Anaphylaxis
Key Points
- Anaphylaxis: Type I (immediate) hypersensitivity — life-threatening systemic allergic reaction; onset within minutes to hours of allergen exposure
- Triggers: Medications (34%), foods (31%), insect stings (20%); in infants, food accounts for 73%
- Mechanism: IgE cross-linking → mast cell/basophil degranulation → histamine + mediator release → vasodilation + bronchoconstriction
- First-line treatment: Epinephrine 1:1,000 IM into thigh — NOT antihistamines alone
- Faster onset = more severe reaction — symptoms within minutes indicate more dangerous anaphylaxis
- Post-episode monitoring: Risk of biphasic reaction (second wave) 4–12 hours after initial reaction
Pathophysiology
Anaphylaxis is a Type I (immediate) hypersensitivity reaction — the most rapid and severe form of allergic response.
Mechanism:
- Sensitization (first exposure): Allergen triggers production of IgE antibodies → IgE binds to mast cells and basophils
- Re-exposure: Allergen binds to IgE on mast cells → degranulation → massive release of chemical mediators
Chemical Mediators and Effects:
| Mediator | Effect |
|---|---|
| Histamine | Vasodilation, ↑ vascular permeability, urticaria, angioedema, hypotension, bronchospasm |
| Prostaglandin D | Bronchoconstriction, pulmonary and cardiac vascular constriction |
| Leukotrienes | Bronchoconstriction, ↑ vascular permeability, airway edema |
| Platelet-activating factor | Bronchoconstriction, ↑ vascular permeability |
| TNF-alpha | Sustained inflammatory response |
Result: Profound vasodilation → hypotension; bronchoconstriction and laryngeal edema → respiratory failure; angioedema → airway obstruction.
Common Triggers
| Category | Examples |
|---|---|
| Medications (34%) | Penicillin, NSAIDs, aspirin, contrast dye, vaccines, chemotherapy agents |
| Foods (31%) | Peanuts, tree nuts, shellfish, fish, milk, eggs, wheat |
| Insect stings (20%) | Bee, wasp, hornet, fire ant |
| Latex | Gloves, medical equipment |
| Other | Exercise-induced, idiopathic (unknown trigger) |
Clinical Manifestations by Severity
| Severity | Manifestations | Onset |
|---|---|---|
| Mild | Peripheral tingling, warm sensations, throat fullness, periorbital swelling, nasal congestion, sneezing, tearing, pruritus | Within 2 hours |
| Moderate | All mild symptoms + anxiety, flushing, laryngeal edema, dyspnea, wheezing, cough, bronchospasm | Within 2 hours |
| Severe (Anaphylactic Shock) | Rapid progression of above + severe bronchospasm, cyanosis, hypotension, dysphagia, seizures, abdominal cramping, vomiting, diarrhea, respiratory arrest, coma | Rapid onset (minutes) |
Airway Priority
Faster onset = more severe anaphylaxis. Symptoms appearing within minutes of exposure require immediate emergency intervention. Laryngeal edema can rapidly progress to complete airway obstruction.
Key systemic signs:
- Respiratory: Wheezing, stridor, dyspnea, cyanosis
- Cardiovascular: Tachycardia, hypotension, shock
- Integumentary: Urticaria (hives), angioedema, erythema, flushing
- GI: Nausea, vomiting, abdominal cramping, diarrhea
- Neurological: Anxiety, “sense of impending doom,” altered LOC, seizures
Hypersensitivity Types (Context)
| Type | Mechanism | Examples |
|---|---|---|
| Type I (Immediate) | IgE-mediated mast cell degranulation | Anaphylaxis, allergic rhinitis, asthma |
| Type II (Cytotoxic) | IgG/IgM against cell-surface antigens | Hemolytic transfusion reactions, ABO incompatibility |
| Type III (Immune Complex) | Immune complex tissue deposition | Lupus (SLE), serum sickness, glomerulonephritis |
| Type IV (Delayed) | T-cell mediated | Contact dermatitis, tuberculin skin test, graft rejection |
Diagnostic Tests
- Clinical diagnosis — rapid assessment and treatment cannot wait for laboratory results
- Tryptase (mast cell enzyme) — elevated up to 3 hours after anaphylactic reaction; confirms diagnosis retrospectively
- Plasma histamine levels, total serum IgE, eosinophil count
- Skin testing — after episode resolves, to identify specific allergen
- CBC with differential
Emergency Management
Emergency Priority: Epinephrine First
Epinephrine is the ONLY first-line treatment for anaphylaxis. Antihistamines alone are NOT adequate and must NOT delay epinephrine administration.
