Depth of general anaesthesia

As described by Guedel with ether induction, with increasing depth of anaesthesia the following events occur:

• awareness abolished by low dose of drug
• movement abolished next
• breathing - tidal volume and frequency altered
• haemodynamic - cardiac and perpheral changes
• tears in eyes - sudomotor, sweating
• hormonal - catecholamines, growth hormones, prolactin, cortisol output altered

With modern, rapidly-acting induction, these events are witnessed in a far shorter time period.

There is no single clinical sign or machine which can indicate that the patient is properly anaesthetised.

In order to maintain controlled anaesthesia by spotting early undesirable trends or sudden complications, and so that a performance-audit can be completed, regular, thorough readings must always be taken and reported on the anaesthetic record sheet.