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Cardiovascular Preventative medicine

DVT prevention for travellers

Last revised in November 2023

Deep vein thrombosis (DVT) can occur as a result of long distance travel. The risk of travel-related DVT in healthy people is extremely low

DVT prevention for travellers: Summary

  • Deep vein thrombosis (DVT) is the formation of a thrombus in a deep vein, which partially or completely obstructs blood flow in that vessel. 
  • Travel-related DVT can occur as a result of prolonged immobility during long-distance travel. This results from a combination of factors, including venous stasis due to prolonged cramped sitting, seat-edge pressure, coagulation activation, and individual risk factors for venous thromboembolism (VTE).
  • The annual incidence of DVT is estimated to be about 1 in 1000. However, the risk of developing DVT is increased two to four fold after long-haul flights (more than 4 hours). Travel by other forms of transport, such as car or train, carries a similar risk.
  • Most clots are small and do not cause symptoms.
  • The risk of travel-related DVT increases with the duration of travel and with multiple flights within a short period. For healthy people, the risk is estimated to be 1 event in 4656 to 6000 flights over 4 hours in length. 
  • The relative risk of travel-related DVT is further increased if other risk factors for developing DVT are present. These include:
    • Active malignancy. 
    • A family history of DVT or pulmonary embolism (PE) in a close family member.
    • Chronic venous insufficiency. 
    • Extremes of height — people taller than 1.90 metres or shorter than 1.60 metres.
    • Inherited or acquired blood-clotting abnormalities.
    • Limited mobility (for example, a lower-limb fracture in plaster, paralysis, and prolonged bed rest). 
    • Obesity.
    • Older age (the risk increases from the age of 40).
    • Pregnancy, or up to 6 weeks postpartum. 
    • Previous DVT or PE. 
    • Recent surgery or trauma, particularly to the abdomen, pelvic region, or legs. 
    • Use of oestrogens, such as oral contraceptives or hormone replacement therapy.
  • An assessment of DVT risk for travellers should consider the planned duration of travel and any pre-existing risk factors for DVT.  
  • People should be considered at high risk of travel-related DVT if they have:
    • An active malignancy. 
    • Given birth in the previous 6 weeks.
    • Had a previous VTE (unprovoked or travel-related).
    • Significant immobility.
    • Undergone recent major surgery (within the previous 4 weeks).
    • More than one risk factor for DVT (pregnancy, hormonal treatment, and BMI ≥30 kg/m2).
  • All people undertaking a long journey should be advised to take measures to reduce immobility.
  • People at high risk of developing a DVT should be advised to consider postponing travel, or if travel is essential, low molecular weight heparin may be considered, with or without graded compression stockings. 

Have I got the right topic?

From age 16 years onwards.

This CKS topic covers the prevention of venous thromboembolism (deep vein thrombosis and/or pulmonary embolism) in people travelling long distances.

This CKS topic does not cover the management of people with deep vein thrombosis.

There is a separate CKS topic on Deep vein thrombosis that covers the identification and management of suspected deep vein thrombosis (DVT), and the subsequent prevention of venous thromboembolism (VTE).

The target audience for this CKS topic is healthcare professionals working within the NHS in the UK, and providing first contact or primary healthcare.

How up-to-date is this topic?

Changes

November 2023 — reviewed. A literature search was conducted in October 2023 to identify evidence-based guidelines, UK policy, systematic reviews, and key randomized controlled trials published since the last revision of this topic. The moderate risk category has been removed in line with the latest guidelines from the British Society for Haematology and the American Society of Hematology, and accordingly minor changes to the recommendations have been made. A section on pregnancy has been added.

Previous changes

July to August 2018 — reviewed. A literature search was conducted in July 2018 to identify evidence-based guidelines, UK policy, systematic reviews, and key RCTs published since the last revision of this topic. No significant changes to clinical recommendations have been made.

March 2013 — reviewed. A literature search was conducted in February 2013 to identify evidence-based guidelines, UK policy, systematic reviews, and key RCTs published since the last revision of this topic. No changes to clinical recommendations have been made.

March 2011 — minor update to the text regarding the role of dehydration as a risk factor for DVT. 

September 2010 — minor update. Text updated to include recommendations from the Working Group of the British Cardiovascular Society report Fitness to fly for passengers with cardiovascular disease.

December 2008 to May 2009 — converted from CKS guidance to CKS topic structure. The evidence-base has been reviewed in detail, and recommendations are more clearly justified and transparently linked to the supporting evidence. There are no major changes to the recommendations.

October to December 2005 — written. Validated in March 2006 and issued in May 2006.

Update

New evidence

Evidence-based guidelines

No new evidence-based guidelines published since 1 November 2023.

HTAs (Health Technology Assessments)

No new HTAs since 1 November 2023.

Economic appraisals

No new economic appraisals relevant to England since 1 November 2023.

Systematic reviews and meta-analyses

Primary evidence

No new primary evidence which reaches the CKS threshold for inclusion published since 1 November 2023.

New policies

No new national policies or guidelines since 1 November 2023.

New safety alerts

No new safety alerts since 1 November 2023.

Changes in product availability

No changes in product availability since 1 November 2023.

Goals and outcome measures

Goals

To support primary healthcare professionals to:

  • Assess the risk of travel-related deep vein thrombosis (DVT).
  • Provide appropriate advice on reducing the risk of travel-related DVT.
  • Recommend appropriate prophylactic measures for people at risk of travel-related DVT.

