Intraoperative Anaphylaxis After Antibiotic Prophylaxis

Differential diagnosis:

• Anaphylaxis to cefazolin, rocuronium, latex, chlorhexidine, or another exposure.
• Septic shock, although the patient was well before surgery and has no fever.
• Hemorrhagic shock, but the surgeon reports no bleeding.
• Cardiogenic shock or pulmonary embolism, which can cause hypotension and hypoxia.
• Severe bronchospasm from aspiration or anaphylaxis.
• Malignant hyperthermia is unlikely because there is no hypercarbia or rigidity at this early stage.

Findings supporting anaphylaxis:

• The temporal relationship to cefazolin, a common culprit.
• Sudden hypotension with tachycardia.
• A rise in peak airway pressure, suggesting bronchospasm and airway edema.
• Urticaria, which is a strong cutaneous sign, although skin signs are absent in up to 20% of cases.
• Low end-tidal carbon dioxide is consistent with low cardiac output, not with hypermetabolism.

Reasoning: The combination of hypotension, bronchospasm, and urticaria immediately after an antibiotic is highly suggestive. However, the diagnosis is clinical and must be confirmed later with mast cell tryptase. Do not wait for confirmation before treating.

Immediate actions:

1. Stop the suspected trigger and call for help.
2. Give 100% oxygen and secure the airway; if bronchospasm is severe, increase volatile anesthetic or give salbutamol through the circuit.
3. Give epinephrine early. With IV access, start with 50 mcg IV boluses and titrate every 1–2 minutes according to blood pressure and heart rate. If repeated boluses are needed, start an infusion at 0.05–0.2 mcg/kg/min.
4. Give a rapid crystalloid bolus of 1–2 L through a large-bore cannula; anaphylaxis causes profound vasodilation and capillary leak.
5. Position the patient supine with legs elevated if blood pressure allows.
6. Give an H1 antihistamine and corticosteroid as adjuncts, but never as first-line treatment instead of epinephrine.

Monitoring:

• Insert an arterial line.
• Consider echocardiography to assess ventricular filling and contractility.
• Monitor urine output and core temperature.
• Check blood gases, lactate, and electrolytes.

Reasoning: Epinephrine is the only drug that reverses both vasodilation and bronchospasm. Delaying it increases the risk of refractory shock and cardiac arrest. Antihistamines and steroids do not treat acute airway or circulatory compromise.

Confirmation:

• Take an acute serum mast cell tryptase sample as soon as possible after the reaction, ideally within 1–2 hours.
• Take a baseline sample at least 24 hours after the event, when the patient is stable.
• A rise in tryptase supports mast cell activation but a normal level does not exclude anaphylaxis.

Documentation and referral:

• Document the timing, drugs, doses, and response to treatment in the anesthetic record.
• Record the suspected culprit and all exposures, including antibiotics, neuromuscular blockers, latex, and chlorhexidine.
• Refer to an allergist for skin testing, usually 4–6 weeks after the event.
• Advise the patient to avoid the suspected drug and to carry an allergy alert.

Counseling: Explain that anaphylaxis during anesthesia is a serious event but that the team recognized and treated it promptly. Warn her that she may need allergy testing before any future surgery. Provide written information and ensure the allergy is flagged in her records. Do not label her with an allergy until testing is complete, but avoid re-exposure in the meantime.