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ECS / D.V.T. - what the experts say…………….

This information is not a substitute for medical treatment.

DEEP VEIN THROMBOSIS or DVT

Vacationing in Belize, Karen Perkins was in her scuba gear preparing for a dive, unaware that during her flight to Belize a blood clot had formed in her calf. As she kicked in the water, part of the clot passed through her heart, blocked her pulmonary artery, and she died. Her husband, Bradley Perkins, Vice President and General Counsel for Alliance Semiconductor Corporation, was on the dive boat but he could not save her; she had died almost instantly.

Dr. Stanley Mohler, Director of Aerospace Medicine at Wright State Medical School, calls this the "Stealth Disease". Most victims are stricken a few days after the flight. They have no idea what is wrong. Those who seek treatment are usually misdiagnosed at first, aggravating the injury and increasing the risk of death. This is a double tragedy. First, passengers could easily avoid this if they knew the simple exercises that prevent it. Second, victims could easily avoid misdiagnosis if they knew how. Arterial clots are less easily avoided, but a little information can be lifesaving.

How much of this is caused by air travel?
l. In England, Dr. John Scurr found that 10% of air travellers developed potentially injurious blood clots. Most are silent or asymptomatic. But they still pose a risk of recurrent DVT and potentially fatal PE. Every preventable DVT should be prevented. US airlines carry about 600 million passengers. If half make journeys over four hours, and 10% of those develop clots, and 6% of those produce symptoms, there would be 1.8 million victims. Allowing for nearly half to be undiagnosed or misdiagnosed, the result is one million victims, consistent with other findings.

2. Several studies tabulated the percentage of DVT/PE victims caused by air travel. Simon found 66% of DVT/PE attributable to air travel. Mercer Brown found 50% and that air travel was the most common risk factor. Benoit found 50%. A Tripler Army Medical Center 4-year study also found 50%. In Honolulu, Eklof et al studied 254 DVT/PE patients and found 20% had developed clots during air travel. Ferrari found 6% in Nice, and Nissen found 5% in Germany.

3. Dr. Russell Rayman of the Aerospace Medical Association says no one knows the incidence of air travel thrombosis, but it is rare. Conclusions: A conservative conclusion is that, of the 2 million treated for DVT, 1 million are caused by air travel. Of 200 thousand PE deaths, 100 thousand are caused by air travel. Of 158,000 stroke deaths, 80,000 may be due to air travel. This is conservative. For every diagnosed and treated DVT, there are 20 silent cases, per Caprini.

Many more deaths due to heart failure and pulmonary hypertension are caused by air travel. Advice for Pilots to Avoid Thrombosis InjuryFainting Often the first sign of pulmonary embolism (PE) is fainting without warning, especially in older victims.

FAA Incident Reports list five cases of pilots fainting in the last ten years. The list of five does not include the Continental pilot who fainted on a December 27, 2000 flight from Houston to Paris, forcing an unscheduled landing, or the US pilot who died of pulmonary embolism at Narita Airport in Japan.

Some of the faintings were listed as heart attacks, although doctors say the description ("went limp") sounds more like the result of a PE. David McKenas, director of medicine at American Airlines, says the most frequent causes of sudden pilot incapacitation are cardiac arrest, arrhythmia, and fainting. All can be caused by pulmonary embolism.

Conclusions:

A conservative conclusion is that, of the 2 million treated for DVT, 1 million are caused by air travel. Of 200 thousand PE deaths, 100 thousand are caused by air travel. Of 158,000 stroke deaths, 80,000 may be due to air travel.

This is conservative. For every diagnosed and treated DVT, there are 20 silent cases, per Caprini. Many more deaths due to heart failure, and pulmonary hypertension are caused by air travel.

What is DVT?Deep Vein Thrombosis is an abnormal process of clotting in the deep veins of the body. Most commonly, the deep veins of the pelvis and legs are affected. The condition is serious, potentially fatal and very difficult to diagnose by external examination.
Some Causes
• Inactivity causes blood flow to slow in the deep veins of the lower legs
• Cramped seating
• Compression of thighs by the seat edge
• Dehydration due to excess alcohol and low cabin relative humidity Some Symptoms• Redness of the lower legs
• Swollen or painful calf or thigh
• Rise in temperature
• Skin discolouration - faint blue-red Assist Prevention
• Wear compression socks
• Exercise in-flight - both walking and simulating walking
• Keep well hydrated by drinking water
• Limit alcohol intake Avoid sedatives How to avoid Economy Class Syndrome, blood clots formed during air travel. Information for passengers, pilots, and healthcare workers.

