Carbon monoxide poisoning
Carbon monoxide poisoning follows inhalation of a colorless, odorless combustion product that binds hemoglobin roughly 200 to 300 times more avidly than oxygen, producing tissue hypoxia that pulse oximetry cannot detect. Diagnosis requires co-oximetry on a blood gas to measure carboxyhemoglobin. Treatment is immediate high-flow 100% oxygen, escalated to hyperbaric oxygen for loss of consciousness, neurologic or cardiac ischemia, or pregnancy.
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What this article covers
- Overview
What it is: inhalation of carbon monoxide (CO), a colorless, odorless, tasteless gas from incomplete combustion; sources include vehicle exhaust, structural fire smoke, and faulty fuel-burning…
- Epidemiology
A leading cause of poisoning death: among the most common causes of poisoning death worldwide, and the leading cause of death in the first 24 hours after a fire.
- Risk factors
Enclosed or poorly ventilated space: running an engine, generator, or fuel-burning appliance indoors or in an attached garage concentrates CO far above ambient levels.
- Pathophysiology
Competitive hemoglobin binding: CO binds the same heme iron site as oxygen with an affinity roughly 200 to 300 times that of oxygen, so it progressively displaces oxygen and forms carboxyhemoglobin.
- Clinical features
Mild-to-moderate exposure: headache (often the earliest symptom), nausea, dizziness, malaise, and myalgias that can be mistaken for a viral illness.
- Differential diagnosis
Cyanide poisoning: can co-occur in an enclosed-space fire, but shows a markedly elevated lactate and anion gap acidosis out of proportion to COHb, since toxicity comes from cytochrome oxidase blockade rather than hemoglobin displacement.
- Diagnosis
The diagnosis is established by measuring carboxyhemoglobin on co-oximetry from an arterial or venous blood gas: standard pulse oximetry and a routine calculated saturation cannot distinguish…
- Management
First, remove the patient from the source and secure the airway: move to fresh air, apply cardiac monitoring, and intubate for depressed mental status, seizure, or airway compromise from smoke inhalation.
- Complications
Hypoxic-ischemic brain injury: ranges from transient confusion to permanent cognitive and motor deficits, most closely tied to loss of consciousness during exposure.
- Prognosis
Neurologic and cardiac findings at presentation, not the peak COHb level, drive prognosis: because cytochrome oxidase inhibition contributes independently of hemoglobin binding, outcome correlates poorly with a single COHb number.
- Prevention
Home carbon monoxide detectors: install on every level and outside each sleeping area, testing monthly; a triggered alarm should prompt immediate evacuation, not investigation from inside the home.
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