In a case where a patient is found unresponsive with cyanosis but a normal pulse oximeter reading, what condition might this indicate?

• A. Severe allergic reaction
• B. Hypothermia
• C. Carbon monoxide poisoning
• D. Cardiac arrest

Answer: (C)

The scenario presented—a patient who is unresponsive with cyanosis accompanied by a normal pulse oximeter reading—strongly indicates carbon monoxide poisoning.

In carbon monoxide poisoning, hemoglobin in the blood binds with carbon monoxide more effectively than it does with oxygen, leading to a situation where the oxygen saturation readings may appear normal on a pulse oximeter. This is because standard pulse oximeters cannot differentiate between oxyhemoglobin and carboxyhemoglobin (the form of hemoglobin bound to carbon monoxide), thus providing a misleadingly normal oxygen saturation level while the patient may actually be hypoxic.

Cyanosis, or a bluish discoloration of the skin, suggests that tissues are not receiving adequate oxygen. The contradiction of a normal reading alongside clear signs of hypoxia and unconsciousness makes carbon monoxide poisoning a primary consideration in this situation.

Other conditions, such as severe allergic reactions or hypothermia, could produce signs of altered consciousness or cyanosis but would typically not result in a normal pulse oximeter reading if there is significant hypoxia. Cardiac arrest might indeed lead to unresponsiveness and cyanosis, but in such cases, a pulse oximeter would generally show a critically low reading reflecting the patient's lack of effective circulation and