Air travel and venous thromboembolism: Minimizing the risk
ABSTRACTFor those traveling on long flights, the risk of deep vein thrombosis or pulmonary embolism, generally referred to as venous thromboembolism (VTE), is real and dangerous if left unrecognized or untreated. The goal of this publication is to provide an overview of how best to prevent VTE during travel, and how to diagnose and treat it.
KEY POINTS
- The risk of VTE is about three times higher in passengers on long-distance flights than in the general population, although the absolute risk is still low.
- All long-distance air passengers should perform stretching exercises once an hour while in flight to prevent VTE. They should also stay hydrated.
- For patients at higher risk due to hypercoagulable conditions, physicians can consider prescribing compression stockings or an anticoagulant drug (a low-molecular-weight heparin or a factor Xa inhibitor) to be taken before the flight, or both.
- The evaluation of a patient with suspected VTE should include an estimation of the pretest probability of disease. If symptoms dictate, duplex ultrasonography of the upper or lower extremity to detect deep vein thrombosis or spiral computed tomography, ventilation-perfusion lung scan, or pulmonary angiography (where available) to diagnose an acute pulmonary embolism should be ordered.
DIAGNOSIS OF VTE
Clinical examination alone is generally insufficient to confirm a diagnosis of deep vein thrombosis or pulmonary embolism. Venous duplex ultrasonography is the most dependable investigation for deep vein thrombosis, but other tests include D-dimer and imaging studies such as computed tomographic venography or magnetic resonance venography of the lower extremities. A more invasive approach is venography; formerly considered the gold standard, it is now generally used only when the diagnosis is in doubt after noninvasive testing. The diagnosis of acute pulmonary embolism is best made by spiral computed tomography.
Other studies that may prove helpful include a ventilation-perfusion lung scan for patients who cannot undergo computed tomography due to a contrast allergy or renal insufficiency. Pulmonary angiography, while the gold standard, is less commonly used today, given the specificity and sensitivity of computed tomography.
Echocardiography at the bedside may be useful for patients too sick to move, although the study may not be diagnostic unless thrombi are seen in the heart or pulmonary arteries.
TREATMENT OF VTE
For acute deep venous thrombosis
Acute deep vein thrombosis is now treated on an outpatient basis under most circumstances.
Unfractionated heparin is given intravenously for patients who need to be hospitalized, or subcutaneously in full dose for inpatient or outpatient treatment.
Low-molecular-weight heparins are available in subcutaneous preparations and can be given on an outpatient basis.
Fondaparinux (Arixtra), a factor Xa inhibitor, can also be given subcutaneously on an outpatient basis. Equivalent products are available outside the United States.
Warfarin (Coumadin), an oral vitamin K inhibitor, is the agent of choice for long-term management of deep vein thrombosis.
Other oral agents are available outside the United States.
For pulmonary embolism
Outpatient treatment of pulmonary embolism is not yet advised: an initial hospitalization is necessary. The same anticoagulants used for deep vein thrombosis are also used for acute pulmonary embolism.
Empiric treatment in underdeveloped countries
VTE may be an even greater concern on an outbound trip to a remote area, where medical care capabilities may be less than ideal and diagnostic and treatment options may be limited.
If there is a high pretest probability of acute VTE (Table 2, Table 3) and no diagnostic methods are available, empiric treatment with any of the parenteral anticoagulant agents listed in Table 4 is an option until the diagnosis can be confirmed. Caveats:
- Care must be taken to be certain there is not a strong contraindication to the use of anticoagulation, such as bleeding or a drug allergy.
- Neither unfractionated heparin nor any of the low-molecular-weight heparins should be given to a patient who has a history of heparin-induced thrombocytopenia.
- In patients who have chronic kidney disease (creatinine clearance less than 30 mL/minute), the dosage of low-molecular-weight heparins must be adjusted and factor Xa inhibitors avoided. Both of these types of anticoagulants should be avoided in patients on hemodialysis.
More aggressive therapy
Under select circumstances a more aggressive approach to the treatment of VTE may be necessary. These options are usually indicated for a patient with a massive deep vein thrombosis of a lower extremity and for certain patients with an upper extremity deep vein thrombosis. Treatments include catheter-directed thrombolytic therapy and endovenous or surgical thrombectomy.
Thrombolytic therapy is recommended for a patient with an acute pulmonary embolism who is clinically unstable (systolic blood pressure lower than 90 mm Hg), if there is no contraindication to its use (bleeding risk or recent stroke or surgery). Thrombolytic therapy is also an option for those at low risk of bleeding with an acute pulmonary embolism who have signs and symptoms of right heart failure proven by echocardiography.
Surgical pulmonary embolectomy for acute massive pulmonary embolism and mechanical thrombectomy for extensive deep vein thrombosis are generally available only at highly sophisticated tertiary care centers.
An inferior vena cava filter is advised in patients with acute deep vein thrombosis or pulmonary embolism who cannot be fully anticoagulated, to prevent the clot from migrating from the lower extremities to the lungs. These filters are available as either permanent or temporary implants. Some temporary versions can remain in place for up to 150 days after insertion.
PREVENTION OF VTE
Prevention is the standard of care for all patients admitted to the hospital and in select individuals as outpatients who are at high risk of VTE.
Mechanical compression (graduated compression stockings, intermittent pneumatic compression devices) has proven effective in reducing the incidence of deep vein thrombosis and pulmonary embolism postoperatively in patients who cannot take anticoagulants. One study has demonstrated that compression stockings may also be effective in preventing VTE during travel.12
ABSOLUTE RISK IS LOW
Over the past decade, special attention has been paid to travel as a risk factor for developing VTE.13 Traveler’s thrombosis has become an important public health concern. Numerous publications and epidemiologic studies have targeted air travel in an attempt to determine who is at risk and what precautions are necessary to prevent this complication.1–7,9
The incidence of VTE following air travel is reported to be 3.2 per 1,000 person-years.4 While this incidence is relatively low, it is still 3.2 times higher than in the healthy population that is not flying.
The more serious complication of VTE, ie, acute pulmonary embolism, occurs less often. In three studies, the reported incidence ranged from 1.65 per million patients in flights longer than 8 hours to a high of 4.8 per million patients in flights longer than 12 hours or distances exceeding 10,000 km (6,200 miles).5,14,15 For the 400 passengers on the average long-haul flight of 12 hours, there is at most a 0.2% chance that somebody on the plane will have a symptomatic VTE).
