Deep venous thrombosis (DVT) and air travel

International press coverage on "economy class syndrome" or deep venous thrombosis (DVT) and air travel has raised concern from the travelling public and aircrew regarding an association between the occurrence of DVT and air travel. 

Current scientific studies do not show a statistically significant increase in cases of DVT when travelling by air in the absence of pre-existing risk factors. Furthermore current evidence indicates that any association between symptomatic DVT and travel by air is weak. 

In addition to the above it must be realised that the term 'economy-class syndrome' is seriously misleading. This description implies that DVT does not occur in business or first class air travellers, or in travellers using other forms of long-distance travel, or indeed in non-travellers. 

Risk factors for development of DVT

DVT occurs because of blood clotting, most frequently in the large veins of the calves. Sometimes these clots break free and travel up the veins through the heart to lodge in the arteries of the lungs, brain or other organs. If a clot lodges in the lung the related condition is known as pulmonary embolism (PE). PE may be life-threatening if the embolus (circulating clot) is large. 

One of the most important factors predisposing to the disease is immobility. For example, the condition has been long recognised as a risk for people confined to bed. Immobility for even short periods can cause DVT. For this reason, preventive measures are frequently taken when people, particularly the elderly, undergo surgical operations, where they are immobilised by a general anaesthetic. Travel by any mode of transport usually requires immobility, for some if not all of the journey.

The second most important factor for development of DVT is individual risk factors. The most important individual risk factors are a family history of DVT or previous episode of thrombosis or embolism. Some people suffer from medical conditions such as cancer, heart conditions and blood illnesses that predispose them to the development of blood clots. Other individual risk factors include increasing age, obesity, smoking, pregnancy, the use of oral contraceptives or hormone replacement therapy and lower limb injury or surgery. Recently there have been speculations that a specific genetic predisposition exists for the disease.

DVT and flying

Seated immobility is recognised as a risk factor for the development of DVT. Many theories have been proposed for additional risk factors associating DVT with flying. These include dehydration, excessive use of alcohol, poor cabin air quality, circadian dysrhythmia, seasonal shifts and hypoxia. However, there is little experimental evidence to support these theories.

General precautions to take when flying

• If you are suffering from any medical condition, consult your doctor prior to flying to determine any risk factor for flight and to obtain advice on how to best manage your illness during the flight. In cases where risk factors for DVT exist, doctors may prescribe supportive stockings or prophylactic drugs.
• Passengers should contact the relevant airline before a flight and inform them of any disease and/or special requirements they may need during the flight. The captain and cabin crew must be informed of the illness and special requirements.
• Passengers must pay attention to cabin crew demonstrations prior to flight and must be made aware of the health advice in the in-flight magazines and on the in-flight videos.
• Prevent immobility by walking around the cabin regularly and performing in-seat exercises. 
• Drink plenty of non-alcoholic fluids during flights.
• Don't cross your legs for long periods of time.
• Eat lightly and wear loose clothing during the flight.
• Do not take any sleeping tablets prior to or during the flight.
• Be on the look-out for any symptoms that may indicate a problem such as pain in the calves, elevation of temperature, calf tenderness and swelling of the leg. 
• Ask the cabin attendant for assistance should you become aware of any symptoms. These symptoms must be reported to the Captain to enable him or her to take further action.
• Treatment for DVT should include supporting bandaging, elevation of leg and administration of anti-inflammatory drugs.
• Be vigilant for the symptoms for up to a month after long flights. If symptoms occur, seek medical advice without delay. 

The role of the CAA

All incidents of suspected DVT or any other medical condition must be reported to the CAA. The Medical Department of the CAA will continue to closely monitor international developments regarding DVT for implementation of recommendations as applicable.