JPH0755236B2 - Anesthesia depth detector - Google Patents

Description

TECHNICAL FIELD The present invention relates to a device for detecting the depth of anesthesia in a living body.

Prior art During anesthesia of a living body during surgery, it is appropriate to avoid the awakening of the living body due to an excessively shallow anesthesia and the inconvenience due to an excessively deep anesthesia, and to make a comprehensive decision based on the physiological information of the living body and the situation of the procedure. In order to maintain a sufficient depth of anesthesia, it is necessary for the anesthesiologist to manually adjust the mixing ratio of the anesthetic mixed in the inspiration accurately. In such anesthesia of a living body, an anesthesia depth detection device that accurately detects the depth of anesthesia of the living body is desired. In this regard, the depth of anesthesia is the electroencephalogram of the living body,
Various types of devices for detecting blood pressure, heart rate, etc. have been studied.

Problems to be Solved by the Invention However, such a conventional device has a problem that sufficient accuracy cannot be obtained when grasping the depth of anesthesia. For example, when detecting the depth of anesthesia by analyzing EEG, even if the depth of anesthesia based on EEG is the same,
The anesthetic concentration in arterial blood was sometimes shifted by 30%. If the accuracy of the anesthesia depth as the feedback information is not sufficient, variations in the control results cannot be avoided when performing manual adjustment or automatic control of the anesthesia depth.

Means for Solving Problems The present invention has been made against the above circumstances.
The gist of the invention is an anesthesia depth detection device for detecting the anesthesia depth of an anesthetized living body by mixing an inhalation anesthetic into the inhalation, and includes (a) the exhalation of the living body. An anesthetic concentration detector that continuously detects the concentration of the inhaled anesthetic and outputs a concentration signal that fluctuates in synchronization with respiration; and (b) an end time that detects the end time of the expiration period in the respiration of the living body. (C) The concentration of the inhaled anesthetic at the end time or a value based on the concentration is output from the concentration signal output from the anesthetic concentration detection device and (c) and is output as a value indicating the depth of anesthesia. And anesthesia depth determining means.

In this way, the anesthesia depth detection means determines the concentration of the inhaled anesthetic at the terminal stage or the value based on the concentration signal output from the anesthetic concentration detection device, and Since the value is output as a value indicating the depth of anesthesia, the depth of anesthesia can be grasped more accurately than in the conventional case. That is, end tidal gas, which is a gas at the end time of exhalation, can be considered as gas in the alveoli, and the inhaled anesthetic concentration contained in it corresponds to the anesthetic concentration in arterial blood,
This is because the anesthetic concentration in the blood corresponds to the anesthetic concentration in the brain cells (anesthetic partial pressure) that is closely related to the depth of anesthesia of the living body.

Here, the end time detection means preferably continuously detects the concentration of carbon dioxide contained in the exhaled breath of the living body, and outputs a signal indicating the concentration of carbon dioxide which changes in synchronization with respiration. It includes a detection device and a carbon dioxide concentration maximum time detection means for detecting the maximum time of carbon dioxide concentration based on the signal output from the carbon dioxide concentration detection device.

Further, the end time detection means is a chest impedance detecting device that continuously detects changes in the chest impedance of the living body, and a chest that detects the minimum period of the chest impedance based on a signal output from the chest impedance detecting device. It may include an impedance minimum time detecting means.

Further, the end time detection means may directly or indirectly detect the end time of the expiration period of the ventilator forcibly breathing the living body, and output a signal indicating the end time. .

Embodiment Hereinafter, one embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows the configuration of an anesthesia depth automatic control system. An electric ventilator 12 is connected to a patient 10 via a pipe 11, and the number of respirations according to a command from a respiration controller 14. And it operates at the ventilation amount, and the inspiration corresponding to the ventilation amount is forcibly sent to the patient 10 and the exhaled air is discharged. Exhaled air from the patient 10 is exclusively sent to a carbon dioxide sensor 16 and an anesthetic concentration sensor 18 through a pipe 13 for delivering the exhaled air, and the inhaled anesthetic concentration in carbon dioxide and exhaled breath is detected there. ing.

