Travel as a risk factor for venous thromboembolic disease.

There is increasing evidence that prolonged travel may be associated with the development of venous thromboembolic disease: ie deep venous thrombosis and pulmonary embolism. The data from case reports, retrospective reviews and case control studies have been confirmed by prospective studies. There have been several prospective studies of subjects embarking on airline flights of greater than 4 hours duration aimed at determining the incidence of DVT as detected by ultrasonography. In unprotected subjects, the incidence of thrombosis in the calf veins or muscular veins ranged between 0% and 10%. There is evidence that the incidence of travel-related pulmonary embolism appears to be related to the distance travelled and immobility during the flights. Whether the imputed causation is merely due to immobility and venous compression or to other factors associated with the aircraft cabin requires further clarification. The use of below-knee graduated compression stockings appears to be highly effective. A 100 AXa U/kg single dose of a low molecular weight heparin, given 2-4 hours before the flight, have been reported to be more effective than aspirin and placebo. However, the benefit/risk ratio of such a strategy remains to be assessed.