Operation monitoring and controlling system for a tracheal respiration device

Description of the invention

The present invention relates to a device for monitoring and regulating a pressure level in an inflatable device including a wall contacting at least a portion of a patient's throat, particularly a laryngeal respirator.

Laryngeal respirators (LMA) are now well known and are in common use in the care of patients, both during and after a surgical procedure, and during procedures that require the maintenance of a clear airway. Such devices and their construction and use have been described in various patent publications, for example, British Patent No. 2,205,499 and US Patent No. 4,509,514; 5,303,697; 5,2241,956; and 5,282,464.

The fact that such LMA devices are widely accepted tools for patient care is based on simple statistics. For example, it is estimated that such devices are used in about 50 percent of all surgical procedures requiring general anesthesia in the UK, and their use is becoming more common in the rest of Europe and the US.

Generally, the LMA device comprises a breathing tube that has dimensions and curvature generally conforming to the patient's airway; the breathing tube extends from the proximal end which is outside of the patient to the distal end which has a cup or concave plate mask structure which faces and covers the patient's laryngeal opening and which is continuously surrounded by a flexible ring or cuff which is can be selectively inflated by for resiliently sealed conformation to the body structure around the laryngeal inlet. In use, the LMA is first fully deflated to facilitate insertion and then passes through the patient's mouth and throat to its correct position with the mask over the laryngeal opening. The inflatable cuff surrounding the mask structure is then inflated to form a seal between the mask and the laryngeal opening. The air pressure with which the cuff is inflated presses the back of the mask cup against the hard tissue at the back of the throat to hold the device in place and maintain a seal. In this way, the device creates an open airway through which the patient's lungs can be ventilated.

Such LMA devices have proven to be both robust in construction and relatively easy to use, even for paramedics with the necessary training; however, if the mask is misplaced, a reliable airway does not actually form and the patient's lungs are then not adequately ventilated. In addition, the soft, compliant silicone material of the cuff is known to absorb nitric oxide from the mixture of anesthetic gases, thereby increasing the pressure inside the cuff, and the cuff itself may leak at times, resulting in a reduction in its internal pressure. In addition, it has been found that too high an inflation pressure causes the cuff to restrict blood flow to the mucosa covering the muscles around the laryngeal inlet, and prolonged use of the LMA in such circumstances may lead to tissue necrosis.

Recently, it has been proposed to monitor a patient's level of consciousness with a device capable of detecting and analyzing cerebral activity in an attempt to avoid consciousness during surgery; however, the equipment required for such monitoring is complex to operate and costly to manufacture. It has also been proposed to use automatic equipment to monitor intra-cuff pressure in a high-volume and low-pressure cuff associated with an endotracheal tube (EDT). Such an EDT device has been reported to be capable of measuring and regulating intra-cuff pressure with a tolerance of ± 3-mm mercury.

We observed that the muscle tone (tonus) in the lower throat (hypopharynx) was related to the observed patient response to pain stimuli; thus, it is possible to obtain information on the depth of anesthesia by monitoring the muscle tone in the lower throat. We have also found that very small changes in muscle tone are reflected by the LMA cuff and are further reflected by the shared air volume, and that such pressure feedback readings can be used both to automatically adjust the inflation pressure of the LMA cuff and to detect changes in lower pharyngeal muscle tone. Of course, detecting such changes is most preferably done without endangering the patient, and for this purpose it has been observed that it is most advantageous to inflate the cuff to pressures no higher than 60-cm H2O; for example, 50 cm H2O, and generally in the range 25 cm H2O to 100 H2O. Permission to use pressures above

PL 192 899 B1

60-cm H2O has been observed to irritate the patient's throat, especially with longer procedures, and may pose a risk of damage to such tissue.

U.S. Patent No. 4,872,483 discloses monitoring the inflatable cuff of a device in contact with a patient.

The object of the invention is to provide a device that is capable of monitoring with accurate sensitivity, e.g. 0.0625-cm H2O, the intra-cuff pressure of an LMS device that has been properly installed inside the patient's airway, and of maintaining a predetermined inflation pressure within tight tolerances. for example, ± 0.5 cm H2O.

It is also an object of the invention to provide a device that can be pre-programmed to recognize the many different patterns of pressure variation within the cuff of the LMA device and, if necessary, to generate an appropriate range of different alerts for the operator in response to these patterns and to respond to anomalous conditions. workloads, jeopardizing the integrity of the LMA.

The specific goal is to develop a monitoring device of the indicated nature in which, in the case of a patient who has been anesthetized for surgery, monitoring of the LMA inflation pressure during the procedure may include such an automatic analysis of the variability of the LMA inflation pressure to alert the operator that the patient has just exhibited an anomaly. indicating the coming stage of awakening, thereby warning the anesthetic or anesthetist (which are terms used here interchangeably hereafter) that the patient immediately requires an additional dose of anesthetic.

A further object is to provide an apparatus that can meet the above objectives, is relatively inexpensive to manufacture and simple to operate, and reliable to operate and maintain.

A still further object is to achieve the above pressure control without resorting to the use of some other form of system whose components would introduce an additional time constant or hysteresis effect on the pressure monitoring functionality; as would be caused by an accumulator type system that relies on an inflated or otherwise pressurized reservoir to restore the operating pressure of the device.

The device for monitoring and regulating the pressure level in inflatable devices including a wall contacting at least part of a patient's throat, in particular a laryngeal respiratory mask, according to the invention is characterized in that it comprises a syringe assembly equipped with a plunger displaceably disposed in an elongated cylinder with an outlet connection connected to the inflatable device for delivering blowing / deflating air, coupled to a reversibly actuated drive sub-assembly for reversibly displacing the piston and cylinder relative to each other so as to selectively move air into or out of the inflatable device, and an adjusting sub-assembly is attached at the outlet connection, which includes a pressure transmitter that responds to the sensed instantaneous pressure, adjustable selection dial inflation pressure settings, and a comparison unit responsive to the set point value and a pressure transducer signal to obtain an output signal representing the polarity of the estimated difference between the instantaneous pressure and the selected set point value, and a unit that connects the output for actuating the drive unit to move the piston and cylinder relative to each other in direction that reduces to zero the output signal provided by the comparison unit.

The installed inflatable device is a laryngeal respiratory mask that includes a breathing tube with mask and an inflatable cuff at its distal end to fit tightly around the patient's laryngeal inlet to the patient's lungs through a breathing tube and through a mask, the inflation flexible tube being connected to the inflatable cuff. .

The cylinder has a head end having a gated connection between the inflation air and the laryngeal respiratory mask, thereby defining a substantially constant air content volume between the piston and the cylinder head end for co-integrating the inflation air into the inflatable mask assembly.

