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Causes and Incidence The most common causes are insect stings, drugs, blood products, and parenteral enzymes. Anaphylaxis occurs in both sexes and across all age groups and races. Individuals with known allergies or previous sensitivity reactions are at greater risk.

Disease Process Histamine, leukotrienes, and other mediators are released when the antigen agent reacts with the IgE (antibody) on the basophils and mast cells. This causes smooth muscle contraction and vascular dilation. Vasodilation and escape of plasma into tissues causes urticaria and angioedema and a decrease in plasma volume, leading to shock. The escape of fluid from the alveoli causes pulmonary edema and angioedema. A prolonged reaction can produce cardiac arrhythmias and cardiogenic shock.

Symptoms

Mild

Queasiness, anxiety, hives, itching, flushing, sneezing, nasal congestion, runny nose, cough, conjunctivitis, abdominal cramps, tachycardia

Moderate

Malaise; urticaria; periorbital edema; pulmonary congestion; hoarseness; edema of the tongue, larynx, and pharynx; dysphagia; bronchospasm; dyspnea; wheezing; nausea; vomiting; diarrhea; hypotension; syncope; confusion

Severe

Cyanosis, pallor, stridor, occluded airway, hypoxia, respiratory arrest, cardiac arrhythmia, circulatory collapse, seizures, incontinence, coma, death

Potential Complications Lack of timely and appropriate treatment results in shock, cardiac and respiratory collapse, coma, and death.

Diagnostic Tests

Clinical evaluation

Rapid development of above signs and symptoms after exposure to a likely offending agent

Complete blood count

Normal or elevated hematocrit

Blood chemistry

Normal until circulatory collapse

Radiology

Normal or hyperinflation; edema

Electrocardiogram (ECG)

Normal until hypoxemia develops

Treatments Treatment centers around immediate and aggressive management of emerging symptoms. Maintaining the airway and blood pressure is critical.

Surgery

Tracheostomy

Drugs

Epinephrine and other drugs to counteract effects of mediator release and to block further mediator release; vasopressors to maintain blood pressure

General

Maintenance of airway, suctioning; monitoring of vital signs; monitoring of blood gases for acidosis; IV volume replacement; ECG monitoring for dysrhythmias; instruction in prophylaxis for those at risk