Cyanide Toxicity Treatment & Management

Administer hydroxocobalamin (Cyanokit) or the Cyanide Antidote Kit if a diagnosis of cyanide toxicity is strongly suspected, without waiting for laboratory confirmation.

Hydroxocobalamin, routinely used in Europe, has been approved by the US Food and Drug Administration (FDA) for treating known or suspected cyanide poisoning. Hydroxocobalamin combines with cyanide to form cyanocobalamin (vitamin B-12), which is renally cleared.^{[7, 8]}

The Cyanide Antidote Kit contains amyl nitrite pearls, sodium nitrite, and sodium thiosulfate. Amyl and sodium nitrites induce methemoglobin in red blood cells, which combines with cyanide, thus releasing cytochrome oxidase enzyme. Inhaling crushed amyl nitrite pearls is a temporizing measure before IV administration of sodium nitrite.

Sodium thiosulfate enhances the conversion of cyanide to thiocyanate , which is renally excreted. Thiosulfate has a somewhat delayed effect and thus is typically used with sodium nitrite for faster antidote action.

Special concerns in pregnancy

Fetal demise is possible in cyanide poisoning. Aggressive support and antidotal treatment of the mother is paramount. An obstetric evaluation following stabilization of the mother is essential. Therapeutic abortion may be indicated in the presence of fetal demise.

Transfer

Avoid transfer of patients with acute cyanide toxicity. However, transfer the patient if antidotes and intensive care are unavailable and if rapid, appropriate medical transport can be assured.

Provide medical stabilization (eg, airway, hemodynamic parameters) before transfer. Ideally, transfer patients to a regional toxicology treatment center.

Consultations

Consult a medical toxicologist for confirmation of the diagnosis, for recommendations regarding the most effective available antidotal therapy, and for insight as to potential sources of poisoning (eg, industrial) that may place others at risk.

Certain cyanide compounds can be absorbed dermally; gloves and other forms of skin protection should be worn.

Aggressive airway management with delivery of 100% oxygen can be lifesaving. (Although theoretically useless, supportive care with administration of oxygen alone has proven effective in a number of poisonings.) It can also treat concomitant carbon monoxide exposure pending the levels.

Prehospital treatment also includes the following:

• Intubation - Intubate the patient if he or she is unconscious or the airway cannot be protected
• Monitoring and fluids - Institute cardiac monitoring and an intravenous line; administer fluids and vasopressors for hypotension
• Sodium bicarbonate - Administer sodium bicarbonate if the patient is unconscious or hemodynamically unstable and acidotic (elevated lactate levels)
• Antidotes - Administer cyanide antidotes in the prehospital setting if the diagnosis is relatively certain; such treatment generally should involve online medical control
• Anticonvulsants - These may be needed for generalized seizures

Initial emergency department care for patients with cyanide exposure is identical to that provided in the prehospital phase.

Provide supportive care, including the following:

• Airway control, ventilation, 100% oxygen delivery
• Crystalloids and vasopressors, as needed, for hypotension
• Sodium bicarbonate titrated according to arterial blood gas (ABG) and serum bicarbonate level

Decontaminate the patient with removal of clothing/skin flushing and/or activated charcoal (1g/kg), as appropriate. Activated charcoal should be given after oral exposure in alert patients who are able to protect the airway or after endotracheal intubation in unconscious patients. Remember to protect the health-care provider from potential contamination.

Administer hydroxocobalamin (Cyanokit) or the Cyanide Antidote Kit if the diagnosis is strongly suspected, without waiting for laboratory confirmation.

Cyanokit

Hydroxocobalamin (Cyanokit), routinely used in Europe, has been approved by the US Food and Drug Administration (FDA) for treating known or suspected cyanide poisoning.^{[7, 8]}

Hydroxocobalamin combines with cyanide to form cyanocobalamin (vitamin B-12), which is renally cleared. Hydroxocobalamin administration resulted in faster improvement in mean arterial pressure but similar mortality and serum acidosis, as compared with sodium nitrite, in animals.^[9]

Coadministration of sodium thiosulfate (through a separate line or sequentially) has been suggested to have a synergic effect on detoxification.

Adverse effects of hydroxocobalamin administration include transient hypertension (a benefit in hypotensive patients), reddish brown skin, mucous membrane and urine discoloration, and rare anaphylaxis and anaphylactoid reactions. It also interferes with co-oximetry (about a 5% increase in carboxyhemoglobin levels) and blood chemistry testing (bilirubin, creatinine kinase and possibly liver enzymes, creatinine, phosphorus, glucose, magnesium, and iron levels) due to its bright red color.^[10] It can also interfere with hemodialysis.^[11]

Certain medications should not be administered simultaneously or through the same line as hydroxocobalamin, including diazepam, dopamine, dobutamine, and sodium thiosulfate.

Cyanide Antidote Kit

The Cyanide Antidote Kit contains amyl nitrite pearls, sodium nitrite, and sodium thiosulfate. Amyl and sodium nitrites induce methemoglobin in red blood cells, which combines with cyanide, thus releasing cytochrome oxidase enzyme. Inhaling crushed amyl nitrite pearls is a temporizing measure before IV administration of sodium nitrite.

Sodium thiosulfate enhances the conversion of cyanide to thiocyanate, which is renally excreted. Thiosulfate has a somewhat delayed effect and thus is typically used with sodium nitrite for faster antidote action.

Avoid the sodium nitrite portion of the cyanide kit in patients with smoke inhalation unless carboxyhemoglobin concentration is very low (< 10%). The induction of methemoglobinemia from the nitrites, in addition to present carboxyhemoglobinemia, significantly reduces the oxygen-carrying capacity of blood. Vasodilatation leading to hypotension is another adverse effect of the Cyanide Antidote Kit.

Appropriate dosing of sodium nitrite has not been established in children, who may develop excessive methemoglobinemia and/or hypotension.

Inpatient care

Patients generally require admission to the ICU for continuous cardiac monitoring, respiratory and cardiovascular support, and frequent neurologic evaluation.

Rapid manifestation of acute poisoning from hydrogen cyanide (HCN) gas and soluble salts causes principal acute care concerns of hemodynamic instability and cerebral edema. Conversely, acute poisoning from cyanogens (nitriles) and poorly soluble salts may not manifest or become life threatening for several hours after exposure.

Monitor disease resolution by clinical criteria, serial plasma lactate concentrations, and arterial and venous blood gases. Perform serial electrocardiograms (ECGs) for patients with cardiac dysrhythmias or complaints of chest pain.

Discharge the patient when neurologic and cardiovascular status has normalized and acidosis and other metabolic abnormalities have resolved.

Outpatient care

Reevaluate patients within 7-10 days of discharge to monitor for onset of delayed neurologic manifestations (eg, Parkinson-like syndrome, neuropsychiatric sequelae).

Smoke alarms significantly reduce incidence of serious smoke inhalation injury. Workplaces using cyanides should have engineering controls in place to avoid inadvertent exposures. Workers should be provided with personal protective equipment and training; they should be instructed to avoid contact between cyanide salts and mineral acids or other compounds with low pH.

Determine blood cyanide concentrations or thiocyanate concentrations in patients receiving sodium nitroprusside at high doses or for more than 5 days. Alternatively, coadminister sodium thiosulfate or hydroxocobalamin to reduce the risk of iatrogenic cyanide poisoning.