The reversible drive unit includes a motor coupled to the lead screw reversible drive and a nut assembly threaded onto the lead screw, longitudinally guided and wedged against rotation, and connected to directly displace the longitudinal piston in the cylinder.

PL 192 899 B1

The reversible drive unit comprises a digitally controlled stepper motor in which the pressure transducer produces a first digital output signal, the set point value is a second digital output signal, and the comparison unit comprises a microprocessor programmed to provide digital signals to start the motor.

The outlet connection includes a valve assembly defining an open or closed state for moving air between the inflatable device and the cylinder head.

The valve assembly includes a first valve and a second valve that has a chamfered connection to the outlet connection at a location between the first valve and the cylinder, the second valve defining an open or closed state of the outlet connection with surrounding air.

Each valve is a normally closed solenoid valve, the first valve being electrically connected to the control unit to thereby regulate the pressure of the inflatable device, and the second valve electrically connected to the control unit to thereby allow automatic release or introduction of air to maintain substantially. a constant, common, accumulative volume of air inside the inflatable device and inside the cylinder head.

The apparatus includes an incremental air addition unit for admitting a predetermined amount of ambient air into the cylinder, the incremental air addition unit including a limit switch unit generating an electrical signal for a detected condition of the piston moving to a predetermined proximity to the cylinder head corresponding to the head limit of the allowable travel of the piston. and a unit containing a microprocessor, responding to a piston proximity signal, the microprocessor being programmed to return the first valve to its normally closed state, then actuate the second valve to the open state, followed by actuation of the drive train with a predetermined reverse stroke to thereby inject fresh ambient air charge to the cylinder due to this predetermined reverse stroke, and turn off the second solenoid valve and allow the comparison unit to re-establish the value of the set point pressure set point within the cylinder before operating the first valve again and returning the compare unit to its inflation pressure control function to a set point value.

The apparatus includes an air purge assembly to purge a predetermined amount of air from the cylinder, the air purge assembly including a limit switch assembly producing an electrical signal for a detected condition indicative of a piston advancement to a predetermined proximity to the trailing end of allowable piston travel, and an assembly including a microprocessor , responding to the signal of the detected proximity of the piston, the microprocessor being programmed to to return the first valve to its normally closed state, then actuate the second valve to the open state, and then actuate the drive unit with a predetermined reverse stroke to thereby remove a predetermined amount of air from the cylinder, and disable the second valve and allow the comparator to reestablish a set point value within the cylinder before actuating the first valve again and returning the comparer to its mask inflation pressure control function to its steady point value.

The head limit switch assembly is arranged to generate an electrical signal of a detected state of piston travel to a predetermined proximity to the head end of the allowable travel of the plunger, with the rear end limit switch assembly positioned to produce an electrical signal of a detected condition of the predetermined proximity to the rear. end of the allowable travel of the piston, with the control unit containing a microprocessor sub-assembly, programmed to define a piston drive toward approaching the head end stop switch, and actuating the first valve to an open state to move air from the cylinder head end to the inflatable assembly, the microprocessor further programmed to define a piston drive in the direction of retraction from the head end, and actuation of the first valve to the open state, to move air from the inflatable assembly to the head end of the cylinder.

The microprocessor assembly is further programmed, in the event of a displacement of the sliding piston, which activates the head end limit switch, to deactivate the first valve and actuate the second valve to the open state, and to define a piston drive inversion to retract the piston and to simultaneously introduce air into the cylinder head end. , wherein the microprocessor is further programmed to terminate

To reverse drive the engine and to deactivate the second valve and to actuate the first valve to re-establish a predetermined air volume sharing between the inflatable unit and the cylinder head end.

The microprocessor is further programmed to move the retracting piston actuating the rear end stop switch to deactivate the first valve and to actuate the second valve to the open state, and to define a reverse drive of the piston for a new direction of travel towards the cylinder head end and for the simultaneous predetermined empty the air from the device without changing the inflation status of the inflatable unit, the microprocessor being further programmed to terminate the travel of the piston in this new direction and to deactivate the second valve and to actuate the first valve to re-establish a predetermined volume of air between said inflatable unit and the head end of the cylinder.

The adjustable unit provides a choice of fixed point values ​​in the range of 25-cm H2O to 100-cm H2O (2450 to 9810 Pa), or in the range of 40-cm H2O to 70-cm H2O (3920 to 6860 Pa).

The selected fixed point value is substantially 50 cm H2O (4900 Pa).

The selected fixed point value is substantially 60 cm H 2 O (5880 Pa).

The device preferably has a precision pressure control sensitivity of 0.06 cm H 2 O (5.88 Pa) for monitoring the pressure within the inflatable mask assembly.

The device preferably is adjustable within relatively narrow tolerances for the pressure within the inflatable mask assembly.

The relatively narrow tolerances mentioned are generally ± 0.5 cm H 2 O (49 Pa).

Said device is adapted to selectively connect to an inflatable laryngeal respirator assembly, the installed mask being any of a number of sizes depending on the given anatomical size of the patient.

The inflatable volume of the inflatable unit of said mask size is within 4 cm³ up to 40 cm³.

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The displacement capacity of the cylinder volume is in the order of 20 cm³.

The cylinder has an orifice that is approximately half the effective displaceable length of the piston displacement within the cylinder.

Preferably, the first, normally closed solenoid valve is connected to the outlet connection of the syringe assembly for positioning between the outlet connection and the inflatable unit, the valve coil electrically communicating with the control unit, thereby actuating the valve open for at least the duration of the electrical output and as long as the electrical output is not zero. A second, normally closed, solenoid valve is connected to an outlet connection of the syringe assembly; when it is turned open, the second valve provides syringe access to ambient air for adding or deflating air from the system while the first solenoid valve is in the closed state.

Preferably, the cylinder should have a gated but otherwise closed long end; and each of the two normally closed solenoid valves was connected to serve as the gated end of the cylinder. The first normally closed solenoid valve is also connected to the LMA inflatable unit and is operable to exchange air between the inflatable unit and the cylinder in the direction of travel of the piston; and the second normally closed solenoid valve is actuatable as described above to admit ambient air into the cylinder or to force air out of the cylinder depending on the direction of travel of the piston. The first limit switch assembly generates an electrical signal for a detected condition of the piston traveling to the predetermined limiting proximity to the closed end, and the microprocessor assembly responds to the detected piston proximity signal, the microprocessor being programmed (i) for a drive unit pre-shutdown and reverse operation. the first solenoid valve to its normally closed position and then (ii) to actuate the second solenoid valve w to the open state with the drive unit operating on the predetermined stroke in reverse, thereby inducing a fresh charge of ambient air into the cylinder on the predetermined stroke in reverse, and (iii) to deactivate the second solenoid valve and allow the comparison assembly to reestablish a predetermined pressure point within the cylinder before restarting the first valve

And returning the comparer to its inflation pressure control function LMA to its set point value.

