Smoke Inhalation, Carbon Monoxide & Cyanide Poisoning

Smoke inhalation poisoning is what happens when you breathe combustion products in an enclosed fire. This page is about the poison part: carbon monoxide (CO) and hydrogen cyanide (HCN). The airway and burn injury get handled alongside it, on the Burns page. Fire releases CO when the burn is incomplete, and burning materials can release HCN too. The two often arrive together, and cyanide may be the main toxin.

• Carbon monoxide: it grabs hemoglobin harder than oxygen does, so less oxygen reaches the brain and heart. It has no signature symptom. Headache, nausea, dizziness and confusion are common.
• Cyanide: the oxygen is there, and the cell cannot use it. Cyanide binds cytochrome a3 (cytochrome c oxidase) in the mitochondria, so the cell is forced onto anaerobic metabolism. Lactate rises.
• Synergy: together, CO and cyanide lower the lethal dose of each one.
• Airway injury: heat and irritant gases hurt the upper and lower airway. The swelling can keep building after the exposure ends.

Delayed neurologic problems can follow CO poisoning, even after the patient seems to recover. Memory, attention, mood and movement are the common domains. That is why hyperbaric referral and follow-up matter. The 2023 UHMS hyperbaric indications chapter lists these domains.

Carbon monoxide

The symptoms are vague, and several people in the same building may have them. Headache, nausea, dizziness, malaise and confusion are the usual ones. Severe exposure goes further: syncope, seizure, coma, chest pain, myocardial ischemia and arrhythmia.

Cyanide

Early cyanide looks like confusion, headache, dyspnea, chest tightness, nausea, tachypnea and mydriasis. Later it turns into seizure or coma, bradypnea or apnea, vomiting and cardiovascular collapse. Blood pressure may climb early and then fall.

Smoke-victim screen

Every smoke victim gets the same three-part screen: exposure to fire or smoke in an enclosed space, soot around the mouth, nose or oropharynx, and altered mental status. The Nithiodote label uses this screen before sodium nitrite. Treatment should not wait for a lactate result.

Red Flags

• Neurologic: any loss of consciousness, confusion, seizure, coma or focal deficit
• Cardiac: chest pain, ischemic ECG changes or arrhythmia
• Cyanide markers: plasma lactate ≥8 mmol/L in isolated cyanide poisoning; ≥10 mmol/L in smoke inhalation
• Airway: hoarseness, stridor, drooling or facial and oral burns

• Panic or hyperventilation: tachypnea and vomiting can look like early cyanide. Altered mental status, mydriasis and lactate tell them apart.
• Burns and trauma without poisoning: not every smoke victim has cyanide poisoning. Burns, trauma and other toxic exposures muddy the picture.
• Hypoglycemia, stroke and postictal state: check glucose, and think about stroke before you blame the confusion on smoke alone.
• Other fire toxins: treat them with the general toxic-exposure approach (see Toxidromes).

1. Scene safety: do not enter a smoke-filled structure without fire department clearance and respiratory protection. Move the patient and crew to fresh air.
2. Oxygen: apply 100% oxygen by non-rebreather mask for any suspected CO or cyanide exposure, regardless of SpO₂.
3. Airway: look for hoarseness, stridor, drooling, facial burns and soot. Keep the airway open. Support breathing with a bag-valve-mask if breathing fails.
4. Monitoring: watch them the whole time. A normal SpO₂ does not rule out CO poisoning.
5. Report: tell the receiving hospital about the enclosed fire, any loss of consciousness and the time of exposure and of oxygen start.
6. Transport priority: get them moving promptly. Cyanide antidote and advanced airway decisions need ALS. Antidote scope varies by state and protocol, so EMT and AEMT crews should request ALS intercept early.

Doses vary by protocol; follow local protocols and medical direction.

• Access and monitoring (Paramedic/RN/CCT): IV or IO access, cardiac monitor and 12-lead ECG. Draw the pre-dose lactate and blood gas with co-oximetry first, only if this causes no delay.
• Cyanide antidote (Paramedic/RN/CCT): hydroxocobalamin 5 g IV over 15 min for suspected cyanide poisoning with smoke inhalation, altered mental status, seizure, coma, hypotension or cardiac arrest. It is the preferred antidote for smoke inhalation (see References). See Hydroxocobalamin.
• Line management: give hydroxocobalamin through its own line. It is chemically incompatible with sodium nitrite and sodium thiosulfate, and reported incompatible with ascorbic acid; never mix or co-infuse these in one line. The label advises against running it through the same line as blood products; blood products can run on a separate line. Use a second IV or IO for resuscitation drugs.
• Nitrite and thiosulfate: the alternative when hydroxocobalamin is unavailable. The Nithiodote label lists it as an option, but it causes hypotension and methemoglobinemia and can worsen hypoxia in smoke or CO, so use it with caution (see ED & ICU Management).
• Seizures (Paramedic/RN/CCT): benzodiazepine per protocol. See Midazolam.
• Bronchospasm (Paramedic/RN/CCT): albuterol per protocol. See Albuterol.
• Airway (Paramedic/RN/CCT): early advanced airway for airway burns or failing ventilation, by the most experienced provider. See RSI and Intubation.
• Arrest: ACLS per the 2025 AHA guidelines (see Adult Cardiac Arrest), with the cyanide antidote on its own line.

