Which statement about carbon monoxide poisoning is true?

• A. Pulse oximetry reliably detects carbon monoxide poisoning.
• B. Pulse oximetry may show normal readings despite poisoning.
• C. CO poisoning only occurs with outdoor exposure.
• D. CO poisoning is not a medical emergency.

Answer: (B)

Pulse oximetry can be misleading in carbon monoxide poisoning because standard devices can’t distinguish carboxyhemoglobin from oxyhemoglobin. Carboxyhemoglobin binds hemoglobin with high affinity, yet it absorbs light in a way that makes the pulse oximeter read as if hemoglobin were fully saturated with oxygen. So despite significant CO binding and tissue hypoxia, the SpO2 reading may appear normal or near-normal. A definitive diagnosis requires co-oximetry on arterial blood to measure carboxyhemoglobin levels. Remember, CO poisoning is a medical emergency: provide high-flow 100% oxygen to displace CO, and consider hyperbaric oxygen if indicated. This is why the statement about pulse oximetry potentially showing normal readings despite poisoning is the true one.