Anaphylaxis

Definition

A life-threatening systemic hypersensitivity reaction to contact with an allergen;

it may appear within minutes of exposure to the offending substance. Manifestations include respiratory distress, pruritus, urticaria, mucous membrane swelling, gastrointestinal disturbances (including nausea, vomiting, pain, and

diarrhea), and vascular collapse. Virtually any allergen may incite an anaphylactic

reaction, but among the more common agents are proteins such as antisera,

hormones, pollen extracts, Hymenoptera venom, foods; drugs (especially antibiotics); and diagnostic agents. Atopy does not seem to predispose to anaphylaxis from penicillin or venom exposures. Anaphylactic transfusion reactions are covered in Chap. 5.

Clinical Presentation

Time to onset is variable, but symptoms usually occur within seconds to minutes

of exposure to the offending antigen:

• Respiratory: mucous membrane swelling, hoarseness, stridor, wheezing

• Cardiovascular: tachycardia, hypotension

• Cutaneous: pruritus, urticaria, angioedema

Diagnosis

Made by obtaining history of exposure to offending substance with subsequent

development of characteristic complex of symptoms.

TREATMENT

Mild symptoms suchas pruritus and urticaria can be controlled by administration

of 0.2 to 0.5 mL of 1:1000 epinephrine solution SC, repeated at 20-

min intervals as necessary.

An IV infusion should be initiated. Hypotension should be treated by IV

administration of 2.5 mL of 1:10,000 epinephrine solution at 5- to 10-min

intervals, volume expanders, e.g., as normal saline, and vasopressor agents,

e.g., dopamine, if intractable hypotension occurs.

Epinephrine provides both _- and _-adrenergic effects, resulting in vasoconstriction

and bronchial smooth-muscle relaxation. Beta blockers are relatively

contraindicated in persons at risk for anaphylactic reactions.

The following should also be used as necessary:

• Antihistamines such as diphenhydramine 50 to 100 mg IM or IV

• Aminophylline 0.25 to 0.5 g IV for bronchospasm

• Oxygen

• Glucocorticoids—IV; not useful for acute manifestations but may help

control persistent hypotension or bronchospasm

Prevention

Avoidance of offending antigen, where possible; skin testing and desensitization

to materials suchas penicillin and Hymenoptera venom, if necessary. Individuals

should wear an informational bracelet and have immediate access to an

unexpired epinephrine kit.