provided

that necessary precautions, such as the need for additional oxygen supply, are

considered in advance.

Those who have underlying health problems such as cancer, heart or lung disease,

anaemia, diabetes, are on any form of regular medication or treatment, have

recently had surgery or have been in hospital, or who are concerned about their

fitness to travel for any other reason, should consult their doctor or a travel

medicine clinic before deciding to travel by air.

Medication that may be required during the journey, or soon after arrival, should

be carried in the hand luggage. It is also advisable to carry a copy of the

CHAPTER 2.TRAVEL BY AIR: HEALTH CONSIDERATIONS

prescription in case the medication is lost, additional supplies are needed or

security checks require proof of purpose.

Frequent travellers with medical conditions

Frequent travellers who have a permanent and stable underlying health problem

may obtain a frequent traveller’s medical card from the medical or reservation

department of many airlines. This card is accepted, under specified conditions, as

proof of medical clearance and for identification of the holder’s medical condition.

Security Issues

Security checks can cause concerns for travellers who have been fitted with metal

devices such as artificial joints, pacemakers or internal automatic defibrillators.

Some pacemakers may be affected by modern security screening equipment and

travellers with these should carry a letter from their doctor. Travellers who need

to carry other medical equipment in their hand luggage, particularly sharp items

such as hypodermic needles, should also carry a letter from their doctor.

Smokers

Almost all airlines now ban smoking on board. Some smokers may find this

stressful, particularly during long flights, and should discuss this with their doctor

before travelling. Nicotine replacement patches or chewing gum containing

nicotine may be helpful during the flight and the use of other medication or

techniques may also be considered.

Travellers with disabilities

A physical disability is not usually a contraindication for travel. Passengers who

are unable to look after their own needs during the flight (including use of the

toilet and transfer from wheelchair to seat and vice versa) will need to be

accompanied by an escort able to provide all necessary assistance. The cabin

crew are generally not permitted to provide such assistance and a traveller who

requires it and does not have a suitable escort may not be permitted to travel.

Travellers confined to wheelchairs should be advised against deliberately

restricting their fluid intake before or during travel as a means of avoiding use of

toilets during flights as this might detrimentally affect their general health.

Airlines have regulations on conditions of travel for passengers with disabilities.

Disabled passengers should contact the airline in advance of their travel for

guidance (the airline’s own web site often gives useful information).

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Communicable diseases

Research has shown that there is very little risk of any infectious disease being

transmitted on board the aircraft.

The quality of aircraft cabin air is carefully controlled. Ventilation rates provide

a total change of air 20-30 times per hour. Most modern aircraft have recirculation

systems, which recycle up to 50% of cabin air. The recirculated air is usually

passed through HEPA (high-efficiency particulate air) filters, of the type used

in hospital operating theatres and intensive care units, which trap particles,

bacteria, fungi and viruses.

Transmission of infection may occur between passengers who are seated in the

same area of an aircraft, usually as a result of the infected person coughing or

sneezing or by touch (direct contact or contact with the same parts of the aircraft

cabin and furnishings that other passengers touch). This is no different from any

other situation where people are close to each other, such as on a train, bus or at

a theatre. Highly infectious conditions, such as influenza, are more likely to be

spread to other passengers in situations when the aircraft ventilation system is

not operating. A small auxiliary power unit is normally used to provide ventilation

when the aircraft is on the ground, before the main engines are started, but

occasionally this is not operated for environmental (noise) or technical reasons.

In such cases, when associated with a prolonged delay, passengers may be

temporarily disembarked.

In order to minimise the risk of passing on infections, passengers who are unwell,

particularly if they have a fever, should delay their journey until they have

recovered. Airlines may deny boarding to passengers who appear to be infected

with a communicable disease.

Aircraft disinsection

Many countries require disinsection of aircraft (to kill insects) arriving from

countries where diseases that are spread by insects, such as malaria and yellow

fever, occur. There have been a number of cases of malaria affecting individuals

who live or work in the vicinity of airports in countries where malaria is not

present, thought to be due to the escape of malaria-carrying mosquitoes

transported on aircraft. Some countries, e.g. Australia and New Zealand, routinely

require disinsection be carried out in order to prevent inadvertent introduction

of species that may harm their agriculture.

Disinsection is a public health measure that is mandated by the current

International Health Regulations (see Annex 3). It involves treatment of the

interior of the aircraft with insecticides specified by WHO. The different

procedures currently in use are as follows:

treatment of the interior of the aircraft using a quick-acting insecticide

spray immediately before take-off, with the passengers on board;

treatment of the interior of the aircraft on the ground before passengers

come on board, using a residual insecticide aerosol, plus additional in-

flight treatment with a quick-acting spray shortly before landing;

regular application of a residual insecticide to all internal surfaces of the

aircraft, except those in food preparation areas.

Travellers are sometimes concerned about their exposure to insecticide sprays

while travelling by air. Some people have reported that they feel unwell after

spraying of aircraft for disinsection. However, WHO has found no evidence

that the specified insecticide sprays are harmful to human health when used as

prescribed.

Medical assistance on board

Airlines are required to provide minimum levels of medical equipment on aircraft

and to train all cabin crew in first aid. The equipment carried varies, with many

airlines carrying more than the minimum level of equipment required by the

regulations. Equipment carried on a typical international flight would include:

one or more first-aid kits, to be used by the crew;

a medical kit, normally to be used by a doctor or other qualified person,

to treat in-flight medical emergencies;

an automated external defibrillator (AED) to be used by the crew in case

of cardiac arrest.

Cabin crew are trained in the use of first-aid equipment and in carrying out

first-aid and resuscitation procedures. They are usually also trained to recognize

a range of medical conditions that may cause emergencies on board and to act

appropriately to manage these.

In addition, many airlines have facilities to enable crew to contact a medical

expert at a ground-based response centre for advice on how to manage in-flight

medical emergencies.

Contraindications to air travel

Travel by air is normally contraindicated in the following cases:

 

Infants less than 7 days old;

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Women after the 36th week of pregnancy (after 32nd week for multiple

pregnancies) and until seven days after delivery;

?

Those suffering from:

angina pectoris or chest pain at rest

any serious or acute infectious disease

decompression sickness after diving

increased intracranial pressure due to haemorrhage, trauma or infection

infections of the sinuses or infections of the ear and nose, particularly if

the Eustachian tube is blocked

recent myocardial infarction and stroke (time period depending on severity

of illness and duration of travel)

recent surgery or injury where trapped air or gas may be present, especially

abdominal trauma and gastrointestinal surgery, cranio-facial and ocular

injuries, brain operations, and eye operations involving penetration of

the eyeball

severe chronic respiratory disease, breathlessness at rest, or unresolved

pneumothorax

sickle-cell disease

psychotic illness, except when fully controlled.

The above list is not comprehensive and fitness for travel should be decided on

a case-by-case basis.

Further reading

Aerospace Medical Association, Medical Guidelines Task Force, Medical guidelines for

airline travel, 2nd edition, 2003

British Medical Association, Board of Science and Education, The impact of flying on

passenger health: a guide for healthcare professionals, 2004