Allergic Reactions and Anaphylaxis - NREMT: AEMT Level

Severe, systemic allergic reaction with airway or circulatory compromise. Involves rapid onset of life-threatening symptoms due to massive histamine release affecting multiple organ systems.

Histamine. Released by mast cells and basophils, it triggers increased vascular permeability and smooth muscle contraction.

Airway compromise (laryngeal edema/bronchospasm). Fatal outcomes often result from asphyxiation due to upper or lower airway obstruction rather than cardiovascular collapse alone.

Respiratory distress or hypotension after allergen exposure. Indicates systemic involvement beyond localized symptoms, requiring immediate intervention to prevent progression.

Deeper swelling of skin/mucosa, often lips, tongue, or airway. Involves histamine-mediated fluid accumulation in subcutaneous or submucosal layers, potentially compromising airways.

Stridor. Results from turbulent airflow through a narrowed upper airway, signaling potential rapid deterioration to complete obstruction.

Wheezing. Arises from bronchoconstriction due to inflammatory mediators, indicating lower respiratory tract involvement.

Epinephrine. Acts rapidly to reverse bronchospasm and hypotension through adrenergic effects, making it essential for stabilizing the patient.

Intramuscular injection into the anterolateral thigh. Provides optimal absorption and onset due to the muscle's vascularity, recommended by guidelines for non-IV access.

$0.3\text{ mg}$ IM (=$0.3\text{ mL}$ of $1!:!1{,}000$). Delivers a standardized dose to achieve therapeutic adrenergic effects without exceeding safe limits for adults.

$0.01\text{ mg/kg}$ IM (max $0.3\text{ mg}$). Weight-based dosing ensures efficacy while minimizing overdose risk, with a cap aligned to adult standards.

$0.3\text{ mg}$ auto-injector. Provides a pre-measured dose suitable for individuals over approximately 30 kg to ensure rapid administration.

$0.15\text{ mg}$ auto-injector. Designed for children under 30 kg to deliver an appropriate reduced dose for safety and effectiveness.

Alpha-1 vasoconstriction raising SVR and blood pressure. Counteracts histamine-induced vasodilation by increasing peripheral resistance, thereby stabilizing hemodynamics.

Beta-2 bronchodilation. Relaxes bronchial smooth muscle to alleviate constriction caused by inflammatory mediators in the airways.

Diphenhydramine (H$1$ antihistamine). Blocks histamine receptors to mitigate secondary symptoms, though it does not address acute life-threatening features.

Corticosteroids (for example, methylprednisolone). Inhibit prolonged inflammatory responses, helping prevent biphasic reactions in the recovery phase.

Albuterol (beta-2 agonist) via nebulizer. Targets residual bronchospasm by promoting bronchodilation as a supportive measure following primary treatment.

High-flow oxygen; titrate to adequate oxygenation and ventilation. Supports oxygenation in hypoxemic patients while avoiding hyperoxia, aligned with EMS protocols for respiratory emergencies.

Raised, itchy wheals (hives) from histamine-mediated skin edema. Occurs when histamine causes fluid leakage into dermal tissues, producing characteristic skin manifestations.

Asthma exacerbation. Presents with similar respiratory symptoms but usually without cutaneous or gastrointestinal signs of allergy.

Recent exposure to a known or likely allergen before symptom onset. Establishes temporal association between trigger and symptoms, crucial for confirming the diagnosis in the field.

Isotonic crystalloid (normal saline or lactated Ringer’s). Replenishes intravascular volume lost to increased permeability, aiding in blood pressure restoration.

Recurrence of anaphylaxis after initial resolution without re-exposure. Involves a secondary release of mediators hours later, necessitating monitoring even after initial symptom resolution.