In-flight Clotting: Is It Something in the Air?

What steps can my 68-year-old patient take to help prevent thrombosis on a 14-hour plane flight?

Recently, a well-designed crossover study assessed the risk of thrombosis during long flights.^1,2 Included were persons with such risk factors as factor V Leiden mutation and oral contraceptive use. All 71 patients (15 men, 56 women) were studied (not randomized) in each limb of the protocol--in random order--during each of the following: an 8-hour flight, 8 hours spent watching movies, and 8 hours of typical daily living. Fifteen of the participants took oral contraceptives, 11 had the factor V Leiden mutation, and 15 had both risks.

The investigators measured markers of an activated coagulation and fibrinolytic system (thrombin-antithrombin complex, D-dimer, and prothrombin fragments 1 and 2). The researchers were blinded to the patients' status when the blood was drawn and the results were tabulated.

Thrombin-antithrombin complex levels increased an average of 30% after the 8-hour flight but decreased after marathon movie watching (by 2%) and after daily activities (by 8%). Levels of markers of stimulated coagulation were highest during flight in participants with factor V Leiden mutation who used oral contraceptives. The results clearly demonstrated that air travel for 8 hours increases coagulant activity.

Why might air travel be different from other situations characterized by varying degrees of inactivity? It may be that sitting in one place and the hypobaric hypoxemia of modern air travel have a synergistic effect.

Reassure patients that age and other risk factors do not preclude long plane flights. Although a previous study found that prophylactic aspirin was unsuccessful in reducing the risk of thrombosis,³ some simple measures may help. Alcohol and sedatives increase immobilization and may heighten risk; thus, they should be avoided. Performing intermittent calf contractions and getting up occasionally may be helpful. In some high-risk patients, compressive stockings are a reasonable option. Further study may identify travelers, such as those with recent joint replacement, who may benefit from prophylactic heparin.