Allergic Reaction

  • Allergic reactions are a key medical emergency topic, involving the body's immune response to substances (allergens) that are typically harmless to most people.

  • Assessment of allergic reactions requires understanding and applying principles from primary assessment (initial evaluation of airway, breathing, and circulation), secondary assessment (detailed patient evaluation), and reassessment (ongoing monitoring).

  • Pharmacological interventions are often necessary in allergic emergencies, such as the administration of epinephrine, which is covered under general pharmacology.

  • Cardiac complications can arise during severe allergic reactions (anaphylaxis), making knowledge of cardiac emergencies relevant.

Standard

  • Fundamental knowledge of immunology is essential for providing basic emergency care to acutely ill patients.

  • Assessment findings guide the application of emergency care and transportation decisions.

  • Understanding immune responses helps in recognizing and managing acute illnesses effectively during emergency situations.

Core Concepts

  • Allergic reactions can present with a range of symptoms, including itching, hives, swelling, sneezing, and watery eyes; more severe reactions may involve difficulty breathing, swelling of the face or throat, and low blood pressure.

  • Mild allergic reactions typically involve localized symptoms such as skin rash, itching, or mild swelling, while anaphylaxis is a severe, life-threatening reaction characterized by airway compromise, rapid swelling, difficulty breathing, and possible shock.

  • Treatment for mild allergic reactions often includes removing the allergen if possible and administering antihistamines.

  • Anaphylaxis requires immediate emergency intervention, including calling for emergency help, administering epinephrine (such as with an auto-injector), and providing supportive care like airway management and oxygen if needed.

Learning Objectives

  • Allergic reactions range from mild symptoms (such as localized itching and hives) to severe, life-threatening anaphylactic shock, which can involve airway compromise, hypotension, and multi-system involvement.

  • Allergic reactions occur when the immune system interacts with a substance (allergen), triggering the release of mediators like histamine that cause symptoms.

  • Common allergens include foods (e.g., peanuts, shellfish), medications (e.g., antibiotics), insect stings, and latex.

  • Latex allergies require special consideration due to their prevalence in healthcare settings and potential for severe reactions.

  • Signs and symptoms of allergic reactions (e.g., urticaria, angioedema, respiratory distress, hypotension) are linked to underlying pathophysiologic processes such as vasodilation, increased vascular permeability, and bronchoconstriction.

  • Prehospital management involves recognizing assessment findings (skin changes, respiratory compromise, circulatory collapse) and distinguishing the severity of the reaction to guide treatment.

  • Effective communication with medical direction is essential, especially when considering the patient’s history and current presentation.

  • Epinephrine is the primary treatment for severe allergic reactions; decision making for its administration is based on severity and risk of progression.

  • Pharmacology of epinephrine includes its action as a vasoconstrictor, bronchodilator, and inhibitor of further mediator release.

  • Epinephrine autoinjectors vary in dose and design; knowing how to use them is important for rapid administration.

  • Intramuscular injection technique for epinephrine should be precise to ensure effective delivery, typically into the lateral thigh.

  • Epinephrine administration is prioritized over other interventions in severe reactions, but airway management and circulatory support remain critical.

  • Calling for paramedic assistance may be necessary for advanced airway management, intravenous access, or if the patient’s condition deteriorates.

Key Terms

  • Allergic reactions vary in severity, ranging from mild symptoms to extremely severe and life-threatening responses.

  • A mild allergic reaction can escalate rapidly into a severe reaction, highlighting the need for vigilance and quick action.

  • Severe allergic reactions (anaphylaxis) require immediate recognition and treatment to prevent life-threatening consequences.

  • Timely assessment and intervention are crucial in managing allergic reactions effectively.

Allergic Reactions

  • The immune system defends the body against foreign substances by neutralizing or eliminating them.

  • An allergic reaction is an exaggerated immune response to a foreign substance (allergen), which can be triggered by almost any substance, such as cat dander.

  • Mild allergic reactions may cause symptoms like itching and sneezing, but are generally not dangerous.

  • Severe allergic reactions, known as anaphylaxis or anaphylactic shock, involve a rapid and overwhelming immune response.

  • Anaphylaxis causes blood vessels to dilate and cells to leak fluid, resulting in a significant drop in blood pressure ().

  • Swelling of tissues, especially those lining the respiratory system, can obstruct airways and lead to respiratory failure.

