Anesthesia ventilating apparatus having a breathing circuit and control loops for anesthetic gas components

• US 5,094,235 A
• Filed: 05/10/1989
• Issued: 03/10/1992
• Est. Priority Date: 05/10/1989
• Status: Expired due to Fees

• Current Assignee: Dragerwerk AG
• Original Assignee: Dragerwerk AG
• Inventors: Westenskow, Dwayne D., Wallroth, Carl-Friedrich, Jaklitsch, Roman R., Loughlin, Patrick J.
• Primary Examiner(s): Burr, Edgar S.
• Assistant Examiner(s): Asher, Kimberly L.
• Application Number:
  US07/349,829
• Time in Patent Office: 1,035 Days
• Field of Search: 128/203.12, 128/204.21, 128/204.22, 128/203.25, 128/204.25, 128/205.12
• US Class Current: 128/204.22
• CPC Class Codes: A61M 16/104 specially adapted for anaesthetics A61M16/18 takes precedence
• CPC Class Codes: A61M 2016/1025 the O2 concentration
• CPC Class Codes: A61M 2230/432 partial CO2 pressure (P-CO2)

Abstract

The invention relates to an anesthesia ventilating apparatus having a breathing circuit and a plurality of control loops for the anesthesia gas, the anesthesia agent and the carbon dioxide exhaled by a patient. A disconnect switch is provided for opening and closing the control loop for adjusting the anesthesia agent. When this control loop is opened, a control unit changes the desired value of the anesthetic agent to a desired flushing value thereof. The control unit includes a processor which monitors the time-dependent course of the concentration of the anesthetic agent to determine breathing circuit system parameters and then computes the adjusting parameters of a controller in the control loop for adjusting the anesthetic agent. A method of operating the apparatus is also disclosed.

Claims

1. Anesthetic ventilating apparatus for administering anesthesia to a patient, the apparatus comprising:

a closed-loop breathing circuit for supplying and recirculating respiratory gas containing an anesthetic agent to the patient and having first and second branches;

a carbon dioxide absorber disposed in one of said branches for removing carbon dioxide exhaled by the patient;

a gas metering unit supplying anesthetic gases into said breathing circuit;

said gas metering unit including;

an oxygen sensor for measuring the oxygen content in said breathing circuit; and

, an oxygen concentration controller connected to said oxygen sensor for determining the quantity of oxygen to be metered into the breathing circuit and for generating a first actuating variable in response to which oxygen is supplied to said breathing circuit;

said gas metering unit further including;

a level detector for measuring the breathing circuit volume; and

, a breathing circuit volume controller connected to said level detector for generating a second actuating variable in response to which anesthetic gas is supplied to said breathing circuit;

an anesthetic agent metering unit for generating a third actuating variable in response to which the amount of an anesthetic agent supplied to said breathing circuit is adjusted;

an anesthetic agent controller connected to said anesthetic agent metering unit and having a set of adjusting parameters;

coupling means for coupling two of said controllers so as to permit one of said actuating values to change another one of said actuating values;

a control unit for changing the concentration of the anesthetic agent supplied by said anesthetic agent metering unit from a first desired value S1 to a second desired value S2 in a discontinuous jump-like manner with said second desired value S2 being a flushing concentration by volume of said anesthetic agent which is many times greater than the concentration by volume of said anesthetic agent corresponding to said first desired value S1;

said anesthetic agent metering unit with said anesthetic agent controller and said control unit conjointly defining a normally closed control loop;

an anesthetic agent sensor for measuring the anesthetic agent actual value present in said breathing circuit;

a logic component for receiving said first desired value S1 of said anesthetic agent and said anesthetic agent actual value for forming a closed loop control signal;

said control unit including;

(a) limit means for registering a difference between said actual value and said first desired value S1 of anesthetic agent in said breathing circuit and for emitting an output signal for a predetermined duration when said difference exceeds a predetermined limit;

(b) a disconnect switch having an output and being switchable in response to said output signal from a first position wherein said normally closed control loop is closed and wherein said logic component is connected to said anesthetic agent controller for applying said closed loop control signal thereto to a second position wherein said normally closed control loop is opened and wherein said first desired value S1 is applied to said output; and

