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Venous Thromboembolism and Air Travel
lnterventional Radiologist at Work
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A
UESTIONand
NSWER
Venous Thromboembolism and Air Travel - -
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What is the evidence, if any, that there is a n association between venous thromboembolism and travel?
Most vascular radiologists are aware of and, almost as surely, believe in the link between long trips and thromboembolism. After all, it makes such good sense. In particular, sitting still for long periods clearly promotes venous stasis, one of the three features of Virchow's famous triad (venous stasis, hypercoagulability, and endothelial injury). Other plausible risk factors of long trips include direct compression of the leg veins, diminished blood flow into the legs, and hemoconcentration resulting from increased filtration of fluid into the interstitial spaces of the leg. Air travel would seem especially risky. Cramped conditions are most severe for those passengers unwilling or unable to pay for first-class tickets, as emphasized by Cruickshank's use of the phrase "economy class syndrome." Air travellers lack the option possessed by automobile passengers of stopping to stretch and walk around. Additionally, dehydration related to low humidity in the cabin and to alcohol consumption and the low atmospheric pressure in an aircraft may exacerbate these tendencies. In 1992, Milne conducted a review of the literature to determine the strength of the evidence supporting long travel as a risk factor. He reviewed the very logical reasons noted earlier to support a connection and points out a situation analogous to prolonged travel in the experience of the London blitz during World War 11, during which an association was noted between sitting overnight on deck chairs in air raid shelters and death from pulmonary embolism. Milne's review unearthed eight references dealing with travel as a risk factor for thromboembolism, all published between 1954 and 1988, including 25 total cases. He pointed out that, unfortunately, none of these articles answered the question. All lacked controls, making it impossible to compare levels of exposure to travel in patients with thromboembolism to those without. Further, most failed to give an idea of how important travel was as a risk factor in the overall burden of this disorder. Milne does point out some interesting features of his review, which may help guide further investigations. One of these is the suggestion that long journeys seem to be more important than short journeys for thromboembolic risk. Of the cases of
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thromboembolism reported, none was associated with a trip of less than 3 hours duration; additionally, in one of the studies reviewed, 10 of 11 persons dying of pulmonary embolism during or after air travel to Heathrow airport had been on flights of more than 12 hours duration, and the other had been on a flight of more than 6 hours duration. Should measures be undertaken to reduce the risk of thromboembolism on long trips? Clearly, occasional walks around the cabin and maintenance of good hydration make sense and have no downside. But what about prophylactic measures such as aspirin, or even heparin, in high-risk passengers? Both have been recommended, despite lack of clear evidence that travel is a risk factor or that these measures will decrease the risk. A comment by O'Donnell highlights some of these issues and is appropriate as an end to this long discussion: ". . . can we honestly suggest prophylactic aspirin for even high-risk travellers when we do not even know the frequency of the condition and can only goggle at the immense numbers necessary to attempt a trial aimed at demonstrating benefit from prophylaxis?" References 1. Bounameaux H. Thromboembolism and air travel (letter). Lancet 1988; 2:797. 2. Cruickshank JM, Gorlin R, Jennett B. Air travel and thrombotic episodes: the economy class syndrome. Lancet 1988; 2:497-498. 3. Milne R. Venous thromboembolism and travel: is there an association? J R Coll Phys London 1992; 26:47-49. 4. Moyses C. Economy class syndrome (letter). Lancet 1988; 2:1077. 5. O'Donnell D. Thromboembolism and air travel (letter). Lancet 1988; 2:797. 6. Voorhoeve R, Bruyninck CMA. Economy class syndrome (letter). Lancet 1988; 2:1077.
Contraindications to Pulmonary Angiography You are called late on a Friday afternoon to perform pulmonary arterzography. The urology resident gives you the following history: A 52-year-old m a n has a history of coronary artery disease, congestive d heart failure, and hypertension. He had suffered a myocardial infarction 4 years earlier, and he required amiodarone for treatment of sustained ventricular tachycardia at that time. He has had no known problems with arrhythmias since then. In addition to the amiodarone, current medications include captopril, trimethoprim lsulfamethoxazole, digoxin, lovastatin, furosemide, and aspirin. On this admission, he
3
Q
A
UESTIONand
NSWER
Venous Thromboembolism and Air Travel - -
3
"
What is the evidence, if any, that there is a n association between venous thromboembolism and travel?
