FI64281B - MAETNINGS- OCH OEVERVAKNINGSSYSTEM - Google Patents

Abstract

A system for monitoring a patient's condition during anaesthesia includes electrode means 1 for detecting bioelectrical signals containing the spontaneous EMG activity of the patient, means 2 for amplifying these signals, means 3, 6 for distinguishing the spontaneous EMG component signals from said signals and for suitably quantifying them e.g. logarithmically as well as separate means 14, 15 for simultaneously measuring the patient's neuromuscular blockage by stimulating a motor nerve by means of electrical impulses and by measuring the muscular reaction by means of EMG. The EGG and EMG signals may be separated from the signals from the electrodes 1 by filtering. Said quantities are recorded and displayed on real-time basis so that the output information of said spontaneous EMG and that of the muscular paralysation measured by stimulation are displayed by a common display unit 10. <IMAGE>

Description

64281

MEASUREMENT AND MONITORING SYSTEM - MÄTNINGS- OCH ÖVERVAKNINGS-SYSTEM

The invention relates to a measuring and monitoring system for monitoring and recording the condition of a patient, especially during anesthesia in surgical operations.

There are two main criteria for monitoring a patient during surgery: on the other hand, care must be taken to ensure that:. the depth of the patient's anesthesia and neuromuscular blockade are sufficient to allow surgical or similar procedures to be performed; on the other hand, care must be taken to ensure that the patient's paralysis and anesthetic condition do not become too deep, thereby endangering the patient's permanent unconsciousness. It will be appreciated that the more and more information 15 is obtained which is as correlated as possible with the patient's anesthetic condition and muscle relaxation, and the clearer and easier to interpret that information, the more reliable estimates can be made and the action required.

20 Traditionally, the depth of anesthesia in a patient is monitored mainly by monitoring the patient's blood pressure, pulse, electrocardiogram, respiration, and eyelid reflexes.

One problem with these variables is that they do not allow universal conclusions to be drawn, but the evaluation depends on which anesthetic and paralyzing agents are used in each case. In addition, several factors can modify these parameters. These include, for example, possible premedication, patient's illness, age and general condition, location and amount of surgical stimulation, interaction of various anesthetic and paralyzing agents, body temperature, blood i i

partial pressure of carbon dioxide (1 ^ 002 ^ Difficulty is also relative

changes in these variables for different dosages of anesthetics and paralyzing agents. ; 1> 6 4 2 8 i

It is also known to assess the depth of anesthesia by monitoring EEG waves (electroencephalogram) representing the electrical activity of the brain to monitor the electrical activity of the patient's brain. Based on this, a team of researchers 5 from Duke University Medical Center (Durham, North Carolina, USA) has proposed a way to substantially simplify the basic patient information observed and recorded that is important for monitoring during anesthesia. Since the EEG authentication recorded from the patient's skull area is often mixed with 10 muscle functions, it was assumed that in addition to EEG monitoring with a plotter, the existing EMG activity (electromyogram) representing muscle electrical activity could be used and recorded, which is later used. appointment-15 spontaneous EMG. Based on the findings of the research team, EMG monitoring can be advantageously used to show adequate relaxation of the patient, as the registered EMG reliably tells the patient's own perception of relaxation, regardless of the observation ability of the external observer.

20 If, in connection with monitoring, it is found that the relaxation of the patient's EMG activity is not sufficient for eg surgical procedures, the matter can be remedied by giving the patient additional either paralyzing agents or an anesthetic. EEG monitoring 25, in turn, can be used to monitor the depth of the patient's anesthetic condition. (References: DA Davis, FF Klein, M, Harmel, L. Burton, L. Dowell: The Electroencephalomyogram, Quantitation of Depth of Anesthesia, Relaxation and Paralysis, American Society of Anesthesiologist.?. San 30 Francisco, October 20-25, 1979; MH Harmel, FF Klein DA Davis: The EEMG - A Practical Index of Cortial Activity and Muscular Relaxation, Acta Anesthesiology Scandinavica.

