Anaphylaxis

Anaphylaxis is a clinical diagnosis, and delayed epinephrine is the major preventable cause of death. The defining pattern is an allergic exposure plus multisystem involvement such as hypotension, skin or mucosal findings, respiratory compromise, or GI symptoms; everything besides IM epinephrine is adjunctive.

Recognizing and Treating Anaphylaxis

• Clinical diagnosis pattern: Anaphylaxis is an allergic reaction with involvement of at least two organ systems, classically hypotension, skin or mucosal findings, respiratory compromise, or GI symptoms.
• Epinephrine comes first: IM epinephrine is the first-line treatment in adults at 0.3 to 0.5 mg of 1:1000 solution, and the memorable hierarchy is first-, second-, and third-line therapy are all epinephrine.
• IM over subcutaneous: Intramuscular delivery matters because epinephrine reaches peak levels far faster than subcutaneous dosing, a practical point that explains why route errors can cost time.
• Adjuncts stay adjuncts: Antihistamines, steroids, albuterol, fluids, and antiemetics may help specific symptoms, but none reverse the core hemodynamic and airway physiology like epinephrine does. We get into the bedside prioritization in the episode.
• Children present differently: Pediatric anaphylaxis may show less early airway involvement and more lethargy, fatigue, and hypotension, an easy way to miss a sick child if you anchor on wheeze or stridor alone.
• Monitor early deterioration: True anaphylaxis can progress to cardiac arrest within minutes, with especially short timelines after medication triggers, so severe reactions belong in a monitored bed immediately.

Shock, Refractory Cases, and Disposition

• When IM epi fails: More than two IM epinephrine doses without resolution should prompt escalation to an IV epinephrine drip rather than repeated delays with adjunctive medications.
• Beta blocker exception: Glucagon is the named rescue agent for patients on beta blockers who remain hypotensive or bradycardic despite epinephrine, because beta blockade can blunt the expected response.
• Anaphylactic shock physiology: Anaphylactic shock is distributive shock with capillary leak, reduced SVR, and direct myocardial effects, so the main treatment is still more epinephrine, not just fluids.
• Airway danger signs: Significant stridor, rising work of breathing, or poor oxygenation should trigger early airway planning, with awake techniques and video laryngoscopy sometimes offering the best chance of success.
• Biphasic reaction reality: Biphasic reactions can recur hours later and are unpredictable enough that observation decisions hinge on severity and response, a nuance we walk through in the chapter.
• Discharge essentials: Patients leaving after improvement should go home with an epinephrine auto-injector and allergy follow-up, especially when the trigger is uncertain or the reaction was severe.

References:

1. 2020 Focused Updates to the Asthma Management Guidelines: A Report from the National Asthma Education and Prevention Program Coordinating Committee Expert Panel Working Group. Link.
2. Patients Presenting in Extremis: Part. Video Link.
3. Bond  K.R, et al. (2018), Non-invasive ventilation use in status asthmaticus: 16 years of experience in a tertiary intensive care. Emergency Medicine Australasia, 30: 187-192. Link.
4. Miller A, et al. Noninvasive ventilation in life-threatening asthma: A case series. Can J Respir Ther. 2017;53(3):33-36. PMID: 30996631.