Final answer:
Bispectral index (BIS) is used to directly monitor the depth of sedation, providing a numerical value that indicates the level of consciousness, unlike blood pressure, heart rate, or respiratory rate.
Step-by-step explanation:
The tool used to monitor the depth of sedation is C) Bispectral index (BIS). The BIS is an EEG-based measure that provides a single number, ranging from 0 (no brain activity) to 100 (fully awake), indicative of an individual's level of consciousness.
This tool is particularly useful in the operating room to assess the effects of anesthetics on the brain and adjust dosages accordingly. While parameters such as blood pressure, heart rate, and respiratory rate are important vitals that are continually monitored during sedation, they do not directly measure the depth of sedation like BIS does.