In England, John Scurr , a consulting vascular surgeon, did ultrasound scans of 100 travellers before and after vacation flights, and found that 10% of them developed potentially injurious blood clots.

In another group wearing compression stockings, no blood clots were detected.

Scurr had carefully excluded anyone with any of the known risk factors such as heart disease.

(The Lancet, 5/12/01) Medical journals say that during flight blood coagulability rises steadily and blood flow slows down, especially in the lower legs.

Blood clots form, usually painlessly, but some cause pain and swelling.

If a clot travels to the lung it can cause pain, fainting and death. A clot in the leg is called deep vein thrombosis (DVT).

A clot in the lung is pulmonary embolism (PE). Clots also form in the arterial system and in the heart, leading to heart failure and stroke.

Simple, effortless exercises prevent DVT and PE. You need to flex your leg muscles during flight.

Turbulence? The usual advice is "Sit tight, enjoy the flight, and keep the seatbelt fastened to avoid turbulence injury." But serious turbulence injuries average only five per year, per FAA records. There are thousands of times more thrombosis victims each year than all the turbulence and crash victims in all of aviation history. Of the two million people hospitalized with DVT each year, probably one million are caused by air travel. PE victims often die, and victims of stroke and heart failure add to the toll, which probably exceeds cancer deaths. For people in their 20's and 30's this is one of the leading causes of death. Never in history could so many injuries and deaths be avoided so easily. More lives are ruined or ended by economy class syndrome than the number of people on board all four of the airliners hijacked on September 11th.Common misconceptions:I'll just upgrade and avoid the cramped seats. Change in altitude causes blood coagulability to rise steadily and the altitude is the same in the front of the plane as in the rear.

A Japanese study found 70% of victims in coach class, 25% in business class, 5% in first class, and one pilot. The term economy class syndrome (ECS) is a misnomer. The ratio of victims is the same in the front of the plane as in the rear. A more accurate term is air travel thrombosis. If I am in good shape, it won't happen to me. Athletic people are at much greater risk than other passengers. See risk factors No one is safe from this. More than half the victims have no risk factor other than air travel. On our Messages page you will see remarks from victims who were young, fit, and active: avid bicyclists, runners, and a scuba diver. A ten year old girl suffered DVT on a flight to Hong Kong. You just need to stretch if you feel a cramp. You probably won't feel a cramp, and if you do, it's too late. Researchers find that 94% of blood clots are silent, symptom less. John Scurr found symptom less blood clots in 10% of air travellers. But symptom less blood clots are not harmless. They can progress to fatal pulmonary embolism without warning . If I get a clot, drugs will dissolve it. The usual heparin/warfarin treatment doesn't dissolve the clot. It just reduces the risk of more clots. The original clot has to be broken down in a natural process called lysing, which can take months. Most victims report serious problems continuing long after the injury. Warfarin is a blood thinning drug and rat poison. If you are a person who tries to avoid toxic substances, you will not enjoy being forced to take rat poison. The treatment usually continues for three to six months; some have to take it for life. Pilots acclimate. They don't need to worry. Pilots are at risk, too, and the first sign often is fainting. Dr. David McKenas, medical director at American Airlines, says that the most common causes of sudden pilot incapacitation are cardiac arrest, arrhythmia, and fainting. (All of which are often caused by a blood clot in the lung.) With DVT, pilots, like other victims, often struggle with symptoms for days or weeks, not knowing what is wrong. During that time they are at risk of sudden collapse, a danger to themselves and their passengers. Pilots are also at risk of sudden collapse due to arterial clots causing heart failure or stroke.

Stroke, PTSD, Pulmonary Hypertension More reasons to take this seriously: - About 10% of adults have a "right/left shunt," a small hole in the heart allowing venous blood to pass into arterial circulation without passing through the lungs and allowing clots to travel to the brain, causing stroke. About 10% of the victims contacting us are stroke victims. - A common after-effect of ECS is post-traumatic stress disorder, PTSD with symptoms such as depression and anxiety. - PE can lead to pulmonary hypertension, a serious lung condition which is often fatal.

