Awareness during Surgery

Ever since Horace Wells failed to produce adequate anaesthesia with nitrous oxide on a celebrated occasion in I844 patients have from time to time complained of being incompletely anaesthetized. In the past these unfortunate incidents were always accepted as failures, due to inexperience of the administrator, inadequacy of the apparatus or idiosyncrasy of the patient. But even today, when there is little excuse for any such failure, there are still patients who claim to have some recollection of a surgical procedure performed under general anaesthesia.7 When surgery is performed on the non-paralysed patient there is usually no doubt as to whether he is ' properly asleep ' or not; his response to surgical stimulation and the absence of muscular relaxation speak for themselves. On the other hand, use of the muscle relaxants introduces new difficulties: only very small quantities of general anaesthetic agents need be used, and the classical' signs of anaesthesia,' being muscular, are interfered with. The convention stages and planes of Guedel1' are neither recognizable nor relevant; what is required for the paralysed patient is not so much an index of anaesthetic ' depth' as an index of consciousness, and the difficulty of establishing reliable signs of ' awareness ' in these circumstances is one of the greatest problems of present-day anaesthesia.