Definition
An embolism is an obstruction in a
blood vessel due to a blood clot or other foreign matter that gets
stuck while traveling through the bloodstream. The plural of embolism is
emboli.
Description
Emboli have moved
from the place where they were formed through the bloodstream to another
part of the body, where they obstruct an artery and block the flow of
blood. The emboli are usually formed from blood clots
but are occasionally comprised of air, fat, or tumor tissue. Embolic
events can be multiple and small, or single and massive. They can be
life-threatening and require immediate emergency medical care. There are
three general categories of emboli: arterial, gas, and pulmonary.
Pulmonary emboli are the most common.
Arterial embolism
In
arterial emboli, blood flow is blocked at the junction of major
arteries, most often at the groin, knee, or thigh. Arterial emboli are
generally a complication of heart disease. An arterial embolism in the brain (cerebral embolism) causes stroke,
which can be fatal. An estimated 5-14% of all strokes are caused by
cerebral emboli. Arterial emboli to the extremities can lead to tissue
death and amputation of the affected limb if not treated effectively within hours. Intestines and kidneys can also suffer damage from emboli.
Gas embolism
Gas
emboli result from the compression of respiratory gases into the blood
and other tissues due to rapid changes in environmental pressure, for
example, while flying or scuba diving. As external pressure decreases,
gases (like nitrogen) that are dissolved in the blood and other tissues
become small bubbles that can block blood flow and cause organ damage.
Pulmonary embolism
In a pulmonary embolism,
a common illness, blood flow is blocked at a pulmonary artery. When
emboli block the main pulmonary artery, and in cases where there are no
initial symptoms, a pulmonary embolism can quickly become fatal.
According to the American Heart Association, an estimated 600,000
Americans develop pulmonary emboli annually and 60,000 die from it.
A
pulmonary embolism is difficult to diagnose. Less than 10% of patients
who die from a pulmonary embolism were diagnosed with the condition.
More than 90% of cases of pulmonary emboli are complications of deep vein thrombosis, blood clots in the deep vein of the leg or pelvis.
Causes and symptoms
Arterial
emboli are usually a complication of heart disease where blood clots
form in the heart's chambers. Gas emboli are caused by rapid changes in
environmental pressure that could happen when flying or scuba diving. A
pulmonary embolism is caused by blood clots that travel through the
blood stream to the lungs and block a pulmonary artery. More than 90% of
the cases of pulmonary embolism are a complication of deep vein
thrombosis, which typically occurs in patients who have had orthopedic surgery and patients with cancer or other chronic illnesses like congestive heart failure.
Risk factors for arterial and pulmonary emboli include: prolonged bed rest, surgery, childbirth, heart attack, stroke, congestive heart failure, cancer, obesity, a broken hip or leg, oral contraceptives,
sickle cell anemia, chest trauma, certain congenital heart defects, and
old age. Risk factors for gas emboli include: scuba diving, amateur
plane flight, exercise, injury, obesity, dehydration, excessive alcohol, colds, and medications such as narcotics and antihistamines.
Symptoms of an arterial embolism include:
Common symptoms of a pulmonary embolism include:
Less common symptoms include:
- coughing up blood
- pain caused by movement or breathing
- leg swelling
- bluish skin
- fainting
- swollen neck veins
Diagnosis
An embolism can be
diagnosed through the patient's history, a physical exam, and diagnostic
tests. The use of various tests may change, as physicians and clinical
guidelines evaluate the most effective test in terms of accuracy and
cost. For arterial emboli, cardiac ultrasound and/or arteriography are
ordered. For a pulmonary embolism, a chest x ray, lung scan, pulmonary angiography, electrocardiography, arterial blood gas measurements, and venography or venous ultrasound could be ordered.
Diagnosing an arterial embolism
Ultrasound
uses sound waves to create an image of the heart, organs, or arteries.
The technologist applies gel to a hand-held transducer, then presses it
against the patient's body. The sound waves are converted into an image
that can be displayed on a monitor. Performed in an outpatient
diagnostic laboratory, the test takes 30-60 minutes.
An
arteriogram is an x ray in which a contrast medium is injected to make
the arteries visible. It can be performed in a radiology unit,
outpatient clinic, or diagnostic center of a hospital.
Diagnosing a pulmonary embolism
A
chest x ray can show fluid build-up and detect other respiratory
diseases. The perfusion lung scan shows poor flow of blood in areas
beyond blocked arteries. The patient inhales a small amount of
radiopharmaceutical and pictures of airflow into the lungs are taken
with a gamma camera. Then a different radiopharmaceutical is injected
into an arm vein and lung blood flow is scanned. A normal result
essentially rules out a pulmonary embolism. A lung scan can be performed
in a hospital or an outpatient facility and takes about 45 minutes.
Pulmonary
angiography is one of the most reliable tests for diagnosing a
pulmonary embolism. Pulmonary angiography is a radiographic test that
involves injection of a radio contrast agent to show the pulmonary
arteries. A cinematic camera records the blood flow through the patient,
who lies on a table. Pulmonary angiography is usually performed in a
hospital's radiology department and takes 30-60 minutes.
An
electrocardiograph shows the heart's electrical activity and helps
distinguish a pulmonary embolism from a heart attack. Electrodes covered
with conducting jelly are placed on the patient's chest, arms, and
legs. Impulses of the heart's activity are traced on paper. The test
takes about 10 minutes.
Arterial blood gas
measurements are sometimes helpful but, alone, they are not diagnostic
for pulmonary embolism. Blood is taken from an artery instead of a vein,
usually in the wrist.