According to a further microprocessor-controlled feature of the presently recommended system, for example for a patient who is anesthetized and undergoing surgery, the mask inflation pressure is monitored continuously. The currently observed mask inflation pressure is monitored for possible violations of a predetermined upper and / or lower threshold of "normal" adjustment; and, when the observed pressure exceeds one of these limits, the first alarm signal is issued with an audible warning that should be interpreted such that while the patient is still asleep and sedated, he has involuntarily exhibited lower pharyngeal / laryngeal muscle spasms, accompanied by , a temporary local compression of the patient's inflated LMA. Further automated monitoring is performed concurrently to determine if any speed related conditions are present beyond the predetermined amount of the estimated criterion. Such speed phenomena are further described below and are determined by continuously reviewing the analyzes performed on the gated sequence of several consecutive readings that are stored within the circuit; and the output of such analyzes is continuously displayed on the system monitor. This velocity-related analysis of the observed inflation pressure provides further clue as to the patient's upcoming and future awakening process and provides first alarm verification, further alerting the anesthetist with a visual warning to "check anesthesia."

The subject of the invention is illustrated in an embodiment in the drawing, in which Fig. 1 shows a control and monitoring device according to the invention coupled to an LMA device installed in a patient, Fig. 1A - the first of two typical percent wake-up readings, which may be part or all of it. of the display screen, Fig. 1B - similar display for the second and subsequent readings of the percent wake-up feature, Fig. 2 - mechanical components diagram of Fig. 1, with a schematic indication of the motorized components, Fig. 3 separate sheets labeled (Part A) and (Part B) showing a more schematic diagram of a control unit including a comparator component and an engine control circuit for the system of Fig. 2, the pressure measured is estimated against a fixed point SP to determine the drive and for the air displacement piston, and is further estimated against the thresholds for a particular pain stimulus alert state, the dashed line 3A of Fig. 3 (Part A) and the dashed line 3B of Fig. 3 (Part B) represent one and the same plane in which Fig. 3 (Parts 3A / 3B) are joined in the complete Fig. 3, Fig. 4 - diagram of an assembly by which the system can pass between the starting, centering and adjustment circuits, Fig. 5 - graphic display of the pressure changes over time observed by the system in the LMA sealing cuff, which is installed in a patient, anesthetized and undergoing surgery, without a stimulus Fig. 5A - graphic display as in Fig. 5, just before and after displaying the system response to an exemplary anomaly that reflects a pain stimulus, Fig. 6A and Fig. 6C - Tables detailing typical calculations performed on sample test data, comparing these values ​​to a set point, and performing the alarm computation associated with 6B and Fig. 6D for each sample, graphical representations of the data shown in Figs. 6A and 6C and Figs. 7 - displaying the observed empirical data obtained during the patient's awakening sequence; such data provide an example of a pain response that is revealed by analyzing the monitoring function of the system.

In Figure 1, the monitoring system or device of Figure 2 is shown as having various control buttons including a system start / stop button 52, a "adjust" start / stop button 53, an alarm reset button 54, an "ENTER" button 55, a rotary knob 56 to select a fixed point or threshold, among others.

The monitoring system 10 has an exhaust connection to the inflation / deflation air supply hose 11 of the LMA 12 installed in patient 13. The LMA 12, as can be seen, includes a breathing tube 14 with a proximal end assembly 15 for externally adjusting a ventilating or anesthetic supply to a patient's lungs through a mask structure 16 having a retrograde plate 17 connected at 18 to the distal end of the tube 14, the retrograde plate being circumferentially. surrounded by an inflatable / deflateable ring or a cuff 19 of a resiliently pliable material, cuff 19 is shown inflated, in a circumferentially sealed relationship with the body structure surrounding the patient's laryngeal inlet 20 and in a position distal to the patient's esophageal inlet 21 (lower pharynx). Internal structure

The mask will be understood to include a known assembly (not shown) for preventing the epiglottis 22 from obstructing the flow of air or anesthetic through the mask through the mask in either direction between the tube 14 and the patient's laryngeal inlet 20.

Conventionally, the LMA inflatable / deflateable ring or cuff 19 is manually operated by a hand held syringe (not shown) that is detachably connected to the check valve assembly 11A forming the outer end of the LMA conduit 11; when the syringe is disconnected, the control valve assembly 11A operates to maintain the current inflation or deflation condition of the LMA. With experience, the anesthetist will have a rough idea of ​​what pressure the cuff can safely be inflated to when the LMA is properly installed in the patient. While the control may be used to inflate the cuff once it has been installed in the patient, especially for smaller cuff sizes, the above-described manual inflation procedure is recommended prior to connecting the LMA 11 inflation / deflation line to the control system of Figure 2.

In Fig. 2, the air control port 11 'will be understood to include a suitable assembly for releasable connection to the pumping / deflation conduit 11 of Fig. 1, and the longitudinal flexible connection or extension lead 11B has (i) an end of a system connector (not shown) that is detachably connected to the control port 11 ', and (ii) an end of the LMA that is consecutively connected to cooperate. with the end of the connector of the control valve assembly 11A, so as to keep the conduits 11 / 11B as a continuous open conduit connecting the system to the LMA inflatable assembly 19. The air displacement assembly includes a syringe assembly 25 of a low friction material such as PTFE (Teflon) with a cylindrical bore 26 having an open (or tail) end to cooperate with the plunger assembly 27. The body 25 is attached to the frame member 28 and extends longitudinally to a closed (or head) end having a port connection 29 with a direct conduit to the LMA 11 'inflate / deflate connection assembly 11', including the direct conduit, the first normally closed solenoid valve V1 must be actuated to the open state if the inflation air is to pass in either direction between the cylinder 26 and the LMA inflatable / deflate unit 19.

The piston 27 is rigidly mounted on or formed with the head end of the longitudinal rod 30, the tail end of which is pressed against the slide block 31. Block 31 locates a rigid, laterally deflected arm for longitudinally stabilized guidance at 32 and for reversibly driven longitudinal displacement by the electric time-lapse actuator assembly 33 and its lead screw output shaft 34, shaft 34 has a threaded overlap with a nut-like hole 34 'in the rigid, laterally biased shoulder of the sliding block 31, and preferably a threaded bore 34 'is formed in the PTFE body, which is attached to the slide block 31. The guide assembly 32 is understood to be a schematic designation for a commercial longitudinal "linear-bearing" assembly (widely known and available under the name or brand name "ROLLON") wherein the elongate first race member is attached to the frame member wherein the elongated second raceway member is a running element is attached to a sliding block 31, and wherein anti-friction elements such as bearing balls ride in and separate the tracks of the respective running elements. The described system of longitudinal support and guidance, obtained by the assembly 32, will be seen as determining the exact longitudinal displacement of the piston 27 along the central longitudinal axis of the cylindrical bore 26, with the block 31 and the piston 27 effectively engaged in rotation about the lead screw.

