Anaphylaxis Overview Quiz

Definition of Anaphylaxis

• Anaphylaxis is a life-threatening reaction caused by immunoglobulin E (IgE) mediated immediate hypersensitivity.
• It is characterized by rapid onset and severe symptoms after exposure to an allergen.

Pathophysiology

• Exposure to allergens stimulates B lymphocytes, leading to the production of IgE antibodies.
• IgE antibodies bind to mast cells and basophils, sensitizing them for future exposure.
• Subsequent exposure to the allergen causes cross-linking of IgE, triggering degranulation of mast cells and basophils.
• Degranulation releases histamine, tryptase, prostaglandins, and leukotrienes, causing vasodilation, capillary leak, and smooth muscle contraction.

Symptoms and Diagnosis

• Symptoms can vary in severity and may include significant cardiac, respiratory, or gastrointestinal distress.
• A decrease in systolic blood pressure (SBP) by 30% from baseline is a key diagnostic criterion.

Emergency Treatment

• Immediate administration of epinephrine is critical; it should be given as soon as anaphylaxis is suspected.
• Utilize an Epinephrine Autoinjector (EpiPen), dosing at 0.01 mg/kg (max 0.5 mg), injected intramuscularly into the mid-outer thigh.
• Patients can self-administer up to 2 doses if symptoms persist.

Supportive Measures

• Prioritize airway, breathing, circulation, and mental status assessment.
• Position the patient supine with elevated legs, unless respiratory distress necessitates upright positioning.
• Administer supplemental oxygen at high flow rates (70% to 100%).

Fluid Resuscitation

• Large-bore IV catheters for intravenous access; normotensive adults receive isotonic saline at 125 mL/hour.
• Hypotensive patients may need 1-2 liters rapidly; up to 7 liters may be required for severe cases.

Monitoring and Advanced Care

• Continuous monitoring of cardiovascular status, blood pressure, heart rate, respiratory rate, and oxygen saturation.
• Intubation may be necessary for patients with stridor or severe respiratory compromise.

Epinephrine Administration

• No absolute contraindication for epinephrine; it is the first-line treatment.
• IM administration can be repeated every 5-15 minutes as needed.
• Avoid IV bolus due to risks of cardiovascular complications; IV infusion is an option if IM is ineffective.

Mechanism of Action of Epinephrine

• Alpha-1 effect: causes vasoconstriction and decreases mucosal edema.
• Beta-1 effect: increases heart rate and contractility.
• Beta-2 effect: induces bronchodilation and reduces inflammatory mediator release.

Side Effects of Epinephrine

• Common side effects include anxiety, restlessness, headache, dizziness, palpitations, and tremors.
• Rare but severe side effects: myocardial infarction, arrhythmias, and intracranial hemorrhage.

Additional Treatments

• Antihistamines (H1 & H2 blockers) for symptomatic relief.
• Inhaled bronchodilators like albuterol to alleviate bronchospasm.
• Glucagon for patients on beta-blockers (1-2 mg IV/IM).
• Corticosteroids (e.g., Methylprednisolone) to prevent secondary phase reactions.

Prophylactic Treatment

• Education on allergen avoidance and the importance of carrying EpiPens.
• Desensitization therapy can be considered for unavoidable allergens, especially in IgE-mediated hypersensitivity.
• Immunologic mechanisms of desensitization include development of non-IgE antibodies, regulatory T cell induction, and immune deviation from Th2 to Th1 response.