New Review Finds Risk of VTE From Flying is Low.

February 23, 2009 (Washington, DC) - The risk of venous thromboembolism (VTE) associated with air travel is low, a new review on medical issues associated with commercial flights concludes [1].

Senior author of the paper, Dr Mark Gendreau (Lahey Clinic Medical Center, Burlington, MA), told heartwire that "despite the hysteria that was created by the association of deep vein thrombosis [DVT] with flying a few years ago, there has been a lot of work recently that shows the risk is relatively low." The research, by Dr Danielle Silverman (Washington Hospital Center, Washington, DC) and Gendreau, was published online in the Lancet on February 19, 2009.

For the review, Silverman and Gendreau searched papers over the past 10 years, and they discuss many other issues, such as in-flight medical events, medical fitness for air travel, jet lag, infectious diseases, and the risks of exposure from cosmic radiation.

DVT/VTE: Immobility is the Biggest Culprit.

Gendreau said the rate of DVT in one study of 9000 business travelers over four and a half years was one case for every 4500 flights. Although studies overall do show an association between VTE and long-haul flights, with risks of up to fourfold, results vary depending on the study methods, he said.

One systematic review calculated a pooled odds ratio of 1.59 for VTE from case-control studies and a relative risk of 2.93 from several prospective controlled cohort studies. These results are consistent with another population-based study (MEGA) that showed an OR of 1.7. The risk of pulmonary embolism (PE) is "even less," he notes.

Gendreau points out that some facts with regard to VTE/DVT associated with air travel are now well established. Risk increases with greater number of flights within a short space of time, certain risk factors "dramatically increase the risk," business-class vs economy class travel has no effect on VTE incidence, and "immobility comes through, time and time again, as probably the biggest culprit," with the highest incidence of VTE seen in those in seats not on the aisle, he says.

Risk factors that are known to increase the risk of VTE associated with flying include: obesity, recent surgery, use of oral contraceptives--which increased the risk 16-fold in one study--and presence of factor V Leiden, which increased the risk 14-fold. One question that has arisen, says Gendreau, is whether frequent business travelers should be screened for factor V Leiden.

Recommendations to reduce the risk of developing VTE during air travel "are based more on common sense than on evidence," say the researchers; they include being well-hydrated, reducing alcohol and caffeine consumption, changing positions or walking throughout the cabin, and doing periodic calf-muscle exercises to reduce venous stasis. Use of graduated compression stockings with an ankle pressure of 17 to 30 mm Hg can reduce risk, and Gendreau said, "We recommend use of [such] stockings in any individual prone to immobility."

With regard to guidelines on the use of anticoagulant thromboprophylaxis, he says, "These are all over the place," with some recommending aspirin, some nothing, and some low-molecular-weight heparin. Gendreau says surveys have shown that "a lot of physicians still say to people 'take an aspirin,' but the studies don't bear this out. Nobody is safe on an aspirin alone."

Overall, use of physical and pharmacological thromboprophylaxis should be based on individual risk assessment, he and Silverman conclude.

In-Flight Medical Events Increasing, But Most Are Minor.

With regard to in-flight medical events, Silverman and Gendreau note that while the numbers of these are increasing due to more and more air travelers having preexisting medical conditions, the majority "are minor."

The studies don't bear this out. Nobody is safe on an aspirin alone. Cardiac, neurological, and respiratory complaints are the most serious, and while passengers older than 70 years have the highest rates of these events, the mean age of such passengers is 44 years for men and 49 years for women .

The researchers present several tables in their paper, including: response to and guidelines for initial management of in-flight medical events; different methods to assess whether patients may require in-flight oxygen; and contraindications to commercial air travel. The latter include a number of cardiac and neurologic conditions: MI seven to 10 days before, unstable angina, CABG surgery 10 to 14 days before, decompensated heart failure, uncontrolled dysrhythmia, and stroke five to 10 days beforehand.

"Passengers should [also] be able to walk a distance of 50 m and climb one flight of stairs without angina or severe shortness of breath" before being allowed to fly, the researchers add.

Gendreau told heartwire there has been little study of specific heart conditions and how such people fare during air travel. There have been "a few studies" looking at travel after MI, but none on how patients with heart failure do, he noted. He pointed out, however, that studies of those with chronic HF who live in elevated areas suggest that up to 2500 m in altitude--which is close to cabin pressure--is okay, but that above this there can be problems. But more research is needed, he says.

1. Silverman D and Gendreau M. Medical issues associated with commercial flights. Lancet 2009; DOI:10.1016/So140-6736(09)60209-9. Available at: http://www.thelancet.com.