He recommends putting your compression socks on first thing in the morning because it's the time your legs are less swollen and when your system starts to adapt. If not first thing, you should certainly put them on before your flight.
When it comes to taking them off again, wait until you get to your hotel — or even some hours afterwards to "allow the system to equate again", Shaw says.
"When that occurs, the number of people who do get reduced swelling in the legs goes up quite significantly."
He also had some helpful tips for dealing with swelling if it occurs.
"I've found in the past that some people find it really useful to find a few acupressure points from the big toe and the next toe.
"Getting up and walking around, massaging the feet, those sorts of things are the important things to do."
My dad had a session of acupuncture in Germany too and that seemed to help a bit.
And when it comes to preventing deep vein thrombosis, or just swelling, you need to do more than just put on compression socks and sit back. Shaw recommends getting up and walking around every four hours, if you can, and drinking a litre of water per eight hours of flight.
"I would also recommend doing some feet exercises, up and down, round and round with the ankles just to get the muscles moving and getting the pump of the muscles within the calves moving as well," he says. "That seems to be quite successful."
When buying compression socks, you'll encounter different strengths — and generally speaking, you should get them fitted by a medical professional.
"There are surgical stockings, which I call grade three and these are approximately 28mm through to 32mm of mercury," he says.
"The level most people have, and the ones I have, that I think are totally adequate, are grade one, which is about 18 through to about 22 of mercury in that range.
"They're quite comfortable, you measure them around the calf and the ankle and certain places will actually do this – this allows a graduated pressure to apply to the calf region and that then equates and equalises the pressures on your legs."
Previously, I've had a reader write in who said she got her doctor to prescribe her a blood-thinning injection like heparin before a flight to put her mind at ease over deep vein thrombosis – my dad was also given one by a GP in Germany for our return flight.
However, according to Shaw, this isn't recommended unless you have a history of clotting.
"Because it is a blood thinner and under certain circumstances it could cause issues, it should only be given under medical supervision — but not as a routine. Aspirin also doesn't help much with those long-haul flights.
"Frankly, drugs shouldn't be used and this ridiculous flight water that you can buy at the airport, supposedly to adjust the electrolytes, is just a load of crap."
I hope this advice helps with your next long-haul flight. I certainly found it very informative and will be following it the next time I fly.
Email your questions to askaway@nzherald.co.nz
Eli cannot answer all questions and can't correspond with readers.
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