,

(c) amplifier means connected to said output of said disconnect switch for receiving said desired value S1 when said disconnect switch is in said second position and having an amplification for amplifying said first desired value S1 many times to form said second desired value S2 indicative of said flushing concentration of said anesthetic agent;

said control unit further including processing means monitoring the concentration of the anesthetic agent measured by said anesthetic agent sensor for determining first and second breathing circuit system parameters (T1 and T2) and for computing said adjusting parameters for said anesthetic agent controller;

said first breathing circuit parameter T1 representing the time to reach a first percentage value of the desired anesthetic concentration and said second breathing circuit parameter T2 representing the time required to reach a second percentage value of the desired anesthetic concentration starting from an initial value SO of anesthetic medium in said breathing circuit;

said limit means being connected to said anesthetic agent sensor and responding to a predetermined value S3 of the concentration of said anesthetic agent in said breathing circuit for switching said disconnect switch back into said first position so as to permit said anesthetic agent controller to adjust said second actuating variable so as to cause said anesthetic agent metering unit to readjust the concentration of said anesthetic agent to said first desired value S1;

the concentration of said anesthetic agent S3 corresponding to approximately (0.9) (S1) when the concentration of the agent is increased and corresponding to approximately (1.1) (S11) when the concentration of the agent is reduced, said S11 being a new desired value applied to said normally closed control loop by said control unit when said disconnect switch is again in said first position;

said system parameter T2 corresponding to the time required to achieve said concentration of approximately (0.1) (S1) when increasing the concentration of the agent in said breathing circuit; and

,

the sum of said system parameters (T1 T2) corresponding to the time required to achieve approximately (0.8) (S1) when increasing the concentration of the agent in said breathing circuit.

2. The anesthetic ventilating apparatus of claim 1, said amplification being selected for amplifying said value S2 up to ten times when increasing the concentration of said anesthetic agent in said breathing circuit thereby permitting said value S2 to be adjusted up to ten times of said value S1 and for reducing said value S2 to zero when reducing the concentration of said anesthetic agent in said breathing circuit.

3. The anesthetic ventilating apparatus of claim 1, wherein said coupling means is a transducer connected between two of said controllers.

4. The anesthetic ventilating apparatus of claim 1, wherein said control unit supplies desired values to respective ones of said controllers corresponding to said actuating variables;

and, said control unit including sequence control means for fixing the sequence with which said desired values are applied.

5. The anesthetic ventilating apparatus of claim 4, further comprising a carbon dioxide control loop for adjusting the ventilating rate in said breathing circuit;

and, wherein the respiratory gas includes oxygen as a component and wherein said gas metering unit includes oxygen supply means for adjusting the supply of oxygen contained in said respiratory gas; and

, wherein said sequence control means is adapted to first operate on said oxygen supply means of said gas metering unit to first adjust the oxygen concentration in said breathing circuit;

to thereafter operate on said anesthetic metering unit to adjust the concentration of anesthetic agent in said breathing circuit to thereby adjust the depth of the anesthesia; and

to then operate on said carbon dioxide control loop to adjust the ventilating rate in said breathing circuit.

6. Anesthetic ventilating apparatus for administering anesthesia to a patient, the apparatus comprising:

a closed-loop breathing circuit for supplying respiratory gas containing an anesthetic agent to the patient and having first and second branches;

a carbon dioxide absorber disposed in one of said branches for removing carbon dioxide exhaled by the patient;

a first closed control loop for generating a first actuating variable in response to which the amount of respiratory gas supplied to said breathing circuit is adjusted;

said first closed control loop including;

an anesthetic gas metering unit for receiving said first actuating variable and metering the respiratory gas into the breathing circuit in response to said first actuating variable; and

, an anesthetic gas controller connected to said metering unit for operating on said first actuating variable and having a set of adjusting parameters;

a second closed control loop for generating a second actuating variable in response to which the amount of anesthetic agent supplied to said breathing circuit is adjusted;

said second closed control loop including;

an anesthetic agent metering unit for receiving said second actuating variable and metering the anesthetic agent into the breathing circuit in response to said second actuating variable; and

