Medical Aspects of Chemical Warfare (2008) - The Black Vault

Cyanide Poisoningcyanide has been ingested the gut should be decontaminatedthrough gastric lavage and the administrationof activated carbon. All cutaneous cyanide can beremoved by washing with water or soap and water.Water temperature should be comfortably warm if possible,but decontamination should not be delayed whilewater is heated. Early decontamination definitelyreduces the extent of illness by decreasing total bodyburden. Decontamination also protects emergencyresponders and healthcare personnel. Personnel conductingdecontamination and any predecontaminationcare require appropriate personal protective equipmentso that they themselves do not become casualties.Personnel conducting autopsy examinations onpersons recently deceased from cyanide poisoningshould also apply safety precautions. At the least, theseinclude adequate ventilation to the outside, frequentbreaks in uncontaminated spaces, and containmentof heavily contaminated organs. Any personnel whobecome symptomatic should refrain from continuedexposure. Documentation of postexposure blood cyanidelevels can be considered. 143Transport of cyanide-intoxicated casualties to definitivecare facilities should be done as rapidly as possibleunless general supportive care and antidotes canbe delivered by emergency responders. In the event ofa suicide attempt, this could be at the home or workplaceor in the ambulance en route to the hospital. Inthe event of an urban release, initial stabilization couldoccur in the warm zone (decontamination corridor).In the event of a military situation, initial stabilizationwould probably occur in the dirty side of the patientdecontamination station. In any case, stabilization ofcritically ill casualties must be done before completedecontamination. Transport vehicles and personnelshould be prepared to provide oxygen (100% if possible),intravenous lines, cardiopulmonary rescusitation,and antiseizure medications. Ideally they willalso be equipped to initiate specific antidotal therapy,particularly with amyl nitrite and thiosulfate. Becauseof its side-effect profile, sodium nitrite should not beadministered unless the care providers are equippedto monitor blood pressure closely and to adjust ratesof administration.Laboratory FindingsSerious cyanide toxicity is characterized by obstructionof aerobic metabolism and forced anaerobicmetabolism. These conditions cause lactic acidosis,manifesting as metabolic acidosis with anion gap andlactic acidemia, and reduced arteriovenous oxygencontent difference. A lactate level measurement refinesthe more general impression of metabolic acidosis;depending on the results, renal insufficiency would bea less likely cause of anion gapped metabolic acidosis.In the setting of severe and potentially fatal cyanidepoisoning, pulse oximetry correctly demonstrates thehigh blood oxygen content. It will not, however, correctlyreflect deficient oxygen delivery and uptake attissue level.As therapy proceeds and cellular respiration resumes,venous oxygen levels will drop, lactic acidlevels will return to normal, and pH will move towardsneutral. 144–148 Estimation of oxygen saturationby pulse oximetry will remain misleading, however,because of the presence of methemoglobin as a consequenceof nitrite therapy. 149 Hemoximetry (in vitromultiwavelength cooximetry) can quantify the deficitin functional saturation resulting from methemoglobinand carboxyhemoglobin but does not account foradditional, and likely significant, decrements causedby cyanomethemoglobin (unless newer machinescapable of directly measuring cyanomethemoglobinare used). 161 Measured methemoglobin levels afteradministration of a 300-mg ampule of sodium nitritewill likely not exceed 7% to 10% and may be lower;the remaining oxygen carrying capacity will be somethingless than 90% to 93%, depending on the degreeof dyshemoglobinemia present.Interpretation of cyanide levels for clinical managementis unreliable. Cyanide is continually eliminatedfrom the body as long as the person remains alive.Cyanide can be measured in either plasma or wholeblood. Whole blood levels more accurately reflect thetotal body burden because most cyanide is rapidlybound into red blood cells, but plasma levels may morecorrectly predict cellular exposure. 144 Blood cyanidelevels do not reliably predict severity of illness. In addition,most centers are unable to receive test resultsquickly enough to support diagnostic use. Therefore,blood or plasma cyanide levels currently have limitedvalue in the acute care setting outside of research hospitals.They remain valuable for confirmatory testingand forensic purposes. In the near future, the cyanidemetabolite ATCA may prove to be a useful additionalbiomarker of excessive cyanide exposure because ofits stability over time. 151Long-Term EffectsComparatively few persons survive acute, highdoseexposures to cyanide. Survivors typically eitherreceive early aggressive medical support or representthe subpopulation with increased resistance to the poison.One other subgroup is those with gastric anacidity.They tolerate large amounts of cyanide salts, apartfrom local erosions. 162 The understanding of the health387