Up in the air: How real is the risk of DVT?

The jury is still out on just how afraid we should be of economy-class syndrome. JILL MALCOLM looks at the latest research.

I'm a travel writer and in any one year I do a lot of flying. Some flights are short, others are up to 20 hours. Over the years I have learned to be outwardly nonchalant and calm but inwardly, I have never entirely stopped fretting. No matter how many times I have done it and survived, I board each flight with a twinge of dread. I am not a happy flyer.

My first worry is who is going to sit next to me on a long-haul flight? Please don't let them be too fat, too garrulous, loud, boring, overbearing or sneezing. The next phase of anxiety is at takeoff: has the engine been checked? Does the pilot know what he is doing? Are we going in the right direction? Is there enough fuel? Why is no one else aware that the engine is on fire?

Gloomy thoughts keep me well occupied until I can swallow a glass or two of wine or champagne, whichever is on offer, then eat everything that is put in front of me. Then, in a more mellow frame of mind, I pop a sleeping pill and blissfully avoid consciousness for four or five hours.

But on my last long-haul flight to Chile, another worry had emerged and it completely altered my regime. Deep vein thrombosis, dubbed economy-class syndrome, had hit the headlines.

They made alarming reading: Let the Flyer Beware - Long Trips are Killers; One in Ten Flyers Risk Clots; Ashford Hospital records 30 deaths from DVT in three years; Economy-class Syndrome Kills up to 30,000 Travellers a Year.

Lord Graham of Edmonton said he spent a week in hospital fighting a near-fatal blood clot and felt like a ninny. Dr John Scurr, a London vascular surgeon, held a survey and discovered that one in 10 people develops clots, albeit often small ones, on long-haul flights unless they wear elastic stockings.

So on the trip to Chile I drank the plane dry of water but no drop of alcohol passed my lips, I ate modestly, slept not at all and spent a large part of the time furiously paddling my feet. I disembarked in San Diego feeling like a bloated frog with rheumaticy ankles, exhausted but grateful to be alive.

Back home and still syndrome-free, I am now required to write about the condition.

My first discovery when I talked to the experts is that I had taken things a little too earnestly. Medical professionals say they were surprised at the high incidence reported by Scurr and that subsequent research has now demonstrated that it is much lower.

"We think the incidence is significantly lower than 10 per cent," says Dr Rodney Hughes, senior respiratory registrar at Green Lane Hospital, who is spearheading the New Zealand DVT-in-air-travel study programme at Green Lane Hospital.

The Balcaro report, which resulted from a combined study undertaken in several countries, has found the incidence of people developing clots after a long flight is more in the region of 4.7 per cent.

Wilbur Farmilo, vascular surgeon at Middlemore Hospital, says: "When you take into consideration the number of people travelling and the number who suffer effects from the syndrome, the risk is small. And it's not only flying that causes blood clots. Many more people get blood clotting after major surgery. Other forms of travel, where people sit for a long time, can cause it as well."

Its link to long periods of immobility was first noticed during the Second World War, when people spent long nights squeezed into air-raid shelters

"I feel that the risk of long-haul travel and economy-class syndrome should not be over-emphasised," says Farmilo. "But that doesn't mean to say that it should not be taken seriously. People must be made aware that there is a risk and how to minimalise it.

"I think that airlines and travel agencies should take that responsibility if they haven't already. If people are aware of the risk before they travel, they can find out if any condition they have means that they need to take more precautionary measures. The preventive measures are relatively simple for most people and there are few people whose conditions are so high-risk that they should not fly at all."

This, of course, is cold comfort for those already suffering the effects of the syndrome or whose loved ones have died suddenly from lung embolism. Some of the victims are making moves to do something about it.

Roger Chapman, of Wellington solicitors Johnston Lawrence, is working in tandem with Melbourne lawyers to process claims against airlines for about 20 New Zealanders who have suffered the death of a relative or their own ill health.

There may be a few more people out there who might be eligible to lodge a claim, he says, "but they need to do it within two years of the incident to have any comeback".

Claims against international airline carriers fall under the rules of the Warsaw Convention, which states broadly that for practical purposes an airline is liable if a passenger suffers an accident when embarking or disembarking or during a flight. The airline is supposed to do everything it can to prevent an accident.

"That poses the question of whether the syndrome can be considered accidental," says Chapman.

Another contention is that some airlines have known there is a link between the syndrome and immobility and cramped conditions on long flights, but they have done little to bring this to passengers' attention.

