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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.
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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?
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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).
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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.
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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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