Pulmonary embolism

Pulmonary embolism is the blockage of the pulmonary artery or one of its branches. The most common cause is a venous thrombus, but the blockage can also be caused by cells, air, drops of fat or foreign objects.

Etiology

Various risk-factors for pulmonary embolism are known. Such are:

• longer immobilization, as in longer trips on bus or plane or after surgery
• female sex, pregnancy, the taking of estrogens as in oral contraceptives
• smoking
• overweight
• old age
• dehydration
• varicose veins.

Especially with recurrent thrombosis, the following factors have to be ruled out:

1. Factors leading to hypercoagulability: Activated protein C resistance, protein S or protein C deficiency, antithrombin deficiency and the antiphospholipid antibody syndrome should all be considered.
2. Factors restraining the venous bloodflow, such as tumors.
3. Carcinoma.

Clinical symptoms and findings

Symptoms of a pulmonary embolism occur abruptly. Classic complaints are shortage of air, which can be very distinct, nonproductive cough and a sensation of thoracic tightness or pressure. Frequencies of heart and breathing are often elevated, while the auscultation of heart and lungs normaly does not lead to abnormal findings.

A scale to estimate the probability of a pulmonary embolism is the so called Wells-Score. According to clinical findings and the medical history of the patient, points are given, which, in its total sum, allow the physician to estimate the likeliness of the disease.

Clinical findings	Points
clinical suspicion on the presence of a deep venous thrombosis of the leg	3,0
other diagnosis apear less probable than a pulmonary embolism	3,0
tachycardia	1,5
immobilization or operation within the last 4 weeks	1,5
pulmonary embolism or a deep venous thrombosis present in the medical history of the patient	1,5
hemoptysis	1,0
presence of a malign disease within the last 6 months	1,0

When the points have been summed up, currently two options on estimating the risk of a pulmonary embolism exist.

Option 1:

Wells-Score	Risk of a pulmonary embolism
>6	high (59%)
2-6	moderate (29%)
<2	low (15%)

Option 2:

Wells-Score	Risk of a pulmonary embolism
>4	High probability of pulmonary embolism. It is suggested to procede with further diagnostic tests like a CT pulmonary angiography.
<=4	Low probability of pulmonary embolism. It is suggested to determine d-dimers to rule out the disease.

To estimate its severeness, a pulmonary embolism can be divided into 4 graduations according to Grosser.

	Grade I	Grade II	Grade III	Grade IV
Symptoms	low and in up to 80% the patient is asymptomatic	acute dyspnea, tachypnea, thoracic pain, fear, hemoptysis and fever		Zusätzlich Schocksymptomatik
Blood pressure	normal	slightly decreased	decreased	very low
middle pulmonary artery pressure (mmHg)	normal	often normal	25-30	>30
oxygen partial pressure (mmHg)	>75	slightly decreased	<70	<60
Affected vessel	peripheral branch	segmental artery	branch of the pulmonary artery or several arteries of pulmonary lobes	the pulmonary artery and several of its branches

Differential diagnosis

The most important differential diagnosis are myocardiac infarction, cardiac tamponade, pneunomia, pleurisy, pneumothorax, asthma attack and aortic dissection.

Diagnostics

An important evidence to a pulmonary embolism is the verification of a deep venous thrombosis, which in combination with the typical symptoms makes the disease rather likely. Still it must not be forgotten that missing evidence of a deep venous thrombosis is not suitable to rule out a pulmonary embolism. On the contrary, up to 50% of patients suffering the disease, have no clear evidence of a deep venous thrombosis neither in their medical history nor in their physical examination or in the findings of doppler ultrasonography.

Further important diagnostic tools are x-ray of the thorax and echocardiography. Analysis of arterial blood gas can also be of great use, normaly showing signs of hyperventilation with consequent hypoxia and hypocapnia. Concededly hypercapnia is also possible in patients with chronic obstructive pulmonary disease.

The electrocardiogram often shows an overload of the right heart.

D-Dimers are elevated and can be used to rule out the diagnosis of acute pulmonary embolism if they are in normal range.

To confirm the suspected diagnosis of pulmonary embolism computed tomography with contrast, also known as CT pulmonary angiography produces relatively reliable results in terms of sensitivity and specificity. Another advantage is the relatively low stress for the patient wherefore the procedure is normaly prefered to the conventional pulmonary angiogram. The latter leads to better results in terms of sensitivity and specificity even with rather small thrombus and thus represents the diagnostic gold standard, but due to the high technical expense, the stress for the patient and last but not least the higher risk caused by the placement of the catheter, it is nowadays only used in questionable cases.

Another diagnostic method is the lung scintigraphy, which leads to poorer results in terms of specificity.

Therapy

Aims of therapy are in first place the hemodynamic stabilization of the patient and later the recanalization of the affected vessel and the prophylaxis of recurrencies. According to this, the application of oxygen should be the first step to counter the respiratory insufficiency. Anticoagulation is indicated and should be initated with heparin and continued with marcumar or warfarin later on. The INR should be maintained between 2 and 3 for at least 6 months. When recurrencies occur or the patients risk is very high, even a lifelong application may be indicated. In cases of severe hemodynamic instability, which can lead to cardiogenic shock, often thrombolysis with rt-PA, urokinase or streptokinase is advised. Fragementation of the thrombus with catheters or operative thrombectomy rarely occur.

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