Hydroxocobalamin for Smoke Cyanide
Objective: Treat closed-space smoke plus unexplained shock, seizure, coma, or arrest as possible cyanide poisoning. Hydroxocobalamin is the antidote if your protocol supplies it. Do not delay the airway or the destination. Your protocol card sets the amount.
Why this matters
Hydroxocobalamin is the antidote many EMS systems carry for suspected cyanide from closed-space smoke. A pulse oximeter is not reliable in carbon monoxide poisoning. There is no field test for cyanide. It is easy to treat the call as ordinary smoke inhalation while the patient is in shock, seizing, or in arrest.
Give it only for that picture, and only if your protocol supplies it. It is not a reason to skip the airway or a burn center. Your protocol card sets the amount. This page does not list grams.
- Closed-space fire, soot in the airway, altered mental status, seizure, or unexplained low blood pressure or arrest: think cyanide and carbon monoxide together.
- Give high-flow oxygen. Manage the airway. Give hydroxocobalamin intravenous or intraosseous if your protocol and your supply allow it.
- It can turn skin, mucous membranes, and urine red, and it can interfere with some lab color tests. Tell the emergency department you gave it.
Clinical sequence
- Get the patient out. Give oxygen. Manage the airway, breathing, and circulation. Stop burning clothing. See the smoke-inhalation lesson.
- If shock, seizure, coma, or arrest is out of proportion to the visible burns, cyanide is possible. You will not confirm it in the ambulance. The picture is closed-space smoke plus one of those findings, without another explanation.
- Give hydroxocobalamin per protocol if you carry it. Read the kit and the dose card. This page does not list grams. Do not wait for a hospital cyanide level.
- Airway swelling can still get worse after the antidote. Go to a burn or critical-care hospital. Carbon monoxide may still need a center that can manage it. Tell the emergency department the drug and the time. Blood and urine may look red.
Teaching points
- This is a suspicion, not a lab result. You will not confirm cyanide in the field.
- Hydroxocobalamin binds cyanide and forms cyanocobalamin, vitamin B12. Many EMS systems prefer it over older nitrite kits because it does not add methemoglobin on top of carbon monoxide.
- It does not fix the pulse oximeter. Treat carbon monoxide and cyanide together in an enclosed-fire victim. See the carbon monoxide lesson.
- Tell the hospital. The red color confuses labs and the chart. Name the drug and the time.
- Closed-space smoke: carbon monoxide and cyanide are both possible.
- Give oxygen and manage the airway first.
- Hydroxocobalamin if the protocol includes it and we have it.
- Tell the emergency department you gave hydroxocobalamin. Some kits are labeled Cyanokit. Give the time. Labs may be altered by the color.
Common errors
- Waiting for a cyanide level that does not exist in the field.
- Giving the antidote and forgetting a swelling airway.
- Using a nitrite kit on a carbon-monoxide patient when your protocol has moved to hydroxocobalamin.
Practice
One-minute check
Apartment fire. The patient is unresponsive in a bathroom, with soot, a blood pressure of 78, and no major burns. Name three treatments in order. What do you tell the emergency department about the urine?
Related: Smoke Inhalation and the Airway, Carbon Monoxide.
Sources & Further Study
Named guidelines for further study. They are not clinical orders and do not replace your protocol or medical direction.
- NASEMSO National Model EMS Clinical Guidelines (2022) — Smoke inhalation and cyanide pathways. Your protocol sets the kit.
- AHA 2025 Part 10: Special Circumstances — Suspected cyanide, including smoke. Hydroxocobalamin is the EMS antidote discussed there.
Education only. Apply learning within your protocols and medical direction. This is not clinical care guidance.
Check Your Understanding
Questions drawn only from this lesson. After you check, the key is highlighted. Education practice — not a certification exam.