Patent EA-001833-B1 (EA)
Title: Monitoring and controlfor a laryngeal mask airway device
Inventor: ZOCCA MARIO
IPC: A61F2/958
Filed: 1998-12-21
Abstract: 1. Apparatus (10) for automatically monitoring the level of unconsciouness of a patient (13) in the course of a surgical procedure on the patient, wherein the patient has an installed inflatable device (19) having wall contact with at least a portion of the patient's pharynx, and wherein the inflatable device has a flexible tubular inflation line (11) accessible externally of the patient; the apparatus comprising: (a) sensing means including a pressure transducer (PI, P2) detachably connectable to the inflation line for producing an electrical output signal responsive to instantaneous sensed inflation pressure as a function of time during the surgical procedure; (b) means including a syringe having a cylinder (26) with a head adapted for detachable connection (11') to the inflation line and a piston (27) in the cylinder to define a substantially constant volume of inflation air within the inflatable device, its inflation line and the head of the cylinder, the piston being displaceable relative to the cylinder to change the proportion of the volume of air between the inflatable device and the head of the cylinder; (c) means for comparing the sensed pressure to a reference value whereby to determine any departure from the reference value; and (d) regulating means including reversibly operable drive means (33) for displacing the piston in the cylinder thereby to restore the pressure to the reference value. 2. Apparatus according to claim 1, wherein the installed device is a LMA device (12) which comprises an airway tube (14) with a mask (16) and an inflatable cuff (19) at its distal end for sealing engagement around the patient's laryngeal inlet (21), with communication to the patient's lungs via the airway tube and through the mask, the flexible inflation line communicating with the inflatable cuff. 3. Apparatus according to claim 2, which includes microprocessor means (60) programmed to establish separate upper and lower tolerable limits of sensed air-pressure and to provide an output warning of a detected occurrence of a pressure which has traversed one of the limits. 4. Apparatus according to any one of claims 1 to 3, further comprising display means operably connected to the sensing means for establishing a display of sensed inflation pressure against time. 5. Apparatus according to claim 4, wherein the display means includes a visual output which displays for a predetermined span of time the pressure amplitude as varying ordinate continuously passing from one to the other limit of the span of time, with the current and most recently observed pressures at the one limit, and the predetermined upper and lower tolerable limits as separate horizontal lines above and below the display of sensed inflation pressure. 6. Apparatus according to any one of claims 1 to 5, wherein the reversibly operable drive means comprises a motor (33) coupled for reversible drive of a lead-screw (34), and nut means (34') threaded to the lead screw and being longitudinally guided and keyed against rotation and connected for direct longitudinal displacement of the piston in the cylinder. 7. Apparatus according to any one of claims 1 to 5, wherein the reversibly operable drive means comprises a digitally controlled stepping motor (33) and wherein the pressure-responsive output is in the form of a first digital signal the reference value is in the form of a second digital signal and the comparator means includes a microprocessor programmed to supply digital signals for operation of the motor. 8. Apparatus according to any one of claims 1 to 7, wherein the cylinder head is detachably connectable to the inflation line via valve means (VI) operable between an open condition to permit communication between the inflatable device and the head of the cylinder, and a closed condition. 9. Apparatus according to claim 8, which includes also a second valve means (V2) operatively connected to the head of the cylinder and operable between an open condition to permit communication with ambient air, and a closed condition. 10. Apparatus according to claim 9, wherein each valve is a normally closed solenoid valve, the first valve having electrical connection to the control means whereby to enable pressure regulation of the inflatable device and the second valve having electrical connection to the control means whereby to enable automatic discharge or induction of air in the maintenance of a substantially constant shared collective volume of air within the inflatable device and the cylinder head. 11. Apparatus according to claim 10, which includes air-incrementing means to admit a predetermined quantity of ambient air into the cylinder, the air-incrementing means comprising: limit-switch means (LS2) producing an electrical signal for a sensed condition indicative of piston advance into a predetermined proximity to the cylinder head and corresponding to a head limit of allowable piston travel; and means including a microprocessor responsive to the signal of sensed piston proximity, the microprocessor being programmed in a manner (i) to return the first solenoid valve (VI) to its normally closed condition; (ii) to actuate the second solenoid valve (V2) to open condition and then operating the drive means for a predetermined reverse stroke, thereby inducing a fresh charge of ambient air into the cylinder; and (iii) to deactivate the second solenoid valve and enable the comparator means to reestablish the set-point value of pressure within the cylinder before reactivating the first solenoid valve and returning the comparator means to its function of regulating inflation pressure to its set-point value. 12. Apparatus according to claim 10 or claim 11, which includes air-purging means to purge a predetermined quantity of air from the cylinder, the air-purging means comprising: limit-switch means (LSI) producing an electrical signal for a sensed condition indicative of piston advance into a predetermined proximity to a tail end of allowable piston travel; and means including a microprocessor responsive to the signal of sensed piston proximity, the microprocessor being programmed in a manner (i) to return the first solenoid valve (VI) to its normally closed condition; (ii) to actuate the second solenoid valve (V2) to open condition and then operating the drive means for a predetermined forward stroke thereby inducing a predetermined purge of air out of the cylinder; and (iii) deactivating the second solenoid valve and enabling the comparator means to reestablish the set-point value of pressure within the cylinder before reactivating the first solenoid valve and returning the comparator means to its function of regulating inflation pressure to its set-point value. 13. Apparatus according to any one of claims 1 to 12, wherein displacement-volumetric capacity of the cylinder is in the order of 20cc. 14. A method for monitoring the level of unconsciousness of a patient in the course of a surgical procedure on the patient, wherein the patient has an installed inflatable device (19) having wall contact with at least a portion of the patient's pharynx, using apparatus according to any one of claims 1 to 13.