JPH0744954B2 - Anesthesia depth automatic control device - Google Patents

Description

TECHNICAL FIELD The present invention relates to an automatic control device for adjusting the anesthesia depth of a living body to a constant level.

Prior art During anesthesia of a living body during an operation, it is usually appropriate to avoid the awakening of the living body due to an excessively shallow anesthesia and the inconvenience caused by an excessively deep anesthesia, and to make an appropriate decision comprehensively from physiological information of the living body and the surgical situation. 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 order to reduce the burden on the anesthesiologist in such an operating room, an automatic adjusting device that maintains the anesthesia depth of the living body at a constant depth is desired. In this regard, various devices have been used to keep the depth of anesthesia constant by detecting the depth of anesthesia based on the electroencephalogram of the living body, blood pressure value, heart rate, etc., and adjusting the mixing rate of the anesthetic to be mixed into the inspiration based on this. Is being considered.

Problems to be Solved by the Invention However, in such a conventional device, sufficient accuracy cannot be obtained when grasping the depth of anesthesia, and the response time from the injection of the anesthetic to the reaction of the living body is long. There was a problem. If the accuracy of the depth of anesthesia as feedback information is not sufficient, no matter how good the control system is, variation in control results cannot be avoided, and if the response time of the living body is long, the automatic control system of depth of anesthesia becomes unstable. Both are important practical problems.

Means for Solving the Problems As a result of various studies conducted by the present inventor against the circumstances described above, when the inhalation anesthetic is used, the concentration of the inhalation anesthetic contained in the end tidal breath of the living body is equal to the anesthesia depth of the living body It is closely related and that the use of inhaled anesthetics having a blood / gas partition coefficient of 1 or less significantly improves the anesthetic response of the living body, which can significantly stabilize the automatic control system of anesthesia depth. I found it. The present invention has been made based on such findings.

That is, the gist of the present invention is an anesthesia depth automatic control device for adjusting the anesthesia depth of a living body to a constant level, wherein (a) an inhalation anesthetic having a blood / gas distribution coefficient of 1 or less is inhaled into the living body. An anesthetic mixing device mixed therein, (b) an anesthetic concentration detecting device for detecting the concentration of the inhaled anesthetic contained in the end tidal breath of a living body, and (c) anesthesia depth for presetting anesthesia depth A setting device, and (d) an inhalation anesthetic mixed in the inspiration by the anesthetic mixing device so that the concentration of the inhalation anesthetic contained in the end tidal breath becomes a value preset by the anesthetic depth setting device. And an adjusting device for adjusting the mixing rate.

By doing so, since the concentration of the inhaled anesthetic contained in the end tidal breath of the living body is used as information on the depth of anesthesia of the living body, it is possible to grasp the depth of anesthesia more accurately than before. You can End-tidal gas, which is the end-stage gas during exhalation, can be considered to be gas in the alveoli, and the concentration of inhaled anesthetic contained in it corresponds to the concentration of anesthetic in arterial blood. This is because it corresponds to the anesthetic concentration in the brain cells (anesthetic partial pressure) that is closely related to the depth of anesthesia.

Further, since the inhalation anesthetic mixed in the inspiration has a blood / gas partition coefficient of 1 or less, the change in the depth of anesthesia with respect to the change in the concentration of the inhalation anesthetic mixed in the inspiration becomes rapid, and the control system is controlled. The stability is greatly improved, and the automatic control of the depth of anesthesia is preferably performed.

Here, the blood / gas partition coefficient, when the respective C _K and C _G concentrations of anesthetics which dissolves respectively to the blood phase and gas (air) phase, a C _K / C _G becomes a value, It can be used as an index showing the easiness of inhalation anesthetic to dissolve in blood. The above blood / gas partition coefficient is a value at 37 ° C.

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 device, in which 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 exhaled air corresponding to the ventilation amount is forcibly sent to the patient 10 and exhaled. Exhaled air from the patient 10 is sent to a carbon dioxide sensor 16 and an anesthetic concentration sensor 18 exclusively through a pipe 13 for delivering the exhaled air so that the inhaled anesthetic concentration in carbon dioxide and end tidal breath is detected. Has become.

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 exhaled breath 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 is expelled in the early stages of exhalation. This is because that.

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, 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 pass 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.

On the other hand, a lower peak detection circuit 50 for detecting the lower peak of the infrared transmission signal SC is provided, and a gate circuit opened by the output signal of the lower peak detection circuit 50.
A signal showing the lower peak value of the infrared transmission signal SM, that is, the anesthetic concentration signal SSM is output through 52. FIG. 3D shows the releasing operation of the gate circuit 52. This anesthetic concentration signal SSM indicates the concentration of the inhaled anesthetic in the end tidal breath, which is the final time point within the expiratory period. The inhaled anesthetic concentration in the end tidal breath indicates the inhaled anesthetic concentration contained in the gas in the alveoli and corresponds to the anesthetic concentration in arterial blood, and the anesthetic concentration in the blood is It corresponds to the concentration of anesthetic in brain cells, which is closely related to the depth of anesthesia in the living body. In FIGS. 3 (a) and 3 (b), the infrared transmission signal SC and the infrared transmission signal SM are flat during the inspiration period, but this is due to the inside of the pipe 13 from which the ventilator 12 exclusively delivers exhaled air. This is because the end exhaled air is staying at. When the carbon dioxide sensor 16 and the anesthetic concentration sensor 18 are provided in the pipe 11, the gate circuit 52 is opened only at the end of the expiratory period as shown by the broken line in (d) of 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 3% 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. 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 rate control valve 74, the concentration of the inhaled anesthetic in the inspiration is adjusted. In this example, sevoflurane is used as the inhalation anesthetic.

