Self-tuning control of hypotension during ENT surgery using a volatile anaesthetic

The generalised minimum-variance self-tuning controller of Clarke and Gawthrop has been used to regulate induced hypotension (reduced blood pressure) in 34 patients undergoing ENT surgery, by automatic adjustment of the inhaled concentration of the volatile anaesthetic agent isoflurane. The purpose of the investigation was: to assess the use of self-tuning control (STC) as an aid to the anaesthetist in normal clinical situations; to obtain information in an acceptable manner to illuminate the clinical situation and any signal conditioning, sources of outliers, and other possible problems to be met therein; to see to what extent STC compares with manual adjustments by an anaesthetist (10 patients); to provide a basis for the design of a stand alone controller for use in anaesthesia which would enable comparison with other drugs in the same situations; and to provide controlled conditions for measurement of various physiological variables of interest to anaesthetists. In summarising our investigations and experiences from an engineering standpoint the potential of STC methods in clinical applications is indicated, and some ways of improving the performance of our implementation are discussed.