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| {{Venous thromboembolism}}
| | #Redirect [[Deep vein thrombosis economy class syndrome]] |
| '''Editors-in-Chief:''' [[C. Michael Gibson, M.S., M.D.]]
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| ==Overview==
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| Venous thromboembolism (VTE) consists of 2 related conditions: 1) deep vein thrombosis (DVT) and 2) pulmonary embolism (PE). DVT occurs when a deep vein is partially or completely blocked by a blood clot, most commonly in the legs. The clot may break off and travel to the vessels in the lung, causing a life-threatening PE.
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| ==Historical Perspective==
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| VTE associated with air travel was first described in the early 1950s.<ref name="pmid14944721">{{cite journal |author=WRIGHT HP, OSBORN SB |title=Effect of posture on venous velocity, measured with 24NaCl |journal=Br Heart J |volume=14 |issue=3 |pages=325–30 |year=1952 |month=July |pmid=14944721 |pmc=479460 |doi= |url=http://heart.bmj.com/cgi/pmidlookup?view=long&pmid=14944721 |accessdate=2012-04-18}}</ref> Previous studies have shown a 2- to 4-fold increased risk of VTE after air travel.<ref name="pmid13119864">{{cite journal |author=HOMANS J |title=Thrombosis of the deep leg veins due to prolonged sitting |journal=N. Engl. J. Med. |volume=250 |issue=4 |pages=148–9 |year=1954 |month=January |pmid=13119864 |doi=10.1056/NEJM195401282500404 |url=http://www.nejm.org/doi/abs/10.1056/NEJM195401282500404?url_ver=Z39.88-2003&rfr_id=ori:rid:crossref.org&rfr_dat=cr_pub%3dpubmed |accessdate=2012-04-18}}</ref>
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| ==Risk Factors==
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| The risk of venous thrombosis and air travel was examined in the WRIGHT (World Health Organization Research Into Global Hazards of Travel) project. Several factors have been associated with an increased risk for developing VTE:
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| {| class="wikitable" cellpadding=5
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| | '''Risk factors for developing VTE include:'''<ref name="pmid12814980">{{cite journal |author=Anderson FA, Spencer FA |title=Risk factors for venous thromboembolism |journal=Circulation |volume=107 |issue=23 Suppl 1 |pages=I9–16 |year=2003 |month=June |pmid=12814980 |doi=10.1161/01.CIR.0000078469.07362.E6 |url=http://circ.ahajournals.org/cgi/pmidlookup?view=long&pmid=12814980 |accessdate=2012-04-18}}</ref>
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| | Recent major surgery
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| | Paralytic spinal cord injury
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| | Multiple trauma
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| | Malignancy
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| | Congestive heart failure or respiratory failure
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| | Hormone replacement therapy, oral contraceptive
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| | Previous venous thromboembolism
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| | Inherited hypercoagulable condition
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| | Acquired hypercoagulable condition
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| | Pregnancy
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| | Age >40 years
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| | Obesity
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| | Immobility
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| | Male gender
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| |}
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| A retrospective cohort study<ref name="pmid17896862">{{cite journal |author=Kuipers S, Cannegieter SC, Middeldorp S, Robyn L, Büller HR, Rosendaal FR |title=The absolute risk of venous thrombosis after air travel: a cohort study of 8,755 employees of international organisations |journal=PLoS Med. |volume=4 |issue=9 |pages=e290 |year=2007 |month=September |pmid=17896862 |pmc=1989755 |doi=10.1371/journal.pmed.0040290 |url=http://dx.plos.org/10.1371/journal.pmed.0040290 |accessdate=2012-04-18}}</ref> shows that the risk of VTE increased with flight duration and with the number of times the employee flew during an 8-week period; the risk of VTE tripled in employees who went on 5 or more long-haul (>4 hours) flights. Each extra flight increased the risk of VTE 1.4-fold. The risk of VTE was highest in the first 2 weeks after a long-haul flight and gradually decreased to baseline after 8 weeks.
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| ==Incidence==
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| A recent meta-analysis investigating the association between travel and VTE found a 2-fold higher risk for VTE in travelers compared with nontravelers. Significant variability was noted in the outcomes of the studies included in the review. This variability was directly related to the method used to select the comparison group in each study. When studies that used people referred for VTE evaluation as comparisons were excluded from the meta-analysis, the remaining studies showed a 3-fold higher risk of VTE associated with travel. The risk for VTE increased with travel duration. Each 2-hour increase in travel duration resulted in an 18% higher risk for VTE.
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| A retrospective cohort study done with 2,499 healthy Dutch commercial pilots showed the incidence of VTE to be 0.3 per 1,000 person-years.When the data were adjusted for age and sex, the rate was not different from that in the general Dutch population.
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| The second study was among 8,755 employees of several international companies and organizations. The overall incidence of VTE after air travel was 1.4 per 1,000 person-years.<ref name="pmid17896862">{{cite journal |author=Kuipers S, Cannegieter SC, Middeldorp S, Robyn L, Büller HR, Rosendaal FR |title=The absolute risk of venous thrombosis after air travel: a cohort study of 8,755 employees of international organisations |journal=PLoS Med. |volume=4 |issue=9 |pages=e290 |year=2007 |month=September |pmid=17896862 |pmc=1989755 |doi=10.1371/journal.pmed.0040290 |url=http://dx.plos.org/10.1371/journal.pmed.0040290 |accessdate=2012-04-18}}</ref> The incidence of VTE within 8 weeks of a long-haul flight (>4 hours) was 3.2 per 1,000 person-years compared with an incidence of 1.0 per 1,000 person-years in employees who did not fly. The absolute risk of VTE per flight more than 4 hours was 1 per 4,656 flights. Incidence was also higher in employees with a BMI more than 25 kg/m2 and those with height less than 1.65 m (5 ft 5 in) or more than 1.85 m (6 ft 1 in).