This sevoflurane is shown below.

Chemical formula: CH ₂ -O-CH (CH ₃ ) ₂ Chemical name: fluoromethyl-1,1,1,3,3,3-hexafluoroisoproph
yl 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 its 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).

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 tidal 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.

In the anesthesia depth automatic control device configured as described above, since the concentration of the inhaled anesthetic contained in the end tidal breath of the patient 10 is used as the information regarding the anesthesia depth of the patient 10, it is more accurate than the conventional one. You can grasp the depth of anesthesia. 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, circulation control becomes remarkable, and when the depth of anesthesia is monitored by the blood pressure value, 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. However, 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.

Further, according to the above-mentioned embodiment, the inhalation anesthetic concentration in the end tidal breath is detected at the time when the concentration of carbon dioxide gas in the tidal breath becomes the highest peak, so regardless of the concentration of the inhalation anesthetic mixed in the inspiration, You can know the depth of anesthesia accurately. That is, when the anesthesia depth becomes too deep relative to the target value in the automatic control system for keeping the anesthesia depth constant and the concentration of the inhaled anesthetic agent mixed in the inspiration is reduced 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.

Next, another embodiment of the present invention will be described. In the following description, the same parts as those in the above-described embodiment will be designated by the same reference numerals and the description thereof will be omitted.

As shown in FIG. 6, various alarm devices such as an exhaled carbon dioxide concentration alarm device 86 and an inspiratory oxygen concentration alarm device 88 may be installed to further enhance the safety during operation of the automatic anesthesia depth control device. it can. That is, the breath carbon dioxide concentration alarm device 86 detects the highest peak value of the carbon dioxide concentration based on the signal from the carbon dioxide sensor 16, that is, the actual carbon dioxide concentration of the end tidal breath, and the carbon dioxide concentration is preset. When it goes out of the allowable range, an alarm is output by an electric signal, a sound signal, or an optical signal in order to notify the abnormality. The allowable range is, for example, 3
Is set within 5%. In addition, the inspiratory oxygen concentration alarm device 88 is configured to exclusively inhale the inspiratory air from the anesthetic mixture device 62 by a ventilator.
It is attached to the pipe 15 leading to 12, and detects the oxygen gas concentration contained in the intake air, and when the oxygen gas concentration deviates from the preset allowable range, an electric signal and a sound signal to notify the abnormality. Alternatively, an alarm is output by an optical signal.

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

For example, the breathing controller 14 and the anesthesia depth controller 58 in the above-described embodiments can be configured by so-called microcomputers. The gate circuit 52 in the anesthetic concentration sensor 18 is also composed of a microcomputer. In this case, as shown in FIG. 7, the infrared transmission signal SC is directly supplied to the anesthesia depth controller 58.

Further, the anesthetic concentration sensor 18 described above is the carbon dioxide gas sensor 16
It is configured to detect the inhaled anesthetic concentration in the end tidal breath based on the infrared transmission signal SC supplied from
It may be configured to detect the inhaled anesthetic concentration in the end tidal breath in synchronization with the minimum timing of the chest impedance detected by the electrode attached to the chest of the patient 10, and output from the ventilator 12. The end of the exhalation signal or the start of the inspiration signal may be used as a trigger to detect the inhaled anesthetic concentration in the end exhalation. Also, the ventilator 12
It is also possible to use the control signal or drive signal supplied from the respiratory controller 14 or the drive circuit 84 to the ventilator 12 in place of the expiratory signal or inspiratory signal output from the ventilator.

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.

If the blood / gas partition coefficient at 37 ° C is 1 or less,
Gaseous inhalation anesthetics may be used. In this case, the inhalation anesthetic vaporizer 76 of FIG. 5 becomes unnecessary.

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 one embodiment of the present invention, and the present invention can be variously modified without departing from the spirit thereof.

BRIEF DESCRIPTION OF THE 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 and 7 are views corresponding to FIG. 1 showing other embodiments of the present invention. 18: Anesthetic concentration sensor (anesthetic concentration detector) 56: Anesthesia depth setting device 58: Anesthesia depth controller (regulator) 62: Anesthetic mixing device

Claims (1)

[Claims] 1. An anesthesia depth automatic control device for adjusting the anesthesia depth of a living body to a constant level, and an anesthetic mixing device for mixing an inhaled anesthetic having a blood / gas partition coefficient of 1 or less into the inspiration of the living body. An anesthetic concentration detector for detecting the concentration of the inhaled anesthetic contained in end tidal breath of a living body; an anesthesia depth setting device for presetting anesthesia depth; and an inhaled anesthetic concentration contained in the end tidal breath An anesthesia depth setting device so that the value is preset by the anesthesia depth setting device, and an adjusting device for adjusting the inhalation anesthetic mixing ratio mixed into the inspiration by the anesthetic mixing device. Automatic control device.