ArticlesFrequency and prevention of symptomless deep-vein thrombosis in long-haul flights: a randomised trial
Introduction
Every year the number of passengers travelling over long distances by air increases. Physicians working close to major airports have seen individual cases presenting with thromboembolic problems after air travel.1, 2, 3 Results of retrospective clinical series4, 5, 6 suggest that up to 20% of patients presenting with thromboembolism have undertaken recent air travel. Ferrari et al7 reported a strong association between deep-vein thrombosis (DVT) and long travel (>4 h) in a case-control study, although only a quarter of his patients with DVT travelled by air. Kraaijenhagen and colleagues8 looked at travel in the previous 4 weeks in patients presenting with DVT. They concluded that travelling times of more than 5 h were not associated with increased risk of DVT. The true frequency of this problem remains unknown and controversial. Episodes of DVT can arise without any symptom. Less than half the patients with symptomless DVT will develop symptoms, and only a few of those go on to have a clinically detectable pulmonary embolism.9, 10 In surgical series, a link between symptomless DVT, symptomatic DVT, and pulmonary embolism has been established.11, 12 Patients undergoing surgical procedures are assessed for risk, and appropriate prophylaxis is implemented.13 We undertook a randomised controlled trial to assess the overall frequency of DVT in long-haul airline passengers and the efficacy of a class-I elastic compression stocking for the duration of the flight.
Section snippets
Participants
Volunteers were recruited by placing advertisements in local newspapers and travel shops, and by press releases. The Aviation Health Institute referred many of the volunteers initially screened for this study, which took place in the Vascular Institute at the Stamford Hospital, London, UK. Passengers were included if they were over 50 years of age and intended to travel economy class with two sectors of at least 8 h duration within 6 weeks. Passengers were invited to undergo preliminary
Results
Volunteers were excluded before randomisation if they did not fulfil the entry requirements or could not attend hospital for investigation both before and after travel (figure). Thus, 231 of 479 volunteers were randomised. 27 passengers were unable to attend for subsequent ultrasound investigation because of ill-health (three), change of travel plans, or inability to keep appointments (24). Two who were upgraded to business class and two taking anticoagulants were also excluded. A similar
Discussion
About one in ten passengers not wearing elastic compression stockings developed symptomless DVT after airline travel, which is a surprisingly large proportion of the study group. The passengers were all aged more than 50 years and undertook long journeys by air (median 24 h), both of which are factors that could increase the risk of thrombosis. As far as we are aware no other workers have undertaken such a prospective study.
Other investigators14 have shown postoperative symptomless DVT
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