Guidelines for the Treatment of Anaphylaxis
Anaphylaxis is a rapid, systemic, potentially dangerous allergic reaction that can escalate to impact various bodily systems. Common triggers include food, insect bites and stings, medications, and specific environmental exposures. Anaphylaxis typically involves airway constriction, which may lead to respiratory difficulties and subsequent respiratory distress. Vasodilation (expansion of blood vessels) and vascular permeability (leakage from blood vessels) can cause distributive and volume shock. If untreated, the respiratory or cardiovascular consequences of anaphylaxis can result in death.
Anaphylaxis presents as a syndrome with a highly variable manifestation, affecting individuals across all demographics, whether or not they have a known allergy or a history of previous anaphylaxis. Field identification of anaphylaxis relies on a known or likely exposure to an allergen, alongside signs and symptoms that meet either of these two criteria:
Immediate onset of itching, hives, or facial swelling accompanied by any of the following: respiratory difficulties, hypotension (low blood pressure), or persistent gastrointestinal symptoms (nausea, vomiting, abdominal pain/cramps, diarrhea).
Sudden onset of hypotension or respiratory distress even without skin symptoms.
In practice, the first criterion directs the caregiver to observe for a sudden onset (minutes to several hours) of symptoms affecting more than one organ system. A suddenly scratchy or tight throat alongside severe abdominal cramps meets this criterion, as does a rapid emergence of hives with feelings of faintness or dizziness, or a patient presenting with facial swelling and shortness of breath.
Treatment
Epinephrine should be administered as quickly as possible once anaphylaxis is recognized, particularly when airway involvement, respiratory difficulties, or a significant cardiovascular issue is present. Epinephrine is the crucial, primary treatment as it counteracts all the mechanisms of anaphylaxis. It stabilizes immune cells, counteracts vasodilation and permeability, and alleviates airway constriction. In situations of potential anaphylaxis, there are no absolute contraindications for administering epinephrine. Patients should be positioned comfortably, ideally sitting or lying down. If feasible, remove the patient from the allergen: extract insect stingers, remove food, and stop cooking, for example. Do not induce vomiting.
Antihistamines (such as diphenhydramine or loratadine) and corticosteroids (like prednisone) are auxiliary, not primary treatments. Evidence supporting their effectiveness in anaphylaxis is inconsistent. They should be regarded as supplementary treatments. Recurrence of symptoms (biphasic reaction) is relatively infrequent but may occur hours later without re-exposure. The treatment remains the same as for the initial reaction: administer epinephrine.
Epinephrine Administration
Intramuscular (IM) injection of epinephrine into the outer thigh provides the quickest delivery of medication. If that muscle is not accessible, the upper arm serves as the next best site for injection. Inhaled epinephrine is generally ineffective.
Epinephrine Injection Devices
Delivery devices are categorized into three types: epinephrine autoinjectors (EpiPen, Auvi-Q, Adrenaclick); a manually administered, commercial pre-filled syringe (Symjepi); and vials/ampules with syringes. Refer to the ensuing section for more information on various devices. The standard IM dose for adults is 0.3 to 0.5 mg. For children weighing up to 25 kg (55 pounds), the dose is 0.15 mg. There is no upper limit on the number of doses for adults or children. Repeat doses can be administered every five to fifteen minutes until improvement is noted.
Epinephrine intended for IM injection is at a concentration of 1 mg/mL—0.3 mL of solution contains 0.3 mg of epinephrine.
Evacuation
Post-treatment for anaphylaxis, medical evacuation is commonly advised, though the timing and method of evacuation will depend on the patient’s condition, location, weather, and available resources. A patient who responds inadequately to treatment or requires multiple doses is considered high-risk. Limited supplies of epinephrine or inability to avoid contact with the allergen also heighten risk. A patient with persistent symptoms should be transported in a position of comfort—lying flat may be distressing to a patient struggling to breathe. Given the risk of another reaction and regardless of the evacuation plan, the patient should be monitored closely.
The primary principles are prevention and rapid response. At a minimum, plans should encompass briefing participants about allergy risks, including food handling precautions. All staff assigned to a group should be aware of where the organization’s epinephrine is located and be updated on its use. Prior to leaving the wilderness, guides/instructors should take a moment with participants who carry their own epinephrine to review the device’s use and agree on its carrying location for optimal availability and protection.
