4. Bispectral Index We will also collect Bispectral Index (BIS) measurements that are generated as part of the anesthesia monitoring from electronic anesthesia record at 30 second intervals. BIS is a monitor of the depth of anesthesia that uses a sensor placed on patient's forehead. BIS monitor calculates a dimensionless number estimating the patient's level of consciousness. The BIS values range from 0 (no brain activity) to 100 (fully awake) with the target range between 40 and 60 for general anesthesia.