Every once in a while, a colleague gives a research presentation that knocks your socks off. John Strang, MD, of Kings’ College London, gave one last week that had the reverse effect.
Strang was discussing randomized clinical trials and noting that they are useless for some very important questions (e.g., “Should I ask that nice girl out?”) and unneeded for others (e.g., “Does wearing a parachute when jumping out of the plane actually confer an advantage over the no-parachute control condition?”). But when randomized trials meet the right sort of question, there is no more powerful method for gaining knowledge that can literally be life-saving.
The example Strang gave was that of compression socks and deep vein thrombosis (DVTs) on long haul flights. Also known as “coach class syndrome,” DVTs are a blood clot which forms in the vein when you sit still for hours. Theoretically you can avoid them by getting up regularly and moving around the plane, but, even if you don’t fall asleep, that’s often hard to do on packed flights (and can feel awkward in an age of post-9/11 wariness among flight crews). Compression socks have none of those practical barriers. But do they work?
Dr. Strang pointed out that whether socks prevent DVTs is a perfect clinical trial question because: (a) We really can’t know the answer from naturalistic observations; (b) a trial could find it out with minimal intrusiveness and minimal effort; (c) there is a firm, easily measureable proximal outcome; and (d) the results have real implications rather than being only of theoretical interest.
The randomized trials in this area have been designed such that passengers are examined for DVTs immediately after long haul flights, allowing measurement of asymptomatic DVTs which generally go unnoticed. The most clever of the trials had subjects wear a compression stocking on one leg on the flight out, and on the other leg on the flight home.
The results, as summarized by a Cochrane Collaboration review, are as plain as pikestaff: Of the 50 people (out of over 2,500) who developed a DVT on a long haul flight, all but 3 had been randomly assigned not to wear compression socks. That works out to a risk ratio of 10:1 for not wearing versus wearing flight socks.
The other striking finding is how often DVTs occur (about one in every 50 or so long flights). Even though most of them disappear without incident, I was disturbed to realize that giving that I have boarded airplanes at least 500 times in the past decade, I might very well have had one or more DVTs in the past. That realization, and the fact that one colleague of mine had a confirmed DVT that ended his ability to travel by air and another had an ever worse one that caused a terrifying heart attack during landing was enough for me to put the impressive clinical trial findings to immediate use. I left the Boots pharmacy at Heathrow looking unstylish but feeling safer. I’d advise all our high-flying readers to look at the Cochrane results and consider the same decision.