1978, Appendix 70, p. 97 - 102). ! i i) 3 64281

On the other hand, it has been found (B.R. Fink: Electromyography in General Anesthesia, British Journal of Anesthesia, 1961, 33, pp. 555-559) that abdominal muscle activity tends to increase upon surgical stimulation and decrease under the influence of anesthetics and muscle relaxants. The said group of researchers has also found that facial EMG provides information about the patient's general state of activity and represents a combination of the following parameters that affect the EMG signal: anesthesia depth 2. neuromuscular blockade 3. pain sensations. Thus, in summary, when this spontaneous EMG during surgical procedures is sufficiently low, the depth of anesthesia and muscle paralysis can be considered sufficient in most cases. Similarly, an increase in the amplitude of the spontaneous EMG signal during the surgical operation gives rise to a Hue. In this case, however, it is difficult to interpret which of the above parameters causes this increase and whether the patient should therefore be given more anesthetic, paralyzing agents or analgesics and how much.

20

The EEG / EMG analyzer based on the above has been implemented by the above-mentioned research group by measuring and processing the signals and printing with a digital voltmeter and plotter the average frequency 25 of the EEG signal and the average rectified amplitude of the EEG and EMG signal. From the user's point of view, the solution is not very illustrative and a particular difficulty is tracking and comparing the history of printed quantities.

30 Instead, quite sophisticated registration and printing solutions have been developed for EEG waves alone.

A known EEG wave monitoring system is disclosed in U.S. Patent No. 4,215,697. According to this solution, the amplitude or power and frequency distribution of the EEG signal 35 recorded from the patient's skull as a function of time is plotted on a 3-dimensional video monitor as a continuously propagating diagram * 4 64281, whereby in addition to real-time information, the monitor can view part of the EEG signal history. In another known EEG monitoring system, the video monitor, in turn, displays the frequency spectrum of the EEG amplitude 5 or power in a second time-describing dimension as continuously propagating dot rows, with the latest dot row depicting real time. The amplitude or power intensity itself is described solely by the relative brightness of the spots. These known systems offer a much more illustrative monitoring solution than the EEG curve obtained with a simple plotter. However, these solutions are quite complicated and expensive and are ill-suited for simultaneous printing of several signals 3a for monitoring.

15

The object of the invention is to provide a new improved patient monitoring system, in which the shortcomings of the prior art have been eliminated and by means of which more reliable information about the anesthetic condition and paralysis of the patient is obtained, presented as clearly as possible.

It is also an object of the invention to provide a user-friendly display for determinable sig-25s describing the anesthetic condition and paralysis of a patient so that complementary and explanatory quantities can be easily compared. It is a further object of the invention to provide an analog display for these quantities so that, on the one hand, the real-time value of the quantities 30 and, on the other hand, the history can be monitored. At the same time, it is also an object to provide an advantageous display of the use of memory and memory media. Other objects and advantages of the invention will become apparent from the following.

The objects of the invention are achieved as specified in claim 1 and the subclaims. According to the invention, during anesthesia of a patient, the anesthetist can continuously monitor and compare spontaneous EMG measured and determined from the patient on the one hand and muscle paralysis on the other hand, which helps him to distinguish between Here, the compactness and real-time nature of the display are important, as wake-up responses are rapid phenomena. If the electrodes are placed in the area of the patient's skull, neck and / or neck, the same electrodes can be used to advantageously monitor the electrical activity (EEG) of the patient's brain and thereby monitor that the patient's anesthetic state is not deep. Thus, spontaneous EMG, given the degree of muscle paralysis, warns anesthesiology of awakening responses, i.e., too light anesthesia, and on the other hand, the EEG warns of metabolic disorders in the brain associated with too deep anesthesia. In addition to real-time information, the display device can also advantageously display a considerable part of the history of registration events at the same time. By selecting a fairly wide band for EMG waves, the reliability of EMG information can be improved, as EMG waves occur over a wide frequency range. Since, on the other hand, it is important whether EMG activity occurs at all and not at what frequency and at what absolute amplitude or power, the bar graph according to the invention and in particular the logarithmization of the values to be printed give; as clear a picture as possible of the patient's activity.

