Understanding the Allergic Response Spectrum
Allergic reactions exist on a spectrum from mild localized responses to severe systemic anaphylaxis. As an EMT, distinguishing between these presentations is critical because treatment urgency varies dramatically. A mild allergic reaction may only require monitoring and transport, while anaphylaxis demands immediate epinephrine administration and rapid transport to prevent cardiovascular collapse and death.
The immune system mediates allergic reactions through immunoglobulin E (IgE) antibodies. When a sensitized individual encounters an allergen, mast cells and basophils release histamine and other chemical mediators. In a localized reaction, this release is confined to the area of exposure. In anaphylaxis, this release becomes systemic, affecting multiple organ systems simultaneously.
Mild to Moderate Allergic Reactions
Localized allergic reactions typically present with itching, hives (urticaria), localized swelling, and redness at the site of exposure. The patient's vital signs remain stable, and there is no respiratory compromise. These patients should be monitored for progression to anaphylaxis, especially within the first 30 minutes of exposure. Common triggers include insect stings, foods (peanuts, shellfish, tree nuts), medications, and latex.
Management of mild allergic reactions includes removing the allergen source if possible (such as scraping away a bee stinger), monitoring vital signs, and transporting for evaluation. If the patient has a prescribed antihistamine, you may assist with administration per local protocol.
Recognizing Anaphylaxis
Anaphylaxis is defined by the involvement of two or more organ systems following allergen exposure. The key systems affected include:
- Respiratory: Wheezing, stridor, hoarseness, dyspnea, throat tightness, tongue or uvula swelling
- Cardiovascular: Hypotension, tachycardia, weak pulse, dizziness, syncope
- Skin: Widespread hives, flushing, angioedema (swelling of deeper tissues)
- Gastrointestinal: Nausea, vomiting, abdominal cramping, diarrhea
The onset of anaphylaxis is usually rapid, occurring within minutes of exposure, though delayed reactions can occur up to several hours later. Biphasic reactions, where symptoms return after initial improvement, occur in up to 20% of cases.
Epinephrine Administration
Epinephrine is the first-line treatment for anaphylaxis and should be administered as soon as anaphylaxis is recognized. The standard dose for adults is 0.3 mg intramuscularly via auto-injector (EpiPen) in the lateral thigh. For pediatric patients, the dose is 0.15 mg (EpiPen Jr.) for patients weighing 15 to 30 kg. Epinephrine works by reversing bronchospasm, reducing airway edema, increasing blood pressure, and suppressing further mediator release. Do not delay epinephrine administration; early use is associated with better outcomes. Be prepared to administer a second dose if symptoms do not improve within 5 to 15 minutes.