Friday, March 9, 2012

Deep Vein Thrombosis - A Look At Prevention

Deep Vein Thrombosis (DVT) is a medical condition that is both dangerous and often preventable. We are all at risk for DVT when we sit too long in one position, as when we get sandwiched into a window seat on a long airplane flight or sit in a chair all day at work.

New recommendations on the prevention of DVT have been recently released. Many of us are at risk of DVT because our lifestyles and jobs often require prolonged sitting of one kind or another. Since a DVT can lead to dangerous and life threatening complications I feel it is well worth your while to understand what you can do to protect yourself.  

So what is a DVT, why is it dangerous, and what are the new guidelines for prevention?


DVT is simply a medical term for a blood clot (called a thrombus) that develops in a vein, usually in the lower part of the left leg. This can happen if a vein is damaged or if the flow of blood slows down or stops (as happens with prolonged sitting). A DVT can be fatal if the blood clot dislodges and moves to the brain or lungs.

To understand how and why a DVT might form, let’s first look at how veins are supposed to work and how they function differently from arteries.


Veins move blood back to the heart from other parts of the body (arteries move blood from the heart to your organs and the rest of your body). The blood inside an artery is moved along by the force of your heart beating which pushes the blood along. Veins, on the other hand, have a different mechanism for moving blood back to the heart. It is the force of the muscles contracting as it surround each vein that forces the blood back up to your heart.

On the way back to your heart a series of valves that line the inside of your veins prevents the blood from moving backwards in the wrong direction. If the blood in your veins cannot move easily back to your heart then it places a lot of pressure on each valve potentially causing it to fail. As you can see, if the blood is not being pushed back up the veins by your muscles contracting then the whole process can back up and you can end up with blood becoming stagnant and eventually even pooling in your legs.

You may be familiar with the idea of valves not working properly if you have ever seen someone who has varicose veins. Varicose veins stand out as purplish lines of backed up venous blood. Varicose veins can be seen easily because the valve problem exists in the superficial veins just below your skin. DVTs on the other hand, form in deep veins that are much deeper in your tissues; they cannot be readily seen even if the valves are not functioning properly. This is one of the reasons that DVT can be so dangerous. There is not any easy way to tell if the valves in your deep veins are not working well, so you may not even notice that you have a problem until it is too late and a clot has silently dislodged and moved into your lungs or brain.

Interestingly, DVT occurs most frequently in the left leg (70-90% of the time). This is because the left iliac vein (the vein that drains blood from your left leg) is compressed slightly by the right iliac artery (the artery that supplies the right leg), making it harder to get blood out of the left leg and back to the lungs. The iliac vein and the iliac artery are in the pelvis and prolonged sitting can lead to DVT because sitting prevents your leg muscles from pushing the blood past this area of compression. While the compression is normally inconsequential it can become problematic during long periods of sitting as the blood stagnates.


A DVT is essentially a blood clot that forms when blood cells clump together. Blood can get caught near the valves in veins where circulation is poor. When this happens blood cells can no longer get enough of the oxygen they need. Your body treats these oxygen starved (hypoxic) red blood cells as damaged and initiates an immune response. White blood cells (leukocytes and monocytes) move into the area to “clean up” the damage and they may then “stick” to the red blood cells as well as the endothelial cells lining the veins. Once the white cells bind to the endothelial cells a protein involved in the clotting of blood called fibrin is deposited into the red blood cell making them “sticky”. This then makes them more likely to stick onto other hypoxic red blood cells which is what ultimately form a blood clot

Blood clots can block off the flow of blood.

A blood clot is a group of red blood cells that stick together to form a solid mass. Blood clots are very important in stopping bleeding, like when you get a cut. However, when this happens inside of veins, the clot can quickly grow to a size that blocks off circulation. It’s sort of like a rock stuck in a garden hose; the water (or blood) still flows, but much more slowly.

Blocked off circulation means that blood is less able to reach all the places that need nutrients in your body. Worse still is if the clot dislodges from the vein where it formed and makes its way to other parts of your body, it can cause severe complications.


When a clot forms it has the potential to break off and flow through the large veins that take blood back to your lungs. Blood in your veins flows back to your lungs to get oxygen, but now the clot is along for the ride. Veins get much smaller where they meet up with the lungs, so a clot can easily act like a small plug as the veins narrow in that area. This is what is called a pulmonary embolism and it can cause severe damage to the lungs. If the blood flow in the lung gets cut off by a blood clot, then parts of your lungs can’t get nutrients and they start to die.

Your heart is also at risk as the blood clot blocks off the blood flowing through veins because this puts extra pressure on your heart as your heart must work harder to overcome the blockage. Blockages like this also cause blood pressure to rise as the heart pumps harder and harder. In people who have a history of heart disease, this can quickly lead to a heart attack. Worse still, if arteries are already partially blocked off by atherosclerosis (narrowing of the arteries) a wandering clot can get stuck very close to the heart, cutting off crucial blood flow and causing a very serious heart attack.

