Anaphylaxis

Carolyn Calpin

Introduction

Definition: potentially life-threatening allergic reaction
Most commonly IgE mediated reaction
Affected systems include skin (90%), respiratory (90%), gastrointestinal, cardiac, and CNS
May have wide range of clinical manifestations, may be subtle
Reliance on good history and examination is crucial
Common causative agents: food (peanuts and shellfish) and drugs (penicillin)
Etiologic agent may not be evident
Biphasic form:
- Episode appears to resolve, and then symptoms recur after several hours
- May occur in up to 30%
- Can occur despite appropriate treatment; therefore, observe all patients for several hours
- Late phase can occur 8-12 hours after the initial attack
- No reliable predictors of biphasic or protracted anaphylaxis

Clinical Presentation

Onset of symptoms within 5-30 minutes of exposure to antigen; however, symptoms may be delayed up to an hour or more
Early administration of intramuscular epinephrine is critical
Delayed administration of epinephrine may increase the risk of a biphasic reaction

Table 5.1 Signs and Symptoms

Respiratory	Upper: hoarseness, stridor, oropharyngeal or laryngeal edema, cough, complete obstruction
	Lower: bronchospasm, tachypnea, cyanosis, use of accessory muscles, respiratory arrest
Skin	Sensation of warmth, flushing, erythema, general pruritus, urticaria, angioedema
Gastrointestinal	Nausea, vomiting, crampy abdominal pain, diarrhea
Cardiovascular	Tachycardia, hypotension, arrhythmias, cardiac arrest
Neurologic	Dizziness, weakness, syncope, seizures
Other	Conjunctival injection, lacrimation, sneezing, mouth burning, itch