The motor assembly 33 is a stepless type with fine directional control by varying the relative excitation of each of the four motor input terminals. The amount of rotation of the shaft 34 (and thus the displacement of the piston 27) is controlled by the engine controller and drive unit 47 as shown in Figure 2.

The legends in Fig. 2 indicate the overall stroke length L of the piston 27 through the bore 26, for the purpose of supplying inflation air from bore 26 to the inflatable / deflateable ring or cuff 19 LMA, as long as solenoid valve V1 remains actuated open, same length it may also be available for the retraction stroke of the piston 27 in which a controlled amount of inflation air may be drawn from the cuff 16. The permanently attached limit switches LS1 and LS2 are schematically indicated by the arrow signs in Fig. 2 so as to suggest stopping and / or inverting the device at each of the longitudinal limits of the overall piston stroke length L. However, as shown in Fig. 2, the piston 27 is at the offset DL outside the cylindrical bore, where the arrow marked LSO identifies the point where the leg interacting.

A plunger or other switch actuator 37 transmitted by the piston rod 30 interacts with the LSO limit switch to electrically or otherwise obtain a signal of the depicted piston retraction position while terminating the drive pulses from the drive circuit in FIG. 3; suitably and preferably, each of the limit switches is an optical device based on a leg or other actuator 37 to be opaque and thus capable of cutting or interrupting the light beam from the source to the photocell at each of the respective positions at which limit switch operation is expected to take place.

As further illustrated in Fig. 2, the head end of the piston rod 30 has a radial flange 38 shape circumferentially surrounded by a resilient cap 39 having an undercut opening that easily snaps into a resiliently positioned overlap with the shape of the flange 38 as it occurs when operated device by replacing the used cap 39 with a new cap 39.

Some pressure control operations may have an effect by interfering with the detection of pressure changes, reflecting the patient's muscular reflex. The system according to the invention is designed to minimize such disturbance due to the idea of ​​its design as a substantially closed volume system in which the adjustment of the pressure variation of the cuff 19 is performed by progressively moving within a common air volume, such as between (i) the volume above the piston 26 and inside the cylinder head end a (ii) by the volume in the cuff 19. This is preferable to systems that regulate the pressure using an accumulator or a pressurized reservoir to compensate for changes in pressure, either by introducing air from such accumulator or by evacuation to atmosphere.

The inherent increase in system stability resulting from the common volume concept that is employed in the system of the invention allows a high degree of accuracy without associated system oscillation or overshoot. Specifically, about 0.0005 ml (0.5 microliters) of air moves with each step performed by stepper motor 33. This capacity is currently not available for a compressed accumulator type system.

Further elements of the device of Figure 2 include the first and second pressure monitoring relays P1, P2. These pressure switches P1, P2, which indicate the overall pressure in the device, are connected to additionally monitor the air pressure in the line between the outlet port of the cylinder 29 and the normally closed first solenoid valve V1.

A second normally closed solenoid valve V2 is shown in communication with an air line between the cylinder port 29 and the first solenoid valve V1. When actuated to the open state, valve V2 follows a path from its open air end 44 to the air conduit from cylinder port 29 to the first solenoid valve, such that with valve V1 in its closed, non-activated state, and valve V2 actuated to its open state, a right-to-left displacement of the piston 27 in the cylindrical bore 26 will induce an influx of fresh (surrounding) air into the described system. Similarly, with the two valves V1 and V2 in the same state (with V2 activated and V1 in its normally closed state), left-to-right movement of piston 27 in bore 26 will release excess air or gas from the system.

Moreover, and analogously, with valve V2 in its normally closed state and valve V1 actuated to its open state, moving piston 27 from right to left will entail blowing air from (and thus deflating) the LMA assembly 19. And for the same states of valve V2 inactive and valve V2 actuated, left-to-right displacement of piston 27 will provide air blown to LMA assembly 19.

The control signals necessary to actuate the valves V1 and V2 are provided by separate outputs that come from basic program sequence signals from a separate controller microprocessor assembly 60 for starting, centering, and resetting.

A.1. System boot

For the purpose of system start-up and centering operations, the control circuit of FIG. 3 is bypassed and the signals to the stepper motor controller and drive 47 are controlled by the controller 60 for starting, centering, and staggering. As shown in Fig. 4, the control circuit of Fig. 3 is bypassed by the operation of two single-pole, two-way switches 42. Such operation 42 will occur when the unit is first turned on, at which point the initiation sequence is subject to the startup sequence. The operation of the stepper motor 33 is timed in the starting sequence by the controller (60) for start, center, and reset.

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Before proceeding to the illustrative description of the automated operation of the adjusting system of Figures 1 and 2, it should be noted that for practical purposes, the system must be compatible with a suitable sized LMA for patients of all ages which requires the ring 19 inflation volumes that will vary. even in a ratio of 10: 1 at the extremes. The following sizes are currently available for selection by the anesthetist:

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Size 1 (small baby), maximum inflation volume 4 cm³.

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Size 1.5 (bigger baby), maximum inflation volume 6 cm³.

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Size 2.0 (small child), maximum inflation volume 10 cm³.

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Size 2.5 (bigger child), maximum inflation volume 14 cm³.

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Size 3.0 (small adult), the maximum inflation volume is 20 cm³.

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Size 4.0 (mid adult), maximum inflation volume 30 cm³.

Size 5.0 (large adult), maximum inflation volume 40cm³.