The carbon dioxide gas sensor 16 detects the concentration by utilizing the absorption spectrum of carbon dioxide gas existing in the infrared region, and is composed of an infrared gas analyzer with a heating tube as shown in FIG. 2, for example. There is. In the figure, infrared light emitted from a light source device 20 is detected by a photocell 30 through a convex lens 22, a glass cell 24 through which breath is passed, an infrared transmission filter 26, and a convex lens 28. The photocell 30 outputs a signal indicating the intensity of infrared rays having an absorption wavelength peculiar to carbon dioxide that has passed through the glass cell 24, and this signal is amplified by an amplifier 32. The magnitude of the infrared transmission signal SC output from the amplifier 32 is inversely proportional to the concentration of carbon dioxide contained in the exhaled breath, and changes, for example, in synchronization with respiration as shown in (a) of FIG. In this figure, the vicinity of the upper peak shows the initial exhalation with a low carbon dioxide concentration, and the vicinity of the lower peak shows the end exhalation with a high carbon dioxide concentration. This is because the same components as inhalation remain in the dead space, which is the part of the mouth, nose, and trachea that does not participate in gas exchange in the alveoli during one-time ventilation, and it is discharged in the early stages of exhalation. Because it is done.

The anesthetic concentration sensor 18 is equipped with an infrared gas analyzer with a heating tube for detecting the concentration by utilizing the absorption spectrum of the inhalation anesthetic in the infrared region as described above.
In FIG. 4, the infrared rays emitted from the light source device 36 are detected by the photocell 46 through the convex lens 38, the glass cell 40 through which the exhaled air passes, the infrared transmission filter 42, and the convex lens 44. The photocell 46 outputs a signal indicating the intensity of infrared rays having an absorption wavelength peculiar to the inhalation anesthetic transmitted through the glass cell 40, and this signal is amplified by the amplifier 48. The magnitude of the infrared transmission signal SM output from the amplifier 48 is inversely proportional to the concentration of the inhaled anesthetic contained in the exhaled breath, and changes in synchronization with respiration, for example, as shown in (b) of FIG. Therefore, the infrared transmission signal SM corresponds to the concentration signal indicating the concentration of the inhaled anesthetic.

On the other hand, an anesthesia depth output circuit 54 having a lower peak detection circuit 50 for detecting the lower peak of the infrared transmission signal SC and a gate circuit 52 opened by the output signal of the lower peak detection circuit 50 is provided. ing. A signal indicating the lower peak value of the infrared transmission signal SM through the gate circuit 52, that is, an anesthetic concentration signal indicating the inhalation anesthetic concentration in the end tidal breath.
Since SSM is output, in the present embodiment, the lower peak detection circuit 50 corresponds to the carbon dioxide concentration maximum time detection means for detecting the maximum time of carbon dioxide concentration, and the carbon dioxide sensor 16 and the lower peak detection circuit 50 end. The gate circuit 52 corresponds to the anesthesia depth determining means, which corresponds to the timing detecting means. The anesthetic concentration signal SSM is supplied to the anesthesia depth indicator 55, where the depth of anesthesia determined based on the inhalation anesthetic concentration in the end tidal breath or the inhalation anesthetic concentration in the end tidal breath from the relationship determined in advance. The displayed index value is displayed. FIG. 3D shows the opening operation of the gate circuit 52, and the anesthetic concentration signal
SSM indicates the concentration of inhaled anesthetic in the end tidal breath, which is the final time in the tidal period. The inhalational anesthetic concentration in this end-expired breath is
It shows the concentration of inhaled anesthetic contained in the gas in the alveoli and corresponds to the concentration of anesthetic in arterial blood,
The anesthetic concentration in the blood corresponds to the anesthetic concentration in brain cells which is closely related to the depth of anesthesia in the living body. The third
In the figures (a) and (b), the infrared transmission signal SC and the infrared transmission signal SM are flat between the inhalers, but this is the pipe 13 for exclusively delivering the exhaled breath from the ventilator 12.
This is because the end exhalation is retained inside. Also, piping 11
When the carbon dioxide sensor 16 and the anesthetic concentration sensor 18 are provided in the gate circuit 52, the gate circuit 52 is opened only at the end of the expiratory period as shown by the broken line in FIG.

In the anesthesia depth setting device 56, an appropriate anesthesia depth determined from the physiological information of the patient 10 and the surgical situation, that is, the anesthetic concentration (%) contained in the end tidal breath is manually set. The anesthesia depth controller 58 compares the anesthesia depth set in the anesthesia depth setting device 56 with the actual anesthesia depth indicated by the anesthetic concentration signal SSM from the anesthetic concentration sensor 18, and eliminates the deviation between them. A control amount is determined based on a control formula stored in advance, and a control signal SS is output to the anesthetic mixing device 62 via the drive circuit 60. The control signal SS is for instructing the mixing rate of the anesthetic in the exhalation supplied to the patient 10, and specifically, for indicating the drive rotation angle of the pulse motor 72 described later. The concentration of inhalation anesthetic at the time of induction of anesthesia is adjusted to 3 to 10 by the anesthesia depth controller 58.
%, And 2 to 30% when maintaining the depth of anesthesia. In order to prevent excessive concentration in the transient state, the control formula includes a limiter corresponding to a value of about 10%.