Outcome measures

No outcome measures were found during the review of this topic.

Audit criteria

No audit criteria were found during the review of this topic.

QOF indicators

No QOF indicators were found during the review of this topic.

QIPP - Options for local implementation

No QIPP indicators were found during the review of this topic.

NICE quality standards

No NICE quality standards were found during the review of this topic.

Background information

What is it?

  • Deep vein thrombosis (DVT) is the term used to describe the formation of a thrombus in a deep vein, which partially or completely obstructs blood flow in that vessel. For more information, see the CKS topic on Deep vein thrombosis. 
  • DVT can occur due to prolonged immobility during long-distance travel (for example, by bus, train, or air).
    • Virchow's triad describes the contributing factors for the development of venous thrombosis: venous stasis, endothelial damage, and hypercoagulability. The pathogenesis of travel-related DVT is not fully understood, but travel and person-specific factors seem to contribute to the development of venous thromboembolism (VTE) as a result of long-distance travel.
      • Venous stasis may result from sitting in a cramped position for prolonged periods of time, and this may be affected further by pressure from the seat on the back of the knees or calves.
      • Pressure from the seat may also contribute to endothelial injury.
      • In air travel, cabin conditions seem to lead to coagulation activation in some people, although hypobaric hypoxia alone, for example, has not been found to cause this in studies.
      • These factors may all be implicated, particularly in people with additional risk factors for DVT. 

 [WHO, 2019; Czuprynska, 2020; CDC, 2023; IATA, 2023]

Prevalence

  • The annual incidence of deep vein thrombosis (DVT) in the general population is estimated to be about 1 in 1000.
  • It is difficult to ascertain the incidence of travel-related DVT. Most (but not all) studies have found that the risk of DVT is increased after long-distance travel, usually defined as travel lasting more than 4 hours.
    • Generally, risk seems to be low. Studies suggest that an average of 1 passenger in 4656–6000 will suffer from venous thromboembolism. In most cases, the clots are small and do not cause symptoms.
    • It has been estimated from studies that long-distance travel increases a person's risk of DVT by two to four fold.
    • The risk is increased with the duration of travel and with pre-existing risk factors for DVT.
    • Risk seems similar to travel by air, car, bus, or train.
    • The risk reduces with time after travel. Most travel-related DVTs occur within 1–2 weeks of travel, and the risk returns to baseline by 8 weeks.
  • Incidence of pulmonary embolism related to air travel seems to be very low, at around 0.4 cases per one million flights taken. Again, the incidence is higher the longer the flight.

[Kuipers, 2007; WHO, 2007; Czuprynska, 2020; McKerrow Johnson, 2022; BMJ Best Practice, 2023; BSH, 2023; CDC, 2023]

  • The relative risk of travel-related deep vein thrombosis (DVT) is further increased if other risk factors for developing DVT are present. These include:
    • Active malignancy. 
    • A family history of venous thromboembolism (VTE).
    • Chronic venous insufficiency.
    • Extremes of height — people taller than 1.90 metres or shorter than 1.60 metres.
      • Shorter people may experience seat edge pressure to the popliteal area. 
      • Taller people have less legroom.
    • Inherited or acquired prothrombotic blood clotting abnormalities.
    • Limited mobility (for example, a lower-limb fracture in plaster, prolonged bed rest, or paralysis). 
    • Obesity (body mass index ≥30 kg/m2). 
    • Older age (increasing risk from age 40). 
    • Pregnancy, or up to 6 weeks postpartum. 
    • Previous DVT or pulmonary embolism (PE). 
    • Recent surgery (in the previous 4 weeks) or trauma, particularly to the abdomen, pelvic region, or legs. 
    • Use of oestrogens, such as oral contraceptives or hormone replacement therapy.

[WHO, 2019; Clarke, 2021; BSH, 2023; CDC, 2023]

Management

Scenario: Deep vein thrombosis - prevention for travellers

From age 16 years onwards.

How should I assess DVT risk in travellers?

  • Assessment should be made on an individual basis and for each travel occasion as the relative risk of deep vein thrombosis (DVT) may change over time. 
  • Consider the pre-existing risk factors for DVT, and the planned duration of travel. Risk increases after 4 hours, and increases with duration of travel.
  • People are at:
    • Low risk of travel-related DVT if they have no pre-existing risk factors.
    • High risk if they have:
      • An active malignancy. 
      • Given birth in the previous 6 weeks.
      • Had a previous unprovoked venous thromboembolism (VTE).
      • Had a previous travel-related VTE. 
      • Significant immobility (such as lower limb immobilisation).
      • Undergone recent major surgery (within the previous 4 weeks).
      • Two or more combined risk factors for DVT, including:
        • Pregnancy.
        • BMI ≥30 kg/m2.
        • Hormonal treatment.

Basis for recommendation

These recommendations are based on the 2023 addendum to the guidelines from the British Society for Haematology on Travel-related venous thrombosis [BSH, 2023], the American Society of Hematology 2018 guidelines for management of venous thromboembolism: prophylaxis for hospitalized and nonhospitalized medical patients [Schünemann, 2018], the Centers for Disease Control and Prevention (CDC) Yellow Book: Health information for international travelers [CDC, 2023], and an expert review article, Annotation: travel and thrombosis [Czuprynska, 2020].

