<prompt> Which of the following is the most common method used to know depth of anaesthesia?BISOesophageal contractilityDepressed responsesHypotension  <response>: Ans:A. BISBispectral index:1st scientifically validated commercially available monitor to check depth of anaesthesia.Utilizes many parameters EEG signals, eye blinks to calculate depth score.Adequate depth:Score of 45-60.Fully awake state:Score of 100Completely silent brain: 0. 