It is now recommended to design the displacement volume-opening volume of a syringe 26 to be substantially 20 cm³, between the operations LS1 and LS2 of the respective ends of the displacement of the piston L in the bore 26; for an opening 26 diameter of 24 mm, a displacement-volume volume of 20 cm³is realized by a displacement of the full stroke L of about 45 mm, which can be taken as an explanatory useful range of displacement of the system. Further by way of illustration, for a stepper motor 33 designed to meet the requirement of 1600 pulse steps for a single revolution of its lead screw 34, and for the pitch of the lead screw (i.e. travel per revolution) of 2 mm, the useful travel range L of the piston 27 is 36,000 discontinuously pulsed stroke steps; for initial starting purposes, the recommended "fast" pulse repeating rate of 5,000 Hz should be applied to produce a piston travel rate of 6.25 mm / s. For normal pressure control travel, the recommended "slow" 500 Hz pulse repeat rate should be applied to produce a piston travel rate of 0.625 mm / s. It is explained below that any correction of the automatic pressure control is obtained by increasing the displacement of the piston, the increase starting from the midpoint of the useful range L, so that the indicated adjustment range of the engine displacement is normally performed within 18,000 pulses for the engine 33, thereby allowing a volume displacement of at least 10 cm³in the direction of inflating the LMA or in the direction of deflating the LMA, as required. For automatically adjusting the LMA inflation to a set point pressure, this limitation range is found to serve any of the above-mentioned LMA sizes, even though the inflation volume range is about 10: 1.

Above, it has been recommended that the arrangement of Fig. 1 and 2 was connected (at 11 ') to the LMA inflatable assembly 19 only after having passed the conventional hand-held syringe procedure (not shown) to the evacuation assembly 19 for the purpose of placing the LMA in the patient and, then, using the same syringe for inflation, which, as the operator knows from experience, will establish a properly positioned seal of assembly 19 around the laryngeal inlet, and with the distal contact with the lower pharynx overlap.

The recommended method of initial inflation of the LMA 19 ring is for the anesthetist to use a syringe assembly. Regardless of whether or not the inflatable ring LMA 19 is manually inflated, the arrangement of Figures 1, 2 and 3 is adapted to rapidly adopt control with pressure monitoring of the inflatable ring 19 to a predetermined set point which is to be understood as being the desired one. set pressure point value SP (e.g. 50 cm H2O) as part of the display 49. While the LMA control 10 is capable of performing an initial cuff inflation task, such initial cuff inflation task 10 may only be practical for cuffs with a lower volumetric capacity and is currently not recommended.

Thus, with a fixed pressure threshold SO selected and fixed for the system of Figures 2 and 3, programmed operation will begin with the controller 60 (for start, center, and reset) controlling the initial startup sequence. The controller 60, as shown in FIG. 4, includes an algorithm that actuates valve V2 to the open state, leaving valve V1 in its non-actuated state (and therefore in its normally closed state). The pulses are then transmitted at high speed (5,000 Hz) via the stepper motor controller and drive 47,

Causing the motor 33 to move at high speed the piston 27 from its retracted position, which is determined by the interaction of leg 37 with the limit switch LSO. The piston 27 quickly travels the full travel L of the piston 27 in the bore 26 in a left-to-right motion. During this movement, leg 37 will actuate the limit switch LS1, thereby initiating in the controller and drive of the stepper motor 47 the counting of the number of pulses required to drive the piston as a function of travel L. Counting only ends when branch 37 actuates the limit switch LS2, at which point the full count enters the memory of the controller 60 and an automatic divide by two operation is performed, with this half count entering the memory of the controller 60 as well as being entered into the memory of the controller and the drive. stepper motor 47. The controller and drive of the stepper motor 47 then follow each successive command which causes the motor 33 to independently keep the position of the piston 27 aware.

The signal is then sent to the controller 60 to begin reverse sweep at the same high speed until a count of pulses is reached, indicating the piston 27 has reached its intermediate position (or "L / 2"). Valve V2 is then turned off, returning to its normally closed state.

Both switches 42 in Fig. 4 then move simultaneously from the first ("1") position to the second ("2") position, thereby allowing the fuzzy logic controller 46 shown in Fig. 3 to take over the control of the motor 33. The fuzzy logic controller 46 will operate according to the logic outlined in Table 1 below, providing the signal necessary for piston 27 to continue its left-to-right travel until the pressure generated at the head end of the cylinder 26 is at the pre-programmed check point pressure, typically 20 cm H2O; and upon reaching such value, for reasons set forth in the following section, the piston 27 will be further actuated to continue its travel until the value of the set point SP is reached. The controller 60 will then actuate valve V1, transferring V1 to the open state.

Should the controller 60 (for start, center and stagger) not take the indication that the pre-programmed check point pressure has been reached in a predetermined number of stages of the stepper motor 33 (e.g., a pre-programmed check point to be reached before advancing a number of stages) required for piston 27 to travel one eighth (1/8) of the L displacement), an audible and visual alarm will be issued and the system will prevent automatic operation of the system.

A. 2. Protection mode

The protection mode can be triggered during the course of regular system operation with a significant variation between the redundant pressure sensors. The pressure is redundantly detected by the pressure conveyors P1 and P2, from which the independently sensed pressure readings are continuously compared by the comparator "A" 40. A hardware error alarm HW will be issued when a difference other than substantially zero is detected between P1 and P2. This hardware error alarm is given as an audible and visual indication to alert the anesthetist to take over manual inflation control of the LMA. Thereafter, shortly after issuing a hardware fault alert, comparator "A" 40 will enter a safety mode, closing V1 and V2 to maintain pressure within the LMA cuff.

B. Normal system control

Operation according to a fuzzy controller is described by the logic laid out in Table 1. The first two columns of Table 1 reflect the previous pressure and the current pressure, each compared to SP. As noted in Fig. 3B, the delay time between the first and second columns is one-half (1/2) seconds. The last column in Table 1 reflects the command that will typically be sent by the fuzzy logic controller 46 to the motor controller 47. Since the stepper motor 33 is only running at low speed in normal operation, the fuzzy command is transmitted in the form of the direction and the number of (N) steps. The described pressure control process, which is performed by the pressure control controller, preferably achieves its purpose within the operating range defined by the 0.5 cm H 2 O range on either side of the fixed point SP.

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Ta bale a 1

Fuzzy Logic Controller Operation 46

<td>Previous actual pressure in relation to set point</td><td>Current actual pressure in relation to a fixed point</td><td>Decision on stages (N) and direction</td>

<td>High</td><td>High</td><td>A large number of steps, vice versa</td>

<td>Medium</td><td>High</td><td>A large number of steps, vice versa</td>

<td>High</td><td>Medium</td><td>Low number of steps, vice versa</td>

<td>Medium</td><td>Medium</td><td>Minimum number of stages, bidirectional</td>

<td>Low</td><td>Medium</td><td>Low number of steps, in line</td>

<td>Low</td><td>Low</td><td>A large number of steps in line with</td>

<td>Medium</td><td>Low</td><td>A large number of steps in line with</td>

C. Typical waveform for an anesthetized patient

Figure 5 shows the respiratory waveform that the system of the invention used to both regulate the LMA 19 cuff pressure and to monitor the LMA inflation pressure. The patient in this example is undergoing surgery and is mechanically ventilated, ie, the patient's breathing is due to positive pressure exerted by the breathing tube 14, also referred to as intermittent positive pressure ventilation, or "IPPV". Figure 5 shows the ability of the inventive device to monitor oscillations (fluctuations) about a fixed point SP (50-cm H2O in this example), such oscillations occurring at approximately twelve cycles per minute, which is typical of a "normal" respiratory cycle. an anesthetized adult patient.

