The purpose of this study is to learn more about an Entropy monitor that the anesthesiologist will be using.

Depth of anesthesia monitors are increasingly used in clinical anesthesia practice. Bispectral Index (BIS) and M-Entropy are examples to these devices, both of which are available at our institution. Both BIS and M-Entropy use a unilateral, single channel of EEG to derive a number indicating the anesthetic depth. These devices have similar disposable skin probes that can be applied on either side of the forehead. Since the depth of anesthesia for an individual is the same over the whole brain cortex at a given point in time, BIS numbers obtained over the left and right side of the forehead should agree. The same should be true for M-Entropy as well.

A recent study, however, showed that two separate BIS probes, applied over the left and right forehead of the same patient at the same time, can give significantly different numbers. This has not been studied for M-Entropy. BIS and M-Entropy use different mathematical algorithms that process the raw EEG signal to compute a numeric value. Therefore, it is possible that M-Entropy may show different results in a similar study setup.

The aim is to investigate the same-patient reproducibility of M-Entropy by monitoring and recording Entropy variables over both the left and the right side of the forehead of patients under general anesthesia.

Inclusion Criteria:

• Patients scheduled to have surgery under general anesthesia, with a minimum of 60 minutes expected duration.

Exclusion Criteria:

• Non-English speaker
• Patients younger than 18 years of age

Patients that are scheduled to have surgery under general anesthesia for which an intraoperative M-Entropy monitoring is planned. Suitable candidates will be identified by speaking to the attending anesthesiologists working at OU Presbyterian hospital.