In the last few years, there has been increasing interest in whether compression stockings (or 'flight socks') reduce the risk of deep vein thrombosis (DVT; blood clots in the legs) and other circulatory problems in airline passengers. The stockings are worn throughout the flight and are similar to those known to be effective in patients lying in bed after an operation. By applying a gentle pressure, to the ankle in particular, compression stockings help blood to flow. Pressure combined with leg movement helps blood in superficial (surface) veins to move to the deep veins and back to the heart. The blood is then less likely to clot in the deep veins, which could be fatal if the clot moves to the lungs.
Study characteristics and key results
This review included eleven trials (2906 participants) and we were able to combine the data from nine trials with a total of 2637 participants (current to February 2016). Almost half of the participants were randomly assigned to wearing stockings for a flight lasting at least five hours while the other half did not wear stockings.
None of the passengers developed a DVT with symptoms (slowly developing leg pain, swelling and increased temperature) and no serious events (a blood clot in their lungs (pulmonary embolism) or dying) were reported. Passengers were carefully assessed after the flight to detect any problems with the circulation of blood in their legs, even if they had not noticed any problems themselves. Wearing compression stockings resulted in a large reduction in symptomless DVT among airline passengers who were allocated to wear compression stockings compared to those allocated not to wear compression stockings. This difference in symptomless DVT between the two groups is equivalent to a reduction in the risk from a few tens per thousand passengers to two or three per thousand. People who wore stockings had less swelling in their legs (oedema) than those who did not wear them. Fewer passengers developed superficial vein thrombosis when wearing compression stockings than those not wearing stockings. Not all the trials reported on possible problems with wearing stockings but in those that did, the researchers said that the stockings were well-tolerated, without any problems.
Quality of the evidence
High-quality evidence shows that airline passengers wearing compression stockings develop less symptomless DVT and low-quality evidence shows that leg swelling is reduced when compared to not wearing compression stockings. Quality of the evidence was limited by the way that swelling was measured. There is moderate-quality evidence that superficial vein thrombosis may be reduced in passengers who wear compression stockings. We cannot assess the effect of wearing stockings on death, pulmonary embolism or symptomatic DVT because no such events occurred in these trials. Randomised trials to assess these outcomes would need to include a very large number of people.
There is high-quality evidence that airline passengers similar to those in this review can expect a substantial reduction in the incidence of symptomless DVT and low-quality evidence that leg oedema is reduced if they wear compression stockings. Quality was limited by the way that oedema was measured. There is moderate-quality evidence that superficial vein thrombosis may be reduced if passengers wear compression stockings. We cannot assess the effect of wearing stockings on death, pulmonary embolism or symptomatic DVT because no such events occurred in these trials. Randomised trials to assess these outcomes would need to include a very large number of people.
Air travel might increase the risk of deep vein thrombosis (DVT). It has been suggested that wearing compression stockings might reduce this risk. This is an update of the review first published in 2006.
To assess the effects of wearing compression stockings versus not wearing them for preventing DVT in people travelling on flights lasting at least four hours.
For this update the Cochrane Vascular Information Specialist (CIS) searched the Specialised Register (10 February 2016). In addition, the CIS searched the Cochrane Register of Studies (CENTRAL (2016, Issue 1)).
Randomised trials of compression stockings versus no stockings in passengers on flights lasting at least four hours. Trials in which passengers wore a stocking on one leg but not the other, or those comparing stockings and another intervention were also eligible.
Two review authors independently selected trials for inclusion and extracted data. We sought additional information from trialists where necessary.
One new study that fulfilled the inclusion criteria was identified for this update. Eleven randomised trials (n = 2906) were included in this review: nine (n = 2821) compared wearing graduated compression stockings on both legs versus not wearing them; one trial (n = 50) compared wearing graduated compression tights versus not wearing them; and one trial (n = 35) compared wearing a graduated compression stocking on one leg for the outbound flight and on the other leg on the return flight. Eight trials included people judged to be at low or medium risk of developing DVT (n = 1598) and two included high-risk participants (n = 1273). All flights had a duration of more than five hours.
Fifty of 2637 participants with follow-up data available in the trials of wearing compression stockings on both legs had a symptomless DVT; three wore stockings, 47 did not (odds ratio (OR) 0.10, 95% confidence interval (CI) 0.04 to 0.25, P < 0.001; high-quality evidence). There were no symptomless DVTs in three trials. Sixteen of 1804 people developed superficial vein thrombosis, four wore stockings, 12 did not (OR 0.45, 95% CI 0.18 to 1.13, P = 0.09; moderate-quality evidence). No deaths, pulmonary emboli or symptomatic DVTs were reported. Wearing stockings had a significant impact in reducing oedema (mean difference (MD) −4.72, 95% CI −4.91 to −4.52; based on six trials; low-quality evidence). A further two trials showed reduced oedema in the stockings group but could not be included in the meta-analysis as they used different methods to measure oedema. No significant adverse effects were reported.