Feed-back monitoring in anaesthesia. II. Pulse rate control of halothane administration.

Automatic anaesthesia using electroencephalographic assessment of depth was described by American authors in 1951 and 1954. A first paper (Soltero, Faulconer and Bickford, 1951) dealt with ether vaporization in a closed circuit with spontaneous respiration. A second communication (Kiersey, Faulconer and Bickford, 1954) was concerned with thiopentone anaesthesia during spontaneous respiration and in the presence of partial curarization. General acceptance and indeed further development of automatic anaesthesia were probably hampered by the choice of the electroencephalogram as the only parameter. The e.e.g. is not a reliable guide to the depth of anaesthesia, not even as an indication of the presence or absence of unconsciousness (Munson, 1970). Moreover it is an unsafe parameter because no warning of respiratory or circulatory failure is given until very late. Other important drawbacks are the time necessary to set the instrument, the special skill required and the need for different "integrators" for each anaesthetic agent.