  • For people assessed as having a relatively low risk of developing travel-related deep vein thrombosis (DVT):
    • Provide advice on general measures to reduce the risk of travel-related DVT.
    • Reassure the person that no specific treatment is required.

Basis for recommendation

These recommendations are based on the 2023 addendum to the guidelines from the British Society for Haematology on Travel-related venous thrombosis [BSH, 2023], the American Society of Hematology 2018 guidelines for management of venous thromboembolism: prophylaxis for hospitalized and nonhospitalized medical patients [Schünemann, 2018], the Centers for Disease Control and Prevention (CDC) Yellow Book: Health information for international travelers [CDC, 2023], and an expert review article, Annotation: travel and thrombosis [Czuprynska, 2020].

  • For people assessed at high risk of developing travel-related deep vein thrombosis (DVT):
    • Assess the individual person's suitability for long-distance travel. If appropriate, either:
      • Consider seeking specialist advice.
      • Recommend delaying or cancelling the trip. (Delay may be appropriate for time-limited risks, such as after surgery, or whilst having active treatment for malignancy. It may be helpful to seek advice from the person's specialist about travel following hip or knee replacement surgery as there is no consensus).
  • If long-distance travel is unavoidable:
    • Provide advice on general measures to reduce the risk of travel-related DVT.
    • Seek specialist advice, depending on local pathways, regarding whether the use of low molecular weight heparin is indicated, and if so, at what dose. If indicated, this should be given subcutaneously 2–4 hours before each flight lasting more than 4 hours.
    • Consider advising, in addition, the use of graduated compression stockings.

Low molecular weight heparin

  • If low molecular weight heparin (LMWH) is prescribed:
    • Ensure that appropriate arrangements are in place for LMWH administration (for example, that a nurse is available) or that the person is given training if the drug will be self-administered.
      • LMWH should be administered before departure.
    • Prescribe sufficient LMWH to cover the outgoing and any subsequent connecting or return flights.
    • Prescribe LMWH as pre-filled syringes for ease of administration.
    • Provide the person with a letter that explains why they have to carry needles and syringes while travelling, to show to security, immigration, and customs officials.
    • Warn about the increased risk of bleeding and bruising.
    • Advise the person to seek urgent medical advice if there is uncontrolled or excessive bleeding or bruising, or if they have a sudden severe headache (possible intracranial haemorrhage), or gastrointestinal pains (signifying possible gastrointestinal bleeding).
    • Advise on the safe storage and disposal of needles and syringes.

Basis for recommendation

These recommendations are based on the 2023 addendum to the guidelines from the British Society for Haematology on Travel-related venous thrombosis [BSH, 2023], the American Society of Hematology 2018 guidelines for management of venous thromboembolism: prophylaxis for hospitalized and nonhospitalized medical patients [Schünemann, 2018], the Centers for Disease Control and Prevention (CDC) Yellow Book: Health information for international travelers [CDC, 2023], a Cochrane systematic review Compression stockings for preventing deep vein thrombosis in airline passengers [Clarke, 2021], and an expert review article, Annotation: travel and thrombosis [Czuprynska, 2020].

Evidence is limited as regards interventions for preventing deep vein thrombosis (DVT) related to travel.

  • There are no studies on the efficacy of general advice measures to prevent DVT related to travel, such as frequent mobilisation or calf muscle exercises. However, immobility is a known risk factor for DVT, indirect evidence suggests that maintaining mobility could reduce the risk, and the CDC Yellow Book and an expert review support this as reasonable, pragmatic advice [Czuprynska, 2020; CDC, 2023].
  • One UK-based study found there was no consensus on air travel following hip or knee arthroplasty. Advice about how long to wait before flying after such surgery from orthopaedic consultants, insurance providers and airlines varied between 2 weeks and 6 months [Oputa, 2023]. CKS concluded it may be wise to seek advice from the specialist of the person wishing to travel following this type of surgery, rather than recommending a blanket time frame.
  • The British Society for Haematology guidance recommends, in individuals assessed as high risk travelling more than 4 hours, considering the use of pharmacological thromboprophylaxis, with or without graduated compression stockings [BSH, 2023]. The document goes on to state that neither low molecular weight heparin (LMWH) or direct oral anticoagulants (DOACs) have a specific license for this indication, but that there is more experience with LMWH.
  • The American Society of Hematology guidelines recommend either LMWH or graduated compression stockings [Schünemann, 2018].
  • A Cochrane systematic review found that there was a reduction in the incidence of symptomless DVT in passengers wearing compression stockings, but was not able to assess the effect of wearing stockings on symptomatic DVT, pulmonary embolism (PE) or death, as no such events occurred in the trials [Clarke, 2021].
  • There are no data from randomized trials on the use of pharmacological prophylaxis for the prevention of travel-related VTE. However, the British and American guidelines above, as well as the Scottish Intercollegiate Guidelines Network (SIGN) guideline Prevention and management of venous thromboembolism [SIGN, 2014] advise that in people deemed to be at high risk of travel-related VTE, prophylactic LMWH administered as a single dose subcutaneously on the day of travel could be considered.
Seeking specialist advice before prescribing LMWH
  • CKS recommends seeking specialist advice before prescribing LMWH because the use of LMWH for the prevention of travel-related DVT is unlicensed, there is a lack of evidence about the benefit, and CKS found no clear guidance on the prescribing of LMWH in this situation (for example the choice of preparation, dosage, time of administration, and duration of treatment) in high risk people, particularly if other risk factors are present (for example people with cancer).
Prescribing LMWH
  • The recommendations on prescribing LMWH are pragmatic and based on what CKS considers good clinical practice.

