Ask the Doctor: ‘I’ve booked a long haul flight and worry about developing deep vein thrombosis (DVT) — How can I reduce my chances?’

”I have just booked a trip to Australia to stay with my sister and her family. I have never done such a long flight and am worried about the chances of developing a DVT (I am a smoker, approx. 15 per day). What can I do to reduce my chances of developing a DVT? I have read that aspirin can be taken, should I be asking my doctor to prescribe this for me prior to my trip? Do flight socks work, if so I am happy to wear these. Thank you for your help!”

Answer from Mr Donagh Healy, Consultant Vascular Surgeon, Beacon Hospital.

Travel for longer than 4 – 6 hours, whether it is by air, sea or land, is associated with a small risk of deep vein thrombosis (DVT). About 1 in 2000 people develop a DVT after prolonged travel. Most of these DVTs are found in the first fortnight after the journey.

The risk of DVT after prolonged travel is very low for most people. Most people who do get a DVT have one or more DVT risk factors. It is very rare for someone to develop a DVT after travel if the person had none of the risk factors.

Here are the risk factors that are relevant:

• Recent major surgery
• Active cancer
• Pregnancy
• Advanced age
• Use of oestrogen hormonal treatment (eg. for contraception or HRT)
• Obesity
• Previous DVT
• Family history of DVT

It is not fully clear why people get DVTs after travel. It is probably because of a combination of factors including reduced blood circulation in the legs, the blood becoming slightly thicker (because the coagulation system may be activated) and dehydration. Alcohol is not proven to cause DVTs but might make someone less mobile. Smoking is associated with DVT but is not considered a major risk factor.

There are some general measures that can be taken to reduce the risk of DVT during travel. I recommend that everybody does these simple things:

• Taking a short walk down the aisle every 2-3 hours
• Doing calf muscle exercises while sitting
• Staying well-hydrated

Patients who have one or more DVT risk factors could consider wearing knee-length graduated compression stockings that provide 15-30mmHg of pressure at the ankle. These stockings prevent blood from pooling and are proven to reduce travel associated DVTs. Blood thinning medications are not generally recommended because of the small risk of bleeding and because we do not know how effective they are for this short-term purpose.

However, if a person is at high risk for DVT (for example, they had a DVT before and have other risk factors as well), medication could be considered. There are several medicines that could be used, and a doctor could advise on this.

I would recommend that you take the general measures described above and you could additionally wear graduated compression stockings.

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