It has been found that such respiratory flow through breathing tube 14, either spontaneously or as a result of IPPV, will have the effect of causing 19 regular compression / expansion cycles to pass through the LMA cuff. One of the objectives of the system of the invention is to measure the magnitude of both compression / expansion cycles as well as detecting deviations from such compression / expansion cycles that may indicate a response to pain stimuli. Although there is a general spread of the signal envelope of Fig. 5 (as such it is shown in Fig. 5 and will be further explained in the section on autoscaling), however, there are no indications of pain stimuli in Fig. 5 yet. Fig. 5A shows an example of a patient experiencing a pain stimulus that the system according to the invention will detect and deliver by the emergency procedures that are given in the discussion below.

The graph of Fig. 5A shows the competing forces acting, once disrupted by a response to a pain stimulus of the nature indicated. First, of course, it is recalled that the system of the invention will be c normal "regulating mode, doing whatever it can, based on its repeated sampling (at 0.5 second intervals) of the measured pressure (e.g., P1) with respect to a predetermined point Sp and using this reading to determine and perform the appropriate displacement of the piston 27. The pattern of neuromuscular-derived pressure variation that follows the pain stimulus, and the piston displacements that will be induced and may not be within the tracking ability of the mechanism, may therefore produce a perturbed pattern of measured pressures while the control regime tries to re-establish itself. Continued, the patient's normal regulatory regimen and neuromuscular system will attempt to adapt to the altered and changing conditions that may result from the patient's neuromuscular response to a deepening ("rescue") dose of anesthesia.

D. Monitoring function

Figures 3, 5 and 5A, and the graphs and tables of Figures 6A, 6B, 6C and 6D illustrate two automatic techniques by which the device of Figures 1, 2 and 3 can alert the anesthetist that during the course of a surgical procedure on a patient anesthetized, the patient gave an early clue nervously12

PL 192 899 B1

- a muscle with a pain stimulus that the patient's current level of anesthesia has failed to block, even though the patient is still sedated enough to be unconscious or otherwise unaware of the pain stimulus. This neuromuscular cue indicates to the attending anesthetist that the patient is contracting the muscles of the larynx and lower pharynx - a phenomenon that indicates an imminent stage in the patient's recovery process - with potentially serious consequences if the surgical procedure is not yet complete.

Although it is known that patients under general anesthesia become insensitive to pain stimuli, such sensitivity has been found to be particularly active and can be observed in the muscular systems surrounding the laryngeal inlet and the lower pharynx. It has further been discovered that such activity of these muscle systems will vary with the depth of anesthesia and can be observed by pressure fluctuations in an inflated LMA 19 cuff having an elastically biased continuous contact with such muscle systems. Specifically, abnormal pressure readings at the output of pressure comparator "A" 40 are recognized by comparators "B" 57, "C" 58 and "D" 59 in Figure 3 in order to issue the output alarms A2 and A2. The inflated ring or cuff 19 of the installed LMA is thus the early detection of a localized neuromuscular response that can be inferred from the sudden regulatory function response of the described system as it is seen to occur in the disturbed and irregular pattern of pressure deviations in Fig. 5A. in which the parentheses and the legend identify the period of the pain stimulus due to the phenomenon occurring during the surgical procedure.

Figure 7 shows the empirical values ​​of the pressure fluctuation variables observed at a time when the anesthetist specifically allowed the patient to escape from the depth of anesthesia, it should be understood that a graph similar to Figure 7 was available in real time on display 49 during the course of the surgical procedure . Pressure changes are displayed on the ordinate in cm H2O, with the SO fixed point selected as 60-cm H2O. Figure 7 displays the events that occurred until the end of the surgical procedure in which the patient, "Patient 5", was anesthetized with the continuous administration of propofol, a common and popular anesthetic.

Three specific time periods are recognizable in Figure 7, and each of these intervals corresponds to the onset of variation in the amount of anesthetic administered to the patient 5. In the first of these periods, starting from a time of 68 minutes, the continuous administration of propofol was stopped. And in the following remainder of the first period, a significant increase in muscle activity in the larynx / pharyngeal area was easily observed in the area in contact with the LMA cuff 19.

The correlation of increased muscle activity (in the laryngeal / pharyngeal region) with the depth of a patient's anesthesia has been found to be a significant benefit in maintaining adequate levels of anesthesia during surgical and other procedures. The use of an LMA device and a monitoring device provides an assembly whereby such observations can be reliably made with the added benefit of not subjecting the patient to further invasive devices.

During the second period depicted in Figure 7, beginning at the approximate time point of 72 minutes, the anesthetist resumes propofol administration. The third period in Figure 7 begins at approximately 73 minutes and is identified by stopping propofol administration again and allowing the patient to fully awake. Note that there are no further readings after approximately 82 minutes as LMA has been removed from the patient's laryngeal area during this time.

The events of Figure 7 provide clear evidence that the monitoring system of the invention operates at a sensitivity level that detects muscle activity indicative of the wake up sequence.

D.1 Automatic alarms

The two preferred techniques for interpreting the automatic anomaly described in FIG. 5A are further described below. These alarms can be monitored by the anesthetist for immediate or early recognition of a pressure abnormality that has been observed as a symptom caused by the early oncoming stage of the patient's awakening process.

Both techniques rely on establishing fluctuation limits (thresholds) on either side of a normal tidal wave and comparing the LMA (ring 19) pressure with those limits; these are shown as the upper and lower limits of E1 and E2 in Figures 5 and 5A and referred to as the "anesthesia control alarm window." As shown in Figure 3, E1 and E2 are values ​​that are automatically compared with each fluctuation in the pressure signal to determine the anesthesia level alarms, A1 and A2. The attending anesthesiologist is able to individually select, i.e. change E1 and E2 via the monitoring device 10.

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A1 is a momentary type alarm, triggered whenever the tidal wave deviates above or below the “check anesthesia” alarm window, which is between E1 and E2. The initial A1 warning alarm is triggered by any single deviation from the "check anesthesia" alarm window. Alarm A1 will be presented to the anesthesiologist audibly. Upon such warning, the anesthetist is alerted to perform an immediate corrective response, for example by increasing the strength of the anesthesia administered to the patient.

