What vital signs may be affected by carbon monoxide poisoning?

• A. Increased heart rate despite low blood pressure
• B. Decreased oxygen saturation despite normal pulse oximetry
• C. Elevated body temperature and high respiratory rate
• D. Normal vital signs overall

Answer: (B)

Carbon monoxide poisoning can have a profound impact on a person's oxygen delivery at the cellular level, which is reflected in the vital signs. The correct choice indicates that there may be decreased oxygen saturation even when pulse oximetry readings appear normal.

This is because carbon monoxide binds to hemoglobin much more effectively than oxygen does, forming carboxyhemoglobin. Standard pulse oximeters are unable to differentiate between oxyhemoglobin and carboxyhemoglobin, resulting in misleading normal readings even when there is significant internal hypoxia. Therefore, patients suffering from carbon monoxide poisoning can have dangerously low levels of oxygen in their tissues while their pulse oximeter displays a normal or only slightly decreased saturation level.

In contrast, other options do not accurately represent the typical clinical picture associated with carbon monoxide exposure. For instance, elevated heart rate and low blood pressure may occur in various emergencies but are not specific to carbon monoxide poisoning. Changes in body temperature and respiratory rate can happen in different contexts but are not hallmark symptoms of carbon monoxide toxicity. Observing overall normal vital signs does not align with the characteristic severe toxicity produced by carbon monoxide exposure.