What general advice should I give to all long distance travellers?

  • Offer reassurance that the risk of travel-related deep vein thrombosis (DVT) is very low in healthy people without risk factors. 
  • Advise the person to:
    • Avoid long periods of immobility. Walk around regularly — for example, a regular trip to the bathroom every 2–3 hours. 
    • Choose an aisle seat when feasible.
    • Perform frequent calf muscle exercises.
    • Ensure hand luggage is not placed in a position where it restricts movement of legs and feet. 
    • Wear clothing that is comfortable and loose. 
    • Maintain a normal fluid intake and avoid excessive alcohol consumption. 
  • Seek urgent medical advice (for example, from a local doctor or the nearest accident and emergency department) if they develop the following after the trip:
    • Swollen, painful legs, especially where one is more affected than the other, and/or
    • Breathing difficulties (suggesting pulmonary embolism).
  • Obtain adequate medical insurance before they travel.

Basis for recommendation

These recommendations are based on the 2023 addendum to the guidelines from the British Society for Haematology on Travel-related venous thrombosis [BSH, 2023], the Centers for Disease Control and Prevention (CDC) Yellow Book: Health information for international travelers [CDC, 2023], the World Health Organization (WHO) publication International travel and health [WHO, 2019], the Scottish Intercollegiate Guidelines Network (SIGN) guideline Prevention and management of venous thromboembolism [SIGN, 2014], and an expert review article, Annotation: travel and thrombosis [Czuprynska, 2020].

All these sources make it clear there is no evidence that any of these measures prevent travel-related venous thromboembolism (VTE), but that they are reasonable and sensible precautions that are unlikely to cause harm, and which may possibly be of benefit. Advice is pragmatic rather than evidence-based, but is supported by the current guidance and literature.

Aisle seats
  • Compared with aisle seats, window seats in one study were reported to increase the general risk of VTE by 2-fold [Schreijer, 2009]. Aisle seats are reported to have a protective effect, compared with window or middle seats, probably because travellers are freer to move around [Czuprynska, 2020; BSH, 2023; CDC, 2023]. 
Seek urgent medical advice
  • The recommendation to advise people to seek urgent medical advice if symptoms of deep vein thrombosis (DVT) develop after a flight is based on what CKS considers to be good clinical practice.
Travel insurance
  • The WHO recommends that all travellers should be strongly advised to seek comprehensive travel insurance [WHO, 2019].  

How should I manage a person with a joint replacement or fracture?

  • For people who have had a hip or knee replacement:
    • Advise them to check with their orthopaedic surgeon, airline and insurance company before planning a flight of any duration after hip or knee replacement, as the advice given may vary.
  • For people with a fracture in a plaster cast:
    • Advise people that airlines usually restrict air travel on short flights (less than 2 hours) for the first 24 hours after a cast has been fitted, and for 48 hours for longer flights (over 2 hours).
    • If air travel is essential before these limits, airlines usually require the cast to be split along its full length before travel. Where pneumatic splints are used, some air should be released to allow for gas expansion at altitude. Patients should contact their treating specialist for advice.
      • Arrangements should be made to have the cast replaced once at the destination. 

Basis for recommendation

Air travel after hip or knee joint replacement
  • This recommendation is largely based on a UK based study, which found there is no consensus on air travel following hip and knee replacements, and that patients are likely to be given very variable advice [Oputa, 2023]. 
    • Advice given by orthopaedic surgeons regarding how long to avoid flying varied between 14 and 180 days, with a median of 45 days for short-haul flights and 90 days for long-haul flights, even for people with no risk factors for venous thromboembolism (VTE), and a median of 90 days for both short and long-haul flights in people with risk factors.
    • Insurance companies had varying restrictions, including requirements for certification and patient screening, and some had periods of time after surgery where cover would not be provided ranging from 6 weeks to 2 years.
    • Some airlines also had restrictions or requirements for passengers flying after hip or knee replacement, mostly up to 2 weeks after surgery, although two airlines required certification of fitness to fly, but without specifying the time period for which this was needed.
  • Joint replacement surgery is a risk factor for deep vein thrombosis (DVT) [NICE, 2019]. Given long-haul travel is also a risk factor, it makes sense to advise avoiding these risks being additive for some period of time. However, like the authors of the study above, CKS found no evidence or guidance relating to how long this period of time should be. Given the wide variety of advice given, CKS considers it to be prudent for a primary care provider to recommend a patient take advice from their surgeon, airline and insurance company.
Air travel with a plaster cast
  • These recommendations are based on health information for passengers given by the Civil Aviation Authority (CAA) [CAA, 2023].

What advice should I give pregnant women about deep vein thrombosis and travel?

  • For women who are pregnant, no special measures to prevent deep vein thrombosis (DVT) are required for travel of less than 4 hours.
  • For travel of 4 hours or more, advise pregnant women with no additional risk factors for DVT:
  • For travel of 4 hours or more, advise pregnant women with additional risk factors for DVT, and women who have had a baby in the past 6 weeks:

Basis for recommendation

These recommendations are based on the 2023 addendum to the guidelines from the British Society for Haematology on Travel-related venous thrombosis [BSH, 2023], the American Society of Hematology 2018 guidelines for management of venous thromboembolism: prophylaxis for hospitalized and nonhospitalized medical patients [Schünemann, 2018], the Centers for Disease Control and Prevention (CDC) Yellow Book: Health information for international travelers [CDC, 2023], and an expert review article, Annotation: travel and thrombosis [Czuprynska, 2020].

