Sanity checking airplane advice re DVT: walk every hour, 2-3 hours? OK to sleep?

Question

Long plane flights carry a risk of DVT. It is easy to find advice on preventing DVT by being active:

• CDC says "walk around every 2-3 hours" and mentions that you should do this when traveling by car also. This article also mentions that you are at higher risk of DVT if you have active cancer or are receiving chemotherapy. It recommends compression socks, too.
• Mayo clinic says "If you're traveling a long distance by car, stop every hour or so and walk around. If you're on a plane, stand or walk occasionally."
• WebMD says "If you are traveling by car, stop every hour or so. Get out and walk around for a few minutes. If you are traveling by bus, train, or plane, get out of your seat and walk up and down the aisle every hour or so. "

None of these mention the possibility of sleeping on the plane. Are they suggesting you should not sleep? We all lie down for 8 hours or so every night, and yes, we can toss and turn a little more freely in a real bed, but I find it hard to imagine this advice means "don't sleep, stay awake so you can walk around a lot."

Further, there is a big difference between "every hour" and "every two or three hours" - and that's not counting good old "occasionally". None indicate whether wearing compression socks means it's safer to go for a longer interval between walks.

So, if a person with at least some risk factor for DVT is going on a long (11 hrs) flight, wearing compression socks, in business with a lie-flat bed, is lying flat in that bed and sleeping actually as dangerous as sitting awake in economy? What about a 13 hour flight in economy, still with the socks, is sleeping for part of that flight dangerous? This is normal sleep without the aid of Ambien or even alcohol, and thus there will be tossing and turning.

Why I'm asking: I have those flights in my future and a doctor told me emphatically to get up "every hour" on the plane and walk around. I didn't think to ask about sleep time, and I have no problem getting up once an hour while awake. But this same doctor knows that I drive two to three hours to and from my appointments, and has never said to pull over the car and walk every hour during a drive. Yet DVT isn't related to altitude, just to sitting still. So I feel the "every hour" is probably a little overcareful. But I am interested in what the studies show, and specifically on the matter of sleeping, in business and in economy. I am not asking for a diagnosis or to override my doctor's advice. I just want to sanity check it since we didn't discuss economy vs business and lying down to sleep. A study showing the effects of following various advice regimens (and that includes overnight flights where people slept or stayed awake) would be great.

Answer 1

Unless you have risk factors, don't worry too much

Dr Gordon Guyatt, chair of the panel, said: "There has been a significant push in health care to administer DVT prevention for every patient, regardless of risk.
"As a result, many patients are receiving unnecessary therapies that provide little benefit and could have adverse effects."

^{Stephen Adams: DVT risk raised by sitting in the window seat. Telegraph.co.uk. 7. February 2012}

Wearing GCS (graduated compression stockings) is actually discouraged for patients without risk factors.

The panel noted that the absolute risk of developing a DVT or a resultant PE due to a long flight - collectively known as venous thromboembolism (VTE) - was "very small".
One person in 4,600 experiences a symptomatic VTE in a month following a flight of four hours or longer, and only a minority of those are serious.

^ibid

Basically, stay well hydrated, this will make you visit the toilet twice in 12 hours and you have the necessary movement.

Get up and walk from time to time, flex your heels, however small the space you can always raise and lower your feet and exercise your calves. Stay well hydrated.

^{Telegraph.co.uk.
Note: The title is misleading: The article basically concludes that for patients without risk factors, flight socks and aspirin won't further decrease risk of the DVT. (Prof Gradwell added that people most at risk from developing deep vein thrombosis (DVT) were those who have a predisposition to blood clots because of existing medical conditions. In these cases, individuals should consult their GPs, and might benefit from specially fitted compression stockings, or be told to take an extra dose of aspirin, he said.)}

If you do have risk factors, wear graduated compression stockings and do exercise your feat, and also consult your doctor

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).

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.

^{Clarke, Mike J; Broderick, Cathryn; Hopewell, Sally; Juszczak, Ed; Eisinga, Anne: Compression stockings for preventing deep vein thrombosis in airline passengers. Cochrane Database of Systematic Reviews. 2016,9. John Wiley & Sons, Ltd CD004002 DOI: 10.1002/14651858.CD004002.pub3}

If one has risk factors of DVT, wearing GCS stockings is encouraged.

For travelers on flights of 6 hours or more who have an increased risk for DVT/PE, the ACCP recommends frequent ambulation, calf muscle stretching, sitting in an aisle seat if possible, or the use of below-knee graduated compression stockings (GCS). For long-distance travelers who are not at increased risk for DVT/PE, the guidelines suggest against the use of GCS. In addition, the guidelines suggest against the use of aspirin or anticoagulant therapy to prevent DVT/PE in long-distance travelers. For travelers who are considered to be at particularly high risk for DVT/PE, the use of antithrombotic agents should be considered on an individual basis because the adverse effects may outweigh the benefits.

“Symptomatic DVT/PE is rare in passengers who have returned from long flights; however the association between air travel and DVT/PE is strongest for flights longer than 8 to 10 hours,” said Dr. Crowther. “Most passengers who do develop a DVT/PE after long-distance travel have one or more risk factors.”

^{American College of Chest Physicians New DVT Guidelines: No Evidence to Support Economy Class Syndrome. Oral Contraceptives, Sitting in a Window Seat, Advanced Age, and Pregnancy Increase DVT Risk in Long-distance Travelers. February 7, 2012}

Furthermore, check with your doctor whether anticoagulants are an option.

TL;DR / Conclusion

Although I gave my best efforts, I have not found studies giving absolute numbers how much risk you are at without walking, with walking, without GCS, with GCS and so on.

But: DVT can get nasty in a worst-case-scenario. Getting up every four hours is not such bad an alternative to a bad case of DVT (however unlikely that is) and it’s not like one would enjoy a deep and healthy sleep in a small plane seat anyway.

As for driving: Be the driver. This way, your feet get great exercise (if you’re not driving an automatic). Or play We Will Rock You every hour or so and stomp along.