Alarm A2 is a rate-related alarm that is determined by (i) a value associated with the ET window (explained below) and (ii) a computed average (Y) based on consecutive samples of the detected LMA alternating inflation pressure wave, sampled for each successive 0.1-second sampling interval and are efficiently integrated and stored as absolute values ​​in the circuit of the word summation table as shown in Fig. 3; each of these absolute values ​​is taken for its sampled size with respect to a fixed baseline, preferably a fixed point value as shown in Figures 6A and 6B. If the average value, i.e. the sum of the last thirty-two consecutive integrated samples, divided by 32 (61, fig. 3A) exceeds the ET value, as further explained below, the alarm A2 will be issued, in the form of the warning "CHECK ANESTHESIA", to the anesthetist by a combination of visual and / or audible signals. The anesthetist is thus further alerted to make an immediate corrective response, such as by increasing the strength of the anesthetic that is administered to the patient. ET is calculated by adding the absolute values ​​of E1 and E2, and dividing their sum by the chosen constant k, i.e.,

ET =¹ [Eli + | E 2 | ] k

where k is a selected value in the range 3 to 6 (and preferably 4), which is explained so that for k = 4, the "divide by 4" relationship establishes a recommended practical safety factor by which the "CHECK ANESTHESIA" alarm is in reliably issued even when the temporary type alarm A1 may not have been issued.

As shown in Figure 3, at the end of each 3.2 second sampling period, the oldest sample is released and the newest sample is included in the new mean value calculation for the next 32 sample comparison with ET.

Thus, for example, the anomaly illustrated in Fig. 5A, which represents a pain stimulus event observed during a surgical procedure, will be seen to elicit terms that represent a significant deviation from the normal situation shown in Fig. 5. If the initial sample exceeds one of alarm window limitations, the first alarm A1 will be triggered, and the second alarm A2 will not be triggered immediately. However, the integration and compilation of the mean value described above may trigger alarm A2 "CHECK ANESTHESIA" even if the threshold exceeded required for the first A1 alarm has not occurred. In addition to these two alarms, the anesthesiologist can monitor continuous progress in the form of Percent Awake, which can be displayed as shown in Figure 1B, the same being discussed below under the "Display Feature" heading.

While the graph of FIG. 5A reflects the interrelationship of the various reactions, it should be particularly noted that upon detection of such reactions, large transient deviations from the SP predetermined point are eliminated in substantially 30 seconds due to the immediate administration of additional anesthesia.

D. 2. Display Features

The display 49 includes a time window through which a continuously varying signal such as shown in Figures 5, 5A, 6B, 6D and 7 will show one last full minute of adjustable pressure variations entering the window at its left margin and exiting visibility. windows on the right margin.

An additional display of the results of the above-described integration / summation process (mean value) is shown in Fig. 1A and Fig. 1B, with the two time-course displays showing progress from a deeper level of anesthesia, as shown for example in the first example of Fig. 1A, to the upcoming level of impending wake-up shown in the second example of Fig. 1B. The display preferably consists of a bar graph that shows,

On a percentage scale, the output is from the sequentially integrated function described above. The initial value of this continuously updated display is determined for each individual patient, preferably after the surgeon anesthetized patient has been positioned on the operating table, ready for surgery. The parameter equivalent to 100% display reading will be equal to the full ET value at which the "CHECK ANESTHESIA" alarm will be issued.

In addition, there is provided, for use by an anesthetist and / or other personnel examining a particular surgical procedure, the ability to connect a separate microprocessor or other data presentation unit to the computer interface 41, thereby ensuring monitoring, recording and analysis of the system indicators on a separate electronic medium when For example, more sophisticated records and analyzes are desirable.

D.3. Autoscaling of the Alarm Window

It has been found that the monitoring function of the system according to the invention can be made more efficient by allowing the automatic shrinkage (or autoscaling) of the size of the anesthesia check alarm window, thereby providing the advantage of faster adjustment of the alarm threshold (i.e., E1 and E2) and thus more accurate monitoring. the level of anesthesia. To autoscale the anesthesia check alarm window, both the upper and lower peak amplitudes from the last eight consecutive waves are sampled, averaged, and the mean values ​​for the upper and lower peaks are determined. Two checks are used to validate the peaks, all eight upper and lower limits to be sampled must be obtained during the same two-minute sampling period, and small oscillations that could otherwise be identified as peaks can be eliminated by operator input initially specified minimum amplitude.

These upper and lower peak amplitudes define, essentially, a "envelope" that typically decreases according to the patient's compliance with positive pressure ventilation (IPPV) as the patient becomes more anesthetized. When considering the usefulness of the need to re-alert thresholds in terms of following an envelope of decreasing amplitude (or size), it should be remembered that a patient's respiratory pressure is generally reduced as the patient becomes more compliant. Limiting the alarm thresholds (i.e., E1 and E2) has been found to be a more efficient and desirable way to automatically re-establish the sensitivity of the monitoring device such that the origin of the pain stimulus will still be detected, despite the reduction in the size of the envelope.

For safety reasons, the recommended device will allow the autoscaling feature to only shrink, not automatically enlarge, the anesthesia check alarm window. The amount by which autoscaling can change E1 and E2 is fully adjustable between zero and one hundred percent. Interestingly, such autoscaling often causes E1 and E2 to no longer be symmetrical about the fixed point SP, similar to the alarm window shown in FIG. 6B.

D.4. A system of re-centering action

As described above, the inventive system will automatically compensate for leaks and excess inflation air monitored. Since the controller and drive of the stepping motor 47 keeps a count of the direction commands given to the stepping motor 33, the drive of the stepping motor 47 is capable and will indicate when the piston 27 has reached the end of its travel. Such an indication will actuate the switches 42 to the "1" position, and trigger the initiation of the "reset" function, managed by the controller 60, for starting, centering, and reset. Depending on the reset command sent by the motor controller 47, i.e. when the abnormal condition requires filling or purging the air of the piston, appropriate action will be taken by the controller 60. For example, when the staging function requires air to be added to the system, the controller 60 will (i) turn off the solenoid valve V1, returning it to its normally closed state; (ii) actuating the solenoid valve V2 to its open state; and (iii) sending appropriate signals to the controller and drive of the stepper motor 47, thereby causing the piston 27 to be driven by the motor 33 at high speed to vent excess "air" (or, where appropriate, draw additional fresh air) through the port 44. The memory of the controller 60 will have saved, from the starting procedure described above, the number of pulses required to drive the piston 27 to its center position (L / 2).

In the normal monitoring and regulating operation of the described system, there will not be much need for large displacements of the piston 27. However, large displacements may occur, for example, loss of monitored inflation air may be caused by contact of a surgical knife.

