Pulmonary embolism (PE) is a potentially life-threatening condition where a blood clot travels to the lungs and blocks blood flow. It requires prompt diagnosis and treatment. The emergency room (ER) has an important role in evaluating patients with suspected PE. This article will discuss how the ER checks for pulmonary embolism.
Clinical Evaluation
The ER doctor will start with a medical history and physical exam. They will ask about risk factors like recent surgery, cancer, immobilization, smoking, obesity, oral contraceptives, and family history. Symptoms of PE include sudden shortness of breath, chest pain, coughing, leg pain or swelling. On exam, vital signs may show tachycardia and decreased oxygen saturation. There may be signs like distended neck veins, enlarged calf, or decreased breath sounds.
The Wells criteria is a scoring system to estimate pre-test probability of PE based on risk factors, symptoms, and exam findings. A score >4 indicates PE is likely and imaging should be done. A lower score means PE is less likely but still possible, requiring further workup.
Blood Tests
Basic lab tests check for signs of heart strain like elevated troponin and BNP levels. A D-dimer blood test is often done which detects fibrin degradation products, but can be elevated in many conditions. A negative D-dimer makes PE very unlikely. An arterial blood gas evaluates for hypoxemia and respiratory alkalosis from PE.
Imaging Studies
Chest X-Ray
A chest x-ray is frequently done first although it is not very sensitive for PE. It may show nonspecific findings like atelectasis, effusion, elevated diaphragm, or pulmonary edema. The main value is excluding other pulmonary diseases.
CT Pulmonary Angiography
CT pulmonary angiography (CTPA) is the gold standard test for diagnosing PE. Intravenous contrast is injected and CT scan visualizes the pulmonary arteries. It can directly show filling defects from blood clots obstructing flow. CTPA has around 90% sensitivity and 95% specificity for PE when interpreted by a radiologist. It can also identify other lung pathologies.
V/Q Scan
A ventilation/perfusion (V/Q) lung scan assesses air flow and blood flow. PE causes decreased blood flow to a segment of lung with normal ventilation, resulting in V/Q mismatch. This test has moderate accuracy with around 80% sensitivity and 97% specificity for PE. It is done when CTPA is contraindicated, like with contrast allergy or renal failure.
Echocardiogram
Echocardiogram uses ultrasound to evaluate heart structure and function. Findings like pulmonary hypertension, right ventricular strain, and thrombi in heart chambers can support PE diagnosis but are nonspecific. It is not adequate to rule out PE but helpful in risk stratification.
Venous Ultrasound
Leg vein ultrasound locates deep vein thrombosis (DVT), which can cause PE if clot fragments break off and travel to lungs. Only around 50% of PE cases have concurrent DVT, so a negative ultrasound cannot exclude PE.
Diagnostic Algorithm
The ER evaluates clinical probability first. In low probability, typically just D-dimer is done. If positive, CTPA should be obtained. In intermediate probability, CTPA is warranted, sometimes preceded by leg ultrasound. High probability warrants immediate CTPA. Some examples are shown:
| Clinical Probability | Initial Workup | If Positive | If Negative |
|---|---|---|---|
| Low | D-dimer | CTPA | PE very unlikely |
| Intermediate | Leg ultrasound | CTPA | CTPA |
| High | CTPA | Treat for PE | Evaluate other causes |
Treatment
Once PE is diagnosed, anticoagulation is started to prevent clot extension and new clots. Initial anticoagulation is typically with intravenous heparin or LMWH. Warfarin or DOACs are later transitioned for long-term therapy. Thrombolytics may be considered for massive PE with hemodynamic instability. Other supportive measures include supplemental oxygen and fluids. Admission for monitoring is warranted in moderate to severe PE.
Conclusion
The ER has an efficient approach to evaluating possible PE. It starts with clinical assessment to estimate pre-test probability. Lab tests and imaging, especially CTPA, provide objective evidence for the diagnosis. Low risk patients may just need D-dimer testing while higher risk warrants more aggressive workup. A timely, accurate diagnosis of PE is crucial for initiating anticoagulation and reducing the risk of complications like pulmonary hypertension and recurrent clots. The ER plays a pivotal role through clinical acumen and judicious use of available resources. A coordinated approach improves patient outcomes in this potentially deadly disease.