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| Both these studies were performed among populations that were younger (mean age 35–40 years) and healthier than the general population and are not, therefore, generalizable to a higher-risk population.
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| == Diagnosis ==
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| ===Symptoms===
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| Symptoms of '''DVT''' include [[swelling]], redness, [[pain]], or [[tenderness]] and increased warmth over the skin. It may be difficult to distinguish from muscle strain, [[injury]], or skin [[infection]]. Prospective studies have shown that many leg DVTs are asymptomatic; therefore, the first symptoms may be due to a PE.
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| Symptoms of '''PE''' range from mild and nonspecific to acute, resembling [[heart attack]] or [[stroke]]. Once a [[clot]] has traveled to the lungs, common symptoms of PE are chest pain and [[shortness of breath]]. Other symptoms include [[dizziness]], [[fainting]], [[anxiety]], and [[malaise]]. PE can occur in the absence of overt signs of DVT.
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| ===Investigations===
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| Specialized imaging tests (duplex venous ultrasound, venography, CT scans, and MRI) are needed to make a definitive diagnosis of DVT. Helical CT or ventilation-perfusion scans are commonly used to diagnose PE.
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| To read more about the diagnosis of DVT, click [[Deep vein thrombosis diagnosis algorithm|'''here''']].
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| To read more about the diagnosis of PE, click [[Pulmonary embolism diagnosis algorithm|'''here''']].
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| ==Treatment==
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| ===Preventive measures for travelers===
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| Several randomized controlled trials have been performed to assess the effect of prophylactic measures on VTE risk after air travel. All studies examined the risk of asymptomatic DVT in travelers making flights ≥7 hours. All travelers were encouraged to do regular exercises and to drink nonalcoholic beverages during the flight. DVT was diagnosed by venous ultrasound from 90 minutes to 48 hours after the flight. Interventions that were studied include compression stockings, aspirin, low-molecular weight heparin, and various natural extracts with anticoagulant properties. Compression stockings (10–20 mm Hg and 20–30 mm Hg) were shown to significantly reduce the risk of asymptomatic DVT; however, 4 travelers wearing compression stockings in one study developed superficial thrombophlebitis. Symptomatic DVT and PE were not observed in any of the travelers enrolled in the studies.
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| A randomized trial<ref name="pmid11863301">{{cite journal |author=Cesarone MR, Belcaro G, Nicolaides AN, Incandela L, De S, Geroulakos G, Lennox A, Myers KA, Moia M, Ippolito E, Winford M |title=Venous thrombosis from air travel: the LONFLIT3 study--prevention with aspirin vs low-molecular-weight heparin (LMWH) in high-risk subjects: a randomized trial |journal=Angiology |volume=53 |issue=1 |pages=1–6 |year=2002 |pmid=11863301 |doi= |url= |accessdate=2012-04-18}}</ref> conducted to compare the effects of [[aspirin]] and a low-molecular-weight [[heparin]] ([[enoxaparin]]) versus no treatment in the prevention of VTE in 300 high-risk patients (such as previous DVT, coagulation disorders, severe obesity, limitation of mobility due to bone or joint problems, neoplastic disease within the previous 2 years, or large varicose veins).Aspirin (400 mg daily for 3 days, starting 12 hours before air travel) did not reduce the frequency of DVT compared with controls (4.8% in people not on prophylaxis; 3.6% in people taking aspirin). No DVT and one superficial thrombosis were identified in people using enoxaparin prophylaxis (1 dose at 1,000 IU per 10 kg of body weight injected 2–4 hours before the flight). Although these results are encouraging for the use of low-molecular-weight heparin to prevent VTE in high-risk patients, the study size and number of patients with DVT were small. Currently no convincing data suggest that pharmacologic interventions reduce the risk of significant VTE in low-risk travelers.
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| To read more about the treatment of DVT, click [[Deep vein thrombosis medical therapy|'''here''']].
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| To read more about the treatment of PE, click [[Pulmonary embolism treatment algorithm|'''here''']].
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| ==Recommendations==
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| The American College of Chest Physicians (ACCP) published the following recommendations for long-distance travel associated VTE:
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| *For travelers who are taking flights >8 hours, the following general measures are recommended: avoidance of constrictive clothing around the lower extremities or waist, maintenance of adequate hydration, and frequent calf muscle contraction (Grade 1C).
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| *For long-distance travelers with additional risk factors for VTE, the general measures listed above are recommended. If active thromboprophylaxis is considered because of a perceived high risk of VTE, the use of properly fitted, below-knee graduated compression stockings, providing 15–30 mm Hg of pressure at the ankle (Grade 2C) or a single prophylactic dose of low-molecular-weight heparin, injected before departure (Grade 2C) are suggested.
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| *For long-distance travelers, the use of aspirin to prevent VTE is not recommended (Grade 1B).
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| ==Related Chapters==
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| *[[Pulmonary embolism]]
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| *[[Deep vein thrombosis]]
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| *[[Venous thromboembolism: Under-recognized and under-treated]]
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| [[Category:Cardiology]]
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| [[Category:Hematology]]
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| [[Category:Angiology]]
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| [[Category:Emergency medicine]]
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| ==Reference==
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| {{reflist|2}}
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