A logarithmic display is also advantageous for the amol-30 or power of EEG waves, as the level of EEG waves decreases substantially as a result of anesthesia, in which case it is important to detect relative changes in EEG activity rather than absolute values of signal peaks. observation. j t i »t k f i * t 6 64281 EEG waves provide a fairly good indicator of a patient's anesthetic status as noted above. The preferred indicator for monitoring is obtained specifically from the possible simultaneous significant decrease in the values of F.EG amplitude or power and EEG center frequency. In practice, an anesthesiologist or similar person performing anesthetic monitoring of a patient in an operating room usually also has other tasks such as monitoring heart function, blood pressure, etc., not to mention the actual administration of anesthetics, paralyzing agents to the patient. In the system according to the invention, it is advantageous to combine the monitoring with an automatic alarm by selecting a suitable limit value 15 for the sum of the values representing the quantities in question. By providing: also for the monitoring of spontaneous EMG signals, the alarm function, by means of which the patient shows too little relaxation, for example for surgical procedures, is freed from uninterrupted monitoring of the display devices.

20

The invention will now be described in more detail with reference to the accompanying drawing, the only figure of which shows a block diagram of a measuring and monitoring system according to the invention.

25 According to the drawing, patient P's cranial bioelectric

activity is detected by detectors 1. Isolated I

the signal amplified in the preamplifier amplifier 2 is fed through the band determination means 3 and 4 to separate the EEG and EMG areas. In reality, the areas overlap f 30 to some extent. Extent of information to be monitored-! However, it is perfectly adequate and simpler for signal processing to completely separate the areas to be analyzed, for example by selecting 1 to 40 Hz for the EEG band, 2 to 25 Hz for in practice, j 35 for 60 and 500 to 500 Hz for the EMG band, 65 - 350 Hz.

64281; 7

One factor influencing the choice of bands is that because EMG waves can be very weak, network interference must be removed before analysis. With a mains frequency of 50 Hz (60 Hz), the selected EEG regions can directly get rid of the basic interference frequency and its harmonics.

Elimination of network interference from the EMG signal component; takes place by means of a filter arrangement 5, which can advantageously be implemented, for example, in the manner described in FI patent application no. 811941 and 10. In this case, the EMG signal component is displayed! by taking the paths and averaging the samples, the basic interference frequency and its odd ones are filtered; harmonics while the signal folds to frequencies lower than the fundamental interference frequency. In this case, the even har-15 multiples can be simply filtered out with a high-pass filter. Said signal folding is not detrimental to monitoring in this case, because only the amplitude or power is determined from the EMG signal component.

After the network interference elimination, the determination of the amplitude or power of the EMG signal component and the logarithmization of the values are provided by means 6 known per se. Correspondingly, the means 7 determine the amplitude or power of the EEG signal component and also perform the logarithmization of the values. Intermediate 25 determines the center frequency of the EEG signal component. :

The processor unit 9 is arranged to take samples preferably representing successive time periods of the same length continuously; from the newly determined quantities and to process the samples in this way! j 30 that they can be displayed on a video monitor or similar display device j 10 as a continuously advancing, large-scale bar graph- i As an integral part of the system, the patient is measured above; independent of the EMG and EEG signals described, neuromuscular blockade. This can take place in a unit 15 known per se, in which case the nerve stimulator 15b gives successive electrical pulses at electrodes 14b in repeated periods. For example, four pulses per second can be given; i

J

♦ β 64281 every ("Train-of-four"), which is repeated every 10 - 00 s. The muscle response is recorded as a completely separate EMG amplitude measurement from the electrodes 14a by the detector and amplifier means 15a as described above for the spontaneous EMG measurement.

