Pulmonary embolism is defined as a blockage of a pulmonary artery caused by a thrombus dislodged usually from the deep veins of the lower limbs.
Presentation
The typical presentation of the pulmonary embolism includes sudden onset of pleuritic chest pain, shortness of breath and hypoxia [7]. Most of the patients might have no clinical presentation at all. Symptoms may also vary from patient to patient. Hence, the diagnosis is made in the case of unexplained respiratory problems after excluding the other probable causes.
Other atypical symptoms include hemoptysis, productive cough, abdominal pain, flank pain, seizures, syncope, wheezing, fever and altered level of consciousness [8].
Workup
The history and clinical examination of a case of pulmonary embolism are usually not sufficient to establish the diagnosis of pulmonary embolism with certainty. Hence, in cases of unexplained respiratory problems, certain investigations must be carried out to reach the final diagnosis [9].
A hypercoaguable workup must be carried out to screen for antithrombin 3 deficiency, protein C or protein S deficiency, connective tissue disorders and homocystinurea.
White blood count, arterial blood gases, D dimer testing, brain natriuretic peptide, serum troponin levels and ischemia modified albumin level are potentially useful laboratory tests that can indicate the presence or absence of pulmonary embolism in the patient.
Imaging techniques that are helpful in confirming the diagnosis of pulmonary embolism include computed tomography angiography, pulmonary angiography, chest radiography, ECG, magnetic resonance imaging (MRI), venography and duplex ultrasonography.
Treatment
In patients with suspected deep venous thrombosis or pulmonary embolism, anti-coagulant therapy is initiated immediately [10].
Anticoagulant therapy with heparin administration decreases the mortality rate from 30% to less than 10%. Various anti-coagulation medications include unfractionated heparin, low weight heparin, warfarin, fondaparinux and factor Xa inhibitors.
Thrombolytic agents such as alteplase/reteplase and urokinase/streptokinase are also used in the treatment of pulmonary embolism.
Surgical options for management of pulmonary embolism include:
- Catheter embolectomy and fragmentation or surgical embolectomy
- Placement of vena cava filters
Along with these treatment options, supportive care to the patient is ensured.
Prognosis
As far as the common causes of sudden death are concerned, pulmonary embolism is second only to sudden cardiac death.
Up to 10% of the patients who develop pulmonary embolism die within the first hour. Recurrence of pulmonary embolism subsequently causes death in 30% of the patients.
With appropriate anti-coagulant therapy, the mortality rate reduced to less than 5%.
Etiology
More than 90% of the pulmonary emboli result from the dislodging of thrombi from the deep veins of the lower limb. Other less common sites of thrombus formation include prostatic and pelvic veins. Pulmonary emboli usually do not originate in the upper limb except in intravenous drug abusers.
The factors that predispose to venous thrombosis in the lower limbs include the following.
- Immobility (bed-rest, surgery and limb paralysis)
- Low cardiac output
- Varicose veins
Venous trauma:
- Trauma
- Intravenous cannulation
Increased coagubility:
- Use of drugs such as oral contraceptives
- Malignancy
- Dehydration
- Polycythemia
- Nephritic syndrome
- Ulcerative colitis
- AIDS (Acquired Immunodeficiency Syndrome) [1]
Inherited coagulation defects:
- Antithrombin III, Protein S and Protein C deficiency
Miscellaneous:
- Smoking [2]
Epidemiology
The per annum incidence of pulmonary embolism in the United States is 1 case per 1000 persons [3]. Although most of these patients are asymptomatic, 60-80% of the patients with DVT develop pulmonary embolism.
In hospitalized patients, pulmonary embolism is the third most common cause of death (up to 650,000 deaths per year). Venous thromboembolism is a major health problem with an incidence of about 250,000 incident cases per year [4] [5].
The incidence of pulmonary embolism and the mortality occurring from it varies from country to country. A research indicates that male sex is more prone to the development of pulmonary embolism with a mortality rate 20-30% higher as compared to females. Pulmonary embolism is much more common in blacks as compared to whites [6].
Pathophysiology
Pulmonary emboli arise most commonly from the deep veins of the calves. Any factor or disease that cases stasis of blood in the veins can predispose to the formation of thrombi. Dislodged thrombi reach the lung after traveling through the right side of the heart.