  • CKS notes that these recommendations differ from advice from the Royal College of Obstetricians and Gynaecologists (RCOG) in the opinion paper Air travel and pregnancy [RCOG, 2013], their patient information leaflet Information for you: Air travel and pregnancy [RCOG, 2022], and the Green-top guideline Reducing the risk of venous thromboembolism during pregnancy and the puerperium [RCOG, 2015]. These resources from the RCOG recommend that all pregnant women should use properly fitted graduated compression stockings for journeys of more than 4 hours, and that those with additional risk factors should be assessed for low molecular weight heparin (LMWH) before and for a few days after the trip.
  • The British Society for Haematology and American Society of Hematology guidelines consider pregnant women with no additional risk factors to be at low risk of travel-related deep vein thrombosis (DVT) and no specific measures are advised, unless a pregnant woman has an additional risk factor for DVT, in which case she should be advised to take additional measures (pharmacological thromboprophylaxis and/or compression stockings) [Schünemann, 2018; BSH, 2023]. Both guidelines consider postpartum women to be in the high risk category.
  • These two guidelines are more recent than the 2015 RCOG Green-top guideline and 2013 opinion paper (on which the patient information leaflet states it is based). In addition, the RCOG patient information suggests that a pregnant woman will need to obtain stockings from her doctor or midwife to ensure a correct fit, whereas information from the NHS Business Services Authority Electronic drug tariff suggests that stockings cannot be prescribed on the NHS for this indication [NHSBSA, 2023]. For these reasons, the recommendations in this section follow the guidelines from the British Society for Haematology and American Society of Hematology.

How should I manage a person with a recent deep vein thrombosis planning long-haul travel?

  • If the person has a new diagnosis of deep vein thrombosis (DVT) or pulmonary embolism, it is usually advisable to delay air travel for 2 weeks. If travel is unavoidable, seek specialist advice.
  • If the person has been taking anticoagulants for 2 weeks or more:
    • Ensure they are stable on their anticoagulant.
    • Reassure them that they are at low risk of developing a further thrombosis.
    • Provide advice on general measures to reduce the risk of travel-related DVT.

Basis for recommendation

These recommendations are based on expert opinion in the British Thoracic Society (BTS) Clinical statement on air travel for passengers with respiratory disease [Coker, 2022], and the Medical Manual for Aviation from the International Air Transport Association (IATA) [IATA, 2023]. The 2023 Addendum to guidelines on travel-related thrombosis from the British Society for Haematology includes only people with previous deep vein thrombosis (DVT) who are no longer on anticoagulants in the risk group for whom graduated compression stockings should be considered, so the recommendation to consider prescribing these in this situation has been removed [BSH, 2023].

What advice should I give about graduated compression stockings?

  • Graduated compression stockings are not available on prescription for the sole indication of preventing travel-related DVT. However, they can be prescribed for people with the following indications:
    • Class 1 stockings (compression at the ankle 14–17 mmHg) for:
      • Superficial or early varicose veins.
      • Varicose veins during pregnancy.
    • Class 2 stockings (compression at the ankle 18–24 mmHg) for:
      • Varicose veins of medium severity.
      • Treatment and prevention of recurrence of leg ulcers.
      • Mild oedema.
      • Varicose veins during pregnancy.
    • Class 3 stockings (compression at the ankle 25–35 mmHg) for:
      • Gross varicose veins.
      • Post-thrombotic venous insufficiency.
      • Gross oedema.
      • Treatment and prevention of recurrence of leg ulcers.
    • For people who require a pair of class 1 graduated compression stockings (with a cost of two prescription charges) who are not exempt from prescription charges, advise that it might be cheaper to buy proprietary flight socks over-the-counter.
  • Proprietary flight socks are widely available from pharmacies, airports, and many retail outlets.
    • They provide a compression of 14–17 mmHg at the ankle (equivalent to class 1 stockings). However, flight socks with higher ratings (18–21 mmHg, similar to class 2 stockings) are also available.
    • Stress the importance of ensuring that the socks are correctly fitted to provide adequate compression.
      • This is particularly important in people with varicose veins, in whom there may be an increased risk of superficial thrombophlebitis.
    • If in doubt, advise the person to seek advice from an appropriate healthcare professional (for example a pharmacist).
  • Measure the ankle-brachial pressure index (ABPI) in both legs using a Doppler machine if the person has symptoms of arterial disease. If the ABPI is less than 0.8, compression stockings are contraindicated.
  • For further information on the use of compression stockings, see the CKS topic on Compression stockings.

Basis for recommendation

These recommendations are based on the NHS Business Services Authority (NHSBSA) NHS electronic drug tariff [NHSBSA, 2023], and a randomized controlled trial Frequency and prevention of symptomless deep-vein thrombosis in long-haul flights [Scurr, 2001]. CKS found no guidance on the strength of stockings to be used, but most commercially available flight socks are equivalent to Class 1 stockings (14–17 mmHg at the ankle), and stockings used to prevent venous thromboembolism (VTE) in other settings are of this level [NICE, 2019].

