Cyanide Exposure in the Field
Cyanide exposure in EMS most commonly occurs during structure fires, where the combustion of synthetic materials (plastics, nylon, polyurethane) releases hydrogen cyanide gas. Cyanide may also be encountered in industrial settings (metal plating, mining) and intentional poisonings. Cyanide inhibits cytochrome oxidase in the mitochondria, blocking cellular oxygen utilization. Even with adequate oxygen delivery, cells cannot use it, leading to cellular asphyxia and rapid death if untreated.
Recognizing Cyanide Toxicity
Suspect cyanide exposure in patients with:
- Smoke inhalation from structure fires (especially enclosed spaces with burning synthetics)
- Altered mental status or seizures after fire exposure
- Cardiovascular collapse (hypotension, bradycardia, cardiac arrest) after smoke inhalation
- Metabolic acidosis (lactate greater than 8 mmol/L) in a fire victim
- Normal or elevated SpO2 with signs of severe tissue hypoxia
- Cherry-red skin (a classic but unreliable finding)
Hydroxocobalamin (Cyanokit)
Hydroxocobalamin is a form of vitamin B12 that binds directly to cyanide ions, forming cyanocobalamin (another form of vitamin B12) which is then excreted by the kidneys. It is the preferred prehospital antidote for cyanide poisoning because it is safe, effective, and has minimal hemodynamic side effects compared to older cyanide antidote kits.
Dosing
- Adult: 5 grams IV infused over 15 minutes. May repeat with a second 5-gram dose if clinically indicated.
- Pediatric: 70 mg/kg IV (maximum 5 grams)
- Reconstitute with 200 mL of normal saline and gently rotate the vial (do not shake)
Side Effects and Interference
Hydroxocobalamin causes a distinctive bright red discoloration of the skin, mucous membranes, and urine that can last several days. This is harmless but can be alarming to the patient and staff. More importantly, it interferes with colorimetric laboratory tests (including SpO2 readings, cooximetry, and some blood chemistry panels) for 24 to 48 hours. Document the administration time and dose clearly so hospital staff can account for this interference.
Empiric Treatment
In structure fire victims with altered mental status, cardiovascular instability, or severe metabolic acidosis, empiric treatment with hydroxocobalamin is recommended even without confirmed cyanide levels. The risk of untreated cyanide poisoning far outweighs the minimal risk of the antidote. Do not delay treatment waiting for laboratory confirmation.