Large emboli occlude the proximal arteries and the right ventricular outflow, causing a rapid decrease in the the cardiac output and leading to right ventricular failure. The prominent features are those of vascular collapse e.g. hypotension and syncope.
On the other hand, small and medium sized emboli occlude the segmental arteries causing infarction of the lung segment involved. It manifests as pleural chest pain and hemoptysis.
In contrast, multiple micro-emboli occlude the capillary beds of the lungs. Due to collateral vascular supply, there is no pulmonary infarction but there insidious loss of the microvascular bed supplying the gas exchange units of the lungs leading to pulmonary hypertension and right ventricular failure.
Prevention
Prevention of the development of venous thromboembolism can effectively reduce the likelihood of the development of pulmonary embolism. This is done by the following measures:
Avoid venous stasis:
Venous stasis during surgery can be avoided by stimulation of the calf muscles. Following surgery, early mobilization and leg exercises are helpful in reducing the likelihood of venous thromboembolism.
Use of anticoagulants in susceptible individuals:
Anticoagulants such as warfarin and heparin are used in the patients who are at high risk for developing thromboembolism.
Summary
Pulmonary emboli are thrombi that dislodge into the lungs usually from the deep veins of the lower limbs. Less common sites of thrombus formation include the veins of the pelvis, prostate and the upper limbs.
Pulmonary emboli may be small, medium or large. Each of these cause respiratory and hemodynamic compromise by different mechanisms. Hence, pulmonary embolism is not a disease; rather it is the complication of deep venous thrombosis (DVT).
It is a life threatening emergency and needs to be diagnosed and treated promptly.
Patient Information
Pulmonary embolism refers to the state in which masses of clotted blood that form in the lower limbs dislodge into the lungs. Males are more prone to the development of this complication.
Smoking, obesity, decreased physical activity and intake of unbalanced diet make the person more prone to the development of pulmonary embolism. It is a very dangerous condition and the patient needs to be hospitalized immediately. High risk patients must be identified and preventive measures must be carried out.
References
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- Stein PD, Beemath A, Matta F, et al. Clinical characteristics of patients with acute pulmonary embolism: data from PIOPED II. The American journal of medicine. Oct 2007;120(10):871-879.
- Horlander KT, Mannino DM, Leeper KV. Pulmonary embolism mortality in the United States, 1979-1998: an analysis using multiple-cause mortality data. Archives of internal medicine. Jul 28 2003;163(14):1711-1717.
- Heit JA. The epidemiology of venous thromboembolism in the community: implications for prevention and management. Journal of thrombosis and thrombolysis. Feb 2006;21(1):23-29.
- Silverstein MD, Heit JA, Mohr DN, Petterson TM, O'Fallon WM, Melton LJ, 3rd. Trends in the incidence of deep vein thrombosis and pulmonary embolism: a 25-year population-based study. Archives of internal medicine. Mar 23 1998;158(6):585-593.
- Schneider D, Lilienfeld DE, Im W. The epidemiology of pulmonary embolism: racial contrasts in incidence and in-hospital case fatality. Journal of the National Medical Association. Dec 2006;98(12):1967-1972.
- Worsley DF, Alavi A. Comprehensive analysis of the results of the PIOPED Study. Prospective Investigation of Pulmonary Embolism Diagnosis Study. Journal of nuclear medicine : official publication, Society of Nuclear Medicine. Dec 1995;36(12):2380-2387.
- Carrascosa MF, Batan AM, Novo MF. Delirium and pulmonary embolism in the elderly. Mayo Clinic proceedings. 2009;84(1):91-92.
- Torbicki A, Perrier A, Konstantinides S, et al. Guidelines on the Diagnosis and Management of Acute Pulmonary Embolism The Task Force for the Diagnosis and Management of Acute Pulmonary Embolism of the European Society of Cardiology (ESC). Revista espanola de cardiologia. 2008;61(12):1330.
- Kearon C, Kahn SR, Agnelli G, et al. Antithrombotic therapy for venous thromboembolic disease: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines (8th Edition). Chest. Jun 2008;133(6 Suppl):454S-545S.