Anaphylaxis | Notion

Pearls:

Anaphylaxis is life-threatening
Stridor, hoarseness, resp distress, hypotension → need rapid intervention
Delayed IM epinephrine is associated with an increased risk of morbidity and mortality
Most children will experience skin manifestations (e.g. urticaria)
Absence of circulatory compromise does not exclude the diagnosis of anaphylaxis
Benadryl and steroids are not considered first line – they are adjunctive therapy with lack of efficacy

Pathophys:

Classic response is an IgE-mediated reaction that occurs after reexposure to an antigen to which the patient has previously been sensitized. IgE binds to high-affinity receptors on mast cells and basophils.
The resultant sudden release of numerous mediators is presumed to be responsible for the pathophysiologic features of anaphylaxis: bronchospasm, increased vascular permeability, altered systemic and pulmonary vascular smooth muscle tone
- E.g. of mediators: histamine, prostaglandin D2, leukotrienes, anaphylatoxins (C3, C4a, C5a), platelet-activating factor, heparin, tryptase, chymas
- Anaphylactoid “reaction”: similar syndrome that is NOT IgE mediated and does not necessarily require previous exposure to the inciting agent
- Unknown mechanisms in: ingestion of aspirin/NSAIDs, in exercise-induced anaphylaxis (usually preceded by an allergenic food like wheat/shellfish ingestion)
Routes of exposure: parenteral, oral, inhalation
Food allergens are the most common inciting agents
- Others: stings, drugs, immunotherapy radiocontrast media, blood products, undetected in many cases