Study Suggests Additional Risk Factors besides Inactivity May Trigger Deadly Blood Clots on Long Flights

By Steven DiJoseph

Potentially Fatal Blood Clots, However, Are far From the Only Medical Condition that Should be Carefully Considered before Traveling by Air

For several years, “economy class syndrome” has been a term used to describe life-threatening blood clots associated with restrictive seating, inactivity during long flights, and frequent flying.

A recent study published in Lancet suggests that additional conditions present during air travel may add to the risk of developing deep vein thrombosis (DVT).
When 71 volunteers were tested, it was found that certain chemicals associated with clotting were higher during an eight-hour flight than when seated at a movie.

DVT is a dangerous condition that occurs when blood flow through the deepest veins in the calf or thigh slows to the point of allowing blood clots to form. It is when a piece of one of these clots breaks off and migrates to the lung where it results in a potentially deadly pulmonary embolism.

When compared to similar points during eight hours of normal daily activities or sitting in a movie theater, the chemical concentrations during air travel were always higher than either of the other situations.

In addition, it was found that about 40% of the subjects carried a gene that also put them at greater risk of DVT. When other DVT risk factors were also present, the chemical concentrations were even higher.

Low air pressure and in-flight oxygen levels were seen as possible reasons for some of the increased risk although restricted activity and inactivity were still regarded as the most significant factors. The study also did not rule out other factors such as stress and air pollution.

Clearly, however, the fact that important chemical levels increase during air travel alone means one or more other factors are involved.

Significantly, the issue of DVT and its link to air travel has been studied and analyzed before. Although prior research has been inconclusive with respect to the effect of low oxygen and air pressure levels, other factors have been considered as increasing the risk of DVT, including:

• Inactivity during flights;
• Restrictive seating (hence the term, “Economy Class Syndrome”);
• Long flights (3,100 to 4,500 miles [1/2,500,000]; 4,500 to 6,215 [1/376,000], over 6,215 miles [1/210,000];
• Consumption of alcoholic beverages;
• Age – elderly passengers are at greater risk;
• Diet – overweight passengers are more at risk;
• Air quality – dry, recirculated air may be a factor;
• Dehydration;
• Constrictive clothing;
• Smoking while in flight;
• Recent surgery;
• Heart failure;
• Blood clotting abnormalities;
• History of DVT (personal or family);
• Pregnancy;
• Stroke;
• Chronic illness;
• Some oral contraceptives (Ortho Evra Patch for example); and
• Low cabin pressure.

There are, however, a number of things that can be done to reduce the risk of DVT when traveling by air:

• Book a better seat (price-wise) or a seat in a better location (by an exit);
• Wear support stockings;
• Avoid alcoholic beverages and other diuretic drinks such as tea and coffee containing caffeine;
• Drink plenty of water or juice;
• Walk up and down the cabin once an hour; and
• Exercise – ankle circles, foot pumps, lifting toes up and down, shoulder rolls, etc.

Current estimates of those dying each year from fatal blood clots linked to flying are as high as 300 or more.

In the past few years, airlines have begun to redesign and reposition seats and to provide for addition leg room on newer planes. Older and smaller planes, however, remain problematic insofar as permitting movement is concerned.

Studies also considered the benefits of recommending the use of aspirin or prescription anti-coagulants to those in high-risk categories.

Symptoms of DVT include:

• Breathlessness;
• Lightheadedness;
• Chest pain;
• Tenderness in one calf that feels like an ache or tightness – pain increases when ankle is flexed;
• Swelling or redness of leg;
• Pain or discomfort over a deep vein; and
• No symptoms if clot forms in a vein other than an arm or leg.

Once DVT is suspected or diagnosed, immediate treatment is recommended. Some treatments include:

• Get to a doctor or hospital emergency room immediately;
• Have a Doppler (ultrasound) test done to confirm the clot;
• Begin a regimen of blood-thinning medication; and
• Surgical intervention.

DVT, however, is far from the only serious medical problem associated with air travel or in need of addressing before planning for a flight of any length.

