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The Wilderness Medical Society convened a panel to review the literature and develop evidence-based clinical practice guidelines on the treatment of anaphylaxis, with an emphasis on a field-based perspective. The review also included literature regarding the definition, epidemiology, clinical manifestations, and prevention of anaphylaxis.

Introduction

Anaphylaxis is an acute, systemic, potentially life-threatening allergic reaction that progresses to involve multiple body systems. Common triggers are foods, insect bites and stings, medications, and exercise.

Anaphylaxis commonly involves constriction of airways, which may progress to respiratory compromise and then respiratory distress. Vasodilation (widening blood vessels) and vascular permeability (leaking blood vessels) may result in distributive and volume shock. Untreated, the respiratory or cardiovascular effects of anaphylaxis can be fatal.

Because no comprehensive reporting system exists for anaphylaxis, it is hard to measure the risk. Observational studies of data from NOLS and Outward Bound (OB) over fifteen years find the incidence of anaphylaxis among students on courses is 10 (NOLS) and 21 (OB) per million person-days. Neither program has ever had an anaphylactic death.

Diagnosis

Anaphylaxis is a syndrome with highly variable presentation that can occur in people of any demographic and who may or may not have a known allergy or a history of previous anaphylaxis. Field identification of anaphylaxis is based on a known or probable exposure to an allergen, and signs and symptoms that meet either of these two criteria:

1.  Sudden onset of itching, hives, or facial swelling with any of these: respiratory compromise, hypotension (low blood pressure), or persistent gastrointestinal symptoms (nausea, vomiting, abdominal pain/cramps, diarrhea).
2. Acute onset of hypotension or respiratory compromise even without skin involvement.
In practice, criterion #1 directs the caregiver to look for an acute onset (minutes to several hours) of illness involving more than one organ system. A suddenly scratchy or tight throat with severe abdominal cramps meets this criterion, as does a sudden appearance of hives accompanied by feeling faint or dizzy, or a patient who presents with facial swelling with shortness of breath.

Criterion #2 is a reminder that, in the context of a known or probable allergen exposure, any critical problem with airway, breathing or circulation (ABCs) on the primary assessment alone indicates treatment with epinephrine. Skin signs are not observed in up to 10-20% of anaphylactic reactions.

Anaphylaxis is highly likely when either of the following two criteria is fulfilled:

Graphic adapted from World Allergy Organization Anaphlyaxis Guidance 2020 - ScienceDirect: Victoria Cardona, et. al. World Allergy Organization Anaphylaxis Guidance 2020, World Allergy Organization Journal, Volume 13, Issue 10, 2020.
Icons courtesy of https://www.flaticon.com

Treatment

Epinephrine should be given as soon as possible once anaphylaxis has been identified, especially in the presence of airway involvement, respiratory compromise or a serious cardiovascular problem. Epinephrine is the essential, primary treatment because it reverses all the mechanisms of anaphylaxis. It stabilizes immune cells, reverses vasodilation and permeability, and relieves airway constriction. In the context of possible anaphylaxis, there are no absolute contraindications for epinephrine.

Patients should be placed in a position of comfort, preferably seated or lying down. If possible, separate the patient from the allergen: remove insect stingers, take food away and cease cooking, for instance. Do not induce vomiting.

Antihistamines (for example, diphenhydramine or loratadine) and corticosteroids (for example, prednisone) are elective, not primary treatments. Evidence of benefit in anaphylaxis is inconsistent. They should be considered supplemental treatments.

Recurrence of symptoms (biphasic reaction) is relatively uncommon but may happen hours later without re-exposure. The treatment is the same as for the initial reaction: give epinephrine.

Epinephrine Administration

Intramuscular (IM) injection of epinephrine into the outer thigh delivers the most medication in the shortest time. If that muscle is inaccessible, the upper arm is the next best injection site. Epinephrine inhalers are generally ineffective.

Epinephrine Injection Devices

Delivery devices fall into three categories: epinephrine autoinjectors (EpiPen, Auvi-Q, Adrenaclick); a manually administered, commercial pre-filled syringe (Symjepi); and vials/ampules with syringes. See the next section for more on the different devices.

Dosage

The standard IM adult dose is 0.3 to 0.5 mg. For children up to 25 kg (55 pounds), the dose is 0.15 mg. There is no maximum number of doses for adults or children. Repeat doses can be given every five to fifteen minutes until there is improvement.

Epinephrine used for IM injection is a 1 mg/mL concentration—0.3 mL of solution contains 0.3 mg of epinephrine.

Evacuation

After treatment for anaphylaxis, medical evacuation is generally recommended, though the timing and method of evacuation will be influenced by patient condition, location, weather and available resources. A patient who responds incompletely to treatment or who requires more than one dose is a high-risk patient. A limited supply of epinephrine or inability to avoid allergen contact also increases risk. A patient whose symptoms persist should be carried in a position of comfort—lying flat may be intolerable to a patient struggling to breathe. Due to the risk of another reaction and regardless of the evacuation plan, the patient should be monitored carefully.

