Anaphylaxis
Alternative names:
anaphylactic reaction; anaphylactic shock; shock - anaphylactic
Definition:
A life-threatening type of allergic
reaction.
Causes, incidence, and risk factors:
Anaphylaxis is an acute
systemic (whole body)
type of allergic reaction.
It occurs when a person has become sensitized (that is, the
immune system has been triggered to recognize a substance
as a threat to the body). On the second or subsequent exposure
to the substance, an allergic reaction occurs. This reaction
is sudden, severe, and involves the whole body.
The immune system releases antibodies.
The tissues release histamine and other substances. This causes
muscle contractions and
constriction of the airways, resulting in wheezing;
difficulty breathing;
and gastrointestinal symptoms such as abdominal
pain, cramps, vomiting,
and diarrhea. Histamine
causes the blood vessels to dilate (which lowers blood
pressure) and fluid to leak from the bloodstream into
the tissues (which lowers the blood volume) resulting in shock.
Fluid can leak into the alveoli (air sacs) of the lungs causing
pulmonary edema. Hives
and angioedema (hives
on the lips, eyelids, throat, and so on.) often occur, and
angioedema may be severe enough to cause obstruction of the
airway. Prolonged anaphylaxis can cause heart arrhythmias.
Some drugs (polymyxin, morphine, X-ray
dye, and others) may cause an anaphylactoid reaction (anaphylactic-like
reaction) on the first exposure. This is usually from a toxic
or idiosyncratic reaction rather than the "immune system"
mechanism that occurs with "true" anaphylaxis.
Anaphylaxis can occur in response to any allergen.
Common causes include insect
bites/stings, horse serum (used in some vaccines), food
allergies, and drug allergies.
Pollens and other inhaled allergens rarely cause anaphylaxis.
Some people have an anaphylactic reaction with no identifiable
cause.
Anaphylaxis occurs infrequently. However, it is life threatening
and can occur at any time. Risks include prior history of
any type of allergic reaction.
Update Date: 02/09/00
Updated by: J. Gordon Lambert, MD, Associate Medical Director,
Utah Health Informatics and adam.com
editorial
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