In flight emergency medical equipment that may or may not be present on any particular flight varies by airline and country. Thus, one or more of the following may be available on a given flight:

Emergency Medical Kit (required on all US-based airlines) includes:
Item / Quantity
Sphygmomanometer / 1
Stethoscope / 1
Oropharyngeal airways / 3 (3 sizes)
Syringes / 4 (different sizes, 2 sets)
Needles / 6 (different sizes, 2 sets)
50% dextrose injection, 50 ml. / 1
Epinephrine 1:1,000 single dose ampule / 2
Injectable diphen-hydramine (Benadyrl) single dose ampule / 2
Nitroglycerine tablets / 10
Instructions for use of medications / 1
Protective latex gloves or equivalent / 1 pair

The emergency medical kit may only be opened during flight when authorized by a physician (on board or from the airline’s medical department)

Emergency First-Aid Kit: Contents are limited and intended for basic emergency care only.

Automatic External Defibrillators: Now provided by a number of airlines along with flight personnel trained in their use.

“Enhanced” Medical Kit: These upgraded medical kits have been installed by some airlines and contain a wide variety of acute cardiac life support drugs and equipment.

Oxygen: Supplemental oxygen is available on an emergency basis only. (Flow rates vary from 2 to 8L per minute). There is a fee for this service which usually requires a minimum of 24 to 48 hours advanced notice as well as a medical certificate certifying the passenger is cleared to fly at a relative cabin altitude of 8,000 feet and specifying the flow rate and type delivery mask to be used. (Note: passengers cannot bring their own oxygen on board).

Respiratory equipment: Other equipment such as nebulizers and pediatric mechanical ventilators may be used on board, but must be pre-approved to prevent interference with sensitive electronic aviation equipment and must comply with applicable Federal Air Regulations (FARs).

One of the most serious medical reasons for avoiding air travel is pre-existing cardiovascular problems. The following cardiovascular conditions are generally regarded as contraindicated to commercial airline flight according to the Aerospace Medical Association guidelines (1997) and a number of airline informational handouts:

• Uncomplicated myocardial infarction occurring with three weeks of flight;
• Complicated myocardial infarction occurring with six weeks of flight;
• Unstable angina;
• Severe, decompensated congestive heart failure;
• Uncontrolled hypertension;
• Coronary artery bypass grafting performed with two weeks of flight;
• Cardiovascular accident occurring within two weeks of flight;
• Uncontrolled ventricular or supraventricular tachycardia;
• Eisenmenger’s syndrome;
• Severe symptomatic valvular heart disease.

There are some basic procedures and preparations that passengers with various forms of cardiac disease can take before flying:

• Have a sufficient supply of all cardiac medications (in a labeled container) and keep them in carry-on luggage;
• Carry a copy of most recent electrocardiogram;
• While pacemakers and implanted cardiac devices are not affected by airport security devices, any new or unfamiliar implanted devices should be cleared for inspection by the manufacturer;
• Arrange for supplemental oxygen during flight if needed;

Diabetics will avoid most problems if they follow a few simple rules before flying:

• Pack twice as much medications and supplies as needed. One half of this should be kept in a carry-on bag;
• Written instructions for administration of medications should be carried in carry-on bag;
• Blood testing equipment (including an extra battery for glucose meter) should be kept in carry-on bag;
• Passenger should carry personal identification card, diabetes identification card, personal physician’s business card, a set of prescriptions (to be filled in the event medications are lost or stolen), glucose tablets, or another form of sugar to treat low blood sugar).
Pregnant women are generally advised not to fly when approaching their expected delivery date. Even brief flights are not recommended within one week of expected delivery. This is to avoid in-flight deliveries rather than to guard against any harm to the fetus.

Pregnant women should request an aisle seat in order to stretch their legs and walk about the cabin as much as possible. Isometric leg exercises are also advised, especially during extended flights.

Seat belts should be worn whenever seated and the belt should be positioned low around the pelvis to reduce the possibility of fetal injury.

Pregnant women should also be aware of the potential for dehydration (due to low cabin humidity), motion sickness, and gastrointestinal discomfort.

