EP1 | Anaphylaxis: Recognition, Pathophysiology & Management

MedSimu Emergency

Tune in for a critical episode as we explore Anaphylaxis, a common medical emergency and a life-threatening acute hypersensitivity reaction.

Defined as a rapidly evolving, generalized, multi-system allergic reaction, anaphylaxis can be fatal due to its swift progression, often leading to respiratory collapse if untreated.

We'll discuss how anaphylaxis, regardless of whether it was historically termed IgE-mediated or anaphylactoid, is now unified under a single diagnosis because the clinical state and treatment are identical. Learn about the common inciting sources, including exposure to medications, foods (like peanuts, tree nuts, fish, shellfish, milk, eggs, wheat, soy, red meat, and sesame), insect stings (bee stings, fire ant bites), latex, and even immunotherapy injections. We'll also touch upon specific types like Alpha-gal anaphylaxis and instances where the cause remains unknown, known as idiopathic anaphylaxis.

Discover the underlying pathophysiology, primarily an IgE-mediated (type 1) hypersensitivity reaction. It involves the rapid release of numerous chemical mediators from the degranulation of basophils and mast cells after re-exposure to a specific antigen. We'll explain how IgE crosslinking triggers the release of powerful substances like histamine, which increases vascular permeability and vasodilation, tryptase, carboxypeptidase A, and proteoglycans. Additionally, we'll cover the formation of arachidonic acid metabolites like leukotrienes and prostaglandins, which contribute to bronchoconstriction and vascular permeability, and platelet-activating factors. You'll also learn about the role of TNF-alpha in mediating the inflammatory response.

The episode will detail the clinical presentation, which often begins rapidly, typically within minutes to hours of exposure. While cutaneous symptoms like flushing, pruritus, and urticaria are common, they may follow respiratory symptoms, especially with oral exposures. We'll highlight the concerning respiratory signs like fullness or a "lump in the throat," persistent throat clearing, difficulty breathing, hoarseness, wheezing, and stridor. The rapid onset and progression correlate with the severity of the disease. Morbidity and mortality are most often linked to loss of airway and distributive shock. We'll also cover other potential symptoms, including hypotension, gastrointestinal issues like painful cramps and vomiting (occurring in 25-30% of patients), and signs of end-organ dysfunction from hypoperfusion like hypotonia, syncope, or incontinence.

Crucially, we'll emphasize that diagnosing anaphylaxis is clinical, and rapid recognition and action are imperative. We'll review the clinical criteria for diagnosis, which involve rapidly developing symptoms in one or more body systems after likely exposure, or symptoms in two or more systems after likely exposure, or hypotension after known exposure.

Learn about the paramount importance of prompt treatment, with intramuscular epinephrine being the treatment of choice. We'll discuss correct dosing, routes (intramuscular preferred over subcutaneous or intravascular), and the importance of not delaying administration. We'll also cover other vital aspects of management, including airway management, decontamination of the offending agent, IV fluid resuscitation for distributive shock, and adjunctive therapies such as corticosteroids (to reduce length or biphasic response), antihistamines (H1 and H2 blockers), inhaled bronchodilators for bronchospasm, vasopressors, and glucagon (especially for patients on beta-blockers).

Finally, we'll discuss the potential for biphasic reactions, which can occur hours after the initial episode, and the importance of observation. We'll touch upon the prognosis with rapid, adequate treatment and the complications that can arise, including wheeze, stridor, hypoxemia, hypotension, end-organ dysfunction, and death.

Join us to gain a deeper understanding of this critical medical emergency, its mechanisms, and the vital steps for recognition and management!