Intraoperative Anaphylaxis: Epinephrine First

Intraop anaphylaxis is mostly invisible. The patient is draped (skin signs missed), paralyzed (no respiratory complaint), monitored (you see the BP drop, but so does every other anesthetic complication). The trigger is right there in the IV bag. Most-cited triggers in OR: neuromuscular blockers (rocuronium, succinylcholine — IgE), latex (delayed onset 20-40 min after exposure), antibiotics (cephalosporins, vancomycin — both true allergy + Red Man infusion-rate effect), chlorhexidine, blood products, contrast, protamine.

Hypotension that doesn't respond to phenylephrine, ephedrine, or fluids. Sudden ↑ peak inspiratory pressure (bronchospasm). ↓ EtCO₂ (cardiovascular collapse + reduced pulmonary blood flow). Cutaneous signs (hives, flushing, periorbital edema) — under drapes; lift them and look. Maintained airway + ventilation but profound shock = think anaphylaxis. Mast cell tryptase peaks 60-90 min after onset → draw + freeze for later confirmation; doesn't change acute management.

Epinephrine is the only drug that addresses all three components of anaphylaxis: α1 vasoconstriction (raises SVR + BP), β1 inotropy (treats myocardial depression from histamine), β2 bronchodilation (reverses bronchospasm) + reduces further mast cell degranulation. NO other drug has this combination. Phenylephrine fails because it doesn't reverse bronchospasm or stop further mediator release. Norepinephrine fails for the same reason (α + β1 only, no β2). Time matters: every minute of delay drops survival.

Adult: 10-100 mcg IV bolus (start at 10 mcg in mild, 50-100 mcg if severe shock or pulseless). Repeat every 1-2 min titrating to BP. Once BP responds, start infusion 0.05-1 mcg/kg/min and titrate. Pediatric: 1-10 mcg/kg IV bolus (lower end first). 100% FiO₂. STOP THE TRIGGER (replace IV tubing if drug-related; remove latex; remove antibiotic). Crystalloid bolus 1-2 L (third-spacing from massive vasodilation). Diphenhydramine + ranitidine + steroids (methylpred) are adjuncts only — they don't replace epinephrine.

Despite epinephrine + fluids + adjuncts, ~5% remain hypotensive. Add: vasopressin 0.03-0.04 U/min (independent of adrenergic axis). Methylene blue 1-2 mg/kg IV bolus (NO synthase inhibition — reverses NO-mediated vasodilation; AVOID in G6PD deficiency or co-administered SSRIs). Glucagon 1-5 mg IV (in patients on β-blockers — bypasses adrenergic block). Hydroxocobalamin 5 g IV (NO scavenger). Continue ICU care 24h post-event for biphasic anaphylaxis (recurrence in 1-20% within 24h). Allergy testing 4-6 weeks post-event identifies trigger for future cases.