The BIS is influenced by multiple parameters, such as age,gender, body weight, height, muscle relaxants, hepatic function, co-administered drugs, surgical stimulation, but is thought to be influenced mainly by propofol and remifentanil infusion dose. As such, the investigators postulate that the BIS value could be predicted by the estimated effects-site concentration of propofol and remifentanil, and try to establish a multiple linear regression model for predicting BIS value.

Total intravenous anesthesia is commonly performed with propofol and remifentanil now-a-days. The combination of these two drugs can achieve the rapid loss of consciousness and analgesia,as the onset and recovery time of these two drugs are very fast within one to three minutes. However, the problem of intraoperative awareness necessitate the monitoring of anesthetic depth, which is commonly performed with Bispectral index (BIS). BIS is a display of number from zero to one hundred which quantify the degree of sedation and hypnosis by anesthetics by analyzing the electroencephalogram. However, it is limited in neurosurgery in which the surgical field is near the forehead where the BIS probe is attached. Furthermore, it is also limited in surgery with prone position. The BIS is influenced by multiple parameters, such as age,gender, body weight, height, muscle relaxants, hepatic function, co-administered drugs, surgical stimulation, but is thought to be influenced mainly by propofol and remifentanil infusion dose. As such, we postulate that the BIS value could be predicted by the estimated effects-site concentration of propofol and remifentanil, and try to establish a multiple linear regression model for predicting BIS value.

Inclusion Criteria:

• Those undergoing gynecologic or urologic surgery with general anesthesia with total intravenous anesthesia
• Adult patients with more than 20 yrs.
• American Society of Anesthesiologists Class I or II.

Exclusion Criteria:

• Those with unstable hemodynamics
• Those who can not undergo Bispectral index monitoring
• Those with previous history of stroke

Those undergoing gynecologic or urologic surgery with general anesthesia with total intravenous anesthesia