Medical Journals The best articles we have found are listed below. If you have time for only one, we recommend the one by Eklof et al. It presents its own results plus a table recapping the findings of other researchers. You can access articles (or abstracts) on the web at PubMed (National Library of Medicine) and other e-libraries.

Three of the strongest studies are very recent. In Norway, Bendz et al put 20 young men in a hypobaric chamber simulating aircraft cabin altitude and found substantial hour-by-hour increases in blood clotting factors in all of the young men. This means that everyone in an airliner is at risk, not just a few with some unusual susceptibility. (The Lancet, 11/11/00) In England, John Scurr, a consulting vascular surgeon, did ultrasound scans of 100 travellers before and after vacation flights, and found that 10% of them developed potentially injurious blood clots.

In another group wearing compression stocking, no blood clots were detected. Scurr had carefully excluded anyone with any of the known risk factors such as heart disease. (The Lancet, 5/12/01) A larger study led by Belcaro in Italy did before and after ultrasound scanning. Nearly 1,900 subjects were divided in seven groups to see:

1. Incidence in low-risk vs. high-risk groups: 13 of 389 developed DVT in the high-risk group. None in the low-risk group.

2. Effectiveness of compression stockings: people who wore compression stocking were about twenty times less likely to develop DVT than people in the control group, where 4.5% developed DVT.

3. Effectiveness of aspirin and heparin as preventive measures: aspirin had very little effect and some undesirable side effects. Heparin was very effective and is recommended for people with risk factors who must fly.

For more details see Belcaro Also see Belcaro in bibliography below. (Note: while aspirin is not effective for preventing venous clotting, it may still be advisable for its effectiveness in preventing arterial clotting.)

At the World Congress of the International Angiology Union in April 2002, Dr. Omer Iqbal presented a paper saying it is a mistake to focus only on venous clotting. As coagulablity rises, the risk of arterial clots also rises, causing heart attacks and strokes. For example, warfarin is frequently prescribed for people subject to atrial fibrillation because of the tendency to form stroke-causing clots. The rise in coagulability demonstrated by Bendz (above) increases the risk of stroke for these people. Aspirin, ineffective for preventing venous clotting, is effective for preventing arterial clotting, which follows a different series of chemical/enzyme interactions. Incidence (How many victims?)We found 21 sources for this report. (An abbreviated version of this analysis and its conclusions appears in The Lancet, September 8, 200l, as one of four letters related to John Scurr's study.)

1. Warfarin is the 11th most-prescribed drug in the US with $500 million sales (per American Family Physician, 2/1/99). This works out to treatment of about 5 million persons. J. Hirsch (Management of Deep Vein Thrombosis and Pulmonary Embolism) says 2 million of those are DVT/PE victims, with 600K hospitalized, 60K fatalities. In '98 the Mayo Clinic Health Letter also reported 600K hospitalized 60K fatalities.

2. Figures from population-based studies are: Heit, .8 per thousand per year, Oger 2 per thousand, and Adam.com, 4 per thousand. Schreiber reports that 5% of the population develops DVT sometime during the course of a lifetime.

3. DVT is, more often than not, silent or asymptomatic. Caprini says 94% are silent. The actual number of cases is about twenty times greater than the number of symptomatic cases. If they are silent, why worry about them? People with silent DVT are at risk of PE, which can strike without warning and may be fatal. No preventable DVT should be allowed to occur, even if silent.

4. DVT/PE is undiagnosed and misdiagnosed more often than not, according to Schreiber, Zamula, and others. The actual number of symptomatic cases is probably twice the number of diagnosed cases. Causes of Death: 1. Dr. Robert McBane of the Mayo Clinic says that PE is the fourth leading cause of death in the US. The July 2000 report of leading causes of death showed 941 thousand heart disease deaths, 541 thousand cancers, 158 thousand strokes. If PE deaths are around 200,000, as many sources report, then PE is the third leading cause of death.