In the anesthetic mixing device 62, as shown in FIG. 5, a mixed gas of oxygen and laughing gas delivered from the oxygen cylinder 64 and the laughing gas cylinder 66 is supplied to the mixer 70 through the throttle 68, while the pulse motor 72 is supplied. Flow control valve driven by 74
And inhalation anesthetic vaporizer 76 to mixer 70. This mixer 70 is a vaporizer of the mixed gas and inhalation anesthetic 76
The gas containing saturated vapor of the inhalation anesthetic from is mixed and supplied to the ventilator 12 as inhalation. The mixed gas of oxygen and laughing gas delivered from the oxygen cylinder 64 and the laughing gas cylinder 66 is mixed in advance to about 4 to 2 by the manual control valves 78 and 80, which is expected to have a secondary effect. Therefore, oxygen alone can be used. Further, the inhalation anesthetic vaporizer 76 is configured to include, for example, a so-called copper kettle (perforated bronze sintered plate) and a container for storing the inhalation anesthetic, and delivers it through the copper kettle immersed in the inhalation anesthetic. The saturated vapor is generated in the gas at the liquid temperature of the inhalation anesthetic at that time. Therefore, by controlling the flow rate of the flow control valve 74, the concentration of the inhaled anesthetic in the exhaled breath is adjusted. In this example, sevoflurane is used as the inhalation anesthetic. This sevoflurane is shown below.

Chemical formula: CH ₂ F-O-CH (CH ₃ ) ₂ Chemical name: fluoromethyl-1,1,1,3,3,3-hexafluoro-isop
ropyl ether Molecular weight: 200 Boiling point: 58.5 ℃ Liquid specific gravity: 1.505g / ml Vapor pressure: 157torr (20 ℃) Blood / gas partition coefficient: 0.59 (37 ℃) MAC: 2.0 (monkey) The above sevoflurane is the blood / gas partition As is clear from the coefficient, in addition to being superior in the induction of anesthesia and wakefulness compared to conventional inhalation anesthetics, it is also excellent in the control of the anesthesia depth due to the small variation in the anesthesia depth. . This fact is shown in the experimental results shown in Table 1. In this experiment, the MAC values and their variability for multiple guinea pigs were compared with those of sevoflurane and the well-known enflurane (molecular weight: 185, boiling point: 56.5 ° C, blood /
Gas distribution coefficient: 1.9).

Here, is the average value of MAC and σ is its standard deviation.

Returning to FIG. 1, the ventilation volume is set in the ventilation volume setter 82. Since the ventilation volume required for the patient 10 is closely related to the carbon dioxide concentration in the end tidal breath, the end tidal breath is set in this embodiment. The inside carbon dioxide concentration (%) is set. The breathing controller 14 determines the carbon dioxide concentration in the end tidal breath based on the signal SC supplied from the carbon dioxide sensor 16. That is, the peak value, which is the maximum value of the carbon dioxide concentration that periodically changes, is detected. Then, from the control formula stored in advance so as to eliminate the deviation between the actual carbon dioxide concentration and the end-tidal carbon dioxide concentration set in the ventilation volume setter 82
Ventilation volume (corresponding to oxygen injection volume per constant time) per 10 constant time (for example, every minute) is determined. Since this ventilation volume is represented by the product of the respiratory rate and the tidal volume, the respiratory controller 14 needs to determine the respiratory rate and the tidal volume per constant time, but the respiratory rate is constant. When set to the value, the same respiratory volume is determined. Then, when the control signal for obtaining the ventilation volume thus determined is supplied from the respiration controller 14 to the artificial respirator 12 via the drive circuit 84, the artificial respirator 12 is supplied from the anesthetic mixture device 62. The patient's inspiration of 10
To be sent to.

According to the above-mentioned embodiment, since the concentration of the inhaled anesthetic in the end tidal breath is detected at the time when the concentration of carbon dioxide gas in the exhaled breath reaches the highest peak, the concentration of the inhaled anesthetic in the inhaled air is accurately determined regardless of the concentration of the inhaled anesthetic. You can know the depth of anesthesia. That is,
In the automatic control system for keeping the anesthesia depth constant, when the anesthesia depth becomes too deep relative to the target value and the concentration of the inhaled anesthetic mixed in the inspiration is lowered to eliminate the deviation at this time, As shown in FIG. 3 (c), the concentration in the initial expiration may be lower than the concentration in the end expiration. At this time, if the end exhalation is simply judged from the minimum peak value of the fluctuation of the concentration of the inhaled anesthetic in the exhaled breath, the concentration of the inhaled anesthetic at the initial stage of the exhaled breath will be detected.

