Toxicology – Carbon Monoxide (CO) Poisoning

Source

Carbon monoxide is a colorless, odorless, nonirritating gas produced by incomplete combustion. Common sources include house fires, furnaces, heaters, grills, gasoline-powered generators, and motor vehicle exhaust. Methylene chloride exposure can also produce carbon monoxide after metabolism in the body.

Typical Presentation

Several people from the same household may develop headache, dizziness, nausea, and vomiting after using a fuel-burning appliance or generator in an enclosed area. Because symptoms are nonspecific, carbon monoxide poisoning can easily be mistaken for a viral illness.

Clinical Features

Common manifestations include:

• Headache
• Nausea and vomiting
• Dizziness
• Fatigue
• Confusion
• Shortness of breath
• Chest pain
• Syncope or loss of consciousness

Severe poisoning can cause neurological injury, myocardial ischemia, arrhythmias, coma, or death.

A carboxyhemoglobin (COHb) level can help confirm exposure. Pulse oximetry may appear falsely normal because standard devices cannot reliably distinguish oxyhemoglobin from carboxyhemoglobin.

Mechanism of Action

Carbon monoxide binds to hemoglobin with much greater affinity than oxygen, forming carboxyhemoglobin. This reduces oxygen-carrying capacity and also impairs release of oxygen to tissues, resulting in cellular hypoxia.

Management

• Immediately remove the patient from the source of exposure.
• Administer high-concentration oxygen.
• Monitor neurological status, ECG, and cardiac biomarkers when appropriate.
• Hyperbaric oxygen therapy may be considered in severe poisoning, especially with loss of consciousness, persistent neurological abnormalities, significant cardiac involvement, severe acidosis, or pregnancy.
• Evaluate fire victims for possible simultaneous cyanide toxicity when severe lactic acidosis or cardiovascular collapse is present.

Key Points

• Headache is the most common symptom of CO poisoning.
• Multiple people with similar symptoms in the same enclosed environment should strongly raise suspicion.
• Standard pulse oximetry can be misleadingly normal.
• Cherry-red skin is uncommon and should not be relied upon for diagnosis.
• Patients with severe smoke exposure may have both carbon monoxide and cyanide poisoning.