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A 50-year-old man is rescued from a fire that occurred in a plastics factory. He is unresponsive on examination by the paramedics. His heart rate is 60/min, the respiration rate is 23/min, and blood pressure is recorded at 80/40 mm Hg. He is treated initially with 100% oxygen, intravenous fluids, and a dopamine infusion. His arterial blood gas reveals a PO2 of 360 mm Hg, PCO2 of 32 mm Hg, and pH of 7.3. The carboxyhemoglobin level is 20%.
Which of the following would be the most appropriate treatment for this patient?
A Methylene blue
B Glucagon
C Sodium thiosulfate
D Nitric oxide
E N-acetylcysteine
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Answer and Critique (Correct Answer = C)
This patient has smoke inhalation with cyanide poisoning. Combustion of natural fabrics (such as wool and silk) and plastics is known to produce hydrogen cyanide gas. Clinical clues include the findings of coma, hypotension, cardiac irritability, and profound anion gap metabolic acidosis (due to lactic acidosis) in the setting of adequate volume resuscitation and oxygen administration. The finding of unexplained lactic acidosis refractory to fluid resuscitation and administration of 100% oxygen in the setting of smoke inhalation should prompt consideration of cyanide poisoning. The patient should be empirically treated for cyanide poisoning with intravenous sodium thiosulfate.
Carbon monoxide poisoning can also cause coma and hypotension, but the fact that this patient does not respond to treatment with 100% oxygen and has only moderately elevated levels of carboxyhemoglobin mandates consideration of other causes of coma. Treatment with hyperbaric oxygen may be indicated on the basis of the patient's comatose state with an elevated carboxyhemoglobin level. Hyperbaric oxygen decreases the half-life of carboxyhemoglobin to approximately 20 minutes but its role in the treatment of carbon monoxide poisoning is controversial. It has been recommended by some authors when the carboxyhemoglobin level is greater than 40%. In cases in which cyanide toxicity is suspected and significant carboxyhemoglobinemia has been ruled out, treatment with both nitrite and thiosulfate is indicated. If the level of carboxyhemoglobin is significant or unknown, thiosulfate can be given alone. If nitrites are given, the sum of methemoglobin and carboxyhemoglobin levels should be below 40%.
Methylene blue is the antidote for methemoglobinemia and has no role in the treatment of this patient. The finding of an elevated osmolal gap in the setting of an anion-gap metabolic acidosis is a clue to poisoning by ethylene glycol or methanol, neither of which pertains in this case. There is no evidence for treatment with glucagon which reverses β-blocker overdose. Nitric oxide has no role in the treatment of this patient. N-acetylcysteine is used in the treatment of acetaminophen overdose.
Key Points
* Clinical findings in hydrogen cyanide toxicity include coma, hypotension, cardiac irritability, and profound anion gap metabolic acidosis in the setting of adequate volume resuscitation and oxygen administration.
* The treatment for cyanide poisoning is intravenous sodium thiosulfate.
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PLASTIC ,SILK WOOL BURNS ...CYANIDE POISONING...SODIUM THIOSULPHATE
