The BiSpectral Index (BiS) is commonly used to monitor the depth of anaesthesia. The Perfusion Index (PI), a non-invasive measure of peripheral perfusion available in modern pulse oximeters, has been studied as a potential alternative for anaesthesia depth monitoring. This study aims to evaluate PI’s validity as a substitute for BiS in adult patients during general anaesthesia.  In this study, forty ASA I-II patients, aged 18-50 years of either gender, undergoing elective surgery under general anaesthesia will be recruited. Only surgical procedures with short operative durations, minimal tissue trauma, and minimal intraoperative fluid shifts will be included. General anaesthesia will be administered as per protocol. The perfusion index and BiSpectral index will be recorded simultaneously at different timestamps during the intraoperative period (before induction, after induction, after intubation, at the start of surgery, and then every 30 minutes during the surgery, at the end of the surgery, at the cessation of anaesthesia and emergence, and lastly, after extubation). The correlation between BIS and PI will be assessed using the Pearson correlation coefficient, and the predictive value of PI concerning the depth of anaesthesia will be evaluated using the ROC curve and its corresponding Area Under the Curve (AUC) analysis.