Since the inhaled anesthetic concentration in the end tidal breath determined as described above is used as information on the depth of anesthesia of the patient 10, the depth of anesthesia can be grasped more accurately than before. In other words, blood pressure, pulse, EEG, respiratory rate, cardiac wave, etc. are physiological reactions that are affected by factors other than the depth of anesthesia, and it is possible to avoid variations in the appearance even with the same partial pressure of anesthetic agent in the brain cells. Absent. In contrast, end-tidal breath is gas in the alveoli, and the concentration of inhaled anesthetic contained in it corresponds to the concentration of anesthetic in arterial blood, and the concentration of anesthetic in blood is closely related to the depth of anesthesia in the living body. This is because it corresponds to the concentration (partial pressure) of the anesthetic in the brain cells. For example, when general anesthesia is given to an elderly person who is thin and whose general condition is not good, especially in the case of halogenated anesthetics, circulatory suppression becomes remarkable, and when the depth of anesthesia is monitored by blood pressure values, etc. It seems that anesthesia is deeply applied, and at this time, there is physical movement and a sudden rise in blood pressure when surgery is performed, and it may seem that anesthesia has suddenly become shallow. But,
This is not the case if the depth of anesthesia is judged based on the concentration of inhaled anesthetic in the end tidal breath.

Further, in the above-described automatic anesthesia depth control device, since the inhalation anesthetic mixed in the inspiration has a blood / gas distribution coefficient of 1 or less at 37 ° C., the concentration change of the inhalation anesthetic mixed in the inspiration is used. The change in the depth of anesthesia with respect to (1) becomes rapid, the stability of the control system is significantly improved, and the automatic control of the depth of anesthesia is suitably performed. That is, it may be considered that the partial pressure of the anesthetic in the brain cells determines the depth of anesthesia,
The anesthetic partial pressure in the brain cells is determined by inhalation anesthetic concentration during inspiration, second gas effect, alveolar ventilation, alveolar / capillary permeability, cardiac output, blood properties, Although there are blood / brain barrier conditions, physicochemical properties of anesthetics, etc., the depth of anesthesia is determined if there is no lesion in the lung, cardiac output and blood properties are constant, and there is no abnormality in the blood / brain barrier. The factor that does this is the anesthetic concentration in the inspiratory air. When the anesthetic concentration in the inspiration is changed, in the short term, the lower the blood / gas partition coefficient, the easier it is to dissolve in the blood, and the anesthetic partial pressure in brain cells reacts sensitively.

By the way, halothane (blood / gas partition coefficient 2.4), enflurane (blood / gas partition coefficient 1.9), isoflurane (blood / gas partition coefficient 1.48), which are commonly used in the past.
Are good anesthetics, but they are not sufficient in the reaction rate of anesthesia and the variation of anesthesia, and when they are used in the anesthesia depth automatic control device, the stability of the control system is not sufficiently obtained for practical use, and The controlled anesthesia depth also varied greatly.

Although one embodiment of the present invention has been described above, the present invention can be applied to other aspects.

For example, in the above-described embodiment, the concentration of the inhaled anesthetic in the end tidal breath is detected based on the infrared transmission signal SC supplied from the carbon dioxide sensor 16, but as shown in FIG. The lower peak detection circuit 50 detects the minimum time of the chest impedance detected by the electrode 86 and the bridge circuit 88 attached to the chest of the patient, and the inhaled anesthetic concentration in the end tidal breath is detected in synchronization with the minimum time. May be configured to do so. In this embodiment, the electrode 83 and the bridge circuit 88 correspond to the chest impedance detecting device, and the lower peak detecting circuit 50 corresponds to the chest impedance minimum timing detecting means. Further, as shown in FIG. 7, a switch provided in the ventilator 12 and actuated at the end time of exhalation in association with the movement of the piston or diaphragm.
The gate signal 52 may be opened by the terminal signal SMT output from 90, and then the anesthetic concentration signal SSM may be output. In this embodiment, the switch 90 corresponds to the end time detection means. In addition, as shown in FIG. 8, in place of the signal SMT output from the switch 90 provided in the ventilator 12, of the control signal or the drive signal supplied from the breathing controller 14 to the ventilator 12. A one-shot multivibrator circuit 92 that opens the gate circuit 52 by outputting a pulse signal of a predetermined width when triggered by the end of the expiration period or the start of the inspiration period may be provided. Further, as shown in FIG. 9, the expiratory flow rate in the pipe 13 is detected by the flow meter 94, and the lower peak detection circuit 50 detects that the expiratory flow rate has become the minimum, so that the gate is operated in the same manner as described above. It does not matter if the circuit 52 outputs the anesthetic concentration signal SSM indicating the concentration of the inhaled anesthetic in the end tidal breath. In this embodiment, the flowmeter 94 and the lower peak detection circuit
50 corresponds to the end time detection means. In short, Figure 4,
Like the output signal of the lower peak detection circuit 50 in FIGS. 6 and 9, the output signal of the switch 90 in FIG. 7, and the output signal of the one-shot multivibrator circuit 92 in FIG. The concentration of the inhaled anesthetic in the end tidal breath may be detected based on the respiratory sync wave indicating the end time.

