Which of the following is the most reliable indicator of effective respiration in a patient?

Comprehensive and Detailed Explanation From Exact Extract:

Mental statusreflects perfusion and oxygen delivery to thebrain, which is highly sensitive to hypoxia and hypercapnia. Even if respiratory rate and SpO₂ are normal, altered mental status suggests ineffective gas exchange or hypoperfusion.

Pulse oximetry may be falsely normal in CO poisoning or poor perfusion. Skin color is subjective and not as sensitive or specific as neurological status.