Varicose veins and increased risk of superficial thrombophlebitis
  • The recommendation to ensure stockings are correctly fitted is based on case reports of people with varicose veins developing superficial thrombophlebitis whilst wearing compression stockings during long-haul flights [Scurr, 2001]. A Cochrane review in 2021, Compression stockings for preventing deep vein thrombosis in airline passengers,  found there were no reports of adverse effects from wearing stockings in any other trials [Clarke, 2021].
  • Do not recommend aspirin for the prevention of travel-related deep vein thrombosis.
  • People already taking aspirin (for primary or secondary prevention of cardiovascular disease) should not increase their dose.
    • If low molecular weight heparin is prescribed, aspirin should not be discontinued without specialist advice.

Basis for recommendation

These recommendations are based on the World Health Organization (WHO) document International travel and health [WHO, 2019], the 2023 addendum to the guidelines from the British Society for Haematology on Travel-related venous thrombosis [BSH, 2023], and the Centers for Disease Control and Prevention (CDC) Yellow book: Deep vein thrombosis and pulmonary embolism [CDC, 2023].

Use of low-dose aspirin
  • The WHO advises that as there is a clear risk of significant side effects and absence of clear evidence of benefit, and passengers should be advised not to use aspirin specifically for the prevention of travel-related deep vein thrombosis (DVT) [WHO, 2019].  
  • Guidance concurs that where pharmacological prophylaxis is indicated, anticoagulants as opposed to antiplatelets are recommended, based on the observation that in other clinical scenarios they provide more effective thromboprophylaxis [Schünemann, 2018; BSH, 2023; CDC, 2023].
  • The guideline from the American Society of Hematology 2018 guidelines for the management of venous thromboembolism: prophylaxis for hospitalized and nonhospitalized medical patients includes a conditional recommendation for the use of aspirin for prophylaxis only where neither stockings or low molecular weight heparin (LMWH) are feasible, based on very low certainty evidence [Schünemann, 2018].
For people already prescribed aspirin for cardiovascular protection
  • The recommendation to advise people not to increase the dose of aspirin if they are already taking it for cardiovascular protection is pragmatic, as:
    • There is no clear evidence of benefit in taking aspirin for prevention of travel-related DVT.
    • Increasing the dose increases the risk of adverse effects.
    • The optimal dose range of aspirin for cardiovascular protection is 75–100 mg. For more information see the CKS topic on Antiplatelet treatment.
  • CKS found no guidance on managing low-dose aspirin therapy for these people if low molecular weight heparin (LMWH) is indicated. Feedback from CKS expert reviewers generally indicated that aspirin for cardiovascular protection should be continued, taking into account the increased risk of bleeding. Consequently, CKS advises seeking specialist advice when LMWH is indicated for people prescribed aspirin for cardiovascular protection.

Supporting evidence

This CKS topic is largely based on the 2023 addendum to the guidelines from the British Society for Haematology on Travel-related venous thrombosis [BSH, 2023], the American Society of Hematology 2018 guidelines for management of venous thromboembolism: prophylaxis for hospitalized and nonhospitalized medical patients [Schünemann, 2018], the Centers for Disease Control and Prevention (CDC) Yellow Book: Health information for international travelers [CDC, 2023], the World Health Organization (WHO) publication International travel and health [WHO, 2019], a Cochrane systematic review Compression stockings for preventing deep vein thrombosis in airline passengers [Clarke, 2021], and an expert review article, Annotation: travel and thrombosis [Czuprynska, 2020]. The rationale for individual recommendations is outlined in the relevant basis for recommendation sections of the topic.

How this topic was developed

This section briefly describes the processes used in developing and updating this topic. Further details on the full process can be found in the About Us section and on the Clarity Informatics website.

Search strategy

A literature search was conducted for guidelines and systematic reviews on primary care management of DVT in travellers.

Search dates

July 2018 - November 2023

Key search terms

The terms listed below are the core search terms that were used for EBSCO MEDLINE (searched 24th July 2018). These terms were combined with search filters for systematic reviews and guidelines in EBSCO MEDLINE. The strategy was adapted for The Cochrane Library databases. 

S10 S5 AND S9

S9 S6 OR S7 OR S8

S8 AB ( travel* or long-haul OR flying or air or airline or aviation or flight* or journey or journeys ) OR TI ( travel* or long-haul OR flying or air or airline or aviation or flight* or journey or journeys ) 

S7 (MH "Aircraft+") 

S6 (MH "Travel+") 

S5 S1 OR S2 OR S3 OR S4

S4 AB ( venous thromboembolism OR VTE or deep vein thrombosis OR DVT or venous thrombosis OR pulmonary embolism ) OR TI ( venous thromboembolism OR VTE or deep vein thrombosis OR DVT or venous thrombosis OR pulmonary embolism ) 

S3 (MH "Pulmonary Embolism+")

S2 (MH "Venous Thrombosis+") 

S1 (MH "Venous Thromboembolism") 

Sources of guidelines

Sources of systematic reviews and meta-analyses

  • The Cochrane Library:
    • Systematic reviews
    • Protocols
    • Database of Abstracts of Reviews of Effects
  • Medline (with systematic review filter)
  • EMBASE (with systematic review filter)

Sources of health technology assessments and economic appraisals

Sources of randomized controlled trials

  • The Cochrane Library:
    • Central Register of Controlled Trials
  • Medline (with randomized controlled trial filter)
  • EMBASE (with randomized controlled trial filter)

Sources of evidence based reviews and evidence summaries

Sources of national policy

Patient experiences

Sources of medicines information

The following sources are used by CKS pharmacists and are not necessarily searched by CKS information specialists for all topics. Some of these resources are not freely available and require subscriptions to access content.