Further, the gate circuit 52, the lower peak detection circuit 50, and the like in the above-described embodiment may be configured by a program of a so-called microcomputer that configures the breathing controller 14 and the anesthesia depth controller 58. In this case, the infrared transmission signals SC and SM are supplied directly to the anesthesia depth controller 58.

Further, in place of the infrared gas analyzer with a heating tube provided in the anesthetic concentration sensor 18 of the above-described embodiment, the crystal adsorbs the halogenated anesthetic and the mass changes, and the change in the mass is supported. Then, a crystal oscillation type gas densitometer that utilizes the phenomenon that the oscillation frequency changes may be provided.

Further, the carbon dioxide sensor 16 and the anesthetic concentration sensor described above are used.
The infrared transmission signals SC and SM output from 18 have a magnitude inversely proportional to the density, but an inversion circuit for making the magnitude proportional to the density may be provided as appropriate.

The above description is merely an example of the present invention,
The present invention can be variously modified without departing from the spirit thereof.

[Brief description of drawings]

FIG. 1 is a block diagram illustrating the configuration of an embodiment of the present invention. FIG. 2 is a diagram for explaining the configuration of the carbon dioxide gas sensor of FIG. FIG. 3 is a timing chart for explaining the operation of the embodiment of FIG. 1, where (a) is an infrared transmission signal SC, (b) is an infrared transmission signal SM, and (c) is an anesthetic during inspiration. Infrared transmission signal SM when concentration becomes low
And (d) is a diagram showing the operation of the gate circuit, respectively. FIG. 4 is a diagram for explaining the configuration of the anesthetic concentration sensor of FIG. FIG. 5 is a diagram for explaining the configuration of the anesthetic agent mixing device of FIG. 6, FIG. 7, FIG. 8 and FIG.
The drawings are views showing other embodiments of the present invention. 16: Carbon dioxide sensor (carbon dioxide concentration detector) 18: Anesthetic concentration sensor (anesthetic concentration detector) 50: Lower peak detection circuit (carbon dioxide concentration maximum time detection means 52: Gate circuit (anesthetic depth determination means) 86 : Electrode (Chest impedance detector) 88: Bridge circuit (Chest impedance detector) 90: Switch (End time detection means) 92: One shot multivibrator circuit (End time detection means)

Claims (4)

[Claims] 1. An anesthesia depth detection device for detecting anesthesia depth of an anesthetized living body by mixing an inhalation anesthetic into inhalation, comprising: An anesthetic concentration detection device that continuously detects the concentration and outputs a concentration signal that changes in synchronization with respiration, an end time detection unit that detects the end time of the expiration period in the respiration of the living body, and the anesthetic concentration An anesthesia depth determining means for determining the concentration of the inhaled anesthetic at the end time or a value based on the concentration signal output from the detection device, and outputting the concentration as a value indicating the anesthesia depth. Anesthesia depth detection device. 2. A carbon dioxide concentration detector for continuously detecting the concentration of carbon dioxide contained in the exhaled breath of the living body and outputting a signal indicating the concentration of carbon dioxide varying in synchronism with respiration. The anesthesia depth detecting device according to claim 1, further comprising: and a carbon dioxide concentration maximum time detecting means for detecting a maximum time of carbon dioxide concentration based on a signal output from the carbon dioxide concentration detecting device. . 3. The end time detection means detects a chest impedance detection device that continuously detects changes in the chest impedance of the living body, and a minimum time of the chest impedance based on a signal output from the chest impedance detection device. The depth of anesthesia detection apparatus according to claim 1, further comprising a means for detecting a minimum chest impedance period. 4. The end time detection means detects the end time of the expiration period of the artificial respirator forcibly breathing the living body, directly or indirectly, and outputs a signal indicating the end time. The anesthesia depth detection device according to claim 1.