Collapse Six Minutes After Cefazolin
A 36-year-old woman (65 kg) with no known allergies has a laparoscopic cholecystectomy. Induction is propofol 160 mg, fentanyl 100 micrograms, and rocuronium 40 mg; cefazolin 2 g is given at incision. Six minutes later MAP falls from 88 to 44 mmHg, heart rate rises to 132 in sinus rhythm, peak airway pressure rises from 18 to 38 cmH2O with a plateau of 22 cmH2O, SpO2 falls to 87%, and end-tidal CO2 falls to 18 mmHg. The lungs sound clear, no rash is visible because the abdomen and chest are draped, and the abdomen is insufflated to 15 mmHg. The propofol and fentanyl syringes are labeled and the vaporizer was checked at the start of the case.
1. Build a differential for this collapse and state what you would do in the first three minutes, before any diagnosis is certain.
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Differential: anaphylaxis to cefazolin, rocuronium, or less likely propofol; acute bronchospasm; a circuit or vaporizer fault; tension pneumothorax; pulmonary embolism including CO2 embolism; hemorrhagic shock from an occult injury; and an ampoule or syringe swap.
First three minutes - treat while diagnosing:
- Stop the cefazolin infusion and call for help and for the difficult airway trolley.
- 100% oxygen, hand-ventilate to feel compliance and exclude a machine fault, and confirm the tube is not displaced.
- Give epinephrine now: 20 to 60 micrograms (roughly 0.5 to 1 microgram/kg) intravenously, repeated and titrated to MAP. In anaphylaxis, delay in giving epinephrine is the main determinant of bad outcome; a clear chest does not exclude it, because the increase in peak-to-plateau gradient points to large-airway or small-airway resistance rather than to alveolar disease.
- Rapid crystalloid 500 to 1000 mL, and start an epinephrine infusion.
- Release the pneumoperitoneum if MAP stays low, and look for a rash on the exposed skin and for urticaria at the injection site.
- Keep the possibility of a wrong drug in play and check every syringe.
2. Show the epinephrine infusion arithmetic for this patient and explain the rationale for your target concentration and rate.
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Concentration: 1 mg in 250 mL equals 4 micrograms/mL.
Starting infusion at 0.05 micrograms/kg/min: 0.05 x 65 = 3.25 micrograms/min, which is 3.25/4 = 0.81 mL/min, or about 49 mL/h. A useful check is that 0.05 micrograms/kg/min in a 65 kg patient is about 50 mL/h at this concentration, so the numbers are internally consistent.
Titration: increase in steps of 0.05 micrograms/kg/min to effect; refractory cases are commonly at 0.1 to 0.3 micrograms/kg/min. At 0.2 micrograms/kg/min the rate would be 13 micrograms/min, or 195 mL/h.
Rationale: epinephrine is an alpha-1 agonist that reverses vasodilatation and an agonist at beta-2 receptors that reverses bronchospasm and stabilizes mast cells. A dilute, peripherally compatible concentration allows fine titration without repeated large boluses causing hypertension and arrhythmia. Beware of giving a concentrated bolus by mistake - double-check the bag label and consider a second clinician as a reader. Once the patient is stable, transition to a push-dose or intermittent bolus regimen only when the infusion can be weaned predictably over 1 to 2 hours.
3. Despite three boluses and an infusion at 0.2 micrograms/kg/min, the MAP is 48 mmHg with a heart rate of 140. What is your next reasoning step?
Read the worked answer
Reframe the diagnosis while escalating. There are three possibilities to settle in parallel:
- The diagnosis is right but the treatment is insufficient. Escalate with a second vasopressor (norepinephrine or vasopressin 1 to 2 units), consider methylene blue 1 to 2 mg/kg for refractory vasoplegia, and give more fluid if the patient is still preload-dependent. If the patient is on a beta blocker, glucagon is a specific adjunct.
- The diagnosis is wrong or incomplete. Re-examine for tension pneumothorax, occult intra-abdominal bleeding, a CO2 embolism from insufflation, or an evolving myocardial infarction. A bedside echocardiogram answers several of these at once: an empty, hyperdynamic ventricle means hypovolemia; a dilated, poorly contracting ventricle means cardiogenic failure; a dilated right ventricle with a shifted septum suggests embolism.
- There is a second process. Anaphylaxis and hemorrhage can coexist, and the insufflation itself can be the cause of the collapse.
Regardless of the answer, send a serum tryptase within the first hour and a baseline sample after 24 hours, since a single normal value does not exclude anaphylaxis, and document the suspected agents so that future exposures are avoided.