Anaphylaxis under anesthesia
Stem
A 46-year-old woman, 70 kg, is anesthetized with propofol and rocuronium for a laparoscopic hysterectomy, and cefazolin is given after intubation. Four minutes later, before incision, her blood pressure is 64/32, heart rate 132, and peak airway pressure has risen from 18 to 34 cmH2O with a falling end-tidal CO2 and an upsloping capnogram. Her arms are tucked under the drapes and no rash is visible.
Question
What do you think is happening, and how will you manage it?
Ideal answer
HeadlineSudden hypotension with bronchospasm shortly after a drug is anaphylaxis until proven otherwise. I treat now; delay kills, and I do not wait for a rash.
- Stop the likely trigger, hold surgery, call for help, and give 100% oxygen, because continued exposure sustains the reaction.
- Epinephrine IV in 50 mcg boluses, escalated to effect, an infusion if I need repeated boluses; systolic below 50 mmHg or arrest means CPR.1
- Crystalloid wide open, 500–1000 mL boluses,1 flat, legs raised, because she has lost intravascular volume into the tissues.
- Still hypotensive: norepinephrine or vasopressin, glucagon if she takes a beta-blocker; once stable, antihistamine, a steroid, and a bronchodilator if wheeze persists.
- Tryptase once she is stable, again at 1–4 hours, timed from onset, and at least 24 hours later;1 every drug and the timeline documented; allergy referral.
Watch for: airway edema and recurrence.
Breaking down the answer
- Why epinephrine, and how much — it treats all three problems: vasodilation, bronchospasm and mediator release. Dose follows severity; the error is being timid with a collapsing patient or giving a full milligram to someone merely hypotensive. Acting before the full picture is graded.
- Stop the trigger and the surgery — in NAP6 antibiotics were the leading culprit (teicoplanin disproportionately), followed by neuromuscular blockers, chlorhexidine and Patent Blue dye;2 I remove chlorhexidine-coated lines and latex from the field if those are plausible.
- Volume — 20 mL/kg in a child, repeated;1 up to half the circulating volume can shift into the interstitium.
- Refractory shock — the second vasopressor is norepinephrine or vasopressin 1–2 units; glucagon 1 mg IV bypasses the blocked beta-receptor.1
- Airway — early intubation if there is any stridor, tongue or lip swelling; I use a smaller tube and have a surgical airway plan.
- Second-line drugs are second-line — hydrocortisone and diphenhydramine do nothing for the acute hemodynamics; I give them after epinephrine and fluids and say so; steroids are for refractory reactions,1 and neither drug prevents a biphasic reaction.3
- Investigation — tryptase confirms mast-cell degranulation but a normal level does not exclude the diagnosis; I give the patient a written account and refer to an allergist for skin testing 4–6 weeks later.
Follow-up question
Despite three boluses of epinephrine, the cuff no longer records a pressure, you cannot feel a pulse, and the monitor shows a narrow-complex rhythm after a period of bradycardia.
What do you do now?
Follow-up answer
HeadlinePulseless electrical activity, the usual arrest rhythm in anaphylaxis, often preceded by bradycardia.2 I announce the arrest and start CPR.
ACLS, modified for anaphylaxis: epinephrine 1 mg IV as in the algorithm, aggressive isotonic volume, ECPR if available, and prolonged resuscitation,4 because the cause is reversible; vasopressin, and glucagon if she is beta-blocked. Capnography confirms the tube is still in; if it is out and the airway edematous, oxygenation by whatever works, then a surgical airway without delay. After return of circulation the epinephrine infusion continues, because biphasic reactions occur in up to 20%, 1 to 78 hours later;3 ICU admission. Elective surgery stops; life-saving surgery continues once she is stable, avoiding the suspected drug.
Pitfalls that cost points
- Quoting the intramuscular dose when you have an IV and the patient is monitored.
- Forgetting the differential: vasovagal or spinal hypotension, light-anesthesia bronchospasm, tension pneumothorax, pulmonary embolism, mesenteric traction syndrome, transfusion reaction if blood is running.
Rapid-fire
Q: Why is the IV epinephrine dose so much smaller than the ACLS dose? A: A patient with a pulse needs titration to effect; 1 mg into a perfusing heart causes hypertensive crisis, arrhythmia and ischemia.
Q: Why does the reaction present as hypotension first under general anesthesia? A: Cutaneous signs are hidden under drapes and the patient cannot report symptoms; in NAP6 every patient became hypotensive, and bronchospasm was the presenting feature in 18%.2
Q: Which neuromuscular blocker is most often implicated? A: In NAP6 succinylcholine carried about twice the risk of the other relaxants, which were similar to one another;2 cross-reactivity through the quaternary ammonium epitope is common, which is why allergy testing matters.
Q: Can the patient be re-exposed to the drug if testing is negative? A: Only after a formal allergy evaluation; for antibiotics and latex, avoidance is simpler than challenge.
Numbers to know
| Item | Value |
|---|---|
| Epinephrine IV bolus (adult) | 50 mcg, repeated and escalated to effect1 |
| Epinephrine, refractory or collapse | Infusion about 0.1 mcg/kg/min; CPR and 1 mg if SBP < 50 or arrest |
| Epinephrine, no IV access | 10 mcg/kg IM, maximum 0.5 mg, lateral thigh1 |
| Crystalloid bolus | 500–1000 mL adult; 20 mL/kg child, repeated1 |
| Vasopressin | 1–2 units IV bolus, then infusion |
| Glucagon (beta-blocked) | 1 mg IV1 |
| Tryptase | Once stable, 1–4 h after onset, and ≥ 24 h later1 |
Links
- Intraoperative bronchospasm, Intraoperative hypotension: differential and management, Vasopressors and inotropes: choosing and titrating, ACLS adapted to the operating room, Transfusion reactions, TRALI and TACO
- Atlas: Monitor atlas: other perioperative and peripartum events
- Association of Anaesthetists / NAP6 report; World Allergy Organization anaphylaxis guidance
Sources
- 1.Perioperative anaphylaxis treatment algorithm · Resuscitation Council UK / Association of Anaesthetists, 2024 · resus.org.ukAdult IV adrenaline 50 mcg; IM 10 mcg/kg max 500 mcg; fluids; glucagon 1 mg; tryptase timing.
- 2.Anaesthesia, surgery, and life-threatening allergic reactions: epidemiology and clinical features of perioperative anaphylaxis in the 6th National Audit Project (NAP6) · Royal College of Anaesthetists NAP6 (Br J Anaesth), 2018 · eprints.whiterose.ac.uk
- 3.Clinical Guideline Highlights for the Hospitalist: Anaphylaxis Management in Adults and Children · Journal of Hospital Medicine (summary of AAAAI/ACAAI 2020 practice parameter), 2021 · mdedge.comPrimary practice parameter (J Allergy Clin Immunol 2020) was not reachable; summary used for biphasic incidence and timing.
- 4.Part 10: Adult and Pediatric Special Circumstances of Resuscitation (2025 AHA Guidelines) · AHA, 2025 · cpr.heart.org
Facts on this page were checked against these sources on Oct 14, 2026. Guidelines change; confirm doses against current institutional protocols.