the severe end of the allergic reaction spectrum is anaphylaxis. Anaphylaxis can be variable in presentation and is defined by rapid progression to multiple system involvement (Box 21.2). In general, the incidence of anaphylaxis is increasing. The most common triggers are insect stings and food ingestions, particularly nuts. Food ingestions are particularly concerning and often the most severe. The faster a reaction develops after exposure to an allergen, the more likely it is to be severe and life‐threatening.
Causative agents
Almost anything can be a potential allergen (Box 21.3). Common agents include medications, foods and food additives, latex, arthropod bites and stings, mold, radiographic contrast media, and certain marine envenomations [1] (see Chapter 38). Some insect bites or stings, such as those of millipedes, caterpillars, and centipedes, most often cause only pain and local skin reactions such as blistering [4, 5]. Certain species of caterpillars have venom‐filled hair and spines that can cause systemic reactions, including anaphylaxis, within 2 hours of the sting [4]. Bites from kissing bugs are painless and usually occur during sleep. Most often, this results in localized swelling at the bite site, but can progress to systemic reactions [6]. There are also occasional rare reports of anaphylaxis from the bites of horse flies, deer flies, rats, and mice.
Hymenoptera account for the majority of severe allergic responses and anaphylaxis related to insect bites. There are three families of Hymenoptera: bees (honey bees and bumble bees), vespids (yellow jackets, hornets, and wasps), and stinging ants (fire ants). Since fire ants are in the Hymenoptera order, the venom in fire ant bites is similar to that of bees and hornets, thus a patient allergic to bee stings will also display an allergic reaction to a fire ant bite [7]. Africanized honeybees (“killer bees”) are an aggressive hybrid of the honeybee and have the same venom and sting repeatedly, thus increasing the risk of a severe reaction [8]. Approximately 1% of children and 3% of adults have reportedly had severe systemic allergic reactions to Hymenoptera venom [9]. Anaphylaxis can occur with a first‐time exposure. Insect stings are the only allergen for which specific immunotherapy currently exists. This is most likely due to the prevalence and severity of such responses in humans [10].
Assessment and general approach
The first step in EMS response to calls regarding allergic reactions and/or bites and stings is to ensure that the scene is safe. No rescue or treatment can occur if EMS personnel fall victim to the same process that is affecting the patient. Next, EMS clinicians should determine if the patient was stung or what activity was occurring before the allergic reaction. This will help determine if there is any special treatment needed and the potential for development of a severe reaction or anaphylaxis. EMS personnel should take all proper equipment, including life support, emergency drugs, and monitoring equipment with them when initially approaching the patient. Failure to do so may delay necessary treatment and result in further physiological decompensation of the patient.
Patient assessment should be done rapidly, first ensuring a patent airway. The patient should be queried about subjective shortness of breath or dysphagia, and the clinician should note if the patient’s voice is hoarse. The EMS clinician should listen to breath sounds, assessing for stridor or wheezing. Facial, tongue, uvula, or orbital swelling should be noted. A full set of vital signs should be obtained. In the case of insect stings, the patient should be removed from the scene to prevent further contact with the allergen. Continuous patient reassessment should center on ensuring a patent airway and monitoring vital signs. Any patient with a significant allergic reaction or potential for deterioration during transport should have at least one large‐bore IV line started with normal saline. The patient should be transported expediently to the closest most appropriate facility, depending on availability of local resources and other factors such as distance, weather, and terrain. The EMS clinician must remain vigilant in recognizing the signs and symptoms of anaphylaxis, as it is often unrecognized or there is a delay in recognition, particularly in children.
Prehospital treatment
If the patient is wheezing or in respiratory distress, 100% oxygen should be given with a non‐rebreather mask. A large‐bore IV with normal saline should be started and a fluid bolus given of at least 500 mL for an adult and 10 mL/kg for a child. If the patient was stung, any wounds should be inspected for retained stingers. If discovered, removal should be accomplished by scraping across the sting with a rigid thin object, such as an identification badge or credit card, to dislodge the stinger. Forceps or other squeezing devices should not be used as they may inadvertently disrupt the venom sac and release more venom into the patient. Local wound care with cool compresses and gauze covering should be applied. If there is the possibility of injected venom, the patient should be kept still and the affected extremity should be kept dependent, below the level of the heart, to slow the spread of venom [10, 11].
Box 21.3 Common causes of allergic reactions
Medications
Antibiotics
Penicillin, vancomycin, trimethoprim‐sulfamethoxazole
Angiotensin‐converting enzyme inhibitors
Aspirin
Nonsteroidal anti‐inflammatory drugs
Radiographic iodine‐based dyes
Skin creams, cosmetics
Human/animal proteins
Vaccines
Transfusions
Foods
Peanuts/nuts
Eggs
Wheat, soybeans
Shellfish
Additives
Red dye Sulfites
Stings/bites
Insects
Hornets/wasps
Fire ants
Scorpion
Caterpillars
Kissing bugs
Centipedes, millipedes
Arachnids
Ticks
Vertebrates (lizards, Gila monster)
Marine bites (sea nettle, man‐o‐war, jellyfish)
Mammals (rats/mice, gerbils, hamsters)
Environmental exposures
Mold
Latex
Pollen
Perfumes