2. Dr Graham Pineo finds 150-200K annual PE deaths. Evelyn Zamula finds 630K PE cases with 220K fatalities. Colucciello found 200K DVT/PE deaths. Schreiber reports 200K deaths and says PE is the leading cause of preventable hospital deaths. 3 . PE is, often as not, undiagnosed and misdiagnosed (Zamula). PE often causes fatal cardiac arrest or arrhythmia. Without an autopsy, no one knows that PE was the cause of the heart failure. Zamula quotes Jan M. Orenstein, MD, professor of pathology, George Washington University School of Medicine and Director of Autopsy, saying "Pulmonary emboli are a relatively common finding at autopsy, usually unsuspected and frequently the cause of death." Angrist reports that PE is the most undiagnosed and misdiagnosed entity in all of medicine.

4. DVT also leads to disability or death from stroke. About 25% of adults have a right/left shunt, a small hole in the heart that allows venous blood to pass into arterial circulation without passing through the lungs. This allows clots to pass on to the brain, causing stroke. Stroke can also result from clots formed in the arterial system, such as in atrial fibrillation, which is more likely during air travel, while coagulability is elevated. In 1950 stroke was the 11th leading cause of death. Today it is third, and it is on track to pass cancer in about ten years. How much of this is due to air travel is not known. Most strokes caused by air travel would occur several days or more after the trip and no one would know it was caused by air travel. Of air travel thrombosis victims contacting Airhealth.org, about 5% suffered strokes.

