Anaphylaxis and Emergency Medicine

Introduction

• Anaphylaxis is the most dramatic and dangerous form of immediate hypersensitivity reactions.
• It poses a significant threat to life in the short term, making it a serious medical emergency.
• It is unpredictable and requires urgent medical attention in emergency medicine and intensive care.

Definitions

• Anaphylaxis: A serious, rapid, and potentially life-threatening systemic hypersensitivity (allergic) reaction.
• Anaphylactic shock: The most severe form of anaphylaxis, characterized by severe hypotension and circulatory failure. It's a life-threatening condition.
• The term "anaphylaxis" encompasses a broader range of allergic reactions, while "anaphylactic shock" specifies severe cases involving profound cardiovascular collapse.

Epidemiology

• Global prevalence: estimated at 0.3% of the general population, ranging from 50 to 200 cases per 100,000 inhabitants.
• Incidence: Shows steady increases across all age groups, varying from 4 to 50 cases per 100,000 people.
• Hospitalization rates: high, reaching 2.3 per 1,000 admissions in adults and 1 per 1,000 among children in Europe.
• Mortality: Difficult to estimate precisely, but falls within a range of 0.65% to 2% for severe cases (with mortality varying from 1 to 3 per million inhabitants).
• Trigger factors: foods are the primary cause in children while medications and hymenopteran venom are more common in adults.
• Increasing trend: Studies indicate a significant rise in hospitalizations, possibly due to improved recognition and coding methods.

Pathophysiology

• Immunological mechanisms (Type I hypersensitivity): The most common type of anaphylaxis is via a rapid and exaggerated immune response to an allergen.
• Sensitization phase: First contact with an allergen leads to the production of IgE antibodies, which bind to mast cells and basophils.
• Activation phase: Subsequent exposure to the same allergen triggers the cross-linking of IgE antibodies, causing mast cell and basophil degranulation.
• Mediator release: This releases a cascade of inflammatory mediators (e.g., histamine, proteases, leukotrienes, prostaglandins, PAF).
• Multisystemic effects: These mediators result in a broad range of effects on different body systems, including the cardiovascular, respiratory, gastrointestinal, and skin systems.

Diagnosis

• Sampson criteria (criteria 1 & 2): Rapid (minutes to hours) onset of cutaneous and mucuous membrane symptoms coupled with respiratory or cardiovascular involvement after known or suspected trigger exposure.
• Sampson Criteria (criteria 3): Severe hypotension or shock following known allergen exposure.
• Complementary tests: No definitive laboratory test exists for immediate or precise anaphylaxis diagnosis. Tryptase blood levels can aid in the diagnosis of suspected anaphylaxis, especially in atypical cases.

Evolution of Anaphylaxis

• Immediate reactions: Symptoms typically appear within minutes to 30 minutes of exposure.
• Delayed reactions (biphasic): A second wave of symptoms can arise hours after the initial reaction. This is significant as reactions can escalate in severity.

Treatment

• Early administration of epinephrine (adrenaline): Is paramount and a vital first-line treatment. Administered intramuscularly, it's essential to act quickly to counteract the effects of anaphylaxis.
• Other treatments: Supporting measures, such as supplemental oxygen, fluid therapy, and treatment for respiratory problems, may be used alongside epinephrine.

Specific Cases

• Anaphylaxis triggered by exercise and cold exposure: This involves a reaction to these triggers.
• Pediatric anaphylaxis in infants and young children: Signs and complications may present differently in children.

Complications

• Anaphylaxis requires prompt intervention as delayed treatment can lead to life-threatening complications. Further complications may arise if the cardiovascular or respiratory system is detrimentally affected.

Prognosis

• Proper immediate medical intervention, including epinephrine injection, can significantly improve the prognosis and outcome of anaphylaxis.
• Prompt detection of anaphylaxis is pivotal as delays can be life-threatening.

Classification of Anaphylaxis Severity

• Criteria for Severity: Classification of mild, moderate, or severe anaphylaxis are based on affected systems and their severity.
• Systems involved: Respiratory, Cardiovascular, Gastrointestinal, and Skin/mucosal symptoms; these systems guide the assessment of severity.

Factors that could exacerbate anaphylaxis

• Underlying medical conditions: Existing cardiovascular diseases or asthma can influence the progression and severity of anaphylaxis.

• Medications: Certain medications, like certain beta-blockers or ACE inhibitors, can impede the effectiveness of adrenaline in managing the reactions.

• Lifestyle factors: Exercise or consumption of certain foods when combined with existing conditions can heighten the risk of severe anaphylactic reactions.

• Consultation: Allergy/immunology specialists are crucial for thorough evaluation and personalized management plans.