Stakeholder engagement

Our policy

The external review process is an essential part of CKS topic development. Consultation with a wide range of stakeholders provides quality assurance of the topic in terms of:

  • Clinical accuracy.
  • Consistency with other providers of clinical knowledge for primary care.
  • Accuracy of implementation of national guidance (in particular NICE guidelines).
  • Usability.

Principles of the consultation process

  • The process is inclusive and any individual may participate.
  • To participate, an individual must declare whether they have any competing interests or not. If they do not declare whether or not they have competing interests, their comments will not be considered.
  • Comments received after the deadline will be considered, but they may not be acted upon before the clinical topic is issued onto the website.
  • Comments are accepted in any format that is convenient to the reviewer, although an electronic format is encouraged.
  • External reviewers are not paid for commenting on the draft topics.
  • Discussion with an individual or an organization about the CKS response to their comments is only undertaken in exceptional circumstances (at the discretion of the Clinical Editor or Editorial Steering Group).
  • All reviewers are thanked and offered a letter acknowledging their contribution for the purposes of appraisal/revalidation.
  • All reviewers are invited to be acknowledged on the website. All reviewers are given the opportunity to feedback about the external review process, enabling improvements to be made where appropriate.

Stakeholders

  • Key stakeholders identified by the CKS team are invited to comment on draft CKS topics. Individuals and organizations can also register an interest to feedback on a specific topic, or topics in a particular clinical area, through the Getting involved section of the Clarity Informatics website.
  • Stakeholders identified from the following groups are invited to review draft topics:
    • Experts in the topic area.
    • Professional organizations and societies (for example, Royal Colleges).
    • Patient organizations, Clarity has established close links with groups such as Age UK and the Alzheimer’s Society specifically for their input into new topic development, review of current topic content and advice on relevant areas of expert knowledge.
    • Guideline development groups where the topic is an implementation of a guideline.
    • The British National Formulary team.
    • The editorial team that develop MeReC Publications.
  • Reviewers are provided with clear instructions about what to review, what comments are particularly helpful, how to submit comments, and declaring interests.

Patient engagement

Clarity Informatics has enlisted the support and involvement of patients and lay persons at all stages in the process of creating the content which include:

  • Topic selection
  • Scoping of topic
  • Selection of clinical scenarios
  • First draft internal review
  • Second draft internal review
  • External review
  • Final draft and pre-publication

Our lay and patient involvement includes membership on the editorial steering group, contacting expert patient groups, organizations and individuals.

Evidence exclusion criteria

Our policy

Scoping a literature search, and reviewing the evidence for CKS is a methodical and systematic process that is carried out by the lead clinical author for each topic. Relevant evidence is gathered in order that the clinical author can make fully informed decisions and recommendations. It is important to note that some evidence may be excluded for a variety of reasons. These reasons may be applied across all CKS topics or may be specific to a given topic.

Studies identified during literature searches are reviewed to identify the most appropriate information to author a CKS topic, ensuring any recommendations are based on the best evidence. We use the principles of the GRADE and PICOT approaches to assess the quality of published research. We use the principles of AGREE II to assess the quality of published guidelines.

Standard exclusions for scoping literature:

  • Animal studies
  • Original research is not written in English

Possible exclusions for reviewed literature:

  • Sample size too small or study underpowered
  • Bias evident or promotional literature
  • Population not relevant
  • Intervention/treatment not relevant
  • Outcomes not relevant
  • Outcomes have no clear evidence of clinical effectiveness
  • Setting not relevant
  • Not relevant to UK
  • Incorrect study type
  • Review article
  • Duplicate reference

Organizational, behavioural and financial barriers

Our policy

The CKS literature searches take into consideration the following concepts, which are discussed at the initial scoping of the topic.

  • Feasibility
    • Studies are selected depending on whether the intervention under investigation is available in the NHS and can be practically and safely undertaken in primary care.
  • Organizational and Financial Impact Analysis
  • Studies are selected and evaluated on whether the intervention under investigations may have an impact on local clinical service provision or national impact on cost for the NHS. The principles of clinical budget impact analysis are adhered to, evaluated and recorded by the author. The following factors are considered when making this assessment and analysis.
    • Eligible population
    • Current interventions
    • Likely uptake of new intervention or recommendation
    • Cost of the current or new intervention mix
    • Impact on other costs
    • Condition-related costs
    • In-direct costs and service impacts
    • Time dependencies
  • Cost-effectiveness or cost-benefit analysis studies are identified where available. 

We also evaluate and include evidence from NICE accredited sources which provide economic evaluations of recommendations, such as NICE guidelines. When a recommended action may not be possible because of resource constraints, this is explicitly indicated to healthcare professionals by the wording of the CKS recommendation.

