An 80-year-old man with carotid stenosis undergoes carotid endarterectomy. He is hypertensive postoperatively and receives a sodium nitroprusside infusion at 4 μg/kg/min. About 24 hours later, he becomes confused, remains hypertensive, and develops metabolic acidosis. Which of the following interventions is MOST appropriate for this patient?
  • □ (A) Increasing the dose of sodium nitroprusside
  • □ (B) Administering hydroxocobalamin
  • □ (C) Initiating nicardipine infusion

Sodium nitroprusside is commonly used for treatment of hypertensive urgencies in the perioperative setting. The medication contains five cyanide groups per molecule. Toxic levels of cyanide may be reached in patients who receive prolonged infusions of sodium nitroprusside. Cyanide inhibits oxidative phosphorylation and forces cells to use anaerobic metabolism, resulting in lactic acidosis. Other signs of cyanide toxicity include confusion, hypertension, abdominal pain, flushing, and renal failure.

The most appropriate intervention in this scenario is to administer hydroxocobalamin, a precursor of vitamin B12 that avidly binds cyanide to form cyanocobalamin. Cyanocobalamin is readily excreted in urine.

Increasing the dose of sodium nitroprusside will worsen cyanide toxicity. Nicardipine would be appropriate to treat hypertension in this clinical setting but would not address the patient’s cyanide toxicity.

Answer: B