Anaphylaxis Updates

Anaphylaxis is a rapid systemic hypersensitivity reaction that can be fatal even without hives or obvious airway findings. Severe disease, biphasic recurrence, and refractory anaphylaxis all change ED diagnosis, observation, and follow-up, with epinephrine remaining the treatment that matters most.

Anaphylaxis Diagnosis and Risk

• Skin findings not required: Severe anaphylaxis can present with life-threatening respiratory or circulatory compromise without rash, wheeze, or shock, a pattern that drives under-recognition in the ED.
• Infant diagnostic criteria: Infants and toddlers lack dedicated anaphylaxis criteria, so NIAD/FAAN or WAO definitions are the practical framework when symptoms look nonspecific. We walk through the gray-zone presentations in the episode.
• Biphasic reaction framing: Biphasic anaphylaxis is recurrence after symptoms have fully resolved for at least 1 hour, without re-exposure, and higher initial severity makes that rebound more likely.
• Refractory disease signal: Refractory anaphylaxis persists despite appropriate epinephrine and symptom-directed care, a high-risk phenotype linked to increased fatality and the need for aggressive escalation.
• Unexpected trigger caution: A first-ever exposure to a new food or medication is an unlikely cause of anaphylaxis, a useful clue when the presumed trigger does not fit the story.

Management, Observation, and Follow-up

• Epinephrine auto-injector dosing: For children under 15 kg, either the 0.1 mg or 0.15 mg IM epinephrine auto-injector is acceptable, reflecting the limited but practical pediatric guidance.
• Observation time principle: The more interventions required to stabilize an anaphylactic patient, the longer ED observation should be, especially when repeat epinephrine is needed. We get into the disposition nuance in the chapter.
• Acute tryptase timing: A tryptase level drawn as early as possible, ideally within 2 hours of symptom onset, can later help an allergist confirm that a true mast-cell event occurred.
• Baseline tryptase comparison: A second tryptase measured months later provides a baseline comparator, letting immunology interpret whether the acute value represented a significant rise.
• Discharge education essentials: High-risk patients should routinely leave with self-injectable epinephrine, technique teaching, and avoidance counseling, including that food anaphylaxis is usually triggered by ingestion rather than contact or inhalation.

References:

1. Golden DBK, Wang J, Waserman S, et al. Anaphylaxis: A 2023 practice parameter update. Ann Allergy Asthma Immunol. 2024;132(2):124-176. PMID: 38108678