4.25: Toxicology - Cyanide Poisoning

A patient was admitted to University Hospital as a result of a gunshot wound. After intensive surgery and care for one month, the patient remained in a coma. At that point, the patient’s condition started to worsen gradually. Most noticeably, there was a large amount of lactic acidosis. Because of the severity of the acidosis and the suspicious nature of the initial cause of the illness, the surgical team orders a stat blood cyanide.

Stat cyanide analyses are difficult to do and require about 4 hours to perform. The technologist in the stat area checks the record of the patient and notes that the patient has been in the hospital for at least one month. The technologist calls the surgical team and asks why a stat cyanide level is being requested. The response is that the patient had received visitors and seemed to worsen after the visits; the team wants to rule out a suspected cyanide poisoning. The lactic acid acidosis could be the result of cyanide poisoning.

QUESTION

What should the technologist’s response be to a request for a cyanide measurement to rule out possible poisoning of a hospital patient?

Questions to Consider

1. Is cyanide an acute or chronic poison?
2. If an acute cyanide poisoning were present, would a stat cyanide request be appropriate? Would the results of the CN^- analysis be crucial for medical decision-making?
3. What other hospital personnel do you think should be contacted?

Answer

The medical technologist brings the request for a stat cyanide level to the attention of the clinical chemist. After discussion, the physicians are notified that if an acute cyanide (CN) poisoning is suspected, it is more accurate and convenient to detect CN in intravenous IV fluids (the suspected route of delivery) than in blood. The team physician explains that this is not possible since the IV fluids suspected of causing the problem were discarded the day before.

Since it was obvious that an acute poisoning was not present, because it was at least 24 hours after the fact, the clinical chemist suggests to the team that a stat cyanide level is probably unnecessary. The team insists on the analysis being made. The chemist suggests that additional hospital personnel should be involved.

Poisoning of patients in a hospital can and does occur. Because of the medicolegal aspects of a suspected poisoning, the technologist should immediately bring the problem to a supervisor.

Answers to Questions to Consider

1. Increased blood cyanide levels are most often seen clinically in cases of acute poisoning usually in industrial settings; see p 998-999 and 1005. Also see Web sites: www.gaiaguys.net/Cyanide_poisoning.htm, chemdef.apgea.army.mil/textbook/Ch-10.pdf (requires Adobe)
2. If an acute cyanide poisoning were taking place, a stat cyanide measurement would be appropriate. However, because of the slow turnaround time of the test compared to the acute effects of cyanide, the antidote (sodium nitrite or oxygen, see page 1005 and the Web site http://www.hse.gov.uk/pubns/misc076.htm) should be given immediately without waiting for the test result. The rationale for nitrite therapy is that the Nitrites cause formation of Methemoglobin by combining with the hemoglobin. Methemoglobin has a higher affinity for cyanide than does cytochrome oxidase and thus promotes its dissociation from this enzyme.
3. Hospital risk management must also be consulted if cyanide poisoning is suspected. The risk management team can then take proper steps to maintain confidentiality and take preventive measures. If a medical consultant is available to the laboratory, this person should be contacted by the technologist.