Electrode 14a is a reference electrode.

The processor 9 controls the operation of the means 15 and modifies the obtained information to be displayed on the video monitor 10. The display can preferably be arranged so that each pulse 10 corresponds to its own bar representing the measured EMG response, whereby the trend of the patient's muscle paralysis is clearly visible.

Essential for interpretation is, on the one hand, the length of the column representing the remaining muscle strength and, on the other hand, the ratio of the first and last columns of the same period, which describes 15 degrees of muscle strength reduction during repeated stimulation. With regard to the practical implementation of muscle paralysis measurement, we refer by way of example to the following articles: Lam, H.S., Cass, N.M. and Ng, R.C. (1981).

Electromyographic monitoring of Neuromuscular block. Br. J.

20 Anaesth., 53, 1351. Lam, H.S., Morgan, D.L., and Lampard, D.G. (1979, January). Derivation of reliable electromyograms and their relation to tension in mammalian skeletal muscles during synchronous stimulation. EEG Clin. Neurophysiol., 46, 72? Ali, H.H., and Savarese, J.J. (1976) 25 Monitoring of Neuromuscular function. Anesthesiology, 45, 216. Muscle paralysis measured separately in this way can be used to interpret what is primarily due to the increase in spontaneous EMG activity measured from the patient's face. inadequate paraysis, resulting in insufficient depth of anesthesia, as EMG activity due to pain stimulation! can be monitored by monitoring the surgical procedure itself! measures.

The system also includes memory means 11 for displaying in-35 information and for storing the displayed information so that any part of the history of the registered signal component can be displayed on a video monitor if desired.

9 64281

When the screen has entered the direction of the time axis, it can be filled, for example, by moving the histograms back 2/3 on the time axis. Thus, if the time axis represents, for example, a 30-minute period, then the last part of the diagram representing 10 5 minutes moves to the beginning of the time axis for the first 10-minute period. It should be noted that for practical reasons, a bar graph representing muscle relaxation may have a different time scale than the other bar graphs mentioned.

In displays representing 10 EEG and spontaneous EMG, each bar may preferably correspond to an average measured and calculated over a period of 10 seconds. If desired, the last column can be updated, for example, every second, in which case 15 practically real-time information is obtained continuously.

Such an arrangement is very advantageous for the memory means, i.e. space-saving. A bar representing real-time information can also be placed on the rest of the bar graph; from which slightly apart as shown in the drawing. Of course, a similar arrangement can also be applied to the recording of muscle relaxation, for example by measuring this period of four pulses more frequently than every minute, whereby these intermediate prints better represent real time.

25

The system can also advantageously be provided with alarm devices 12 which, under the control of the processor unit 9, automatically give or will give an alarm, for example an audible or visual signal, when one of the monitored quantities falls below / exceeds certain limit values.

In connection with EEG monitoring, the alarm can advantageously be arranged to occur when the frequency and amplitude / power values simultaneously fall below certain limit values. With the monitor, the alarm limit can be illustrated. with a common, certain [35 lowest length of the bars indicating the quantities, which may, if desired, be marked on the display! displayed on the implement. This alarm indicates the excessive depth of the anesthetic condition of patient J. ‘Il i l’ · »10 64281

Similarly, spontaneous EMG monitoring may provide a particular mode of alarm, for example, when the patient's anesthetic status and relaxation are sufficient for surgical procedures 5, and may provide an alarm if EMG activity above a certain threshold indicates that: that the anesthetic condition of the patient is inadequate.

If desired, the quantities can also be printed with their real-time value, alarm limit value, etc. digitally as shown in the drawing.

The invention is not limited to the embodiment shown, but several variations of the invention are conceivable within the scope of the appended claims.