5. PE leads to pulmonary hypertension in perhaps 5% of victims, which can be fatal.

In 1997 Dr. Donald Hudson, ALPA, reported 75 cases of DVT and PE among 46,000 pilots over a five year period. This is only the tip of the iceberg, since 94% of DVT is silent and, even when symptoms are observed; both DVT and PE tend to be undiagnosed and/or misdiagnosed. Silent DVT does not mean harmless DVT. Silent DVT can suddenly manifest itself as PE without warning. Some pilots are sceptical about the need to take this seriously, having flown for years without a problem. But pilots with a broader perspective and the FAA are taking this very seriously. John Walker, chairman of the Allied Pilots Association Medical Committee wrote: “Mike, we have taken a look at your website and it is terrific. We are putting a link to it on our APA (Allied Pilots Assn.) website. Thank you very much for your interest in this topic." Dr. Charles Ruehle of the FAA wrote "You're on the right track. You'll get cooperation faster on a voluntary basis than by legislative or regulatory action." Clots in the arterial system cause heart attack and stroke. If you are being treated for any heart condition, hardening of the arteries, diabetic arteriopathy, or similar conditions, taking aspirin may reduce your risk. Your doctor may also recommend taking warfarin, a blood thinner. lots in the venous system are more likely and more easily preventable. A simple exercise you can do in your seat is described on the Passengers page. If you have no risk factors, doing it every half hour is probably sufficient. The more risk factors you have, the more frequently you need to do it. Being athletic accounts for ten times more victims that any other risk factor. Airhealth.org has documented 62 such victims, including six pilots. If you are athletic, flexing at fifteen minute intervals would be wise. Some doctors recommend five minute intervals. You don't need to worry about doing it during takeoff or landing. You have plenty of other things to think about then, and you are more active. If you are athletic and also have any other risk factors, using compression stockings would be advisable. They're hard to put on, but several studies have found them very effective. More below on compression stockings. How to recognize symptoms. Pilots, like other victims, often struggle for days or weeks with strange symptoms, not knowing what is wrong. During this time you are at risk of sudden collapse. If you notice leg swelling, a bruise behind the knee, or a painful calf, these could indicate DVT, but remember, most DVT is silent. Shortness of breath or chest discomfort can indicate PE. You'll find a more complete list of symptoms on the Passengers page. How to avoid misdiagnosis. More often than not, misdiagnosis aggravates the injury and increases the risk of death. There are two simple ways to avoid misdiagnosis listed on the Passengers page. Since you will probably forget the details a few days after reading this, we urge you to print out the wallet-size reminder on the Leaflet page and carry it with you. The Physicians page discusses preventive measures for people with risk factors. For many people the best alternative is medical compression stockings and exercise. One pilot told us that he would be reluctant to wear compression hose because it might raise questions of fitness. Having had a DVT does not disqualify a pilot. Also, compression hose need not be obvious. They are available in some of the same colors as regular hose. But medical compression hose are different from drugstore support hose, which can actually be harmful. See Links page for compression stocking vendors. Compression hose are not recommended if you have circulation problems caused by arterial insufficiency. DVT risk is the same in the front of the plane as in the rear. Altitude raises blood coagulability and the altitude is the same in the front of the plane as in the rear. An eight-year study of 25 ECS deaths at the Tokyo airport found 70% from economy class, 25% business class, 5% first class, and one US pilot. About 5% of victims contacting Airhealth.org are pilots. Flight attendants' risk is low on working flights (the muscles get plenty of exercise) but on a deadhead flight the risk is substantial, especially if coagulability is already high from a previous flight and they fall asleep sitting upright. Can you advise deadheading flight attendants about this?Airline Pilot Magazine storyWe found a '97 article in Airline Pilot, the union magazine, written by Capt. Henry Hoffman who was an ECS victim. His father, a pilot on another airline, was also a victim. We asked Gary DiNunno, editor of Airline Pilot, if he would like a new story updated with new research findings. We wrote it and it was reviewed by aero medical experts including Don Hudson's staff in Colorado. It was printed in the June/July issue accompanied by a reprint of an article by Stanley Mohler, Director of Aerospace Medicine at Wright State Medical School, who calls this the "stealth disease" because victims usually don't know what is wrong or why. The story does not include the strongest and most recent scientific studies. In Norway, Bendz et al (The Lancet, 11/11/00) put twenty young men in a hypobaric chamber simulating aircraft cabin altitude and found hour by hour increases in blood clotting factors in all of them. The increases were substantial and serious. This happened in all of the young men, not just a few with some unusual susceptibility. This means that everyone in an airliner is at risk. Some are at greater risk if they have other risk factors such as heart disease but no one is safe. A ten year old girl who slept on a flight to Hong Kong was among recent victims. People who are athletic account for ten times more victims than any other risk factor. In England, John Scurr (The Lancet, 5/12/01) did ultrasound scans of 200 travellers before and after their vacation flights. There were two subgroups, one wearing compression stockings and the other not. In the non-stocking group, 10% developed detectable blood clots. The clots were symptom less, but symptom less clots are not harmless. They can progress to PE without warning. Several of the people with clots were advised to undergo blood-thinning treatment. In the group wearing compression stockings no clots were found. Advice for Passengers to Avoid Thrombosis InjuryCoagulability rises steadily during air travel. The longer the flight, the greater the risk. Clots in the arterial system cause heart attack and stroke. If you are being treated for any heart condition, hardening of the arteries, diabetic arteriopathy, or similar conditions, taking aspirin may reduce your risk. Your doctor may also recommend injection (in the stomach fat) of a low molecular weight heparin, LMWH, such as Lovenox.
Clots in the venous system are probably more likely and are more easily preventable.

• Don't wear anything that could impede the circulation (like a knee brace).

• Frequent leg flexing, as described below, is the best preventive for ECS. You need to activate the muscles enough to push the blood through the veins. Do it firmly and deliberately but not strenuously. If you are bothering your seatmates, you are doing it too vigorously.

How often? The UK Department of Health recommends 30 minute intervals, more frequently if you have any of the risk factors listed below.

1. Extend your legs straight out in front of you and flex your ankles, pulling up and spreading your toes, then pushing down and curling the toes. If your shoes limit toe movement, just make the effort and don't worry, or remove the shoes.

2. If there isn't room to extend your legs, start with your feet flat on the floor and push down and curl your toes while lifting your heels from the floor. Then, with your heels back on the floor, lift and spread your toes. Repeat this heel - toe cycle ten times.3. Exercise your thigh muscles by sitting with your feet flat on the floor and slide your feet forward a few inches, then slide them back and repeat.

Avoid:

1. Sleeping. A thirty minute nap would probably be OK, perhaps using an alarm watch to waken. You could sleep longer if there is enough room for you to lie with your legs up on the same level as your upper body. Flex thoroughly when you wake.

2. Massaging the leg muscles (as some experts recommend) could be dangerous if a clot has formed, and a clot may have formed without your knowing about it.

