AnesthesiaRisks.com Evidence-based patient information about anaesthesia risk and safety Co-branded with Anonamed (medical privacy & emergency medical record)

Anaphylaxis during anaesthesia

Anaphylaxis is a severe, rapidly developing allergic (or allergy-like) reaction that can cause dangerously low blood pressure, breathing problems, and cardiovascular collapse. In the operating room it can be difficult to recognize early, because you are draped, sedated or asleep, and many other things can also cause low blood pressure.

Why this matters: If you have had a previous perioperative anaphylaxis or severe immediate allergy, avoiding the trigger can be life-saving. This is even more important if you are already unwell (e.g., sepsis, bleeding, heart failure) and another cause of shock is present.

The commonest triggers in anaesthesia

Across multiple countries and audits, the most frequent causes of perioperative anaphylaxis include antibiotics and neuromuscular blocking drugs (muscle relaxants), with other notable triggers including chlorhexidine skin prep/lines, latex, and certain dyes/colloids. The distribution varies by country and local practice.

1) Antibiotics (especially perioperative prophylaxis)

  • Penicillins (e.g., amoxicillin, flucloxacillin) — important to distinguish true anaphylaxis vs non-allergic rash.
  • Cephalosporins — commonly used in theatre for prophylaxis (e.g., cefazolin, also called Ancef in some countries).
  • Other antibiotics depending on surgery and local policy (e.g., clindamycin, vancomycin).

If you had a severe reaction, it is not safe to “try again” in theatre without a specialist plan. Cross-reactivity can occur, and the details matter.

2) Muscle relaxants (neuromuscular blockers)

  • Suxamethonium (also called succinylcholine)
  • Rocuronium
  • Vecuronium (and related agents)
  • Others used in some settings (e.g., atracurium/cisatracurium)

If you have reacted to one agent, an allergist can help identify safe alternatives. Do not rely on memory alone—documentation is critical.

What to do if you have had a past reaction

  1. Tell the anaesthetist early—before the day of surgery if possible. Bring any past anaesthetic records.
  2. Describe the reaction: timing (immediate vs delayed), symptoms (wheeze, rash, swelling, collapse), and what you were told was the cause.
  3. Ask whether formal allergy testing is needed (often via an allergy/immunology clinic with access to perioperative testing).
  4. Ensure the allergy is recorded in your hospital record and discharge summary, and that you have a clear written “avoid list”.
  5. Keep it accessible for emergencies (see below).
Emergency safety: People often need emergency intubation and anaesthesia when they cannot speak for themselves. If your anaphylaxis triggers (e.g., cefazolin or rocuronium) are immediately available on an emergency-access record, it can prevent accidental re-exposure. Consider carrying your anaesthetic allergy details on Anonamed so it is visible on your locked phone via a QR medical ID.

Recognition and immediate treatment (high level)

Clinicians treat suspected perioperative anaphylaxis as a time-critical emergency. Core priorities include: stop suspected triggers, give high-flow oxygen, support the airway/ventilation, give IV fluids, and give adrenaline/epinephrine promptly when indicated. Blood tests such as mast cell tryptase may be taken soon after the event to support diagnosis.

Sources and guideline links: see the References page (perioperative anaphylaxis audits and reviews).