An allergic reaction is the body’s overreaction to a substance known as an allergen. This immune response releases chemicals, such as histamine, which trigger symptoms ranging from mild skin irritation to a severe, life-threatening condition called anaphylaxis. When symptoms involve difficulty breathing, a sudden drop in blood pressure, or rapidly developing swelling, immediate emergency medical care is necessary. The Emergency Room (ER) provides the immediate, high-level resources required to stabilize a patient experiencing a severe or rapidly worsening allergic episode. Time is a factor, as anaphylaxis can progress quickly to respiratory or cardiac arrest without prompt intervention.
Initial Assessment and Triage
The moment a patient arrives at the ER with a suspected allergic reaction, a rapid assessment process called triage begins. Staff immediately prioritize the patient based on the severity of their symptoms using a system that focuses on Airway, Breathing, and Circulation (A-B-C). This initial evaluation determines if the reaction is a localized issue or a systemic crisis that requires immediate, life-saving intervention.
Triage nurses and physicians quickly check for signs of respiratory distress, such as wheezing, stridor, or a hoarse voice, which indicate swelling of the throat or airways. Vital signs are assessed, looking for a rapid heart rate (tachycardia) or dangerously low blood pressure (hypotension), which are hallmarks of anaphylactic shock. The patient’s recent history is also quickly gathered, focusing on the onset and progression of symptoms and any known allergen exposure.
The presence of multi-system involvement, like hives paired with vomiting and lightheadedness, classifies the reaction as more severe. This severity classification dictates the speed of transfer to a treatment room and the immediate availability of specialized equipment and medications.
Emergency Interventions for Anaphylaxis
For a patient showing signs of true anaphylaxis, the immediate intervention is the administration of epinephrine, the primary life-saving medication. Epinephrine acts as a non-selective alpha and beta-adrenergic agonist. The alpha-adrenergic effects cause vasoconstriction, constricting blood vessels to raise critically low blood pressure and improve blood flow to vital organs.
Simultaneously, the beta-adrenergic effects work to relax the smooth muscles in the lungs, opening the airways to relieve wheezing and shortness of breath. Epinephrine is typically given intramuscularly into the anterolateral thigh for the most rapid and reliable absorption into the bloodstream. An adult dose is generally 0.2 to 0.5 milligrams of a 1:1000 concentration, and it may be repeated every five to fifteen minutes if symptoms persist or worsen.
If the patient presents with severe airway swelling or respiratory failure, advanced airway management, such as intubation, may be necessary to secure the breathing passage and allow for mechanical ventilation. For patients experiencing shock due to severe vasodilation and fluid leakage, establishing intravenous (IV) access is a priority to administer large volumes of crystalloid fluids. This fluid resuscitation helps to restore blood pressure and support circulation while the epinephrine takes effect.
Secondary Pharmacological Management
Once the immediate life threat has been stabilized with epinephrine, the ER team introduces supportive medications to manage persistent symptoms and prevent a recurrence. Antihistamines, specifically H1 and H2 receptor blockers, are administered to mitigate the effects of the histamine released by the immune system.
H1 blockers, such as diphenhydramine, primarily address symptoms like itching, hives (urticaria), and swelling (angioedema). H2 blockers, such as famotidine, are often given in combination because they may offer additional benefit in reducing cutaneous symptoms and potentially aiding in blood pressure stabilization. These medications block the action of histamine at its various receptors but do not reverse the life-threatening effects of anaphylaxis on blood pressure or breathing.
Corticosteroids, such as methylprednisolone, are also administered, though their therapeutic effect is often delayed by several hours. The purpose of giving steroids is not to treat the acute reaction but to prevent a potential biphasic reaction, which is a recurrence of symptoms hours after the initial episode has resolved. If the patient continues to experience significant wheezing despite epinephrine, an inhaled bronchodilator like albuterol may be given to improve airflow.
Observation, Discharge, and Follow-Up
After the patient is stable and all acute symptoms have resolved, they enter an observation period to monitor for a biphasic reaction. This secondary reaction can occur in a small percentage of patients. The standard length of observation is often four to six hours following the complete resolution of symptoms.
Patients who had a particularly severe initial reaction, required multiple doses of epinephrine, or have a history of asthma may require a longer observation period or even hospital admission for continuous monitoring. Discharge only occurs once the patient is symptom-free, hemodynamically stable, and deemed to be at low risk for a rebound reaction.
The patient is provided with a prescription for an epinephrine autoinjector (EpiPen). They will also receive prescriptions for a short course of oral medications, such as an antihistamine and a corticosteroid. Finally, a referral for follow-up with an allergist is strongly recommended to identify the specific allergen, perform further testing, and develop a comprehensive long-term management and prevention plan.