Deep venous thrombosis (DVT) and pulmonary embolism (PE) are the major causes of morbidity and mortality in immobile patients or travellers, especially where long-haul flights duration begins to exceed 3-4 hours. There is observational evidence that intercontinental air travel is associated with higher incidence of venous thromboembolism (VTE) during or within 48 hours of long-distance flights. It affects approximately 2–3 individuals per 1000 per year. VTE is the third cause of death by vascular diseases, only surpassed by myocardial infarction and ischemic stroke.

More than a billion people fly by air each year and it is believes that at least 5% have some degree on chronic illness or risk factors. 94% of intravascular blood clots are silent; the process continues without showing any symptoms and resolves within months. Thus becomes a health problem and can become life threatening when VTE becomes a circulatory disorder caused by thrombus and begins to travel within the vasculature.

Even though the incidence of symptomatic passenger thrombosis is unknown, it is believed that there are 30,000 cases per year in the UK. The annual incidence is 1/1,000 among the general population, 0.4–3/10,000 among travellers, and 1–2.5/10,000 among airplane passengers.

The incidence of DVT and PE because of age and sex varies. For instance, it may be 10.7% among male patients around the age of 80 years. DVT is more common in women in the reproductive age group, whereas it is more common in men after 45 years of age. In general, it is more common in men than in women (1.2/1).

MacCallum et al. demonstrated that on flights lasting less than 4 hours, the risk of VTE was approximately two times higher than in patients who did not travel and remained high in the 4 subsequent weeks. 

In a cohort of healthy subjects, the absolute risk of VTE on flights lasting more than 4 hours was 1 in 6,000. A meta-analysis involving 14 studies reported 4,055 cases of VTE in trips lasting up to 8 hours. These studies included both air and overland trips with the follow-up time after the journey ranging from 2 to 8 weeks. The relative risk for VTE was 2.8 and at each increment of 2 hours in travel time, there was an approximate 18% increase in the risk of VTE. Considering only air travel, this risk increased to 26%, suggesting a cumulative effect of flight time in the genesis of VTE.

Several factors may directly impact the passenger such as obesity, thrombophilia, oral contraceptive use, hormone replacement therapy and cancer that act together, predisposing an individual to excessive blood coagulation, which can result in VTE. Therefor knowing ones own risk factors prior to departure becomes really important when flying long-haul. Risk factors can be both genetic and acquired, and are associated with VTE. Acquired risk factors include age, pregnancy, surgery, obesity, cancer, hormonal contraceptives and hormone replacement therapy, antiphospholipid syndrome, infections, immobilization, and smoking.

Encouraging better overall preparation prior to departure, risk awareness, compression devices and  movement in-flight to alleviate venous stasis is key to preventing long-haul related VTE.   

Happy flying, have a great week.