  • Anaphylaxis is a life-threatening condition that can result in shock and/or respiratory compromise.

Causes of Allergic Reactions

  • Allergic reactions can be triggered by various sources, including insect stings (bees, wasps, hornets), certain foods (nuts, eggs, milk, shellfish, and especially peanuts), plants (poison ivy, poison oak, poison sumac, and pollen), medications (notably antibiotics like penicillin), and other substances (dust, chemicals, soaps, makeup, and latex).

  • Severity and onset of allergic reactions vary by allergen; insect stings and peanut allergies often cause rapid and severe reactions, while other foods and plant contact typically result in slower or less severe responses. People allergic to one food or antibiotic may also react to related substances, but peanut allergies are unique since peanuts are legumes, not nuts.

  • Latex allergies are common among patients with frequent medical procedures and healthcare professionals due to repeated exposure, prompting many medical facilities to adopt latex-free environments to prevent reactions.

  • Allergic reactions do not occur upon first exposure to an allergen; the immune system initially forms specific antibodies. On subsequent exposures, these antibodies bind to the allergen, triggering the release of histamine and other chemicals.

  • The release of histamine and related substances causes physiological changes such as dilation of blood vessels, increased capillary permeability (leading to fluid leakage), bronchoconstriction, and increased mucus production in the lungs, which can result in a range of symptoms from mild to life-threatening anaphylaxis.

Signs and Symptoms of Allergic Reactions

  • Allergic reactions cause dilation of blood vessels, which reduces blood return to the heart, decreases cardiac output, and increases the risk of shock.

  • Skin symptoms include flushing, hives (urticaria), and angioedema (swelling), especially around injection or sting sites, the face, eyes, lips, ears, tongue, and airway.

  • Swelling near the vocal cords can lead to a muffled voice or stridor (a harsh, high-pitched sound during inspiration).

  • Histamine release leads to hives, itching, and swelling, with hives appearing as red, itchy, possibly raised blotches.

  • Bronchoconstriction and thick mucus decrease airflow in the lungs, causing wheezing and difficulty breathing.

  • Irritation of nerve endings results in itching.

  • Key skin findings: itching, hives (localized or generalized), flushing, swelling (face, neck, hands, feet, tongue), and a warm, tingling feeling.

  • Respiratory symptoms: tightness in throat or chest, cough, rapid or labored breathing, noisy breathing, hoarseness, muffled or lost voice, stridor, and wheezing.

  • Cardiac symptoms: increased heart rate and decreased blood pressure.

  • General symptoms: itchy, watery eyes, headache, runny nose, and a sense of impending doom.

  • Anaphylactic shock signs: altered mental status, flushed or pale/clammy skin, nausea or vomiting, and changes in vital signs (increased pulse and respirations, decreased blood pressure).

Distinguishing Anaphylaxis from Mild Allergic Reaction

  • Allergic reactions can be unpredictable in timing and severity, with severe reactions often occurring immediately but sometimes being delayed by 30 minutes or more.

  • Mild allergic reactions can rapidly progress to anaphylactic shock, so even minor symptoms (like localized swelling) after exposure to a known allergen require close monitoring.

  • Airway compromise is a critical risk, as swelling can quickly close off the airway; you must be ready to manage the airway and administer epinephrine if needed.

  • Recognizing the progression from a mild to a severe or anaphylactic reaction is essential, and immediate treatment with epinephrine is required if anaphylaxis is suspected.

  • A standardized scheme exists to help identify when anaphylaxis is highly likely, emphasizing the importance of early recognition and intervention.

Box 23-1

  • Anaphylaxis is highly likely when there is a sudden onset of illness involving skin or mucosal tissue (such as widespread hives, itching, flushing, or swelling of lips, tongue, or uvula) plus either sudden respiratory symptoms (shortness of breath, wheeze, cough, stridor, low pulse oximetry) or sudden reduced blood pressure/end-organ dysfunction (collapse, incontinence).

  • Anaphylaxis can also be identified if two or more of the following occur suddenly after exposure to a likely allergen: skin/mucosal symptoms, respiratory symptoms, reduced blood pressure/end-organ dysfunction, or gastrointestinal symptoms (crampy abdominal pain, vomiting).

  • A third criterion is reduced blood pressure occurring within minutes to several hours after exposure to a known allergen for the patient.

  • Presentation of anaphylaxis can vary widely, and patients with a history of previous anaphylactic reactions are at high risk for recurrence.

