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One of your patients is a newly minted volunteer firefighter in a rural community in Colorado. That morning he was called to a metal finishing plant where a chemical accident, involving hydrochloric acid and cyanide salts occurred. Fearing that the HCl might interact with the CN, the area surrounding the plant was evacuated. The local hazmat team entered the area wearing SCBA gear and chemically protective clothing.

Your patient did not enter the building, but complained of feeling tired, dizzy, and short of breath in the building’s parking lot and was told to seek medical attention. In your office, he denies any headache, coughing, or GI complaints. No other firefighters complained of any symptoms. His physical exam was unremarkable: specifically no tachycardia, tachypnea, or flushing. Your differential diagnosis includes mild cyanide toxicity or possible anxiety reaction. What tests, if any, would you order?


Cyanide has been used for thousands of years in intentional poisonings, though it wasn’t until the end of the 18th century that the actual compound was identified. Its role in infamy is unquestionable with such uses by Nero to murder his family and “friends,” by Reverend Jim Jones in Guyana for a mass cult suicide of over 900 people in 1978, and in the 1982 Tylenol contamination episode in which seven people died. More recently, Iraqi military used cyanide gas as part of the Iraqi chemical attack on Kurdish citizens, killing thousands in the late 1980s (Fig. 26–1).

Figure 26–1

The bodies of Iraqi Kurds after attacks with, among other things, cyanide gas in the late 1980s.

Courtesy of the Kurdistan Democratic Party.

Hydrogen cyanide (HCN) is a byproduct of the combustion of molecules containing carbon and nitrogen, including most plastics. HCN is felt to be a major cause of inhalational injury from residential and commercial fires. Worldwide, probably the single biggest source of cyanide exposure comes through cigarette smoking.

Cyanide (CN) itself is omnipresent in living things. In fact, cyanide is naturally occurring in relatively low levels in many plants as well as in plant foods; such as corn, spinach, lima beans, cherries, soy, tapioca, peaches, bitter almonds, and cassava beans (Fig. 26–2). It is even produced by certain species of bacteria, fungi, and algae and is an important and vital part of many metabolic processes such as in the making of vitamin B12. Cyanide becomes toxic beyond a certain threshold of exposure. Because of the biological ubiquity of cyanide, there are intrinsic metabolic pathways for its removal. However, exposure levels at sufficiently high levels can readily overwhelm normal clearance mechanisms.

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