3. Crossing legs for more than a few minutes at a time is dangerous.

4. Some experts recommend avoiding caffeine and alcohol. Others say this makes no difference. Drinking extra non-caffeine and non-alcoholic fluids is recommended.

Risk Factors:

Our data is showing that being young and athletic is the biggest risk factor for flight-induced DVT.

The risk is compounded if you have one or more of the following:

1. Personal or family history of DVT.

2. Cancer, heart disease, diabetes, obesity.

3. Recent injury or surgery, especially to the legs or lower torso. "Recent" means about six weeks, but if you still have any soreness, bruising, or other after-effects, you are still in danger.

4. Women who are pregnant or taking oestrogen as birth control or hormone replacement.

5. Age past 60. (But remember, being young and fit is the biggest risk factor.)

Precautions:

The more risk factors you have, the more frequently you need to flex. Compression stockings have proven very effective in several studies. A pre-flight self-administered shot of heparin is recommended if you can't stay awake to flex.

Studies such as Belcaro's show that aspirin, often recommended, is not effective as an anti-DVT treatment. If you feel the symptoms listed below, see a doctor. A few days after reading this you will probably forget exactly what symptoms to watch for, so carry the wallet-size Leaflet. After 30 days you are probably safe, but you must still avoid surgery for three months. If surgery is unavoidable, see the article by Patel referenced in the bibliography.

Leg symptoms (Deep Vein Thrombosis, DVT) may appear during flight or in the next few days.
• Sudden swelling in one lower leg. (A little swelling in both legs is normal in flight.)
• Cramp or tenderness in one lower leg.
• Bruise or swelling behind knee.

Chest symptoms (Pulmonary Embolism, PE) usually appear 2-4 days or more after the initial blood clot, which you may not have noticed:
• shortness of breath
• rapid breathing, panting
• cramp in your side, painful breathing
• chest pain accompanied by shoulder pain
• fever
• coughing up blood
• fainting (often the first sign, especially in older people)

Tell the doctor that you have flown recently and that you suspect a blood clot. Misdiagnosis More often than not, flight-induced DVT is initially undiagnosed or misdiagnosed, aggravating the injury and increasing the risk of death. Here are two simple ways to avoid misdiagnosis.

1. If you have leg symptoms and the doctor says you have only a muscle sprain (or anything else other than DVT), insist on an ultrasound scan of the leg. Without it, your chances of a correct diagnosis are only 50/50.

2. If you have chest symptoms and you are being told you have a chest infection, anxiety attack, cold, or anything else other than PE, ask for a blood oxygen measurement. A small device (no needle) placed on your fingertip measures blood oxygen. If the reading is below 80, you need a lung scan to check for PE (unless there is some other reason for low blood oxygen, such as emphysema.) Deep vein thrombosisIn deep vein thrombosis, a blood clot forms in one of the veins lying more deeply in the body. Clots that form in the deeper veins most often occur as a result of poor or sluggish blood flow through the veins and/or increased the stickiness of the blood (making it more likely to clot).

Factors that can contribute to poor or sluggish blood flow through the veins:
• sitting for long periods of time with infrequent changes of position (e.g. long car trips, air travel)
• standing in one place for long periods of time without moving around
• periods of prolonged bed rest
• wearing clothing that interferes with the blood flow.

Factors that can contribute to an increase in the stickiness of your blood include:
• taking oestrogen or The Pill (oral contraceptive)
• having recent surgery or a trauma
• having polycythemia (a high number of red blood cells)
• having severe infection
• having liver disease
• having some types of cancer.

Symptoms of a deep vein thrombosis include:
• redness, swelling and heat in the area over the path of a deep vein
• a deep vein feeling like a hard piece of rope or cord
• pain or discomfort over the path of a deep vein
• discoloration or ulceration of the skin over a deep vein
• no symptoms for some people, especially if the thrombus forms in a vein other than in the leg or arm.

NOTE: It can sometimes be difficult to tell if a person has a thrombophlebitis or a deep vein thrombosis. In these situations a Doppler - ultrasound or a venogram (x-rays done after injection of dye into the vein) may be done to make the correct diagnosis.
If you have symptoms such as swelling, pain, redness or warmth over the path of a vein, contact your doctor immediately.

