DVT: Scare on wheels

It’s the holiday season – over the next few weeks millions of Britons will be setting off in their cars in search of sun and fun.

Which is presumably why the RAC Foundation, ‘the independent body established to take on the role of protecting the interest of the motorist’ (1), chose 7 August to warn people of the danger that they might develop deep-vein thrombosis (DVT) after long-haul car and coach journeys.

RAC Foundation spokesman Kevin Delaney told me that: ‘If people think that DVT can only occur when sitting in an aeroplane, perhaps they are misleading themselves. People should be aware; when taking long journeys, they should take precautions.’ The Foundation advises passengers to take breaks every two hours, drink water, avoid alcohol before journeys, wear loose clothing, avoid the crossing of legs and ‘massage…feet and lower legs while seated and do seat exercises such as ankle rolls and toe pointing’ (2).

Turning car journeys into sessions in ankle-rolling and toe-pointing will only make them more of an ordeal. What is the basis for the RAC Foundation’s advice?

There has been no firm evidence linking long-haul air travel to DVT – and there is no evidence of a link between blood clots and car travel.

The RAC Foundation quoted a study in 2001 by heart expert Emile Ferrari at the Pasteur Hospital in Nice, which found that blood clot risk was increased by any journey over four hours. Ferrari compared a group of 160 patients admitted for blood clots with 160 patients admitted for some other kind of blood problem, and found that there were four times as many travellers among the blood-clot patients than in the non-clot group (3).

Among the 39 travellers who suffered from a blood clot, 28 had travelled by car, nine by plane and two by train. At the time, Ferrari said that he thought that the risks of road journeys had been overlooked: ‘My gut feeling is that if I had to travel 3000 miles, I would prefer to do it by plane rather than by car. I would think the risk of deep-vein thrombosis for the same distance is much lower by plane.’ (4)

If we look at Ferrari’s empirical evidence rather than his gut feelings, there is little to justify the RAC Foundation’s warning to motorists. Ferrari only surveyed people in hospital with blood problems. It would be unwise to generalise findings of such a small and unusual group to the majority of motorists. According to Dr John Scurr, consultant surgeon at Middlesex and University College Hospitals, London, the risk from air travel mainly affects passengers already at risk (5) – the same is likely to be true for car travel.

Predisposing factors mentioned by a UK House of Lords select committee on DVT included: pregnancy; blood disorders leading to increased clotting tendency; inherited or acquired impairment of blood-clotting mechanisms; some types of cardiovascular disease or insufficiency; recent major surgery or injury, especially to lower limbs or abdomen (6).

Perhaps somebody recovering from major surgery or suffering from an inherited blood disorder would do well to head the RAC Foundation’s warnings – but they are probably already receiving advice from their doctor.

The RAC Foundation’s advice looks less like a sensible dissemination of information than an attempt to promote good behaviour in the car. ‘It may sound like we are preaching at people’, admitted Kevin Delaney. ‘But we all take driving far too lightly, and this is good advice anyway.’ It’s good to keep hydrated, said Delaney – and why not do exercises? ‘People are sitting in cars, they’re not doing much’, he said.

Delaney says that the new advice to drink water may conflict with the advice to drink coffee if you feel tired. He explained how motorists should deal with this contradiction: ‘If you feel tired, you should drink coffee. You have to appreciate what is the greatest risk at that time – if you fall asleep, DVT will not be an issue. But if you are feeling okay and you have a cup of coffee, it will dehydrate you.’

So drink coffee if you are tired, but not otherwise…got it? Don’t cross your legs, don’t drink alcohol the night before, and remember those ankle rolls.

Happy holidays, everyone.

Read on:

spiked-issue: Blood clots

(1) See the RAC Foundation website

(2) The Times (London), 8 August 2002

(3) Blood clots risk ‘for any journey over four hours’, Daily Telegraph, 9 April 2001

(4) Blood clots risk ‘for any journey over four hours’, Daily Telegraph, 9 April 2001

(5) Financial Times, 13 March 2001

(6) Report by the house of lords select committee