Anaphylaxis is a severe, potentially life-threatening allergic reaction that can occur rapidly and requires immediate medical intervention. It is a systemic hypersensitivity reaction that involves multiple organ systems.
Anaphylaxis is triggered by the release of mediators from mast cells and basophils, typically due to the cross-linking of immunoglobulin E (IgE) bound to high-affinity IgE receptors. Non-IgE-mediated mechanisms also exist and can involve direct activation of mast cells and basophils by substances like drugs, contrast agents, and physical factors.
Common Triggers
- Foods: Peanuts, tree nuts, shellfish, fish, milk, eggs, soy, and wheat.
- Medications: Antibiotics (penicillin, cephalosporins), NSAIDs, anesthetics, and monoclonal antibodies.
- Insect stings: Bees, wasps, hornets, and fire ants.
- Latex: Common in healthcare settings due to gloves and other equipment.
- Exercise: Sometimes in combination with food or drugs.
Clinical Presentation
Symptoms typically appear within minutes to hours after exposure to the allergen and may include:
- Skin: Urticaria (hives), angioedema, flushing, itching.
- Respiratory: Dyspnea, wheezing, stridor, bronchospasm, laryngeal edema.
- Cardiovascular: Hypotension, syncope, tachycardia, arrhythmias.
- Gastrointestinal: Nausea, vomiting, diarrhea, abdominal pain.
- Neurological: Dizziness, confusion, sense of impending doom.
Diagnosis
Anaphylaxis is primarily a clinical diagnosis based on the rapid onset of symptoms following exposure to a known allergen. Diagnostic criteria include:
- Acute onset of symptoms involving the skin, mucosal tissue, or both, along with respiratory compromise or reduced blood pressure.
- Two or more of the following after exposure to a likely allergen: involvement of skin/mucosal tissue, respiratory compromise, reduced blood pressure, or persistent gastrointestinal symptoms.
- Reduced blood pressure after exposure to a known allergen.
Management
Immediate Actions:
- Epinephrine: Administer intramuscularly in the mid-outer thigh. Dosage is typically 0.3-0.5 mg for adults and 0.01 mg/kg for children, up to a maximum of 0.3 mg.
- Call for emergency medical services: Even if the patient appears to be recovering.
- Positioning: Lay the patient flat, elevate legs if hypotensive, and avoid sudden changes in posture. Keep the patient sitting if there are breathing difficulties.
- Oxygen: Administer high-flow oxygen if there are respiratory symptoms or hypoxemia.
- Intravenous access: Establish to administer fluids for hypotension.
Adjunctive Treatments:
- Antihistamines: Diphenhydramine or cetirizine can help alleviate skin symptoms but are not a substitute for epinephrine.
- Corticosteroids: Methylprednisolone or prednisone to prevent biphasic reactions, though evidence of their efficacy is limited.
- Bronchodilators: For bronchospasm, inhaled beta-agonists such as albuterol.
Monitoring and Follow-Up:
- Observation: Patients should be observed for 4-6 hours after initial treatment due to the risk of biphasic reactions.
- Education: Patients should be educated about avoiding known triggers, recognizing symptoms, and using an epinephrine auto-injector.
- Referral: Refer to an allergist/immunologist for further evaluation and management, including possible desensitization therapies.
Prevention
- Identification of Allergens: Through history, skin prick testing, or serum-specific IgE testing.
- Education: On avoidance strategies and proper use of epinephrine auto-injectors.
- Emergency Action Plan: Develop and review an anaphylaxis emergency action plan with the patient and caregivers.