Controller anaesthesia: an approach using patient characteristics identified during uptake.

A system to control the alveolar anaesthetic concentration of patients undergoing halothane anaesthesia with controlled ventilation is described. Parameters characterizing the alveolar concentration response are determined on-line from breath-by-breath measurement of the inspired and end-tidal concentrations and the mixed venous anaesthetic partial pressure is estimated throughout the procedure. The method does not depend on the use of reference models or pre-programming and the inspired concentration required to control the alveolar concentration is determined as induction proceeds. Results using both computer simulations and data from patients undergoing routine clinical anaesthesia are analysed. Off-line verification results illustrate the operation of the technique and in 20 cases the inspired concentration, as controlled by the anaesthetist, was compared with that predicted by the automated system. These results indicate the feasibility of the system as a method for the control of anaesthesia.