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Claims (14)

A measuring and monitoring system for monitoring and recording a patient's condition, in particular during anesthesia 5 in surgical operations, characterized by a combination of electrode means (1) for detecting and detecting bioelectrical signals containing spontaneous EMG activity in the patient's skull, neck and / or neck, means (2, 10) for amplifying said signals, means (2, 6) for separating the EMG component signals from the received signals and quantifying them as desired, and means (9) for processing the true signal information, the system further comprising means (14, 15) for monitoring the patient's neuromuscular to measure the blockade separately, substantially simultaneously with said spontaneous EMG activity in a manner known per se by stimulating a muscle nerve with electrical impulses and measuring the muscle response, for example by means of EMG 20, and that said, determined quantities are in order tty to be recorded and displayed on displays in substantially real time, preferably such that said spontaneous EMG and said measured linen paralysis of the stimuli are printed on a common display device-25a (10). 1 1 64281 A system according to claim 1, characterized in that said electrode means (1)! is also arranged to detect the patient's EEG signals,! And means (4, 7, 8) for separating the EEG components from said bioelectric signals and quantifying them as desired. ; ί A system according to claim 1 or 2, characterized in that said components of the EEG and EMG signals are arranged to be distinguishable from each other by means of band determination means such that a band i to 40 Hz is arranged to be selectable for said EEG component signal. preferably 2-25 Hz, and that a band of 60 to 500 Hz, preferably 65 to 350 Hz, is provided for said fi 12 64281 EMG component signal. A system according to any one of the preceding claims, characterized in that power values are arranged to be displayed on said EMG signal component, and in that the system comprises filter means (5) for said EMG signal component arranged to filter out the fundamental frequency of the electrical network and all its 10 harmonic frequencies. A system according to any one of claims 2, 3 or 4, characterized in that amplitude or power and frequency values are arranged to be determined from said EEG signal component. System according to one of the preceding claims, characterized in that the determined quantities are arranged to be displayed simultaneously as an analog, large-scale histegram 20 in the form of a displaceable 2-dimensional symbol sequence, one dimension arranged to indicate a quantized value and another dimension consistent with the symbol sequence direction. time. A system according to any one of claims 2, 3, 4, 5 or 6, characterized in that said quantized EEG and EMG signal components and representative analog »symbolic are arranged to form a bar graph thus; that the bars of each desired quantity are arranged to represent averages representative of the selected time periods, and that the bar graph further comprises a bar arranged! to indicate a large real-time value. f i A system according to any one of claims 5, 6 or 7, characterized in that the display of said EEG signal is arranged such that analog bars representing power and frequency values are arranged to indicate opposite | f * 1 3 64281 directions while their O-quantities are at least substantially arranged to abut each other, for example directly or via a narrow intermediate zone. A system according to claim 8, characterized in that it comprises alarm devices (12), for example for giving an audible or visual signal, arranged to be activated when a common bulb indicating the real value of the columns representing said EEG power and frequency values falls below a selected limit. value. System according to one of Claims 4, 5, 6, 7, 8 or 9, characterized in that it comprises alarm devices (12) which are arranged to be activated by an EMG signal component when the power values are above a certain limit value. System according to one of the preceding claims, characterized in that a so-called 'Train-of-four' stimulation, in which the nerve stimulator delivers four separated electrical pulses at short intervals at repeated intervals, and that the measured EMG signal representing the electrical response of the muscle is arranged to be displayed so that each electrical pulse corresponds to its own bar, preferably indicating 25 integrated values of the measured EMG signal for a much shorter time interval than the mutual output interval of said four pulses. A system according to any one of the preceding claims, characterized in that it comprises an analog-to-digital converter and memory means (11) for storing the displayed information in digital form so that the desired part of the history of the detected signal can be re-visualized by said display device. j i i System according to one of the preceding claims, characterized in that it comprises means (6, 7, 8) for printing the amplitude or power values of the at least one component signal as logarithmic values. : [»14 64281