Travel as a Risk Factor for Venous Thromboembolic Disease
Abstract & Commentary
Synopsis: This study demonstrates that any mode of transport increases the risk of VTED, with a mean duration of 5.4 ± 2.1 hours.
Source: Ferrari E, et al. Chest 1999;115:440-444.
Venous thromboembolism is a vascular disease with a multifactorial pathogenesis resulting in deep venous thrombosis (DVT) and pulmonary embolism (PE). Symptomatic PE occurs in approximately 30% of patients with DVT.1 Virchow first stated that venous stasis predisposed to DVT and Simpson described an increased rate of PE in Britons who were cramped in bomb shelters during the World War II Blitz. In 1988, Cruickshank reported on the "economy class syndrome." He reported PE in six patients after air travel of no less than seven hours.2 Despite these suggestions, there has never been a study demonstrating travel as an independent risk factor for venous thromboembolic disease (VTED).
Ferrari and colleagues performed a case-control study to assess travel as an independent risk factor for VTED. All patients hospitalized in Ferrari et al’s cardiology department answered a questionnaire at admission and prior to discharge. All patients who made a journey lasting longer than four hours within four weeks prior to admission were considered cases regardless of mode of transport. All cases were evaluated for conditions that might favor VTED. In addition to a thorough history, patients were evaluated for protein C, protein S, and antithrombin III deficiency, and occult cancer was investigated with a blood count, chest radiograph, abdominal exam, and pelvic ultrasound.
One hundred sixty cases were included from 1992 to 1995. Control subjects were patients admitted for a first-time event to the cardiology department. Controls were excluded if they had any disease that would limit mobility or if they received anticoagulation or antiplatelet therapy. The two patient groups differed in that the cases contained fewer men, more frequently had a history of prior VTED, and had a greater proportion of obese patients. Of the 160-patient study group, 85 patients had VTED associated with risk factors and 75 patients were idiopathic. Thirty-nine of the 160 cases had a recent travel history and 29 of these were in the idiopathic group. Among patients without a travel history, only 46 of 121 (38%) had an idiopathic VTED, while 29 of 39 (75%) patients with a travel history had idiopathic VTED (P = 0.0001). There was no significant difference in the venous location or limb where the clot was found between the travel and nontravel groups.
Comment by DAVID OST, MD, FCCP
VTED is a common disorder affecting one in 1000 persons yearly.1 Prevention strategies against VTED have been outlined for persons undergoing operative procedures or those who are expected to have prolonged bed rest. Yet prevention of VTED associated with travel is not commonly explained to patients. It is unclear if this is due to the fact that although travel has long been associated with VTED, it was never shown to be an independent risk factor. The patients in this study were not evaluated for activated protein C resistance, currently the most common hematologic condition associated with VTED. Approximately 20% of patients with VTED will be positive for this Factor V Leiden.1 If we assume that 20% of the idiopathic VTED patients in this study had a positive Factor V Leiden, then the percent of idiopathic post-travel VTED and idiopathic nontravel VTED patients would be 59% and 31%, respectively. This study demonstrates that any mode of transport increases the risk of VTED, with a mean duration of 5.4 ± 2.1 hours.
All travelers should be told to ambulate frequently while traveling regardless of the mode of transport. The duration and frequency of ambulation to prevent VTED is unknown. Daily commuters to work have never demonstrated to be at increased risk of VTED. Thus, a recommendation of ambulating every 1-2 hours is probably sufficient prophylaxis. (Dr. Ost is Assistant Professor of Medicine, NYU School of Medicine, Director of Interventional Pulmonology, Division of Pulmonary and Critical Care Medicine, Northshore University Hospital, Manhasset, NY.)
References
1. Hyers TM. Am J Respir Crit Care Med 1999;159:1-14.
2. Cruickshank JM, et al. Lancet 1988;2:497-498.
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