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Pulmonary Embolism

A pulmonary embolism occurs when a clot, usually originating in the deep veins of the calf, breaks off and travels into the blood vessels that feed into the lung. Patients at risk for pulmonary embolism include those who are at bed rest or immobile, patients who are recovering from major surgery or trauma, and patients whose blood tends to clot abnormally easily (hypercoagulable). Additionally, patients with cancer are at increased risk for pulmonary embolism.

The most common signs and symptoms of this disorder include shortness of breath, chest pain, and palpitations. The chest pain is generally pleuritic in nature. This type of pain occurs primarily on deep inspiration and is often described as sharp and knife-like.

Many different tests are used to diagnose pulmonary embolism. While all patients suspected as having a pulmonary embolism receive a chest x-ray and EKG, these studies cannot diagnose this disorder. The two most commonly used tests to diagnose pulmonary embolism are ventilation/perfusion lung scan (also known as V/Q scan) and duplex doppler ultrasound of the leg. The V/Q looks to demonstrate abnormalities and flow of blood to the lungs. A protein is injected into the blood stream with a very low level of radiation attached to the protein. The lung is then scanned, and the areas where blood flows to the lung can be seen. Should there be areas where no blood flow is seen, this suggests a clot is blocking blood flow. This study is then correlated with the ventilation part of the study when a low level radioactive gas is inhaled to demonstrate the distribution of gas flow. The radiologist or a nuclear medicine physician who interprets this study is looking for areas that have ventilation (i.e. airflow) but no perfusion (blood flow) that would indicate a possible blood clot.

The duplex doppler ultrasound scans the legs noninvasively to look for blood clots and blood flow through the vein. The purpose of this study is to look for the source of the clot. Should neither of these studies be conclusive, the patient may undergo a pulmonary arteriogram for a definitive diagnosis. This test has been considered the gold standard for many years. This involves placing a small catheter into a blood vessel (usually from the groin) and advancing it directly up to the blood vessel that feed into the lungs. Dye is then squirted into these blood vessels to look for an area that the dye does not distribute indicative of blood clot.

More recently, CAT scanning using a specially timed injection of contrast dye into a small peripheral vein (i.e. arm) is being used to diagnose pulmonary embolism. The advantage of the CAT scan is that it is noninvasive and a specialist in performing the procedure is not necessary to obtain the study.

The pulmonary and critical care physician's approach to pulmonary embolism is prevention. Patients at risk for lower extremity clots and pulmonary emboli are often given low doses of anticoagulants such as heparin. When they cannot go on blood thinners, sequential compression devices are applied to the legs to minimize the chance of blood clots in these deep veins. While these preventive measures can dramatically reduce the chance of pulmonary thromboembolism, it does not completely eliminate it. When these events do occur, it is imperative that the physician recognizes and treats the disorder appropriately. Treatment generally involves blood thinners such as heparin and warfarin (Coumadin). In patients that cannot tolerate blood thinners, such as patients who have just undergone major surgery or who have other bleeding problems, an umbrella type filter can be placed in a large vein in the body to prevent clots from traveling to the lungs.

In summary, physicians strive to prevent pulmonary thromboembolism from occurring. Should they be clinically suspected, the patient may undergo a variety of noninvasive and/or evasive diagnostic techniques to confirm the diagnosis. Once the disorder is diagnosed, the patient may go on blood thinners or even high dose clot dissolvers similar to those used for a heart attack or stroke to treat the blood clot. In patients who cannot tolerate blood thinners, a vena caval (umbrella) filter may prevent further clots from traveling to the lungs.

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