Validation of Phase Lag Entropy(PLE) as an Indicator of Depth of Sedation in Patients Undergoing Spinal Anesthesia: Comparative Analysis With Bispectral Index

For verifying the phase lag entropy as the tool for measurement of level of consciousness, the investigators compared phase lag entropy to bispectral index. Using Target-Controlled Infusion pump, propofol was infused for sedation during the spinal anesthesia. The investigators measured Observer's Assessment of Alertness/Sedation Scale as the propofol concentration rises. At the same time, The investigators observed phase lag entropy score and bispectral index score.