Chapter 22 Debra G. Perina and Douglas R. Gallo Potential allergic reactions and their sequelae are common complaints encountered in the EMS system. Allergic reactions can be triggered by many agents, such as foods, medications, topical products, and limitless environmental exposures including arthropod stings. Severity can vary from local reactions and discomfort to life-threatening systemic anaphylaxis. EMS physicians and other providers must be able to rapidly recognize the manifestations of allergic reactions and begin to provide prehospital treatment that can be life-saving. Allergic reactions are hypersensitivity reactions resulting from the exposure to an allergen [1]. In milder forms they may result in localized edema and pruritus. Systemic reactions can also be mild, resulting in a more widespread rash that can be pruritic. In their most severe form, allergic reactions progress to anaphylaxis with multisystem and potentially life-threatening manifestations that include respiratory failure, circulatory collapse, and shock. There are four types of hypersensitivity reactions (Box 22.1). Type I accounts for most cases of anaphylaxis. Type II reactions are typically seen in the setting of blood transfusions, drug reactions, and cases of idiopathic thrombocytopenic purpura. Type III reactions are responsible for serum sickness, reactions to tetanus toxoid, and poststreptococcal glomerulonephritis. Type IV reactions are T-cell-mediated and delayed hypersensitivity responses which do not cause anaphylaxis. Urticaria, or hives, is an often-encountered symptom and physical sign of an acute allergic reaction. Although the potential etiologies of urticaria are numerous, the temporal link to a likely allergen can often be made upon consideration of recent exposures. For example, the patient might have recently started a new medication, been stung by an insect, or eaten a certain food. Urticaria, itself, is not particularly concerning. However, its potential as an indicator of a reaction in the evolution of systemic effects should not go unrecognized. Allergic reactions that present as urticaria can progress to angioedema that results in facial or tongue swelling. Subsequently, airway obstruction might develop precipitously with obvious consequences. Angioedema also often occurs without other apparent manifestations of an allergic reaction. One of the more common causes is angiotensin-converting enzyme inhibitors. The patient may have been taking the medication for some time before such a reaction occurs, which can be confusing to some who assume that a reaction would have occurred earlier if the patient was going to exhibit one. Hereditary angioedema, on the other hand, does not represent a response to a specific allergen, but it deserves mention because of its similar presentation to allergic reactions and other forms of angioedema. Hereditary angioedema is an autosomal dominant genetic disorder caused by a defect in the complement pathway that results in either a low C1 esterase level or a high level of dysfunctional C1 esterase. Symptoms can include pruritus, urticaria, wheezing, facial and tongue swelling, dizziness, hypotension, syncope, and gastrointestinal distress [2]. At 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 22.2). 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 most 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. Almost anything can be a potential allergen (Box 22.3). Common agents include medications, foods and food additives, latex, arthropod bites and stings, mold, radiographic contrast media, and certain marine envenomations [1] (see Volume 1, 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 [3,4]. Certain species of caterpillars have venom-filled hair and spines that can cause systemic reactions, including anaphylaxis, within 2 hours of the sting [3]. 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 [5]. 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 (honeybees and bumblebees), 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, so that a patient allergic to bee stings will also display an allergic reaction to a fire ant bite [6]. Africanized honeybees (“killer bees”) are an aggressive hybrid of the honeybee and have the same venom, but they sting repeatedly, thus increasing the risk of a severe reaction [7]. Approximately 1% of children and 3% of adults have reportedly had severe systemic allergic reactions to Hymenoptera venom [8]. 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 [9].
Allergic reactions
Introduction
Physiology of allergic reactions
Causative agents
Assessment and general approach
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