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 An allergic reaction is a response to chemicals the body releases to combat certain
stimuli, called allergens. Almost any substance can trigger the body’s immune system
and cause an allergic reaction. Allergic reactions occur most often in response to five
categories of stimuli: insect bites and stings, medications, foods, plants, and
chemicals.
 An allergic reaction may range from mild and local, involving itching, redness, and
tenderness, to severe and systemic, including shock and respiratory failure.
 Anaphylaxis is a life-threatening allergic reaction mounted by multiple organ systems
that must be treated with epinephrine. Wheezing and skin wheals can be signs of
anaphylaxis.
 The immune system protects the human body from substances and organisms that are
considered foreign to the body.
 Allergens enter the body through oral ingestion, injection or envenomation,
inhalation, or topical absorption. Injected or inhaled allergens tend to cause the most
severe reactions.
 When a foreign substance first invades the body, the primary response begins. If the
body is unable to identify the substance, immune cells record the features of the
outside substance and produce antibodies to inactivate the foreign substance. This
process is called development of sensitivity.
 Basophils and mast cells contain antibodies and can recognize the foreign substance
should it enter the body again. Basophils are stationed in specific sites within the
tissues. Mast cells are on patrol throughout the body.
 Chemical mediators are essentially the body’s weapons against foreign substances.
They release substances when an antigen invades the body and combines with one of
the antibodies. If this response spreads throughout the body (becoming systemic), it
causes the signs and symptoms of an anaphylactic reaction. Allergic reactions are
more localized.
 Histamines are some of the primary chemical mediators. They cause the blood vessels
in the local area to dilate and the capillaries to leak; this translates into flushed skin,
hypotension, tissue swelling, and fluid secretion. Leukotrienes are another chemical
mediator and cause additional dilation and leaking of fluid into the tissues.
 Signs and symptoms of an allergic reaction are varied but can include hives, pruritis
(itching), flushed skin, swelling, respiratory symptoms (wheezing, stridor, dyspnea,
and angioedema), cardiovascular symptoms, gastrointestinal symptoms, neurologic
symptoms, and even shock if the reaction is severe.
 In assessing a person who may be having an allergic reaction, check for flushing,
itching, and swelling skin; hives; wheezing and stridor; a persistent cough; a decrease
in blood pressure; a weak pulse; dizziness; abdominal cramps; and headache.
 The patient history will help to identify problems specific to the allergic reaction.
When assessing a patient with an allergic reaction, ask if the patient has a history of
allergies, what the patient was exposed to, when the exposure occurred, and how the
patient was exposed. Determine the onset of symptoms, what the effects of the
exposure have been, and how they have progressed.
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All patients with suspected anaphylaxis require oxygen. Management of anaphylaxis
also includes removing the offending agent, providing fluid resuscitation as needed,
administering epinephrine, and transporting promptly.
People who know that they are allergic to bee, hornet, yellow jacket, or wasp venom
often carry a bee sting kit that contains epinephrine in an auto-injector. You may help
to administer this medication in this form with authorization from medical control.
Always provide prompt transport to the hospital for any patient who is having an
allergic reaction or has been bitten by a poisonous insect. Remember that the patient’s
condition can deteriorate rapidly. Carefully monitor the patient’s vital signs en route,
especially for airway compromise.