Availability of medical care and insurance coverage at the point of destination should be checked in advance.

Finally, any woman with a history of complicated pregnancies or complicating factors for the current pregnancy should not fly.

People suffering from conditions such as middle ear infections, effusions, sinusitis or allergies or infections creating nasal congestion, should check with their physician before flying.
Congestion should be controlled as much as possible to avoid simple (pain) or severe (rupture of tympanic membrane) complications.

Those having undergone recent surgery involving the inner or middle ear should not fly.

Simple ear problems can usually be controlled or alleviated by the use of decongestants or effective Valsalva maneuver (closing the nose with the thumb and index finger and exhaling gently with the mouth closed), chewing gum and frequent swallowing.

Infants should be given a bottle or pacifier to avoid discomfort, especially during take-off and landing.

All potential passengers who have recently undergone any surgical procedure should check with their doctor before flying.

In certain situations, a physician’s certificate may be required before flying.

Many types of surgery such as abdominal, neurological, laparoscopic, ophthalmologic, and thoracic, are associated with pressure related problems caused by the expansion of trapped gases.

Other conditions requiring attention:

Scuba divers – should wait 12 hours (1 dive per day) to 24 hours (multiple or deep dives) before flying.

Jet lag – (physiologic reaction to traveling long distances in short periods of time) – some suggestions include:

• Sleep well before beginning trip;
• Keep sleep amounts (in a 24 hour period) the same as at home;
• Avoid excessive alcohol;
• Avoid overeating;
• Attempt to stay on home time;
• Adjust as quickly as possible to new time zone;
• Moderate exercise;
• Limit use of sleep medications

Orthopedic injuries: Use bi-valve casts to avoid circulatory problems. Keep extremely elevated. Before flight, release air from pneumatic splints (if allowed).

Epilepsy: Wear identification bracelet or other easily found epilepsy identification. Carry anti-epileptic medications in carry-on luggage. Discuss a temporary small increase in medication with your doctor.

Psychiatric conditions: Avoid alcohol and consider using a mild sedative. Notify airline in advance. Travel with a responsible companion if possible. (Note: In 2005 a man with psychiatric problems was shot to death by an air marshal when he behaved irrationally just before his flight took off. Although he was accompanied by his wife, events unfolded so quickly that the tragedy could not be averted. Thus, anyone with a psychiatric condition that might present unusual behavior should be discussed ahead of time with the airline and flight crew. With enhanced post-9/11 security, it is better to be safe than sorry.)

Medical devices with pneumatic components such as feeding tubes, pneumatic splints, urinary catheters and other closed infusion devices should be capped off during take-offs and landings.

Dehydration: Since cabin humidity levels are usually less than 25%, passengers often experience dryness in the eyes, nose, and throat. Contact lens wearers can experience irritation. Suggestions for dealing with these problems include:

• Avoid alcohol, coffee, tea, and other diuretics;
• Drink water or juices frequently;
• Wear glasses instead of contact lenses if possible;
• Use a skin moisturizer

Motion sickness: Can be brought on by turbulence or staring at moving objects. Over-the-counter and prescription medications are usually effective. You should consult your doctor, however, in this regard.

Non-medication suggestions include pressure bands, keeping your eyes fixed on a non-moving object and looking at the ground, sea or horizon if possible.

Muscle problems: These include tension, fatigue, aches, and stiffness. Recommendations include walking about the cabin occasionally, doing exercises such as ankle circles, foot pumps, knees lifts, shoulder rolls and knee to chest, for 3-4 minutes every hour if possible.

Clearly, while air travel is one of the safest means of transportation, it presents some conditions that are not found at ground level or where there is access to outside air.

Thus, cabin pressure, decreased oxygen levels, potential air pollution (chemical, particle, and bacterial), restrictive seating, limited mobility, inability to obtain immediate emergency medical care, limited access to medical equipment and medications, stress, and psychiatric conditions that may be triggered or aggravated by confined quarters or stress requires that passengers anticipate medical contingencies that may affect them or a person traveling with them.

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