Case #17: Nitro Boost
Author: Erin Clark, MD
Peer Reviewer: Michael Nelson, MD
A 59 year-old male with a past medical history of hypertension presents with a headache and blurry vision over the past eight hours. He reports that he has never experienced this before. Of note, he states that he ran out of his blood pressure medications (Lisinopril and HCTZ) two weeks ago. Physical exam is notable only for blurring of the optic disc margins on ophthalmoscopy.
Vitals: Temp: 98.2, HR: 88, BP: 210/130, RR: 18, O2 Sat: 98% on RA
After establishing the diagnosis of Hypertensive Emergency, you decide to start Sodium Nitroprusside (SNP).
How common is Cyanide (CN) toxicity from SNP?
CN toxicity is uncommon at rates of less than 8-10 mcg/kg/min, but has been reported at rates as low as 4 mcg/kg/min after 3 hours.
What signs and symptoms would you expect to see with this toxicity?
CNS: Anxiety, Headache, Confusion, Decreased level of consciousness, Seizures, Paralysis, Coma.
Cardiovascular: Tachycardia, Hypotension, Ventricular fibrillation, Asystole.
Pulmonary: Tachypnea (early), Hypoventilation (late).
In what patient population should you be especially concerned about this toxicity?
One must be especially careful using SNP in patients with Liver Failure. The mitochondrial enzyme rhodanase, which is most abundant in the liver, catalyzes the reaction between CN and thiosulfate to make thiocyanate, which is then renally excreted. Patients with Liver Failure have difficulty catalyzing this reaction leading to extremely elevated levels of CN. Also, be careful with Renal Failure patients due to decreased CN excretion.
What is the treatment for CN toxicity?
Hydroxocobalamin, given as
5 g IV infused over 15 minutes, is the treatment of choice. This may be followed by a second dose in cases of severe toxicity.
Note: A common, benign side effect of this medication is a discoloration of mucus membranes, serum, and urine.
An older, but still utilized treatment is Amyl/Sodium Nitrite with Sodium Thiosulfate. The patient is initially treated 300mg IV Sodium Nitrite (or Amyl Nitrite pearls if no IV access) followed by 12.5 mg IV sodium thiosulfate. As Amyl/Sodium Nitrite can cause significant Methemoglobinemia, be careful with patients who are at risk of CO poisoning (for example, house fires).
References:
Borron SW, Baud FJ. Acute cyanide poisoning: clinical spectrum, diagnosis, and treatment. Arh Hig Rada Toksikol. 1996 Sep;47(3):307-22.
Shepherd G, Velez LI. Role of hydroxocobalamin in acute cyanide poisoning. Ann Pharmacother. 2008 May;42(5):661-9.
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