Pulmonary Embolism: Diagnosis & Management :

What is a pulmonary embolism?

A pulmonary embolism (P.E) is a condition where a pulmonary vessel in the either or both lungs becomes blocked. The blockage is usually caused by one or more blood clots which have travelled through the venous system from another part of the body. Commonly pulmonary embolisms are caused by a clot being transferred from smaller vessels in the leg, arm or heart (Fell, 2005). The blood clot travels around the venous system until it reaches a point where it can no longer travel freely. As a result of this, blood flow is reduced to the affected area of the lung.

Symptoms of a pulmonary embolism

The following are the common presenting symptoms of a pulmonary embolism:

• Chest pain – often exacerbated by taking a deep breath. • Shortness of breath – the patient may struggle to complete a sentence. • Perspiration – the patient may be sweaty and clammy • Change in pallor – in severe cases of pulmonary embolism the patient may look pale and ashen.

If the blood clot is large, or the patient has not received medical assistance in adequate time, a pulmonary embolism can result in a cardiac arrest.

Diagnostic Tests

Because the symptoms of a pulmonary embolism can mimic other medical conditions (such as acute myocardial infarction), specific diagnostic tests are required to give a definitive diagnosis. The following tests are carried out when the patient is taken into medical care:

1. Electrocardiogram (ECG) – ECG changes can be present in a patient presenting with a pulmonary embolism. Pulmonary embolism should not be ruled out in cases where there are no significant ECG changes. Inverted anterior T-waves on an ECG can be indicative of a P.E however this is usually in the case of a ‘massive’ embolism.

2. Erect chest x-ray - In most cases of a suspected P.E a physician will request a chest x-ray. This test is unlikely to display any abnormality which will assist the diagnosis of a P.E however it can highlight other potential conditions which may be causing the symptoms.

3. Arterial Blood Gases – This test involves the physician taking a small sample of blood from the radial artery. If the patient is cyanosed or hemodynamically unstable then a sample may need to be taken from the femoral artery. The blood sample is analyzed within minutes, on a machine usually available in the E.R. Arterial blood gases may be helpful in the overall assessment and management decisions of a dyspneic patient, but will not help rule in or out a P.E (Stein, 1996).

4. C.T Scan – This involves a contrast dye being injected into a venous cannula, images are then taken to observe the flow of the dye through the venous system and into the pulmonary vessels. If there are any areas blocked or poorly perfused then a C.T scan will indicate this.

5. Pulmonary Angiography – This test requires the insertion of a catheter into a large vein located in the groin (inferior vena cava). Contrast dye is then injected into the catheter and images of the dye are then observed to identify its course and determine any poor filling or blocked areas. Pulmonary angiography is the accepted "gold standard" test, but it is invasive and difficult to interpret, and can give false-negative results (Walling, 2003).

Causes of a pulmonary embolism

There are many known causes of a pulmonary embolism; the main ones are listed below:

1. Deep Vein Thrombosis (DVT) – A deep vein thrombosis is a blood clot which is located in the deep veins of the leg. Sometimes the clot which has formed in the leg can make its way up the venous channel causing problems such as pulmonary emboli. DVT’s are not uncommon and usually present with calf pain and redness to the area. If treated promptly a DVT can be contained just to the local area without further complications occurring.

2. Post-operative complications – Patients that are due to have surgery that may render them immobile for a time are usually given anti-coagulant (blood thinning) injections prior to, and immediately following the operation. Due to the lack of mobility patients (especially those undergoing major surgery) are at risk of forming clots due to circulatory disruption caused by the surgery, and subsequent immobility which slows up the flow of blood around the body.

3. Pregnancy – Pulmonary embolism is the primary cause of death in pregnancy and childbirth. During pregnancy the body encounters changes to its internal blood clotting system. The blood is therefore more viscous and prone to clot. Those women who undergo caesarean section deliveries have an additional risk as a result of major abdominal surgery.

4. Prolonged periods of bed rest – The elderly and infirm are a large risk group simply due to decreased mobility and prolonged periods of inactivity that go with age.

5. Leg injury – In the case of orthopaedic fractures and crush injuries, patients are at greater risk of pulmonary embolism. Direct trauma to the leg veins can increase the risk of DVT and therefore increases the risk of developing pulmonary embolism.

6. Cancer – Those suffering from cancer are at a notable risk for pulmonary embolism due to altered clotting during the period of illness.

7. Birth control pills - Estrogen in birth control pills can increase clotting factors in your blood, especially if you smoke or are overweight. On the other hand, the risk of clots from birth control pills is small compared with the risks associated with pregnancy (MFMER, 2005)

Management of pulmonary embolism

The outcome for a patient suffering from a pulmonary embolism will depend entirely on hemo-dynamic stability such as the maintenance of a blood pressure which does not compromise the patient’s oxygenation, or reduce cardiac output. The crucial determining factors in every case are:

• The size of the blood clot (emboli) • The location of the clot • And the presence of any pre-existing cardiopulmonary disease

It is essential that a full examination of the patient is undertaken on immediate arrival to the E.R, along with details of the patient’s full medical history.

Pulmonary emboli do not go away without treatment. In cases of a suspected P.E the physician will commonly prescribe a prophylactic (preventative) course of anti-coagulant injections until a definite diagnosis has been confirmed. These injections are given subcutaneously and comprise of a low molecular weight heparin. In some cases intravenous heparin is commenced during the critical period following diagnosis.

Heparin’s primary function is to thin the blood, and in the treatment of pulmonary embolism the function of thinning the blood, in time, results in depletion of the blood clot. Heparin is commonly given for a restricted period of time, usually in the acute phase of diagnosis and for several weeks after. The patient will then be anti-coagulated with Warfarin therapy, which can be closely monitored in the primary care environment.

During the course of anti-coagulant therapy it is crucial that the patient undergoes frequent blood tests to measure clotting levels in the blood. As well as ensuring the blood is thinned enough to dissolve a clot, or prevent any future clot, it is also important that the blood is not thinned too much. In cases where a patient becomes critically ill as a result of a massive pulmonary embolism, it is usually necessary to treat them aggressively with a thrombolytic agent (Hyers et al, 1998). Similar to treatment for acute myocardial infarction, this treatment which is given intravenously, dissolves the clot which is likely to cause imminent death if not removed rapidly. Patients suffering from a massive P.E are prone to becoming hemodynamically unstable with associated severe respiratory distress also. Therefore intense treatment is necessary.

In cases where thrombolysis is deemed clinically necessary, once again a full medical history must be sought as the process of thinning the blood by administration of a thrombolytic drug can cause problems such as the onset of a stroke due to the risk of bleeding to the brain.

In the case of a massive P.E which does not clearly respond to thrombolysis treatment and cardiogenic shock looks likely, it may be necessary as a treatment ‘last resort’ to perform a surgical ‘embolectomy’. This is the surgical removal of the clot directly from the affected vessel or lung. Surgery of this severity also carries risks, particularly if the patient is hemodynamically unstable (Augustinios, 2004).