Most vascular radiologists are aware of and, almost as surely, believe in the link between long trips and thromboembolism. After all, it makes such good sense. In particular, sitting still for long periods clearly promotes venous stasis, one of the three features of Virchow's famous triad (venous stasis, hypercoagulability, and endothelial injury). Other plausible risk factors of long trips include direct compression of the leg veins, diminished blood flow into the legs, and hemoconcentration resulting from increased filtration of fluid into the interstitial spaces of the leg. Air travel would seem especially risky. Cramped conditions are most severe for those passengers unwilling or unable to pay for first-class tickets, as emphasized by Cruickshank's use of the phrase "economy class syndrome." Air travellers lack the option possessed by automobile passengers of stopping to stretch and walk around. Additionally, dehydration related to low humidity in the cabin and to alcohol consumption and the low atmospheric pressure in an aircraft may exacerbate these tendencies. In 1992, Milne conducted a review of the literature to determine the strength of the evidence supporting long travel as a risk factor. He reviewed the very logical reasons noted earlier to support a connection and points out a situation analogous to prolonged travel in the experience of the London blitz during World War 11, during which an association was noted between sitting overnight on deck chairs in air raid shelters and death from pulmonary embolism. Milne's review unearthed eight references dealing with travel as a risk factor for thromboembolism, all published between 1954 and 1988, including 25 total cases. He pointed out that, unfortunately, none of these articles answered the question. All lacked controls, making it impossible to compare levels of exposure to travel in patients with thromboembolism to those without. Further, most failed to give an idea of how important travel was as a risk factor in the overall burden of this disorder. Milne does point out some interesting features of his review, which may help guide further investigations. One of these is the suggestion that long journeys seem to be more important than short journeys for thromboembolic risk. Of the cases of
A
"
L
"
thromboembolism reported, none was associated with a trip of less than 3 hours duration; additionally, in one of the studies reviewed, 10 of 11 persons dying of pulmonary embolism during or after air travel to Heathrow airport had been on flights of more than 12 hours duration, and the other had been on a flight of more than 6 hours duration. Should measures be undertaken to reduce the risk of thromboembolism on long trips? Clearly, occasional walks around the cabin and maintenance of good hydration make sense and have no downside. But what about prophylactic measures such as aspirin, or even heparin, in high-risk passengers? Both have been recommended, despite lack of clear evidence that travel is a risk factor or that these measures will decrease the risk. A comment by O'Donnell highlights some of these issues and is appropriate as an end to this long discussion: ". . . can we honestly suggest prophylactic aspirin for even high-risk travellers when we do not even know the frequency of the condition and can only goggle at the immense numbers necessary to attempt a trial aimed at demonstrating benefit from prophylaxis?" References 1. Bounameaux H. Thromboembolism and air travel (letter). Lancet 1988; 2:797. 2. Cruickshank JM, Gorlin R, Jennett B. Air travel and thrombotic episodes: the economy class syndrome. Lancet 1988; 2:497-498. 3. Milne R. Venous thromboembolism and travel: is there an association? J R Coll Phys London 1992; 26:47-49. 4. Moyses C. Economy class syndrome (letter). Lancet 1988; 2:1077. 5. O'Donnell D. Thromboembolism and air travel (letter). Lancet 1988; 2:797. 6. Voorhoeve R, Bruyninck CMA. Economy class syndrome (letter). Lancet 1988; 2:1077.
Contraindications to Pulmonary Angiography You are called late on a Friday afternoon to perform pulmonary arterzography. The urology resident gives you the following history: A 52-year-old m a n has a history of coronary artery disease, congestive d heart failure, and hypertension. He had suffered a myocardial infarction 4 years earlier, and he required amiodarone for treatment of sustained ventricular tachycardia at that time. He has had no known problems with arrhythmias since then. In addition to the amiodarone, current medications include captopril, trimethoprim lsulfamethoxazole, digoxin, lovastatin, furosemide, and aspirin. On this admission, he
3