Anaphylaxis — Emergency Protocol
The client is wheezing, hypotensive, and covered in hives after a contrast injection. You have seconds to act — and the order of your interventions determines survival.
Core Concept
Anaphylaxis management follows a fixed priority sequence. Epinephrine IM is always the first drug — not diphenhydramine, not a steroid, not a fluid bolus. Adult dose is 0.3–0.5 mg of 1:1,000 (1 mg/mL) concentration given intramuscularly in the lateral thigh (vastus lateralis). This can be repeated every 5–15 minutes if symptoms persist. IV epinephrine (1:10,000) is reserved for cardiac arrest or refractory shock and requires continuous monitoring. After epinephrine, establish large-bore IV access and infuse 1–2 L of 0.9% normal saline rapidly to counteract distributive vasodilation. Adjunct medications follow: diphenhydramine 25–50 mg IV for histamine blockade and methylprednisolone 125 mg IV to prevent biphasic reactions. Position the client supine with legs elevated unless respiratory distress requires a semi-Fowler's position. Monitor for biphasic reaction — a second wave of symptoms occurring 1–72 hours later — which is why clients require observation for at least 4–6 hours post-event. Remove the causative agent immediately (stop the infusion, remove the stinger).
Watch Out For
Don't confuse IM epinephrine concentration (1:1,000) with IV cardiac arrest concentration (1:10,000) — giving 1:1,000 IV can cause fatal arrhythmia. Students often prioritize diphenhydramine first because it treats hives, but antihistamines cannot reverse airway edema or cardiovascular collapse — only epinephrine does. Anaphylaxis fluid resuscitation uses crystalloid boluses like septic shock, but the root cause is massive vasodilation from histamine, not infection.
Clinical Pearl
Epi first, epi fast, epi in the thigh. Benadryl treats hives; epinephrine saves lives. Never let an antihistamine jump the line ahead of epinephrine.
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