• Oxygen: keep the 100% oxygen running until repeat COHb falls to the protocol end point. That end point varies by protocol.
• Hyperbaric referral: the UHMS 2023 indications chapter says to consider hyperbaric oxygen (HBO) for all acute symptomatic CO poisoning. It indicates HBO when CO poisoning is complicated by cyanide. Treat it as urgent for loss of consciousness, neurologic signs, cardiac ischemia or arrhythmia, severe acidosis, pregnancy or COHb ≥25% in some protocols. HBO versus normobaric oxygen is a decision for the treating clinician and the hyperbaric center. Criteria depend on the protocol, so use local hyperbaric criteria.
• Second hydroxocobalamin dose: a second 5 g over 15 min if needed (15 min in extremis, up to 2 hr otherwise); total maximum 10 g.
• Sodium nitrite and thiosulfate (Nithiodote label): adults receive sodium nitrite 10 mL (300 mg) IV at 2.5–5 mL/min, then sodium thiosulfate 50 mL (12.5 g) immediately. Monitor blood pressure; halve both doses if poisoning recurs. Nitrite causes hypotension and methemoglobinemia, and worsens hypoxia when CO is present.
• Labs: repeat lactate after each dose. Check co-oximetry and methemoglobin after nitrite, because standard pulse oximetry is unreliable once methemoglobin is up. After hydroxocobalamin, track renal function (BUN and creatinine) for 7 days and follow urine output. Acute renal failure is a labeled risk, and hemodialysis may be needed. Hydroxocobalamin can set off a false blood-leak alarm and shut down hemodialysis machines, so warn dialysis staff before they start.
• Airway and ventilation: intubate for airway edema or failing ventilation. Set ventilator support per ICU protocol.
• Cardiac: serial ECG and troponin. Involve cardiology for ischemia.
• Burns: follow burn resuscitation and referral on the Burns page.

• Destination: hyperbaric center when CO criteria are met (protocol-dependent); burn center for burns with inhalation injury; ED with airway and ICU capability for cyanide poisoning.
• In transit: keep 100% oxygen running. Monitor the airway, ECG, blood pressure and mental status, and watch for seizure.
• Hydroxocobalamin effects: blood pressure climbs soon after the infusion starts. Red skin and red urine are expected after the drug.
• Kit and diluent: the hydroxocobalamin vial holds powder. Diluent is not in the kit, so carry 0.9% sodium chloride. The label says lactated Ringer's or D5W are also compatible.
• Handoff: time of exposure, time oxygen started, pre-dose sample labels, each drug and time, total hydroxocobalamin dose, last blood pressure and mental status trend.

• Pediatrics: hydroxocobalamin 70 mg/kg IV over 15 min (2.8 mL/kg of 25 mg/mL). A cap of 5 g per dose is a common protocol limit, not a label statement. The second dose is per protocol and medical direction, which the US label does not define; do not exceed the adult 10 g total. The US label says safety and effectiveness are not established in children; the 70 mg/kg dose comes from non-US use. Nitrite and thiosulfate in children: sodium nitrite 0.2 mL/kg (6 mg/kg; max 10 mL), then sodium thiosulfate 1 mL/kg (250 mg/kg; max 50 mL). Neonates and infants are more susceptible to nitrite-related methemoglobinemia and need reduced dosing. See Weight-Based Dosing and Pediatric Vital Signs.
• Pregnancy: fetal hemoglobin binds CO more strongly than maternal hemoglobin. A 2018 narrative paper in burned pregnant patients supports strong consideration of HBO. Cyanide poisoning is a medical emergency for mother and fetus. Pregnancy is no reason to withhold life-sustaining therapy or the antidote (both labels, section 8.1). Human data on hydroxocobalamin are insufficient. In animal studies it caused skeletal and soft-tissue abnormalities. The Nithiodote label recommends sodium nitrite with thiosulfate for known or suspected cyanide poisoning in pregnancy, but it advises considering alternatives that are not linked to methemoglobinemia. For smoke inhalation and CO, hydroxocobalamin is the usual choice in US practice. Medical direction makes the final call. Call the hyperbaric center and medical direction.
• Lactation: hydroxocobalamin appears in human milk. The label advises against breastfeeding during treatment, and it gives no guidance on when to restart.
• Older Adults: about 50 patients aged 65 or older got hydroxocobalamin in clinical studies. No dose change is required.
• Renal Impairment: the kidney clears hydroxocobalamin unchanged. Its safety in renal impairment has not been studied. Renal injury is a labeled risk.
• Anemia and G6PD deficiency: in anemia, scale the nitrite dose down with the hemoglobin. G6PD deficiency raises the risk of hemolysis with nitrite, so consider alternatives.

• Error: holding hydroxocobalamin until lactate, a cyanide level or COHb comes back. Do not delay the antidote for these results.
• Error: clearing a smoke victim with SpO₂ or SpCO. A normal reading does not rule out CO. Send co-oximetry.
• Error: reaching for sodium nitrite first in a smoke victim. Nitrite can cause severe hypotension and methemoglobinemia, and it worsens hypoxia when CO is present.
• Error: running hydroxocobalamin in a shared line. Give it a dedicated line. It is chemically incompatible with sodium nitrite and sodium thiosulfate. Blood products belong on a separate line.
• Error: drawing post-dose blood for chemistry, hematology, coagulation or urinalysis without noting the timing. Hydroxocobalamin colorimetric interference distorts results. Expect about 24 h for chemistry (bilirubin up to 4 days), 12–16 h for hematology, 24–48 h for coagulation, and up to 8 days for urinalysis, with up to 24 h more after a 10 g dose. Label post-dose samples.
• Error: calling red skin or red urine bleeding. Both are expected after hydroxocobalamin.
• Error: waiting for stridor or respiratory failure before you plan the airway. Hoarseness, drooling or facial burns call for early airway planning.
• Error: discharging someone once symptoms clear, with no hyperbaric assessment. Delayed neurologic problems can follow CO poisoning.