PL 192 899 B1 with the LMA ring 19 inflated. This condition will be observed by the system, prompting a continuous supply of either additional or reduced inflation air, depending on whether the leg 37 covers any of the limit switches LS1 or LS2, thereby indicating that the piston 27 reaches the end of its travel. Such a limit switch signal will cause: (i) switches 42 to bypass the control circuit of FIG. 3; (ii) sending an alerting the anesthetist, such as an audible alarm, visually displaying the message "CHECK FOR LEAK"; and (iii) triggering the reset function of controller 60 as described above.

The above description highlights the additional advantage of the automatic device that it fills the volume of air in cylinder 26 in about 3.6 seconds as described, which is much faster than is typically possible by manual operation. Despite this advantageous automatic recovery time, the pressure adjustments performed by the system are discrete enough to allow the pressure of the smallest LMA cuff to be adjusted without causing unnecessary pressure reflection within a small volume.

All such operations are automatic, as are alerts or alarms which are part of ensuring that the set point pressure is maintained as long as circumstances may require for a given patient, or for a given LMA size that the patient requires.

The described device and its method of use, as will be seen, achieve all stated goals, acting as the LMA cuff pressure controller, as a device that will monitor and correct leaks, as a monitor of the possible pain stimulus delivered to the patient's neuromuscular system while it is present. it is anesthetized for the course of the surgical procedure and as a monitor to prevent the patient from remaining under the influence of a muscle relaxant, when he is not sufficiently anesthetized. Especially:

1. The device is controlled by a microprocessor unit that carries out all tasks including, but not limited to, diagnostics checks, engine and valve operation and control, and pressure measurement.

2. The apparatus comprises a graphic display and a control unit as well as an interface for pre-monitoring and control, thus allowing data evaluation by various commercially available software.

3. The device provides instantaneous pressure values ​​of the LMA cuff thanks to redundant pressure sensors that are pneumatically connected to the LMA cuff inflation tubing. For safety reasons, the pressure measurement is performed by redundant conveyors, which are automatically compared continuously.

4. The device is normally operated with the same volume of air in an attempt to maintain the set point pressure to inflate the LMA cuff, where for each LMA cuff sample pressure measurement, deviation from the set point value causes the plunger to move in a direction such as to reduce to zero (or substantially to zero). zero) the deviation of the measured pressure from the steady-point pressure.

5. The device is detachably connected to the LMA inflation / deflation air line so as to allow the normal procedures for installing the LMA in the patient without relying on any automatic feature of the device. Consequently, the patient can be "prepared" for surgery by installing the LMA, with the cuff inflated, and fully inspected to ensure that it has been properly installed before the patient enters the operating room, thereby relying on the control valve to maintain pressure. inflation, before connecting the device to the patient and the inflated LMA cuff.

6. If, for some reason, the system is not operating or is not operating properly, the system will switch to protective mode, with the service valves returning to their normally closed state, thereby maintaining the LMA cuff inflation pressure.

7. In its normal control mode, the pressure is sampled by the system every one tenth (1/10) of a second, with sufficient time to judge against a predetermined point pressure, and the issuing of a series of pulses serves to displace the piston to correct the measured pressure to substantially fixed point pressure. Normal adjustment occurs if the estimated pressure sample exceeds the threshold value by ± 0.5 cm H2O from the set point value set.

8. It is important to emphasize that normal operation of the described LMA system has significant advantages that result from the fact that the system operates with a practically closed air volume.

PL 192 899 B1

Increasing the measured pressure will rapidly displace a portion of the air volume from the LMA cuff i into a volume defined between the piston and the cylinder head end; and this volume of air will be returned to the LMA cuff virtually as soon as a decrease in the measured pressure is detected. This sharing of the same volume of air is always true, except when, due to a leak or some other unexpected event, the piston reaches the end of its travel as this will be tracked by the operation of a position counter held inside the stepper motor controller or when one of the switches is reached. restraining point, at which point the piston will reposition itself, releasing air or drawing in fresh air, depending on the circumstances, while the LMA cuff can maintain its inflation pressure.

9. Once stabilized, the described system proves to be sensitive to very small changes in pressure (in the order of 1/16-cm H 2 O) and can be fast and accurate in its response without disturbing the time constant monitoring function or hysteresis transitions. It is believed that such a response is obtained from the described stepper motor and lead screw drive in combination with normal regulating displacements within a practically closed air volume. The reliance on a virtually confined air volume translates into only one time constant involved in increasing or decreasing the pressure within the LMA cuff.

10. As an aid to the anaesthesiologist and during the surgical procedure on the patient, the described system allows several simultaneous algorithms to process, in real or near real time, the initial, oncoming and completely independent muscular symptoms of an anesthetized patient awakening from an induced sleep and / or paralyzed state , by a sensitive response to the muscular action observed around the patient's laryngeal inlet and / or in contact with the patient's lower pharynx. Audible and visual alerts are provided to the anesthetist to detect the patient's onset of awakening, in good time to "check anesthesia", and to implement corrective measures without waking the patient. The described system is seen to be internally adaptable to increased accuracy in detecting loss of depth of anesthesia as the focus gradually narrows on the predetermined margin of safety in estimating the observed LMA inflation pressure fluctuations.

11. The monitoring function of the described system may be useful in detecting and providing a way to protect against the circumstance in which a patient administered both an anesthetic and a separate relaxant (e.g., atracurium or vercuronium) has consumption of the anesthetic but remains immobilized due to the ongoing effect of only the anesthetic. Such a circumstance is known to be highly unpleasant due to the patient's inability to reveal that the patient is experiencing the full effect of the surgical manipulations. The LMA monitoring system may be useful as a protection against such an event in view of the more limited effect of certain relaxants on the pharyngeal sphincter muscles with which the LMA 19 cuff necessarily contacts, along with its ability to monitor muscle activity. Others observed that the contraction curve of the pharyngeal sphincter muscles was unchanged during partial paralysis caused by a popular muscle relaxant. See, Ericsson, et al., Functional Assessment of the Pharynx at Rest and during Swallowing in Partially paralyzed Humans; Anaesthesiology, V 87, No. 5, November 1997.

12. It should further be noted that although the monitoring and other detection functions of the described system are preferably in the context of a response to an LMA inflation, the LMA context is merely an illustration of the use of a suitable device inflated inside the pharyngeal cavity to respond to and generate an appropriate warning of muscle activity in the contact area. material that is inflated with one or more regions of muscle activity.

13. It should further be noted that the recommended numerical values ​​given herein as 4, 8, 32, etc. are merely exemplary and have been chosen as power 2 values ​​with a view to relying advantageously on digital circuit operation.