Pulmonary embolism

PE is a common condition that results in the occlusion of the pulmonary arteries by thrombotic material originating from a deep vein thrombosis. It can cause acute life-threatening, but potentially reversible, right heart failure. Nonthrombotic PE (resulting from fat, tumour, amniotic fluid, air, etc.) will not be discussed in this chapter.

Epidemiology

European incidence estimates of PE range from 6–20 cases per 10 000 inhabitants per year.

Causes/pathogenesis

PE and deep vein thrombosis are each clinical presentations of venous thromboembolic disease and share the same predisposing factors. PE is usually a consequence of a thrombosis in the veins of the legs or pelvis. Predisposing factors include age, previous venous thromboembolic disease, active malignancy, neurological disease that impairs mobility, medical and surgical events causing prolonged bed rest (such as heart or acute respiratory failure), trauma  and orthopaedic surgery, congenital or acquired thrombophilia, hormone replacement therapy and oral contraceptive therapy (table 1).

Clinical manifestations and consequences

PE is often difficult to diagnose, and may be missed because of its nonspecific presenting features. Patients may be asymptomatic or present with various signs and symptoms (breathlessness, chest pain, haemoptysis, cough, fever, tachycardia (rapid heart rate), tachypnoea (rapid breathing)). Syncope (fainting), hypotension and shock are signs of severity, indicating reduced haemodynamic reserve. Signs of deep vein thrombosis of the lower or upper limbs may be present.

Diagnosis

When considered in isolation, clinical signs, symptoms and routine tests, such as electrocardiograms, arterial blood gases and chest radiography, do not allow acute  PE to be definitively confirmed or excluded, although they do influence the index of suspicion. Despite the limited sensitivity and specificity of individual symptoms, signs and common tests, the combination of these variables, along with clinical judgement or use of a prediction rule, makes it possible to categorise patients with suspected PE in terms of increasing likelihood of PE. A low blood concentration of the fibrin degradation product D-dimer safely excludes PE in patients with a low or moderate clinical probability. Imaging of the proximal deep leg and pelvic veins by ultrasonography may identify a deep vein thrombosis (about 70% of patients with PE have a lower-limb deep vein thrombosis). A normal perfusion lung scan is reliable for excluding PE, while a high-probability ventilation/perfusion lung scan may confirm PE. The value of CT angiography for decision-making in suspected PE has been revolutionised by recent technological improvements and invasive pulmonary angiography is now rarely needed (figure 3). The performance of ventilation/perfusion scanning is poor when there is underlying chronic lung disease; CT angiography is superior in that context. In a patient with suspected PE who is in a critical condition (cardiogenic shock or hypotension), bedside echocardiography is particularly helpful in emergency management decisions (figure 4). In such patients, the absence of echocardiographic signs of right ventricular overload or dysfunction practically excludes PE as the cause of haemodynamic compromise.

 

Predisposing factor Patient-related Setting-related
Strong predisposing factors (risk increased >10-fold)
     Fracture (hip or leg)   x
     Hip or knee replacement   x
     Major general surgery   x
     Major trauma   x
     Spinal cord injury   x
Moderate predisposing factors (risk increased 2–9-fold)
     Arthroscopic knee surgery   x
     Central venous lines   x
     Chemotherapy   x
     Chronic heart or respiratory failure x  
     Hormone replacement therapy x  
     Malignancy x  
     Oral contraceptive therapy x  
     Paralytic stroke x  
     Pregnancy/postpartum   x
     Previous VTE x  
     Thrombophilia x  
Weak predisposing factors (risk increased <2-fold)
     Bed rest >3 days   x
     Immobility due to sitting (e.g. prolonged car or air travel)   x
     Increasing age x  
     Laparoscopic surgery (e.g. cholecystectomy)   x
     Obesity x  
     Pregnancy/antepartum x  
     Varicose veins x  
Table 1 – Predisposing factors for venous thromboembolism (VTE). Reproduced and modified from Anderson and
Spencer, 2003, with permission from the publisher.

Prevention

Antithrombotic prophylaxis with low-molecular weight heparin significantly reduces the risk of venous thromboembolic diseases in patients who are at risk. After an acute PE, long-term anticoagulation with anti-vitamin K drugs is necessary. The duration of treatment depends on the clinical circumstances and history of previous thromboembolic disease. In some patients at high risk of recurrent embolism it may be necessary to introduce an inferior vena cava filter.

Management

Initial management includes anticoagulation (unfractionated heparin, low molecular weight heparin or fondaparinux), which should be initiated without delay in patients with confirmed PE and in those with a high or intermediate clinical probability of PE, while the results of the diagnostic tests are awaited. Supplementary oxygen should be given to hypoxaemic patients. Systemic hypotension or shock should be managed aggressively to prevent progression of right ventricular failure and death. Thrombolytic therapy is the first-line treatment in patients with high-risk PE presenting with cardiogenic shock and/ or persistent hypotension. Surgical pulmonary embolectomy is a valuable therapeutic option in patients in whom thrombolysis is absolutely contraindicated or has failed.

Prognosis

The fatality rate of acute PE is 7–11%. Recurrent episodes are much more likely in individuals who have had a previous PE than after an initial deep vein thrombosis alone (about 60% after PE versus 20% after deep vein thrombosis). A small proportion (0.1– 4%) of patients will develop chronic thromboembolic PH (CTEPH) after acute PE, even after subclinical PE.

Future developments

Oral anticoagulants that require neither laboratory monitoring nor dose adjustment are currently in development. Preventive methods should also be implemented more widely.

Research needs

Better diagnostic methods are still required and the optimal duration of anticoagulation therapy needs to be clarified. The mechanisms of CTEPH are poorly understood and should be identified.

See the entire Pulmonary vascular disease Chapter