Some airlines have already responded to the increasing concern by placing a safety warning on tickets and screening information about the syndrome and how to avoid it in inflight videos. Air New Zealand stamps tickets, timetables and itineraries with a notice advising passengers what they can do to reduce the risk.

New Zealand has also taken a lead in research. One of the most comprehensive studies to date has started in Auckland and Wellington. The project, costing up to $NZ250,000 is headed by Green Lane's Dr Hughes . "The study is trying to clarify the true incidence and the factors that will identify high-risk travellers," he says. "Between 5 and 7 per cent of people have a genetic blood abnormality known as thrombophilias, for instance, and we need to know if they are more at risk.

"We already know that people who are overweight or pregnant, who have cancer or heart failure, or are taking contraceptive tablets or hormone replacement therapy have a slightly higher risk of developing blood clots in any circumstances where they are immobile for long periods."

So there are some known risk factors, but there are other things about which we are still flying blind. For instance, although we know that immobility is a large contributor, we do not really know whether drinking large amounts of water makes a difference - except that the more water you drink, the more you have to get up to empty out, so the more you move.

And we really do not know whether DVT occurs more in passengers in economy class than it does in those in business class.

"We have 580 people already who have joined the programme and we hope to have tested l000 by the end of this year when we publish the results," says Hughes. "Participants have blood samples taken before they leave for any overseas flight that lasts more than four hours.

"When they return they have another. The tests are highly sensitive to the presence of blood clots. If a person initially tests negative for clots but tests positive when they return from their trip, we will scan their lower limbs and chests.

"We also ask the volunteers to fill out questionnaires about their behaviour on their flights, how much they slept and exercised, ate and drank, and any measures they took to decrease their risk, such as wearing surgical stockings.

"We are picking people from across the board, aged from 18 to 70 and flying in first, business and economy classes. They are encouraged to behave in the way they normally behave when they are flying."

"One of the problems if the syndrome is present is that, unless you have a blood test, it is hard to detect from symptoms alone. Sometimes all symptoms are present - swelling and pains in the calf, redness or warmth in one leg - but other times there are no symptoms. And the severity of the symptoms doesn't indicate the size of the clot."

If a clot stays in the leg, it is uncomfortable but not life-threatening. The danger is that it will break off and travel along the venous system, through the heart, into the arterial system and then to a lung. Here it will lodge, blocking an artery and preventing the lung tissue behind the blockage from being oxygenated. The symptoms will be difficulty in breathing, chest pain, rapid heart beat or a sudden cough.

But most flyers are more interested in what they can do to prevent it occurring in the first place.

If you have an underlying illness or condition which involves any part of your vascular system, it is a good idea to get advice from your GP. Also seek advice if you have a possible increased risk through pregnancy, by having cancer, if you are overweight or have a history of blood-clotting in your family or have had recent major surgery.

If you are over 40 or have varicose veins (both of which might put you more at risk) or if you have any of the conditions above, here are some precautions you might consider:

* Walk around as often as you can, although sometimes this is difficult if there is turbulence or if the plane is full and you are sitting by the window.

* As well, or as an alternative, do static leg exercises. The two best are pulling your feet up towards your body, then pushing them down and circling your ankles. To be effective it is suggested you do each of these exercises for five minutes every hour.

* Minimise alcohol consumption. Drink plenty of water or other fluids. Tea and coffee are dehydrators so it's best not to have too much of these. Even if increased intake of water does not directly affect the risk of blood clots, it is generally good to keep your body well hydrated.

* Wear properly measured and fitted surgical stockings. Any old support hose will not do the same job. Dr Farlo warns that a stocking must give more pressure around the ankle and gradually less as the stocking moves up the leg, otherwise it just forms a tight band around the calf and allows swelling to pool in the ankle. Some pharmacies have people who measure and supply these stockings and show you how to put them on. They cost anywhere between $50 and $60.

* Avoid sleeping tablets because they will keep you immobile for four or five hours which could cause the blood flow to slow and fluid to pool in your ankles.

* If you are a smoker, try to cut down or not smoke at all for a few days before a flight.

* Some people advocate taking half an aspirin a day for several days before a flight to thin the blood. The effectiveness of this is still controversial.

My own inclination, given a neurotic disposition, is to do anything that is thought to be beneficial, even if its benefits have not been proven.

I am flying to Los Angeles this month. The flight is about 10 hours, but by the time I have worked out a strategy to deal with any terrorists on board and followed my own regime for working my feet, walking around the plane and replenishing my drinking glass with water, we'll just about be descending.

And then, just then, I plan to ask for one wee glass of champagne to celebrate a safe arrival.