  • Immediate treatment with epinephrine is critical at the first sign of anaphylaxis, even if classic symptoms (such as stridor) are not present.

  • There are important differences between mild allergic reactions (limited to skin or mild symptoms) and anaphylaxis, which involves rapid progression and multiple organ systems.

Patient Assessment

  • Assessment of allergic reactions and anaphylaxis involves a primary assessment to address immediate threats to airway, breathing, or circulation, followed by a secondary assessment focusing on allergy history, exposure details, symptom progression, and interventions already taken.

  • Key differences between allergic and anaphylactic reactions include:

    • Allergic reactions typically present with sneezing, normal respiratory sounds, local hives/redness/swelling, normal or near-normal vital signs, normal mental status (possibly anxious), and no gastrointestinal symptoms.

    • Anaphylactic reactions are more severe, with symptoms such as dyspnea, cough, chest tightness, abnormal respiratory sounds (wheezing, muffled voice, stridor), widespread hives, pallor, diffuse redness, swelling of the face/lips/eyes/tongue/mouth/uvula, abnormal vital signs (tachycardia, hypotension, tachypnea, decreased oxygen saturation), altered mental status (syncope, feeling of impending doom), and gastrointestinal symptoms (nausea, vomiting, abdominal pain, incontinence).

  • Critical decision points include determining whether the reaction is allergic or anaphylactic, assessing the potential for progression to anaphylaxis, and deciding if epinephrine administration is necessary.

Patient Care

  • Distinguishing between allergic and anaphylactic reactions is critical; only anaphylactic reactions require epinephrine administration.

  • Initial care focuses on airway, breathing, and circulation (A-B-Cs): ensure the airway is open, provide high-concentration oxygen via nonrebreather mask if the patient is in distress or shows signs of anaphylaxis, and ventilate if breathing is inadequate.

  • Mild allergic reactions do not require oxygen, but if unsure, apply oxygen and reassess as needed.

  • Prompt administration of epinephrine is the most important intervention for anaphylaxis; administer it if the patient has a history of exposure and shows respiratory distress, tongue or lip swelling, or signs of shock.

  • Document epinephrine administration and reassess the patient after 2 minutes, recording findings.

  • If unable to administer epinephrine and the patient meets criteria, request ALS (Advanced Life Support) intercept, as paramedics and advanced EMTs can administer epinephrine.

Think Like an EMT

  • Anaphylaxis is characterized by severe, life-threatening symptoms such as airway compromise (e.g., throat closing up), respiratory distress, and/or circulatory collapse (e.g., rapid pulse, dizziness with unstable vitals).

  • Allergic reactions are typically limited to localized or mild symptoms such as itching, mild swelling, or gastrointestinal upset without systemic involvement.

  • Throat closing up after a bee sting and facial/neck swelling with difficulty breathing and rapid pulse after peanut exposure are examples of anaphylaxis due to airway and respiratory compromise.

  • Itching all over the skin without other systemic symptoms and upset stomach/diarrhea after dairy exposure are examples of mild allergic reactions.

  • Dizziness after penicillin exposure with stable vital signs suggests a mild allergic reaction, not anaphylaxis, unless symptoms progress to instability.

Epinephrine

  • Epinephrine is used to treat severe allergic reactions by constricting blood vessels (raising blood pressure and improving perfusion) and dilating bronchioles (opening the airway and improving breathing).

  • Epinephrine strengthens heart contractions, which is especially beneficial for patients in shock due to dilated blood vessels and poor blood return to the heart.

  • Overdosing epinephrine can be dangerous, particularly for patients with heart conditions, as it forces the heart to work harder than necessary.

  • Careful assessment and weighing of risks versus benefits is essential before administering epinephrine, and consulting medical direction may be necessary to adjust dosing.

  • Epinephrine autoinjectors (e.g., EpiPen®, Adrenaclick®) are prescribed for individuals at risk of severe allergic reactions because these reactions can become life-threatening rapidly, making immediate self-administration crucial.

  • Autoinjectors are spring-loaded devices that deliver a single dose of epinephrine automatically; some models, like Auvi-Q®, provide voice instructions for use.

  • Standard injection site preparation (rolling up clothing, cleansing with alcohol) is not required for autoinjector use due to the minimal infection risk, but you should always follow your local protocols.

