By Kevin O. Hwang, MD, MPH
November 22, 2013
Full Story: http://www.medpagetoday.com/resource-center/DVT-and-PE/travel/a/37714
Take Note
- The absolute risk of symptomatic VTE after travel is low.
- The risk of travel-related VTE increases with long-haul flights and in individuals with other clinical risk factors for VTE.
The association between venous thromboembolism (VTE) and travel was recognized as early as the 1950s, when John Homans, MD, best remembered in connection with Homans’ sign—pain in the calf on active or passive dorsiflexion of the foot that may signal deep venous thrombosis (DVT)—advised that “physicians should be alert to recognize the significance of lameness after airplane flights, automobile trips and other occasions of a prolonged seated position.”1This article will review the risk of developing VTE associated with travel.
The notion that prolonged travel in a sedentary position increases the risk of VTE seems easy to accept, and clinicians are accustomed to asking about recent travel when they suspect VTE. However, symptomatic VTE after air travel is rare, as demonstrated in a cohort study of 8755 employees of large international companies and organizations.2 A total of 22 symptomatic, objectively confirmed VTE events occurred within 8 weeks after 102,429 long-haul flights, defined as 4 hours or longer. This corresponded to an absolute risk of 1 VTE event per 4656 long-haul flights.
A systematic review by Philbrick and colleagues also found a low rate of symptomatic VTE after air travel, with an incidence of 0.5 pulmonary embolisms per 1 million travelers presenting on the day of arrival in the airport, and 27 VTEs (pulmonary embolism and DVT) per 1 million travelers presenting within 2 weeks of arrival.3 When ultrasounds are performed routinely in travelers, the rate of diagnosed DVT may be as high as 1.2%, but the majority of cases are asymptomatic. The risk of an asymptomatic DVT progressing to clinically significant disease is currently unknown.
While some large studies have documented a positive relationship between travel and VTE, others have not. Chandra and colleagues conducted a meta-analysis of observational studies to clarify the conflicting evidence.4 In the 14 included studies, the pooled relative risk for VTE associated with travel was 2.0 (95% CI, 1.5-2.7). However, there was significant heterogeneity, with 7 studies reporting an association between travel and VTE, and the other 7 reporting no association. The authors conducted a sub-analysis to exclude 8 case-control studies that had a certain bias in selecting the control participants. In the remaining 6 studies, the relative risk for VTE associated with travel was 2.8 (95% CI, 2.2-3.7). These results appear to resolve the conflicting data and point to an elevated risk of VTE with travel.
The Chandra meta-analysis also reported a significant travel dose-response relationship. The risk for VTE rose by 18% for each 2-hour increase in travel by any mode, and by 26% for each 2-hour increase in travel by air.4 The Philbrick systematic review also documented a dose-response relationship, with greatest risk for DVT occurring with flights longer than 8 hours.3
The data on VTE associated with car or train trips is less clear. In the Chandra meta-analysis, the risk of VTE with air travel was slightly higher than for ground travel, but the difference was not statistically significant.4 In the Philbrick systematic review, only air travel was associated with VTE, although not all studies assessed other modes of travel.3
Other than flight duration, baseline clinical factors may also influence the risk of VTE. A prospective cohort study monitored travelers with surveillance ultrasound within 24 hours after long flights (average duration, 12.4 hours).5 Eleven of the 389 high-risk travelers (previous history of DVT, known coagulation disorder, severe obesity, limited mobility, cancer, large varicose veins) were found to have DVT. In contrast, DVT was not found in any of the 355 low-risk travelers.
In conclusion, symptomatic VTE after travel is not a common event. But considering the popularity of air travel, it is important to recognize the elevated risk of VTE associated with long air flights, especially among patients with other risk factors for VTE. Patients at high risk for DVT induced by prolonged travel should be identified and counseled before they start their journeys.
References:
- Homans J. Thrombosis of the deep leg veins due to prolonged sitting. N Engl J Med. 1954;250:148-149.
- Kuipers S, Cannegieter SC, Middeldorp S, et al. The absolute risk of venous thrombosis after air travel: a cohort study of 8,755 employees of international organisations. PLoS Med. 2007;4:e290.
- Philbrick JT, Shumate R, Siadaty MS, et al. Air travel and venous thromboembolism: a systematic review. J Gen Intern Med. 2007;22:107-114.
- Chandra D, Parisini E, Mozaffarian D. Meta-analysis: travel and risk for venous thromboembolism. Ann Intern Med. 2009;151:180-190.
- Belcaro G, Geroulakos G, Nicolaides AN, et al. Venous thromboembolism from air travel: the LONFLIT study.Angiology. 2001;52:369-374.