Pulmonary Embolism

History

sudden onset shortness

recent history of surgery or trauma

signs or symptoms of DVT

immobility

hypercoagulability

medications: oral contraceptives

Physical Exam

General appearance: degree of respiratory distress or fever

increased pulmonic component of 2nd heart sound

Assess for DVT.

Identify pleural rubs, wheezes, crackles, or signs of pneumothorax.

Hypotension, tachycardia, tachypnea, fever

Lab Investigations

A D-dimer should be done only if low probability.

Arterial blood gases may show acidemia, hypoxemia, and hypercapnia, but even sublte changes such as mild alkalosis may be present (why?) Elevated LDH can result from tissue infarction, but is neither sensitive nor specific.

D-dimer is sensitive (95-97%) but not specific (45%). It is useful in people with low pre-test probability.

If there is a high probability, not as useful, except to exclude PE.

Degradation product of cross-linked fibrin

Other factors, such as troponin, can help with prognosis, though not diagnosis

Thrombophilia workup

FVL

Protein C and Protein S (though do not measure if on warfarin)

antithrombin III

prothrombin gene mutation

APLA, ACl-A, LAC

Diagnostic Imaging

CT or VQ scan should be done if risk is low but D-dimer is high

CT/VQ should be first-line if risk is high

ECG is abnormal in 70%.

• sinus tachycardia and arrhythmia/flutter
• RAD, RVH
• most specific sign is S₁Q₃T₃ - S in I, Q and inverted T in III

Chest X-ray

Chest X-ray can often show pulmonary infarction, though most cases are normal and its main role is to exclude other causes. A wedge-shaped area is strongly suggestive. Chest X ray is often normal but can show atelectasis, isolated infiltrates, or small pleural effusion.

Abrupt cutoff of pulmonary vessels or enlarged central pulmonary arteries may also be present (Westermark's sign).

CT

CT angiography (spiral CT) is useful for PE. Use contrast material, excuding those at risk of nephrotoxicity. Sensitive for main, lobar, and segmental arteries, but not subsegmental. Can also help identifty differential diagnoses. More specific than VQ scan.

Ventilation-Perfusion Scan

V/Q scan. is a nuclear test. More sensitive, but less specific than spiral CT. Nucleotide injection peripherally and assess for areas of low perfusion. Step 2: Radionuclides inhaled, and lung fields assessed.

Tests reveals

• low
• intermediate
• high probability (~80% of PE)

If underlying lung disease, like COPD, makes tests less diagnostic.

Negative predictive value of 91%.

With low probability V/Q and low clinical probability: 4% cahnce of PE

CT angiography

CT pulmonary angiography (CT PA): dye injected just as they enter the CT. If patients have poor kidney function, or are allergic to dye, will not work.

Capable of evaluating to 5th order pulmonary arterial branch, to 2-3 mm or even smaller.

Findings include:

• central intra-arterial filling defect
• complete occlusion of pulmonary artery

With a high-quality CTPA, a negative result will safely rule out PE.

However, it is invasive, requires contrast, and is not readily available.

U/S

Doppler compression ultrasound of legs is the most effective bedside test.

Echocardiography