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Journal of Internal Medicine Dec 2007In the past decade, numerous publications on the association between venous thrombosis (VT) and travel have been published. Relative and absolute risks of VT after... (Review)
Review
In the past decade, numerous publications on the association between venous thrombosis (VT) and travel have been published. Relative and absolute risks of VT after travel, and particularly after travel by air, have been studied in case-control and observational follow-up studies, whereas the effect of prophylaxis has been studied through intervention trials of asymptomatic clots. The mechanism responsible for the association between travel and VT was addressed in pathophysiologic studies. Here, we systematically reviewed the epidemiologic and pathophysiologic studies about the association between travel and VT. We conclude that long-distance travel increases the risk of VT approximately two to fourfold. The absolute risk of a symptomatic event within 4 weeks of flights longer than 4 h is 1/4600 flights. The risk of severe pulmonary embolism (PE) occurring immediately after air travel increases with duration of travel, up to 4.8 per million in flights longer than 12 h. The mechanism responsible for the increased risk of VT after (air) travel has insufficiently been studied to draw solid conclusions, but one controlled-study showed evidence for an additional mechanism to immobilization that could lead to coagulation activation after air travel.
Topics: Aircraft; Humans; Hypoxia; Incidence; Movement; Pulmonary Embolism; Risk Assessment; Travel; Venous Thrombosis
PubMed: 18028182
DOI: 10.1111/j.1365-2796.2007.01867.x -
Journal of General Internal Medicine Jan 2007Despite multiple attempts to document and quantify the danger of venous thromboembolism (VTE) following prolonged travel, there is still uncertainty about the magnitude... (Review)
Review
CONTEXT
Despite multiple attempts to document and quantify the danger of venous thromboembolism (VTE) following prolonged travel, there is still uncertainty about the magnitude of risk and what can be done to lower it.
OBJECTIVES
To review the methodologic strength of the literature, estimate the risk of travel-related VTE, evaluate the efficacy of preventive treatments, and develop evidence-based recommendations for practice.
DATA SOURCES
Studies identified from MEDLINE from 1966 through December 2005, supplemented by a review of the Cochrane Central Registry of Controlled Trials, the Database of Abstracts of Reviews of Effects, and relevant bibliographies.
STUDY SELECTION
We included all clinical studies that either reported primary data concerning travel as a risk factor for VTE or tested preventive measures for travel-related VTE.
DATA EXTRACTION AND ANALYSIS
Two reviewers reviewed each study independently to assess inclusion criteria, classify research design, and rate methodologic features. The effect of methodologic differences, VTE risk, and travel duration on VTE rate was evaluated using a logistic regression model.
DATA SYNTHESIS
Twenty-four published reports, totaling 25 studies, met inclusion criteria (6 case-control studies, 10 cohort studies, and 9 randomized controlled trials). Method of screening for VTE [screening ultrasound compared to usual clinical care, odds ratio (OR) 390], outcome measure [all VTE compared to pulmonary embolism (PE) only, OR 21], duration of travel (<6 hours compared to 6-8 hours, OR 0.011), and clinical risk ("higher" risk travelers compared to "lower," OR 3.6) were significantly related to VTE rate. Clinical VTE after prolonged travel is rare [27 PE per million flights diagnosed through usual clinical care, 0.05% symptomatic deep venous thrombosis (DVT) diagnosed through screening ultrasounds], but asymptomatic thrombi of uncertain clinical significance are more common. Graduated compression stockings prevented travel-related VTE (P < 0.05 in 4 of 6 studies), aspirin did not, and low-molecular-weight heparin (LMWH) showed a trend toward efficacy in one study.
CONCLUSIONS
All travelers, regardless of VTE risk, should avoid dehydration and frequently exercise leg muscles. Travelers on a flight of less than 6 hours and those with no known risk factors for VTE, regardless of the duration of the flight, do not need DVT prophylaxis. Travelers with 1 or more risk factors for VTE should consider graduated compression stockings and/or LMWH for flights longer than 6 hours.
Topics: Aircraft; Anticoagulants; Exercise; Heparin; Humans; Phytotherapy; Pulmonary Embolism; Stockings, Compression; Time Factors; Travel; Venous Thrombosis
PubMed: 17351849
DOI: 10.1007/s11606-006-0016-0 -
Journal of Travel Medicine 2005Anecdotal evidence suggests a possible link between travel and venous thromboembolism (VTE). We systematically evaluated the evidence from observational studies. (Review)
Review
BACKGROUND
Anecdotal evidence suggests a possible link between travel and venous thromboembolism (VTE). We systematically evaluated the evidence from observational studies.
METHODS
We searched studies evaluating the risk of venous thrombosis in relation to traveling from MEDLINE and EMBASE up tp March 2004, together with a hand search of reference lists from retrieved literature, and we contacted some of the experts. Observational studies estimating the risks of VTE and isolated calf vein thrombosis were eligible. Methodologic quality was assessed based on prior criteria, and meta-analysis was considered where applicable.
RESULTS
A total of 194 English-language publications were initially identified. Sixteen studies were included: 9 case-control, 2 prospective controlled, and 5 other observational studies. They differed drastically in study designs, selection of controls where applicable, mode and duration of travel, and subtypes of VTE under consideration. Ten studies concluded that travel, mostly through air and of prolonged duration, is a risk factor for venous thrombosis and/or pulmonary embolism, and the risk increases for passengers with preexisting venous thrombosis risk factors. Outcomes examined ranged from asymptomatic isolated calf muscle vein thrombosis to severe fatal pulmonary embolism.
CONCLUSIONS
Current literature is controversial over any association between travel and VTE, and although the quality and power of these studies have been variable, studies of higher quality have shown a strong and significant association between prolonged air travel and VTE. No conclusions could be drawn about other modes of transportation. Since VTE is a disease of multifactorial causation, those with preexisting VTE risk factors are most vulnerable.
Topics: Aerospace Medicine; Case-Control Studies; Female; Global Health; Humans; Incidence; Male; Prevalence; Risk Assessment; Risk Factors; Sex Distribution; Time Factors; Transportation; Travel; Venous Thrombosis
PubMed: 15996443
DOI: 10.2310/7060.2005.12303