Unit
- Immune mechanism: Anaphylaxis is a severe, life-threatening hypersensitivity reaction mediated primarily by immunoglobulin E (IgE). Upon exposure to an allergen, IgE cross-links on mast cells and basophils, triggering rapid release of histamine, leukotrienes, and other inflammatory mediators. This cascade leads to systemic vasodilation, bronchoconstriction, and increased vascular permeability, which can progress to shock within minutes.
- Common triggers: Food allergens such as peanuts, tree nuts, shellfish, eggs, and milk account for a large proportion of community anaphylaxis. Medications including antibiotics, nonsteroidal anti-inflammatory drugs, and contrast agents are frequent iatrogenic triggers. Insect venom from bees, wasps, and fire ants can also induce severe reactions. In healthcare settings, latex and certain chemotherapeutic agents are notable triggers.
- Non-IgE-mediated mechanisms: Some reactions mimic anaphylaxis without IgE involvement, such as direct mast cell activation by opioids or vancomycin, and immune complex-mediated reactions. These are termed anaphylactoid or non-allergic anaphylaxis. Distinguishing these mechanisms is critical for selecting appropriate emergency management and future prevention strategies.
- Biphasic reactions: Approximately 1-20% of anaphylaxis cases experience a recurrence of symptoms 1-8 hours after initial resolution, often without re-exposure. This biphasic pattern necessitates a period of observation and readiness for a second intervention. Operational plans must account for monitoring periods and criteria for discharge or escalation.
- Co-factors and risk modifiers: Factors such as exercise, alcohol, nonsteroidal anti-inflammatory drugs, acute infections, and psychological stress can lower the threshold for anaphylaxis or amplify symptom severity. Patient history should include assessment of these modifiers to stratify risk and inform management plans.
- Organ system involvement: Symptoms can involve the skin (urticaria, angioedema), respiratory tract (wheezing, stridor, hypoxia), cardiovascular system (hypotension, tachycardia, shock), gastrointestinal tract (nausea, vomiting, diarrhea), and central nervous system (dizziness, confusion). Not all systems are affected in every patient; recognition requires pattern awareness.
- Operational significance of pathophysiology: Understanding the underlying mechanisms guides operational decisions, including medication selection (epinephrine is first-line due to its alpha-1 and beta-2 effects), equipment needs (airway management supplies, intravenous access), and monitoring protocols (continuous pulse oximetry, blood pressure).
- Trigger avoidance strategies: Operational teams should implement policies for allergen identification in food services, medication allergy documentation in health records, and environmental controls (e.g., latex-free supplies). Educational materials for patients and staff about common triggers reduce exposure risks.
- Epinephrine administration: Epinephrine is the first-line treatment and should be administered intramuscularly in the mid-outer thigh at a dose of 0.01 mg/kg (max 0.5 mg for adults, 0.3 mg for children). Repeat dosing may be needed every 5-15 minutes if symptoms persist. Auto-injectors facilitate rapid administration by trained personnel and should be readily accessible in all clinical and community settings.
- Staff training and simulation: Operations must include regular anaphylaxis simulation drills for all clinical staff to ensure rapid recognition and appropriate response. Training should cover proper use of epinephrine auto-injectors, airway management techniques, and effective communication during emergencies. Debriefing after each drill identifies knowledge gaps and reinforces adherence to protocols. Documentation of training attendance and competency assessments supports continuous quality improvement and regulatory compliance.
- Post-reaction monitoring and discharge criteria: After initial stabilization, patients should be observed for at least 4-6 hours due to risk of biphasic reactions. Monitoring includes vital signs every 15 minutes, pulse oximetry, and assessment for recurrence of symptoms. Discharge criteria include stable vital signs, resolution of symptoms, and availability of an epinephrine auto-injector. Clear instructions for follow-up with an allergist and when to seek emergency care should be provided.
Terminology
- Anaphylaxis
- A severe, life-threatening systemic hypersensitivity reaction characterized by rapid onset of airway, breathing, or circulatory problems, usually associated with skin and mucosal changes.
- IgE
- Immunoglobulin E, an antibody involved in allergic reactions, bound to mast cells and basophils.
- Biphasic reaction
- A recurrence of anaphylaxis symptoms after initial resolution, without further allergen exposure.
- Mast cell
- A type of white blood cell that releases histamine and other mediators during allergic reactions.
- Vasodilation
- Widening of blood vessels, leading to decreased blood pressure in anaphylaxis.
Quick Revision
- Anaphylaxis is an IgE-mediated reaction causing systemic vasodilation and bronchoconstriction.
- Common triggers include foods, medications, and insect venom.
- Biphasic reactions require observation periods in operational plans.
- Co-factors like exercise and stress can lower reaction thresholds.
- Understanding mechanisms informs medication, equipment, and monitoring protocols.