Hypnosis control based on the minimum concentration of anesthetic drug for maintaining appropriate hypnosis

Abstract

This paper proposes a novel hypnosis control method using Auditory Evoked Potential Index (aepEX) as a hypnosis index. In order to avoid side effects of an anesthetic drug, it is desirable to reduce the amount of an anesthetic drug during surgery. For this purpose many studies of hypnosis control systems have been done. Most of them use Bispectral Index (BIS), another hypnosis index, but it has problems of dependence on anesthetic drugs and nonsmooth change near some particular values. On the other hand, aepEX has an ability of clear distinction between patient consciousness and unconsciousness and independence of anesthetic drugs. The control method proposed in this paper consists of two elements: estimating the minimum effect-site concentration for maintaining appropriate hypnosis and adjusting infusion rate of an anesthetic drug, propofol, using model predictive control. The minimum effect-site concentration is estimated utilizing the property of aepEX pharmacodynamics. The infusion rate of propofol is adjusted so that effect-site concentration of propofol may be kept near and always above the minimum effect-site concentration. Simulation results of hypnosis control using the proposed method show that the minimum concentration can be estimated appropriately and that the proposed control method can maintain hypnosis adequately and reduce the total infusion amount of propofol.

Comparison of Pharmacokinetic Models for Hypnosis Control Based on Effect-Site Propofol Concentration to Maintain Appropriate Hypnosis

“…Therefore, such c e,min can be used to differentiate between consciousness and unconsciousness. In [8], c e,min is called the minimum effect-site propofol concentration and estimated utilizing this property.…”

“…Therefore, an accurate patient-specific estimation of the appropriate concentration is critical to maintain appropriate hypnosis. Recently, a hypnosis control method that maintains effect-site concentration of an anesthetic drug above a minimum estimate (henceforth minimum effect-site concentration) to keep appropriate hypnosis has been proposed [8]. It also needs an accurate patient-specific estimation of effect-site anesthetic drug concentration to maintain appropriate hypnosis.…”

“…However, propofol concentration corresponding to appropriate hypnosis cannot easily be obtained from BIS since the very same value does not always indicate the same hypnosis level even though it is being widely used as a hypnosis index and has fairly high reliability. On the other hand, in [8], an estimation method of minimum effect-site propofol concentration using aepEX has been proposed. This estimation method utilizes the property that aepEX barely changes in the range of sufficient hypnosis while it rapidly increases near awakening, hence a good estimate of a patientspecific effect-site propofol concentration for maintaining appropriate hypnosis is expected to be obtained.…”

“…To realize such hypnosis control, many open-loop and closed-loop control systems have been developed [1][2][3][4][5][6][7][8]. Among them, target controlled infusion (TCI) systems [1], which maintains hypnosis level by keeping anesthetic drug concentration in plasma or effect site at a target level, are often used clinically.…”

“…Therefore, in order to realize a desirable hypnosis control an appropriate PK model for calculating effect-site propofol concentration must be selected among the existing ones. In [8], some existing PK models with the specific rate constant of effect-site compartment were compared from the viewpoint of the accuracy of distinction between unconscious and conscious states based on a small number of clinical data. However, it is not sufficiently clear what is the best PK model because only a limited number of them are considered and because each rate constant is not adjusted for clinical data.…”