Encyclopedia of Health and Medicine

pulmonary embolism 225
typically the deep veins of the legs. It most commonly
develops as a consequence of venous stasis,
in which the blood moves sluggishly through the
veins. The blood’s slow movement allows blood to
pool, permitting clots to begin to form especially
on and around the valves in the veins. Clot fragments
or the entire clot can break free, floating
through the bloodstream.
Because the veins become larger as they
approach the HEART, the bloodstream easily carries
the clots through the right heart and into the pulmonary
arteries and the lungs. Occasionally the
clot that causes a pulmonary embolism originates
in the heart’s right atrium. Large clots can occlude
(block) the pulmonary arteries at the point where
the right and left pulmonary arteries diverge
(bifurcation of the pulmonary artery).
As a consequence of the intimate correlation
between alveolar function and the flow of blood
through the capillary network that enmeshes the
alveoli, the loss of capillary flow resulting from
pulmonary embolism effectively shuts down all
alveoli beyond (distal to) the site of the occlusion.
Any loss of functioning alveoli subsequently limits
the ability of the lungs to convey oxygen to the
blood. The larger the occluded artery, the more
immediate and significant the pulmonary consequences.
Symptoms and Diagnostic Path
The symptoms of pulmonary embolism vary
widely and can be subtle or may be as severe and
immediate as those of HEART ATTACK, and are similar.
Such symptoms include
• sudden, severe CHEST PAIN
• DYSPNEA (difficulty BREATHING)
• diaphoresis (breaking into a cold sweat)
• HYPOTENSION (low BLOOD PRESSURE)
• TACHYCARDIA (rapid heart rate)
• TACHYPNEA (rapid BREATHING)
A person who experiences a massive pulmonary
embolism may have little time between
feeling fine and going into shock and cardiovascular
collapse. Smaller emboli or recurrent (chronic)
pulmonary embolism episodes generally produce
milder variations of these same symptoms along
with productive COUGH and HEMOPTYSIS (blood in
the SPUTUM).
The diagnostic path seeks immediately to determine
whether the symptoms are cardiovascular
(heart attack) or pulmonary. An ELECTROCARDIO-
GRAM (ECG) does not show evidence of acute cardiac
injury in pulmonary embolism, which is the
first major point of differentiation. Arterial blood
gases show how severely the pulmonary
embolism is affecting the body’s oxygenation.
Diagnostic imaging procedures the pulmonologist
may conduct include COMPUTED TOMOGRAPHY (CT)
SCAN, MAGNETIC RESONANCE IMAGING (MRI), pulmonary
angiography, and a specialized imaging
procedure called ventilation/perfusion scan.
Treatment Options and Outlook
Hospitalization with intensive pulmonary support
and immediate ANTICOAGULATION THERAPY is necessary
for most circumstances of pulmonary
embolism. The risk of death is highest within the
first few hours of the embolism. Anticoagulation
therapy targets preventing the formation of additional
emboli. THROMBOLYTIC THERAPY (“clot buster”
drugs) to dissolve the clots that have already
formed is appropriate for some people. Surgery
(either OPEN SURGERY or via catheterization) to
mechanically break up the clot may be an option
in severe situations. Recovery depends on the
extent of lung affected, the existence of any
underlying causes or health conditions, and the
rapidity of diagnosis and treatment. People who
recover from pulmonary embolism often require
ongoing anticoagulation therapy though do not
have significant permanent lung damage.
Risk Factors and Preventive Measures
Pulmonary embolism is most likely to occur in
people who have restricted venous flow due to
lower extremity VARICOSE VEINS or incompetent
veins (veins that have lost elasticity and valve
function), who are physically inactive, or who
have recently had surgery or a major trauma
(which means the body is forming clots for HEAL-
ING and also usually means limited physical movement).
People who have untreated ATRIAL
FIBRILLATION have increased risk for pulmonary
embolism. OBESITY also increases the risk for pulmonary
embolism because it exerts additional