Managing the Risk of Anaphylaxis

Changes to US federal law in 2013 cleared a legal path for doctors to prescribe epinephrine to schools, venues and other entities, and for lay providers to receive training to use it. These “stock epinephrine entity laws” stipulate the qualifications of trainers; training content and how long the certificate is valid; how epinephrine must be obtained, stored and used by the organization or individuals; and reporting responsibilities and liability protections for entities and employees. Most such laws name autoinjectors specifically. Organizations and individuals planning to obtain epinephrine to treat others should be familiar with the regulations where they operate.

Selecting Equipment

When selecting an epinephrine delivery device, organizations and individuals should reference local laws and weigh the considerations of cost, staff training, and staff and client safety.

Epinephrine Delivery Devices

  • Epinephrine autoinjector devices that deliver a pre-measured dose are widely available and easy to use with a little training. They are designed to work through clothing, though winter or thick protective layers may need to be removed. People with known anaphylactic responses to food or environmental allergens often carry them. However, they are expensive.
  • Commercial pre-filled syringes are sterile, manual injectors. With these devices, the operator pushes a plunger to inject a pre-measured dose. They are less expensive than autoinjectors.
  • Vials/ampules and syringes, which are available in a kit (Epi Kit) or can be purchased separately, allow the epinephrine to be drawn up into syringes when needed. The dosage flexibility is an advantage when treating small children; however, additional training to calculate and draw up the correct dose is needed. The time to prepare a dose and the risk of an overdose can be reduced by pre-filling a syringe prior to the trip. (The unused syringe and epinephrine should be discarded after 90 days.) It is the least expensive option.
  • Needles for adults should be 22- to 25-gauge and at least 16 mm (5/8 inch) long. Ideally, syringes should be 1 cc or smaller and easy to read, with a safety feature to help prevent accidental needlestick. Consult with a physician when selecting needles and syringes.

Training

In addition to wilderness medicine or state-determined epinephrine training curriculum, regular practice with administration devices is important to prevent error and delay in the field. Companies that sell commercial injectors often also sell an empty, needle-less, reusable training version.

Staff and participants with known anaphylactic responses to food or environmental allergens often carry epinephrine autoinjectors. Even if an organization selects a different delivery system for the first aid kit, guides/instructors should also be trained to use the most common autoinjectors.

Storage

Regulations often require that epinephrine be stocked in a location that is reasonably secure and reasonably accessible, and that someone is assigned to monitor inventory and expiration.

Experience in austere conditions and during manufacturing shortages provides evidence that epinephrine retains its potency for up to nine months past its expiration date. In practice, that provides rationale, but not regulatory approval, for using recently expired epinephrine when no other option is available.

In the field, keeping medications within manufacturers’ temperature ranges is often a challenge. Limited research indicates that the temperature ranges and short-duration extremes as may occur in the field would not be expected to inactivate epinephrine. However, epinephrine should be protected from freezing in the field to ensure that it can be injected when it’s needed. Used devices, needles and syringes are biohazard materials and should be disposed of properly.

Including Participants with Allergies

Risk Tolerance

There is a growing expectation that people with severe allergies can and should be able to participate in the same opportunities as their peers. Organizations need to determine what allergies and what degree of sensitivity they can accommodate on programs, and establish clear processes for making such accommodations. Regardless of screening, some number of participants will arrive at the trailhead, put in, or dock with unknown severe allergies.

Risk Mitigations

Appropriate precautions and mitigations for people with allergies can reduce but not eliminate the risk of a reaction. Food stocking and packing need to be carefully organized to prevent cross-contamination. Even if the food issued to the group is closely controlled, participants and staff alike need to acknowledge the possible presence of food allergens in containers and equipment used by the group as well as public shelters, campsites and picnic areas along their route.

Medical History

History of previous anaphylactic reactions is an important but imperfect indicator of future risk. In the NOLS and OB data, just over 20% of reactions encountered in the field “were first-time reactions in persons without known histories of allergy.” Precipitants of anaphylaxis change as a person ages and desensitization protocols are becoming more available. Many features of wilderness trips, such as new foods, new physical environments, new challenges and stressors, or new OTC medication, may trigger an unexpected allergic reaction in people with or without a history.

Beginning a Trip

Once the devices are selected, the staff are trained and equipped, and the risks are understood by all parties, good field protocols are essential to managing the risk of anaphylaxis. The key principles are prevention and prompt response. At minimum, plans should be in place for briefing participants on allergy risks, including food handling precautions. All staff assigned to a group should know where the organization’s epinephrine will be carried and be refreshed on its use. Before leaving the frontcountry, guides/instructors should take a moment with participants who carry their own epinephrine to review the use of that device and agree on where it will be carried for the best balance of availability and protection.

Conclusion

The data show that classifying epinephrine use for the treatment of anaphylaxis by trained first aid providers is a low-risk solution to a high-risk problem.

Reference

Gaudio FG, Johnson DE, DiLorenzo K, Anderson A, Musi M, Schimelpfenig T, Leemon D, Blair-Smith C, Lemery J. Wilderness Medical Society clinical practice guidelines on anaphylaxis. Wilderness Environ Med. 2022;33(1):P75-91.

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