, an anesthetic agent controller connected to said metering unit for operating on said second actuating variable and having a set of adjusting parameters;

a third closed control loop for generating a third actuating variable in response to which a ventilating frequency in said breathing circuit is adjusted;

said third closed control loop including;

a ventilating unit for receiving said third actuating variable and adjusting said ventilating frequency in said breathing circuit in response to said third actuating variable; and

, a carbon dioxide controller connected to said ventilating unit and having a set of adjusting parameters;

coupling means for coupling two of said loops so as to permit one of said actuating values to change another one of said actuating values;

a control unit for changing the concentration of the anesthetic agent supplied by said anesthetic agent metering unit from a first desired value S1 to a second desired value S2 in a discontinuous jump-like manner with said second desired value S2 being a flushing concentration by volume of said anesthetic agent which is many times greater than the concentration by volume of said anesthetic agent corresponding to said first desired value S1;

said anesthetic agent metering unit with said anesthetic agent controller and said control unit conjointly defining said second closed control loop as a normally closed control loop;

an oxygen sensor of said first control loop for measuring the anesthetic gas actual value present in said breathing circuit;

an anesthetic agent sensor of said second control loop for measuring the anesthetic agent actual value present in said breathing circuit;

a carbon dioxide sensor of said third control loop for measuring the carbon dioxide actual value present in said breathing circuit;

a logic component for receiving said first desired value S1 of said anesthetic agent and said anesthetic agent actual value for forming a closed loop control signal;

said control unit including;

(a) limit means for registering a difference between said actual value and said first desired value S1 of anesthetic agent in said breathing circuit and for emitting an output signal for a predetermined duration when said difference exceeds a predetermined limit;

(b) a disconnect switch having an output and being switchable in response to said output signal from a first position wherein said normally closed control loop is closed and wherein said logic component is connected to said anesthetic agent controller for applying said closed loop control signal thereto to a second position wherein said normally closed control loop is opened and wherein said first desired value S1 is applied to said output; and

,

(c) amplifier means connected to said output of said disconnect switch for receiving said desired value S1 when said disconnect switch is in said second position and having an amplification for amplifying said first desired value S1 many times to form said second desired value S2 indicative of said flushing concentration of said anesthetic agent;

said control unit further including processing means monitoring the concentration of the anesthetic agent measured by said anesthetic agent sensor for determining breathing circuit system parameters T1 and T2 and computing said adjusting parameters of said anesthetic agent controller of said second closed control loop;

said first breathing circuit parameter T1 representing the time to reach a first percentage value of the desired anesthetic concentration and said second breathing circuit parameter T2 representing the time required to reach a second percentage value of the desired anesthetic concentration starting from an initial value SO of anesthetic medium in said breathing circuit;

said limit means being connected to said anesthetic agent sensor and responding to a predetermined value S3 of the concentration of said anesthetic agent in said breathing circuit for switching said disconnect switch back into said first position so as to permit said anesthetic agent controller to adjust said second actuating variable so as to cause said anesthetic agent metering unit to readjust the concentration of said anesthetic agent to said first desired value S1;

the concentration of said anesthetic agent S3 corresponding to approximately (0.9) (S1) when the concentration of the agent is increased and corresponding to approximately (1.1) (S11) when the concentration of the agent is reduced, said S11 being a new desired value applied to said normally closed control loop by said control unit when said disconnect switch is again in said first position;

said system parameter T2 corresponding to the time required to achieve said concentration of approximately (0.1) (S1) when increasing the concentration of the agent in said breathing circuit; and

,

the sum of said system parameters (T1 T2) corresponding to the time required to achieve approximately (0.8) (S1) when increasing the concentration of the agent in said breathing circuit.

7. The anesthetic ventilating apparatus of claim 6, said coupling means being a transducer coupling two of said loops.

8. The anesthetic ventilating apparatus of claim 7, said transducer being a first transducer coupling said first and second control loops and said apparatus further including a second transducer for coupling said second and third loops.