09/12/2015 06:40 GMT | Updated 08/12/2016 05:12 GMT

Travellers Thrombosis

The recent tragic death of All Black rugby legend Jonah Lomu from a reported pulmonary embolus after a long haul flight is a timely reminder of one of the health risks of travel and particularly sad for those of us who saw the man in his pomp, destroying opponents on the rugby field in the 1990's.

A pulmonary embolus is a clot which forms usually in the leg veins after prolonged immobility - in rare but serious cases, this clot can dislodge from the legs vein and travel in the bloodstream until it sticks in the arteries to the lung - in bad cases this can be instantly fatal.

The condition of 'travel related thrombosis' is not new - deaths from pulmonary embolus had been reported during WW2 after long periods of immobility in Air Raid Shelters and the first written reports of DVT (or clots in the leg veins) were published in the 1950's. However, it was not until the expansion in long haul airline flights during the 1980's and 1990's that the incidence of thrombosis related events began to make an impact in the popular press.

The phenomenon was initially dubbed 'economy class syndrome' because it was thought that cramped conditions in packed aircraft were more likely to cause a person to have a DVT than in the more spacious accommodation towards the front of the plane. In fact, as with so many issues around travel related thrombosis, the actual increased risk of an economy seat vs a first class seat is quite difficult to prove. The reason for this is that fortunately the risk of getting a DVT or pulmonary embolus after the flight is actually quite low - it's so low, in fact, that calculating and proving the actual risk in numerical terms has still not been done, because the statistical study would involve such a large number of people it is practically impossible to achieve.

Various factors such as low cabin pressure and low humidity have been found to have influences over the way in which blood clots in the body, and some associations between frequency of long haul flight and clotting events have been noted, but in statistical terms, the absolute risks have not yet been quantified.

This of course is very interesting to the academic, but of limited value to the travelling public, who want to know the answers to two basic questions:

1. What is my risk of DVT / PE?

2. What can I do to reduce it?

The good news is that in healthy people with no known risk factors, the risk of DVT / PE is actually very low - estimates vary from 1 in 200,000 to 1 in 70,000, but these are really no more than educated guesses.

Having a known risk factor can increase the dangers substantially - known risks include obesity, active cancer, heavy smoking, history of previous DVT or a known condition which makes an individual's blood more likely to clot (such as the Leiden V mutation) or any serious chronic health complaint - sadly Jonah Lomu was known to suffer from kidney failure and to be on regular haemodialysis - this may have played a part in his untimely death.

The extent to which these factors increase risk is still the matter for intense debate - some experts suggest that in known high risk patients the risk may be as high as 1 in 90.

For the vast majority of patients there is little cause for concern - simply walking around the cabin intermittently should be sufficient to ward off clots in the legs. For patients known to be at higher risk, the use of compression stockings or even injections of anti-coagulant drugs such as heparin, will probably reduce the hazards significantly, but needs to be assessed and prescribed by a suitably qualified health professional.