SCAN 23-2

  • Epinephrine autoinjectors are used for severe allergic reactions that involve respiratory distress or shock, require a prescription or ambulance supply, and may need medical direction per local protocol.

  • No contraindications exist in life-threatening situations; epinephrine should be administered if criteria are met.

  • Medication is delivered as a liquid via autoinjector or IM syringe; common devices include EpiPen®, Auvi-Q™, Adrenaclick®, and Symjepi®.

  • Dosage: Adults receive 0.3 mg; infants and children receive 0.15 mg via the appropriate autoinjector.

  • Administration steps: Confirm the “five rights” of medication, check prescription and medication integrity, obtain medical order if required, remove safety cap, grip the center, place on the lateral thigh (midway between hip and knee), press firmly to activate, hold for 10 seconds, document administration, and dispose of injector in a sharps container.

  • Epinephrine actions: Dilates bronchioles, constricts blood vessels, and reduces capillary permeability.

  • Possible side effects: Increased heart rate, pallor, dizziness, chest pain, headache, nausea, vomiting, excitability, and anxiety.

  • Reassessment: Transport the patient, monitor airway, breathing, and circulation; if condition worsens, seek medical direction for another dose, treat for shock, and prepare for CPR/AED. If improved, continue supportive care and oxygen, and treat for shock as needed.

Pediatric Note

  • Signs and symptoms of anaphylaxis are similar in children and adults, but treatment differs due to children's smaller body size.

  • Epinephrine autoinjectors are available in two doses: 0.3 mg for adults and 0.15 mg for children weighing less than 30 kg (66 pounds).

  • Infants rarely have anaphylactic reactions because their immune systems are not mature enough to produce the necessary antibodies, while allergic reactions are more common in older children, many of whom may outgrow their allergies as they age.

  • Parents are often a valuable source of information regarding a child's medical history and allergies.

Administering Epinephrine via IM Injection

  • Many EMS systems now train EMTs to administer epinephrine intramuscularly (IM) using a hypodermic needle and syringe instead of relying solely on autoinjectors, due to the high cost and expiration issues associated with autoinjectors.

  • This IM administration method is significantly less expensive (saving hundreds of dollars per dose) and, when performed under proper conditions, is both safe and effective.

  • The same indications, contraindications, actions, dosages, side effects, and reassessment strategies apply to both IM epinephrine and autoinjectors.

  • The Ready-Check-Inject system is commonly used for IM epinephrine administration and includes several safety measures:

    • Only 1 mL vials or ampules of 1:1,000 concentration (1 mg/mL) are allowed, preventing accidental overdoses.

    • If a glass ampule is used, a filtered needle must be used to draw the medication.

    • Containers larger than 1 mL are not permitted to avoid megadoses.

    • A second provider must verify the correct dose is drawn: 0.3 mL for adults and 0.15 mL for children under 30 kg (66 lbs).

    • EMTs select the appropriate syringe and needle size for IM injection.

    • All necessary supplies are packaged together with a review card for reference.

  • EMTs must complete additional training and demonstrate competency in drawing up and administering the correct dose of IM epinephrine. Agencies keep records of this training.

  • Familiarity with local protocols and requirements for medical direction is essential before administering epinephrine using this method.

Further Treatment

  • Allergic reactions can compromise airway and respiratory function, so you must continuously monitor the patient's airway and breathing during care and transport.

  • If the patient's condition does not improve during reassessment, additional doses of epinephrine may be necessary, following local protocols.

  • Diphenhydramine, an antihistamine, may be administered by EMTs in some systems to counteract histamine, which causes itching in allergic and anaphylactic reactions; administration can be oral or intramuscular, depending on protocols.

  • Always adhere to local protocols regarding medication administration and patient management.

Point of View: Patient

  • Severe nut allergies can cause rapid and life-threatening reactions, including swelling, difficulty breathing, and wheezing, often within seconds of exposure.

  • Immediate recognition and response are critical; friends and bystanders play a vital role by calling emergency services and retrieving necessary medication like an EpiPen®.

  • Epinephrine administration is essential in treating severe allergic reactions (anaphylaxis), and may need to be given more than once if symptoms are severe.

  • Emergency medical personnel act quickly by providing oxygen, administering epinephrine, and preparing for hospital transport, which can be lifesaving in critical situations.

  • Support from friends and quick access to medical care can make the difference between life and death during an anaphylactic episode.