TRAVELERS MEDICAL GUIDE 2.3 Disorders Caused by Travel–Deep Vein Thrombosis

DEEP VEIN THROMBOSIS

Deep vein thrombosis (DVT) is an acute condition in which a blood clot (thrombus) forms in one or more of the body’s deep veins, usually in the legs. These blood clots can then break free, travel through the bloodstream and cause life-threatening conditions such as a pulmonary embolism (PE), which is a blood clot that lodges in the lungs.

Symptoms: While approximately half of all DVTs cause no noticeable symptoms, symptoms may include the following:

swelling of the affected leg, ankle and foot
pain in the calf that spreads to the ankle and foot
warmth across the affected area
a change in skin color to pale, red or blue

DVTs are often recurrent; individuals who have experienced a DVT frequently endure long-term complications such as postthrombotic syndrome or pulmonary hypertension after a PE.

Travel may increase the likelihood of a DVT. Most air-travel-related DVTs occur within the first two weeks after a flight and resolve within eight weeks. In about 25 percent of cases, an untreated DVT of the calf can spread upward into the thigh and pelvis veins. If a DVT of the thigh or pelvis is left untreated, there is a risk of a life-threatening PE if the blood clot becomes lodged in a pulmonary vessel. Symptoms of PE include the following:

sudden onset of shortness of breath
chest pain or discomfort that worsens with a deep breath or cough
lightheadedness, dizziness or fainting
rapid pulse
sweating
coughing up blood
anxiety or nervousness

Anyone who develops a PE immediately needs emergency care. The diagnosis can be confused with dive-related injuries in divers. An emergency medical evacuation may be needed in remote locations.

Another DVT complication is a paradoxical embolism, in which a traveling blood clot passes into arterial circulation instead of lodging in or being filtered out in the pulmonary circulatory system. The paradoxical embolism may occur in individuals with a congenital condition such as patent foramen ovale (PFO), which is a hole in the wall that separates the heart’s right and left chambers. A PFO enables venous blood to pass to the arterial system. A paradoxical embolism that enters the brain may cause a stroke.

The risk of DVT in healthy people is small. Most DVT cases occur in people with preexisting risk factors who are forced to sit still for a long time — such as travelers who take long plane, car or train journeys; bedridden patients; and office workers who sit at their desks for many hours. Immobility slows the blood flow in the veins (venous stasis), and pressure exerted on the calf by poorly designed seats can injure the vein walls. After sitting for 90 minutes, the blood flow in the calf drops by half, which doubles the chance of a clot developing. For every hour spent sitting, the risk of a blood clot increases by 10 percent.

The incidence of DVT in the general population is only 0.1 percent, but it is greater in high-risk subpopulations. Long-distance air travel is thought to increase the risk of DVT two- to fourfold. Although DVT is often referred to as the “economy-class disease,” travelers in business class are not spared

About 75 percent to 99.5 percent of individuals who develop a travel-related DVT have more than one of the following risk factors:

age (risk increases after age 40)
obesity (risk increases in individuals with a body mass index (BMI) more than 30 kg/m²)
estrogen use (either hormonal contraceptives or hormone replacement therapy)
pregnancy or recent childbirth (within two to three months)
thrombophilia (an abnormally increased tendency to develop clots)
a previous DVT or family history of DVT
active cancer
serious medical illness
recent surgery, hospitalization or trauma
limited mobility
central venous catheterization

Treatment: Anticoagulants (blood thinners) are medicines that inhibit your blood’s ability to clot, thus reducing your risk of developing a clot. They range from over-the-counter medications such as aspirin to more potent prescription drugs such as warfarin (Coumadin).

Patients who can’t take anticoagulants, who have a DVT recurrence despite taking anticoagulants or who have repeated pulmonary embolisms can have a filter inserted in their inferior vena cava, which is the vein that returns blood from the lower body to the heart. Individuals with vena cava filters may return to normal daily life.

Regular use of compression socks or stockings can help prevent the swelling associated with DVT. It is usually advisable to wear compression footwear for at least a year after experiencing a DVT.

Prevention: People with a predisposition to blood clots should wear knee-high compression socks or thigh-high stockings when flying and consult their physician regarding the use of an anticoagulant medication such as aspirin. Compression footwear reduces the chance that blood will pool and clot, and anticoagulants inhibit the blood’s ability to clot. There is no evidence that healthy people without preexisting risks for DVT benefit from compression footwear or aspirin. Everyone should avoid long periods of immobility; it is good to stand up periodically and walk around while traveling, but this may not be allowed on the airplane during times of pandemic. It also helps to exercise or flex your feet and calf muscles while seated and to stay well hydrated.

Considerations for divers: During the acute phase of a DVT or while taking anticoagulants, it is highly inadvisable to dive. A return to diving after a DVT is possible, but the evaluation must be made on an individual basis. The same is true of returning to diving after a stroke. A return to diving after a pulmonary embolism is less likely, but your physician may approve it if your recovery has been satisfactory and your risk of a repeated embolism is minimal.

For a referral to a physician near you who has expertise in dive medicine, contact DAN Medical Services at apps.DAN.org/Ask-a-Medic.