Venous thrombosis is an accumulation of clot in the vein system (deep or superficial), normally in the legs, that in certain instances may dislodge to the lungs giving rise to a pulmonary embolism, a clinical situation that may be fatal. The term venous thromboembolism (VT) brings together all of these phenomena.
VT may result from alteration in the blood flow (stasis), diseases of the vein wall, diseases of blood (thrombophilia – inherited or acquired tendency to thrombosis), or a combination of several or all of the above.
The first report of the relation between flying and VT dates back to 1954.
In the past few years, there has been increased interest in this subject, since the publication in the media of case-reports of sudden death from pulmonary embolism after long flights.
During long flights, one or several of the abovementioned causes may play a role in the appearance of VT. Immobilisation during flight, the waiting periods in airports, dehydration and hypoxia (reduced oxygen in blood from low cabin oxygen pressure) are important contributing factors to VT.
On the other hand, some individual-related risk factors may explain why it happens in some people and not in others. These may include older age, obesity, cancer, previous VT, hormone therapy, exuberant varicose veins, blood diseases (thrombophilia), chronic heart disease, and others.
The true incidence of these phenomena is not really known. Some studies have reported a near-zero incidence in low-risk passengers and at the other end around 5% in so-called high risk groups.
The more risk factors a passenger accumulates the more risk he/she has.
Considering the prevention of VT in travel, particularly in long-haul flights, there are general measures every passenger (even the low risk, with no or few risk factors) should enforce, and these include: avoid tight clothes, keep mobile (stretch the legs whenever possible, move the feet, avoid keeping bags in front of the seats) and maintain adequate hydration (avoiding too much alcohol).
In passengers with a tendency to get leg swelling (edema) after prolonged sitting, the use of graduated below-knee stockings (pressure 14-30mmHg) is adequate.
In some individuals with increased risk to VT because of previous illnesses, some preventive pharmacologic measures, like taking low dose aspirin or heparin (an anticoagulant), have been suggested by some studies but are not currently a standard measure.
In higher-risk cases, a more individually tailored policy is probably wiser than the same advice and prescriptions for all.
Certainly, the general care measures abovementioned are in order. Some passengers who associate several and important risk factors might benefit from taking prophylactic medication and a discussion with a physician, who knows the patient’s previous history, is the best way to evaluate the risk and benefit of taking these medications in order to prevent VT without undesirable side effects.
By Dr. Hugo Valentim
|| features@algarveresident.com
Dr. Hugo Valentim is an angiologist and vascular surgeon at Hospital Particular Algarve.
