Deep vein thrombosis explained

By Andrew Demaria
CNN.com writer

A thrombosis is the formation of a blood clot in a blood vessel. Deep vein thrombosis (DVT) is a form of thrombosis that develops in one of the deep veins of the body.

DVT often begins in the calf or thigh because blood moves relatively slowly in these areas, particularly if exercise is limited. As the blood begins to pool in an area, a clot develops and can attach itself to the wall of a vessel or in more severe cases become wedged within a vessel, blocking blood flow.

Blood clots are common. And while a blood clot itself is not life threatening it can cause serious complications. Professor Reginald Lord, head of the vascular group of St. Vincent's hospital in Sydney, says only one percent of venous thromboses cause complications.

As a clot develops in size, it can shed pieces of the clot. These are referred to as emboli. The emboli float through the blood system and can travel through the heart to major arteries in the lung causing serious and sometimes fatal complications.

One of the most serious is referred to as a pulmonary embolism where blood flow to the lung is blocked.

In rarer cases, the clot could also be pumped towards the brain and block arteries that supply the brain. If this happens, a potentially fatal stroke may result.

Symptoms

Generally symptoms include:

  • Chest pain
  • Pain in the calf or leg
  • Swelling of the leg or lower limb
  • Shortness of breath
  • Surface veins becoming more visible

But often there are no symptoms at all. Only half of patients diagnosed with DVT had symptoms. According to David Grosser, a vascular surgeon in the Gold Coast, Australia, clots behave in many different ways.

"Patients can have a significant clot floating around unattached or have end bits that are the size of your thumbprint. Some can be a couple of feet long attached by a tiny little area. In examples like these there can be no symptoms and often these can be the most lethal," Grosser says.

Professor Lord agrees that identifying symptoms is difficult, particularly in severe cases.

"One of the commoner causes of sudden death is a pulmonary embolism that may occur a week to ten days later after a thrombosis formed," Lord says.

Diagnostic ultrasound is the best method to detect restrictions in blood flow, often in combination with blood tests.

Diagnostic ultrasound is the best method to detect restrictions in blood flow, often in combination with blood tests.

Treatment sometimes requires hospitalization to dissolve the clot and try and reduce the risk of other clots developing. The main treatment is blood-thinning medication administered intravenously and orally.

Exercise also stimulates blood flow.

Prevention

But, as with many complications, prevention is often the best strategy.

Professor Lord advises patients to make sure they exercise and flex their leg muscles, especially if they are sitting in a cramped position for a long period of time.

"Nature sends out a lot of signals. If you have been sitting in one position that the body doesn't like, you will feel cramped. That's the body telling you to change position or get up and move about," he says.

In relation to air travel, he advises those more at risk of developing DVT to begin taking half an aspirin a day for 10 days prior to travel.

Medical professionals also recommend seeking medical advice before travel and during the flight to wear special compression socks and drink lots of water.

But Professor Lord admits there are a number of factors associated with air travel that need researching and may increase the risk of DVT.

"Airline cabins are generally pressurized at 6000 feet. This may have an adverse effect on the endothelial cells [the cells lining blood vessels]. If damaged, that's often the beginning of the clot," he says.

"And at the end of a long flight, people have swelling in their feet and often can't put their shoes back on. The dynamics in flow has been altered. Fluid going up through the legs is passing out through local tissue. This could also be effective in increasing the risk."

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