<prompt> Which of the following is the most common method used to know depth of anaesthesiaOesophageal contractilityDepressed ResponsesHypotensionBIS  <response>: BIS- Bispectral index BIS monitoring was first introduced for clinical use in 1996. It was approved by FDA as a technique of monitoring depth of anaesthesia and reducing the incidence of intraoperative awareness during General anaesthesia in 2004. 100 - Awake 80 - light moderate sedation 60 - General anaesthesia 40 - Deep hypnotic state 20 - burst suppression 0 - isoelectric EEG Ref:- Understanding Anesthetic Equipment and Procedures - Baheti Laheri Pg num:- 304,305 