Venography is used to
look for the most likely source of a pulmonary embolism, deep vein
thrombosis. It is very accurate, but it is not used often, because it is
painful, expensive, exposes the patient to a fairly high dose of
radiation, and can cause complications. Venography identifies the
location, extent, and degree of attachment of the blood clots and
enables the condition of the deep leg veins to be assessed. A contrast
solution is injected into a foot vein through a catheter. The physician
observes the movement of the solution through the vein with a
fluoroscope while a series of x rays are taken. Venography takes between
30-45 minutes and can be done in a physician's office, a laboratory, or
a hospital. Radionuclide venography, in which a radioactive isotope is
injected, is occasionally used, especially if a patient has had
reactions to contrast solutions. Venous ultrasound is the preferred
evaluation of leg veins.
As noninvasive methods
such as high-speed computed tomography (CT) scanning improve, they may
be used to diagnose emboli. For instance, spiral (also called helical)
CT scans may be the preferred tool for diagnosing pulmonary embolism in
pregnant women.
Treatment
Patients with
emboli require immediate hospitalization. They are generally treated
with clot-dissolving and/or clot-preventing drugs. Thrombolytic therapy
to dissolve blood clots is the definitive treatment for a severe
pulmonary embolism. Streptokinase, urokinase, and recombinant tissue
plasminogen activator (TPA) are used. Heparin has been the anticoagulant
drug of choice for preventing formation of blood clots. A new drug has
been approved for treatment of acute pulmonary emboli. Called
fondaparinux (Arixtra), it usually is administered with Warfarin, an
oral anticoagulant. Warfarin is sometimes used with other drugs to treat
acute embolism events and is usually continued after the
hospitalization to help prevent future emboli. Arixtra also has been
used on an ongoing basis to prevent pulmonary emboli.
In
the case of an arterial embolism, the affected limb is placed in a
dependent position and kept warm. Embolectomy is the treatment of choice
in the majority of early cases of arterial emboli in the extremities.
In this procedure, a balloon-tipped catheter is inserted into the artery
to remove thromboembolic matter.
With a
pulmonary embolism, oxygen therapy is often used to maintain normal
oxygen concentrations. For people who can't take anticoagulants and in
some other cases, surgery may be needed to insert a device that filters
blood returning to the heart and lungs.
Prognosis
Of
patients hospitalized with an arterial embolism, 25-30% die, and 5-25%
require amputation of a limb. About 10% of patients with a pulmonary
embolism die suddenly within the first hour of onset of the condition.
The outcome for all other patients is generally good; only 3% of
patients die who are properly diagnosed early and treated. In cases of
an undiagnosed pulmonary embolism, about 30% of patients die.
Prevention
Embolism
can be prevented in high risk patients through antithrombotic drugs
such as heparin, venous interruption, gradient elastic stockings, and
intermittent pneumatic compression of the legs. The combination of
graduated compression stockings and low-dose heparin is significantly
more effective than low-dose heparin alone.
Gradient
elastic stockings, also called antiembolism stockings, decrease the
risk of blood clots by compressing superficial leg veins and forcing
blood into the deep veins. They can be knee-, thigh-, or waist-length.
Many physicians order the use of stockings before surgery and until
there is no longer an elevated risk of developing blood clots. The risk
of deep vein thrombosis after surgery is reduced 50% with the use of
these stockings. The American Heart Association recommends that the use
of graduated compression stockings be considered for all high-risk
surgical patients.
Intermittent pneumatic
compression involves wrapping knee- or thigh-high cuffs around the legs
to prevent blood clots. The cuffs are connected to a pump that inflates
and deflates, mimicking the heart's normal pumping action and reducing
the pooling of blood. Intermittent pneumatic compression can be used
during surgery and recovery and continues until there is no longer an
elevated risk of developing blood clots. The American Heart Association
recommends the use of intermittent pneumatic compression for patients
who cannot take anticoagulants, for example, spinal cord and brain
trauma patients.
Resources
Periodicals
Doyle, Nora M., et al. "Diagnosis of Pulmonary Embolism: A Cost-effective Analysis." American Journal of Obstetrics and Gynecology September 2004: 1019-1024.
Truelove, Christiane. "First for Pulmonary Embolism." Med Ad News August 2004: 82.
Organizations
American Heart Association. 7320 Greenville Ave. Dallas, TX 75231. (214) 373-6300. http://www.americanheart.org.
Key terms
Anticoagulants — Drugs that suppress, delay, or prevent blood clots. Anticoagulants are used to treat embolisms.
Artery — A blood vessel that carries blood from the heart to other body tissues. Embolisms obstruct arteries.
Deep vein thrombosis — A blood clot in the calf's deep vein. This frequently leads to pulmonary embolism if untreated.
Emboli — Clots or other substances that travel through the blood stream and get stuck in an artery, blocking circulation.
Thrombolytics — Drugs that dissolve blood clots. Thrombolytics are used to treat embolisms.
Gale Encyclopedia of Medicine. Copyright 2008 The Gale Group, Inc. All rights reserved.
embolism /em·bo·lism/ (em´bŏ-lizm) the sudden blocking of an artery by a clot or foreign material which has been brought to its site of lodgment by the blood current.
air embolism that due to air bubbles entering the veins from trauma, surgical procedures, or severe decompression sickness.
cerebral embolism embolism of a cerebral artery.
coronary embolism embolism of a coronary artery.
fat embolism obstruction by a fat embolus, occurring especially after fractures of large bones.
miliary embolism embolism affecting many small blood vessels.
paradoxical embolism
blockage of a systemic artery by a thrombus originating in a systemic
vein that has passed through a defect in the interatrial or
interventricular septum.
pulmonary embolism obstruction of the pulmonary artery or one of its branches by an embolus.