If you have these symptoms AND chest pain or shortness of breath – call your emergency services.
Deep vein thrombosis is generally treated by:

• restricting activity, if there is a danger of the clot travelling to the lungs.

• being careful not to rub over the affected area, as clots may be broken off or dislodged.

• elevating the arm or leg if the deep vein thrombosis is in a limb

• taking a blood thinning medication to prevent an increase in the size of the clot (the clot can then gradually be absorbed by the body).

Blood thinning medication is usually given by intravenous infusion or injections under the skin for the first few days after a deep vein thrombosis is discovered. Many people are then switched to blood thinner tablets (to be taken by mouth for a longer period of time), but some may remain on the injections under the skin for the longer period of time instead of pills. It is important to start blood thinner treatment with the intravenous infusion or injections because they work immediately (the pills take several days to be effective). Deep vein thrombosis
VOL 108 / NO 4 / SEPTEMBER 15, 2000 / POSTGRADUATE MEDICINE Deep vein thrombosis is a fairly common problem. It is a disorder that affects mainly the veins of the lower leg and thigh. A blood clot (or thrombus) can form in the veins deep in these areas, and the clot then blocks the flow of blood and causes swelling and inflammation. This swelling and redness are sometimes called thrombophlebitis, or just phlebitis. In the most serious cases, a blood clot from the leg breaks off and travels through the bloodstream. The moving clot is called an embolus, and it can lodge in the lungs, brain, or heart and cause serious damage.

Who is likely to have thrombosis?
It tends to develop during long periods of inactivity, such as lengthy road trips or airplane flights, as well as during illness or after surgery. Sometimes it occurs because a person's blood clots too quickly, and sometimes it is associated with trauma. Old age, overweight, and some types of drug therapy also increase the risk.

What do you need to know about it?
Blood clots in the veins buried deep in the calf or thigh can be difficult to detect. Symptoms typically occur in just one leg and may include:
• Pain or tenderness in one leg but not the other
• Swelling (oedema) in one leg
• Increased warmth in one leg
• Changes in color, such as a reddish or bluish color, in one leg
• Joint pain

If you have any of these, check with your doctor immediately.
What might happen next?
In most cases, deep vein clots heal without any special treatment, but extra care may be needed to keep the clot from breaking off and travelling to the lungs, heart, or brain. Hospitalization is a good idea in many cases, at least at first. Bed rest, elevation of the leg, and warm, moist heat to the area may relieve pain. Prolonged sitting must be avoided.

Why be concerned?
Although most blood clots in the leg dissolve on their own, complications may occur and can be life-threatening. The most dangerous complication is called pulmonary embolism. In pulmonary embolism, a blood clot moves into the lung and lodges there. It often cuts off circulation, making it difficult for the heart to pump blood and decreasing the amount of oxygen available to the rest of the body. About 90% of blood clots that travel to the lungs start in the legs.
Pulmonary embolism requires immediate medical care. It can occur with no warning whatsoever, but being aware of possible leg symptoms can be a great help in prevention. The best way to protect yourself from pulmonary embolism is to prevent it from happening. And that involves getting up and moving around during long trips and following your doctor's advice if you are recovering from illness or taking drugs. Words that might be confusing
Your doctor might use some of these terms when discussing deep vein thrombosis.
Anticoagulant drugs: Medications used to stop blood clots from getting bigger and to keep new clots from forming; sometimes called blood thinners
Deep vein thrombosis (DVT): A condition in which a blood clot forms in the deep veins in the calf or thigh
Oedema: Swelling caused by an accumulation of fluid
Embolectomy: A surgical procedure to remove a large clot
Embolus: A blood clot that breaks off from its original site, moves through the bloodstream, and lodges in another blood vessel
Phlebitis: Shortened term for thrombophlebitis (see below)
Pulmonary embolism: The closure of a pulmonary artery or one of its branches by a pulmonary embolus
Pulmonary embolus: A blood clot that has lodged in an artery in the lungs
Thrombolytic agents: Drugs that can break up large clots; also called clot busters
Thrombophlebitis: Name for tenderness, pain, redness, and swelling that occur when a clot and inflammation develop in a vein
Thrombosis: Formation of a blood clot in a blood vessel
Thrombus: A stationary blood clot that forms along the wall of a blood vessel