Declarations of interest

Our policy

Clarity Informatics requests that all those involved in the writing and reviewing of topics, and those involved in the external review process to declare any competing interests. Signed copies are securely held by Clarity Informatics and are available on request with the permission of the individual. A copy of the declaration of interest form which participants are asked to complete annually is also available on request. A brief outline of the declarations of interest policy is described here and full details of the policy is available on the Clarity Informatics website. Declarations of interests of the authors are not routinely published, however competing interests of all those involved in the topic update or development are listed below. Competing interests include:

  • Personal financial interests
  • Personal family interest
  • Personal non-financial interest
  • Non-personal financial gain or benefit

Although particular attention is given to interests that could result in financial gains or losses for the individual, competing interests may also arise from academic competition or for political, personal, religious, and reputational reasons. An individual is not obliged to seek out knowledge of work done for, or on behalf of, the healthcare industry within the departments for which they are responsible if they would not normally expect to be informed.

Who should declare competing interests?

Any individual (or organization) involved in developing, reviewing, or commenting on clinical content, particularly the recommendations should declare competing interests. This includes the authoring team members, expert advisers, external reviewers of draft topics, individuals providing feedback on published topics, and Editorial Steering Group members. Declarations of interest are completed annually for authoring team and editorial steering group members, and are completed at the start of the topic update and development process for external stakeholders.

Competing interests declared for this topic:

None.

References

  • BMJ Best Practice (2023) Deep vein thrombosis. BMJ Publishing Group. https://bestpractice.bmj.com
  • BSH (2023) Travel-related venous thrombosis. BSH Guideline. Addendum 17 April 2023. British Society for Haematology. https://b-s-h.org.uk [Free Full-text]
  • CAA (2023) Surgical conditions: Information for health professionals on assessing fitness to fly. UK Civil Aviation Authority. https://www.caa.co.uk [Free Full-text]
  • CDC (2023) Deep vein thrombosis & pulmonary embolism. CDC Yellow Book 2024. Centers for Disease Control and Prevention. https://wwwnc.cdc.gov [Free Full-text]
  • Clarke, M.J., Broderick, C., Hopewell, S., et al. (2021) Compression stockings for preventing deep vein thrombosis in airline passengers (Cochrane Review). Issue 4. John Wiley & Sons, Ltd. http://www.cochranelibrary.com [Free Full-text]
  • Coker, R.K., Armstrong, A., Church, A.C., et al. (2022) BTS Clinical statement on air travel for passengers with respiratory disease. Thorax 77(4), 329-250. [Abstract] [Free Full-text]
  • Czuprynska, J. and Arya, R. (2020) Annotation: travel and thrombosis. British Journal of Haematology 188(6), 838-843. [Abstract] [Free Full-text]
  • IATA (2023) Medical Manual for Aviation. International Air Transport Association. https://www.iata.org [Free Full-text]
  • Kuipers, S., Cannegieter, S.C., Middeldorp, S., et al. (2007) The absolute risk of venous thrombosis after air travel: a cohort study of 8,755 employees of international organisations. PLoS Medicine 4(9), e290. [Abstract]
  • McKerrow Johnson, I., Shatzel, J., Olsen, S., et al. (2022) Travel-associated venous thromboembolism. Wilderness & Environmental Medicine 33(2), 169-178. [Abstract] [Free Full-text]
  • NHSBSA (2023) The November 2023 electronic drug tariff. NHS Business Services Authority. https://www.drugtariff.nhsbsa.nhs.uk [Free Full-text]
  • NICE (2019) Venous thromboembolism in over 16s: reducing the risk of hospital-acquired deep vein thrombosis or pulmonary embolism [NG89]. National Institute of Health and Care Excellence. http://www.nice.org.uk [Free Full-text]
  • Oputa, T.J., Patil, A., Amissah-Arthur, J.B., et al. (2023) Is there a consensus on air travel following hip and knee arthroplasty? Cureus 15(8), e43814. [Abstract] [Free Full-text]
  • RCOG (2013) Air travel and pregnancy. Royal College of Obstetricians & Gynaecologists. https://www.rcog.org.uk [Free Full-text]
  • RCOG (2015) Reducing the risk of venous thromboembolism during pregnancy and the puerperium. Green top guideline No. 37a. Royal College of Obstetricians and Gynaecologist. http://www.rcog.org.uk [Free Full-text]
  • RCOG (2022) Information for you: Air travel and pregnancy. Royal College of Obstetricians & Gynaecologists. https://www.rcog.org.uk [Free Full-text]
  • Schreijer, A.J.M., Cannegeiter, S.C., Doggen, C.J.M. and Rosendaal, F.R. (2009) The effect of flight-related behaviour on the risk of venous thrombosis after air travel. British Journal of Haematology 144(3), 425-429. [Abstract] [Free Full-text]
  • Schünemann, H.J., Cushman, M., Burnett, A.E., et al. (2018) American Society of Hematology 2018 guidelines for management of venous thromboembolism: prophylaxis for hospitalized and nonhospitalized medical patients. Blood Advances 2(22), 3198-3225. [Abstract] [Free Full-text]
  • Scurr, J.H., Machin, S.J., Bailey-King, S., et al. (2001) Frequency and prevention of symptomless deep-vein thrombosis in long-haul flights: a randomised trial. Lancet 357(9267), 1485-1489. [Abstract]
  • SIGN (2014) Prevention and management of venous thromboembolism. Scottish Intercollegiate Guidelines Network. http://www.sign.ac.uk [Free Full-text]
  • WHO (2007) WHO research into global hazards of travel (WRIGHT) project. Final report of phase 1. World Health Organization. http://www.who.int [Free Full-text]
  • WHO (2019) International travel and health. Situation as on 1 January 2012 - Updates 2019. World Health Organization. https://www.who.int [Free Full-text]
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