If a blood clot makes it’s way to your brain and blocks off blood flow, it is called a non-hemorrhagic stroke. This type of stroke is from a lack of oxygen to the brain caused by a blockage rather than from bleeding. This can happen when a clot is relatively small and doesn’t get stuck in the lungs, but makes its way through and into the even smaller arteries and veins that feed the brain. If a clot gets stuck in the brain, then it stops blood from delivering oxygen and nutrients to brain tissue which causes the brain cells there to die. The resulting brain damage can be very severe.


Sitting down for long periods of time is, by far, the biggest risk factor for developing deep vein thrombosis. Sitting for 6 hours or more, as might occur during air travel, greatly increases the risk of DVT. Your legs, as we discussed above, have a hard time pushing blood back up when you’re in a sitting position. Some blood cells get trapped without nutrients (oxygen, etc.) and get damaged, leading to a clot.

Obesity and diabetes also greatly increase the risk of DVT. Even metabolic syndrome (thought to be the start of developing diabetes) can lead to conditions inside veins that make DVT much more likely. Because all three of these conditions are linked with chronic inflammation, they all carry additional risk for poor circulation and “sticky” (more likely to clot) blood; both creating an environment in veins that practically begs for DVT.

The types of places you might sit for long periods of time (e.g. airplanes, office buildings) also happen to have dry air. Dehydration can also contribute to DVT, by lowering the amount of fluid in your blood stream, making blood “thicker”. Low air pressure (as in airplane cabins) tends to make dehydration worse. Low air pressure also lowers the pressure your muscles are able to put on veins, making them less effective in pushing blood back up from your legs.

Other risk factors:

  • Pregnant women or women using contraceptive medications (“birth control”)
  • older age
  • recent surgery or broken bone
  • smoking


Recognizing the symptoms of DVT early is extremely important. The sooner you get treatment, the lower the risk that a clot will break off and wreak havoc elsewhere in your body. If you experience any of these symptoms, it is crucial that you seek medical attention as soon as possible.

Symptoms of DVT include:

DVT in this person's right leg clearly
displays several classic symptoms.
  • Changes in skin color (redness) in one leg
  • Increased warmth in one leg
  • Leg pain in one leg
  • Leg tenderness in one leg
  • Skin that feels warm to the touch
  • Swelling (edema) of one leg


Generally speaking, unless you are considered “at risk” for developing a deep vein thrombosis you won’t need to do very much in the way of prevention. Standing up or “stretching your legs” at regular intervals may be enough for most people to eliminate the risk of a DVT forming.

If you are considered “at risk” for developing DVT, however, there are some other easy ways to greatly reduce your risk.

Compression socks (or stockings) add external pressure to your legs, helping keep the blood flowing out. Wearing compression stockings is one of the best ways to avoid DVT. You should consult with your doctor about what level of compression is right for you, as too tight or too loose won’t give you any benefit. These stockings/socks are also recommended for people with diabetes for the same reason -- to increase circulation.

Other tips:

  • Stay hydrated - This keeps plenty of fluid in your blood stream, separating blood cells so they’re less likely to stick together.
  • Avoid alcohol, caffeine, or other diuretics - You want to avoid getting dehydrated and these things make you lose more water by peeing more.
  • Sit in an aisle seat - So you can stand up and stretch at regular intervals (even if just to let other people get to the restroom).
  • Fish oil - The omega-3 fatty acids in fish oil have been shown to help reduce inflammation. Inflammation is one of the things that can lead to vein damage (endothelial cells) and clot formation.


After a thorough review of research and data about DVT, the American College of Chest Physicians (ACCP) changed some of the commonly suggested ways to prevent DVT. One of the biggest changes was to remove blood thinning medications (e.g. warfarin, coumadin, etc.) and aspirin as a recommendation for prevention. While aspirin (and other blood thinners) can be helpful in preventing clot formation, some of the research shows that aspirin may actually make a DVT more likely to detach allowing the blood clot to potentially wreak havoc further down the line.

Aspirin is still useful as a preventive measure to prevent heart attacks. In the case of heart disease, there is not a risk of encouraging a clot to move into a more dangerous location than the coronary artery itself.


Deep vein thrombosis is a dangerous condition that, with a few simple precautions, can be avoided. If you think you might be at risk of developing DVT, it is important to be mindful of what you can do to lower that risk. If your doctor prescribes you aspirin specifically to reduce the risks of DVT, you might want to discuss the reasons why and other options that are available.

You might not ever have heard of deep vein thrombosis before today. The symptoms might seem strange if you didn’t know anything about DVT, so they might be easy to overlook. Early treatment is crucial with DVT, so recognizing the symptoms immediately is especially important. You can prevent most DVT occurrences with these simple precautions.

Researched and written by Dr. Rebecca Malamed, M.D. with assistance from Mr. Malcolm Potter.

1 comment:

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