Patent ID: 6216690
Filing Date: 2001-04-17
Classification: A61M

Abstract:
An anesthetic agent delivery system for delivering a desired dose of anesthetic agent to a patient comprising:an anesthetic agent supply having a controller for controlling the amount of anesthetic agent provided by the supply;a gas supply for providing respiratory gas, said gas supply being in fluid communication with said anesthetic agent supply to receive the anesthetic agent from said anesthetic agent supply to form fresh gas, said gas supply having a gas flow controller for controlling the fresh gas flow rate;a breathing circuit containing and recirculating breathing gas for the patient, said breathing circuit having a supply end and a patient end that is in communication with the patient, said breathing circuit being formed such that a gas volume displacement at the supply end will cause a rapid, corresponding volume displacement at the patient end, said supply end being in communication with the gas supply and the anesthetic agent supply to receive fresh gas into the breathing circuit, the breathing circuit providing a minute volume of breathing gas to the patient;a sensor connected in the breathing circuit to provide a signal indicative of the anesthetic agent concentration delivered to the patient; anda system control connected to the gas flow controller and anesthetic agent supply controller, said system control receiving the signal from said sensor for forming an anesthetic agent concentration error signal indicative of the difference between desired and delivered patient anesthetic agent concentrations, the system control having a plurality of control paths to control the anesthetic agent concentration delivered to the patient, said system control employing, when the fresh gas flow rate is less than or equal to the minute volume, a first control path comprising a feedforward control loop for said anesthetic agent supply for establishing the amount of anesthetic agent provided in the fresh gas by said anesthetic agent supply, and employing a second control path comprising a feedback control loop between said anesthetic agent concentration error signal and said gas flow controller to rapidly and incrementally change the fresh gas flow rate in a manner to rapidly minimize an error between desired and delivered patient anesthetic agent concentrations, said system control having switching means responsive to the fresh gas flow rate to switch from said first and second control paths to third and fourth control paths when the fresh gas flow rate exceeds the minute volume, said third control path comprising a feedforward control loop which is coupled to said gas flow controller for establishing the flow rate of the fresh gas, and said fourth control path comprising a closed, feedback control loop between the anesthetic agent concentration error signal and said anesthetic agent supply controller to vary the amount of anesthetic agent provided by said anesthetic agent supply in the fresh gas in a manner to minimize the error between desired and delivered patient anesthetic agent concentrations.