Pulmonary embolism

Learning objectives

A pulmonary embolism (PE) is a blood clot that blocks blood flow to an artery in the lung
Most often the blood clot originates in a deep leg vein and moves through the venous circulation to the heart
Severe PE is an immediately life-threatening situation
Low cardiac output and a ventilation/perfusion mismatch contribute to hypoxemia
Right ventricular failure due to acute pressure overload is considered the primary cause of death in severe PE

Predisposing factors for venous thromboembolism (VTE) are:

Strong (OR > 10)	Moderate (OR 2–9)	Weak risk factors (OR < 2)
Fracture of the lower limb Hospitalization for heart failure or atrial fibrillation/flutter ≤ 3 months Hip or knee replacement Major trauma Myocardial infarction ≤ 3 months Previous VTE spinal cord injury	Arthroscopic knee surgery Autoimmune diseases Blood transfusion CVCs IVs Chemotherapy Congestive heart failure Respiratory failure Erythropoiesis-stimulating agents IVF Oral contraceptive therapy Postpartum period Infection IBD Cancer Paralytic stroke Superficial vein thrombosis Thrombophilia	Bed rest > 3 days Diabetes mellitus Arterial hypertension Immobility due to sitting (e.g. prolonged car or air travel) Increasing age Laparoscopic surgery Obesity Pregnancy Varicose veins

Symptoms of PE are aspecific and can include:

Respiratory	Dyspnea Hemoptysis Hypoxemia Hypocapnia Chest pain
Cerebral	Syncope
Cardiac	Hemodynamic instability ECG might show sinus tachycardia, S1Q3T3 pattern, incomplete or complete right bundle branch block (usually in more severe cases), or atrial arrhythmias

Diagnostic scores like the pulmonary embolism rule-out Criteria (PERC) can help to determine whether further investigations for PE are warranted
D-dimers have a high negative predictive value, meaning that a normal D-dimer level renders acute PE or DVT unlikely
The positive predictive value of elevated D-dimer levels is low, meaning it isn’t useful as a test to confirm PE
Use age-adjusted D-dimers (age x 10 µg/l) for patients aged >50 years
Computed tomographic pulmonary angiography (CTPA) is the gold standard for diagnosing PE

The pulmonary embolism severity Index (PESI) reliably identifies patients with a low risk for 30-day mortality
Administer supplemental oxygen to patients with PE and SaO2 <90%
Initiate mechanical ventilation if necessary and start with non-invasive techniques if possible
Treat right heart failure in hemodynamically unstable patients with PE
- Fluids
- Vasopressors
- Mechanical circulatory support
Anticoagulant patients with a high or intermediate clinical probability of PE while awaiting diagnostic test results
Low-molecular-weight heparin (LMWH) and fondaparinux are preferred over unfractionated heparin UFH for initial anticoagulation in PE
Administer UFH in patients with overt hemodynamic instability and patients with renal impairment (≤ G4)
When using vitamin K antagonists:
- Continue anticoagulation with UFH, LMWH, or fondaparinux in parallel with the oral anticoagulant for ≥ 5 days
- Until the INR has been 2.0–3.0 for 2 consecutive days
Start thrombolysis in patients with high-risk PE
Perform a thrombectomy if thrombolysis is contraindicated or has failed in patients