Anaphylaxis in a Patient on a Beta-Blocker
45-year-old woman stung by a hornet while gardening. Within 5 minutes she developed hives, lip swelling, and a hoarse voice. She is anxious and sitting upright with audible inspiratory stridor and diffuse wheeze. HR 128, BP 92/58, RR 30, SpO2 91% on room air. Her husband says she took two diphenhydramine tablets 10 minutes ago. History includes hypertension treated with atenolol. You carry epinephrine 1:1,000, albuterol, oxygen, and a BVM. Transport time is 15 minutes.
1. What is your first drug, at what dose and route, and why is the diphenhydramine she took not sufficient?
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Epinephrine 0.3 mg IM (1:1,000) into the lateral thigh - immediately, before anything else. Repeat every 5-15 minutes if symptoms persist or recur; she may need more than one dose given the stridor.
Why the antihistamine is not enough:
- Diphenhydramine blocks H1 receptors but does not reverse laryngeal edema, bronchospasm, or vasodilation - the three things killing her.
- It has no effect on mast-cell degranulation and takes far too long to matter against airway swelling.
- Epinephrine's alpha-1 effect reduces mucosal edema and raises BP; beta-2 effect bronchodilates and further stabilizes mast cells.
The stridor is the decision point: this is airway compromise, not just a rash.
2. Does atenolol change your plan? Explain what you would watch for and what adjuncts you would consider.
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Yes - beta-blockade can make her refractory to epinephrine, and it also blunts the tachycardia you would otherwise use as a gauge of response. That is a reason to give epinephrine earlier and reassess aggressively, not a reason to withhold it.
Plan:
- Give epinephrine as above; do not reduce the dose because of her cardiac history.
- Add nebulized albuterol for the wheeze as an adjunct.
- If she does not respond to repeated epinephrine, glucagon is the classic consideration because it bypasses the beta receptor and increases intracellular cAMP; follow local protocol and medical direction.
- Watch for hypotension that does not correct and for bradycardia rather than tachycardia as a sign of deterioration.
- Have suction, BVM, and airway equipment ready; if laryngeal edema progresses, BVM may be impossible and a surgical airway may be needed.
3. How will you position and transport her, and what is the trap in 'sitting her up because she is short of breath'?
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Keep her sitting upright while she has stridor and respiratory distress - she is protecting her own airway, and forcing her flat can worsen both breathing and panic. If she becomes hypotensive without respiratory distress, supine with legs elevated improves preload.
The trap: anaphylactic patients who are stood up or walked can suffer sudden fatal cardiovascular collapse (empty ventricle / profound vasodilation). So:
- Do not make her walk to the stretcher; use the stretcher or a carry.
- Do not force a position she is fighting.
- Transport promptly, pre-alert, and continue reassessment every few minutes - she can obstruct between your first and second set of vitals.