aspirin is more than a hundred years old, yet new uses are still being found for it. The 16th Annual Scientific Conference on aspirin held at the Royal College of Surgeons in Ireland covered not only its well-known use in heart disease, but recently discovered uses against thromboses in veins, to prevent and treat stroke, in healthy people at high risk of heart attacks, in colon cancer, and in women with ‘Hughes syndrome’ which combines gynaecological with blood vessel problems.
Chaired by Professor Desmond Fitzgerald, of the College’s Department of Clinical Pharmacology, speakers included Colin Prentice, Professor of Medicine of the University of Leeds; Dr Raymond Johnston of the Civil Aviation Authority; Dr Anne MacGregor, Clinical Research Director, the City of London Migraine Clinic; Dr Katherine Sheehan, Registrar in Pathology at the Beaumont Hospital, Dublin; Professor Giovanni de Gaetano, President of the European Thrombosis Research Organisation; Dr Norman Delanty, consultant neurologist in the Beaumont Hospital, Dublin; and Dr Graham Hughes, of the Rayne Institute, St Thomas’s Hospital, London.
Professor Prentice reported on the Pulmonary Embolism Prevention (PEP) trial, which studied 13,356 patients having fractured hip surgery randomised to aspirin 162mg daily or matching placebo for 5 weeks. PEP showed that aspirin reduced post-operative symptomatic deep vein thrombosis (DVT) by 29%, total post-operative DVT by 36% and pulmonary embolism by 43 per cent, all the differences being statistically and clinically significant. Of greater importance, the most feared complication of fatal pulmonary embolism was reduced by 58%. The expected downside, deaths due to bleeding, did not differ between the aspirin and control group. aspirin prevented 8 pulmonary emboli, 4 fatal, per 1,000 patients treated. The benefit lasted beyond the time of hospital discharge (12 days) until at least 35 days.
Professor Prentice concluded from these results that aspirin should be considered routinely in all surgical and medical groups at a high risk of venous thromboembolism. The clinical data supporting aspirin, he said, ‘is more secure than the data for other antithrombotic agents including heparin and warfarin’. For major surgery, the benefits of aspirin outweigh its costs. It is the best researched thromboprophylactic agent. The PEP study, said Professor Prentice, is a challenge to heparin makers to perform a similar trial to prove its effects are better.
Dr Johnston continued with the theme of aspirin prevention of DVT. The role of stasis in venous thrombosis was highlighted in 1940, when it was noted as a common complication of sleeping in deck chairs in underground stations during the blitz. However, until now air travel has not been highlighted as a major cause of DVT. A review in 1999 listing risk factors for DVT, for example, did not mention air travel. Yet the evidence is there. Eklof et al in 1996 showed that of 253 patients with DVT and PE 44 developed symptoms after flights of 5-17 hours. Ferrari in 1999 reported a case control study of 160 people with DVT. There was a history of travel for more than 4 hours at a time in the previous 4 weeks in 24.5% of those with DVT and in 7.5% of those without it. Twenty eight of the DVT patients had travelled by car and 9 by aircraft.
The most obvious factors linking DVT to air travel are dehydration, alcohol (which increases dehydration), immobility, a medical history of previous deep venous thrombosis or surgery, possible venous compression due to seating, the oral contraceptive pill and hormone replacement therapy.
Seat pitch in economy in scheduled aircraft has shortened from 33 to 34 inches in 1992 to 31 to 32 inches in 1999. In chartered airlines it may be 28 or 29 inches. This may have implications on a narrow bodied aircraft which may operate flights more than 5 hours long.
To avoid DVT in high risk travellers the top priority is to keep hydrated and mobile. Anti-embolism stockings and perhaps low molecular weight heparin may be useful in people at very high risk. It is reasonable to take aspirin before long haul flights, but there should be some medical guidance and a bar to people who have had a previous peptic haemorrhage. Buying first class tickets may be worthwhile, but DVTs also occur in seats in first class – and even in Air Force One, as the case of President Nixon proves.
Interestingly there have been no DVTs in UK pilots even though they are less mobile than cabin staff. There has not been a reported incidence of DVT on Concorde which one might expect as the flight time is always less than 4 hours.