Assessment of depth of anaesthesia

The aim of this chapter is to discuss some of the recent findings on monitoring the depth of anaesthesia, both in general and with respect to α2-agonists. Defining the depth of anaesthesia for intra-operative monitoring is more complex than describing increasing and decreasing pharmacodynamic drug effects. Ideally, monitoring would indicate the specific components of anaesthesia—hypnosis, sedation, and analgesia—quantitatively. So far, all the parameters available reflect only parts of this whole system. Beside common clinical parameters, electrophysiological parameters (EEG and evoked potentials) have been suggested for use in evaluating the depth of anaesthesia because of their dose-related, almost unspecific signal changes. Unfortunately, defining the threshold for preventing awareness and quantifying painful events for requirement-specific treatments have not been resolved in any detail. This is fraught with even more difficulties when α2-agonists are involved because the haemodynamic response is directly attenuated and there is controversy surrounding α2-agonist-mediated EEG and evoked potential findings. The challenge of obtaining more information about the target organ—the brain—has recently been addressed by several innovative EEG analysing techniques.