Fuzzy-logic control of blood pressure through enflurane anesthesia.

OBJECTIVE

The objective of our study was to construct a closed-loop blood pressure control system using fuzzy logic during enflurane anesthesia.

METHODS

Direct systolic blood pressure (SBP), the input variable, was assessed by a special fuzzy-logic membership function--that is, a triangulate continuum of grades between 0 and 1. We also set up the output membership function for the inhaled enflurane concentration. Four fuzzy-rule maps, or matrices, which determined the relationship between the changes of input variables and output values, were constructed based on published anesthetic values. The first map was based on the end-tidal anesthetic concentration known to block an adrenergic response. The fourth map was derived from the anesthetic effective dose (AD95). Fuzzy inference, arrived at by using fuzzy logic, followed the minimum-maximum center of gravity method. Anesthetic control started with the first map and was maintained with the succeeding maps.

RESULTS

During anesthesia, the SBP remained within +/- 20% of the preanesthetic SBPs in 82% of the fuzzy control cases and within 83% during manual control. The difference was not significant.

CONCLUSION

The anesthetist's management of the administration of the inhaled anesthetic enflurane was imitated by fuzzy-logic control of the blood pressure.