Epinephrine Administration
- Concentration: 1:1,000 (1 mg/mL) for IM injection
- Route/Site: Intramuscular injection into outer mid-thigh (fastest absorption)
- Dose: 0.3–0.5 mg IM in adults; may repeat every 5–15 minutes
- IV epinephrine: Lower concentration 1:10,000 continuous infusion for refractory hypotension
- Mechanism: Vasoconstriction (raises BP), bronchodilation, reverses urticaria and angioedema
Additional Interventions
| Intervention | Purpose |
|---|---|
| Airway management | Positioning, supplemental O2; intubation if laryngeal edema compromises airway |
| IV access | Large-bore IV; fluid resuscitation (normal saline, lactated Ringer’s) |
| Diphenhydramine (H1 blocker) | Reduces urticaria and pruritus — adjunct only, NOT substitute for epinephrine |
| Ranitidine/famotidine (H2 blocker) | Additional antihistamine effect — adjunct |
| Corticosteroids (methylprednisolone) | Reduce late-phase inflammation and biphasic reaction risk |
| Bronchodilators (albuterol) | Treat persistent bronchospasm |
| Vasopressors (norepinephrine, dopamine, vasopressin) | Refractory hypotension unresponsive to epinephrine |
| Glucagon | For patients on beta-blockers (beta-blockers blunt epinephrine response) |
Nursing Interventions
Immediate Actions (Emergency):
- Call rapid response team/provider
- Administer epinephrine IM into thigh immediately
- Maintain airway — position upright if breathing difficulties; prepare for intubation
- Supplemental oxygen — high-flow if cyanosis or dyspnea
- Remove/stop the offending allergen (stop IV medication, remove stinger)
- Establish IV access — administer fluids for hypotension
- Monitor vital signs continuously; place on cardiac monitor
Post-Episode Care:
- Observe for biphasic reaction — second wave of anaphylaxis may occur 4–12 hours after initial episode
- Minimum observation period: 4–6 hours (longer for severe reactions)
- Prescribe or educate on epinephrine auto-injector (EpiPen) for home use
- Medical alert bracelet recommendation
- Referral to allergist for trigger identification and desensitization
Patient Education:
- Avoid identified triggers at all times
- Always carry 2 epinephrine auto-injectors — inject at first sign of reaction, then call 911
- Notify all healthcare providers of allergy history
- Wear medical alert identification
- Antihistamines alone are insufficient — use EpiPen for anaphylaxis
Related Concepts
- hypersensitivity-types-and-anaphylaxis-response — Detailed hypersensitivity type classifications
- immune-system — IgE and mast cell immune mechanisms
- blood-transfusion-verification-initiation-and-reaction-response — Transfusion reactions (Type II)
- medication-side-effect-surveillance-and-reporting — Medication-induced anaphylaxis monitoring
- bronchodilators — Bronchodilator therapy for bronchospasm
- oxygen-therapy — Oxygen delivery in respiratory emergency
- antibiotics — Penicillin as most common drug cause of anaphylaxis
Self-Check
- A patient who just received IV ampicillin suddenly develops urticaria, wheezing, and hypotension. What is the priority intervention, and what specific medication must be administered first?
- A patient was treated for anaphylaxis 3 hours ago and appears to have recovered. The nurse is preparing to discharge the patient. What teaching and monitoring considerations are essential before discharge?
- A patient in anaphylaxis is not responding to epinephrine administration. The patient is known to take metoprolol for hypertension. What medication should the nurse anticipate administering, and why?