CA1199846A - Patient monitoring apparatus - Google Patents
Patient monitoring apparatusInfo
- Publication number
- CA1199846A CA1199846A CA000472073A CA472073A CA1199846A CA 1199846 A CA1199846 A CA 1199846A CA 000472073 A CA000472073 A CA 000472073A CA 472073 A CA472073 A CA 472073A CA 1199846 A CA1199846 A CA 1199846A
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- Prior art keywords
- probe
- balloon
- oesophagus
- patient
- pressure
- Prior art date
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Abstract
ABSTRACT OF THE DISCLOSURE
An elongate probe for measuring oesophogeal contrac-tions and useful in a patient monitoring apparatus which generates an output indicative of the depth of the anaes-thesia of a patient, is described. In one embodiment, the probe has a distal end adapted to pass downwardly through the oesophagus of the patient and a proximal end adapted to lie externally of the mouth of the patient.
The probe includes stimulating means adapted in use to lie within the oesophagus of a patient and operable by means of external to the patient for stimulating the oesophagus, to cause contractions therein. Pressure sensing means adapted in use to lie within the oesophagus of the patient enables the measurement of pressure within the oesophagus, thereby to sense contractions of the oesophagus .
An elongate probe for measuring oesophogeal contrac-tions and useful in a patient monitoring apparatus which generates an output indicative of the depth of the anaes-thesia of a patient, is described. In one embodiment, the probe has a distal end adapted to pass downwardly through the oesophagus of the patient and a proximal end adapted to lie externally of the mouth of the patient.
The probe includes stimulating means adapted in use to lie within the oesophagus of a patient and operable by means of external to the patient for stimulating the oesophagus, to cause contractions therein. Pressure sensing means adapted in use to lie within the oesophagus of the patient enables the measurement of pressure within the oesophagus, thereby to sense contractions of the oesophagus .
Description
PATIENT ~ONITORING EQUIPMENT
This invention relates to patient monitoring equipment, It has application in monitoring the depth 05 oi anaesthesia o~ patients to whom anaesthetic or sedatlve drugs are administered. The term anaesthesia is used herein in its broadest sense and is intended to include not only anaesthesia for surgery, but also ~he lighter levels o~ anaesthesia or sedation used in ~ritically ill patients receiving intensive care. The term anaesthetic is to be understood accordingly.
This application is a division of our copending Cana-dian patent application Serial No. 388,712 filed October 26, 1981.
The response of individual patients to drugs is highly variable~ Especially in the case of anaes-thetic drugs an anaesthetlst is required to employ a considerable degree of clinical judgement in order to obtain an optimum effect~ Clinical anaesthesia is not an "on-off" state but a state of unconsciousness and variable reflex suppression produced by one or more drugs. It is traditional to describe the degree of refle~ suppression as the depth of anaesthesia. At present the depth of anaesthesia is judged by the ch~nge in various clinical slgns produced ln response to surglc~l stimulus. It would be o~ great assistance 1~ some obJectlve ln~ormatlon were av~ ble l~dlcatin~ the depth o~ annesthesia. Attempts have b~en made to us~ indirect me~surement~ o~ ~ patient's ~,, vltal physiologlcal functions such as he~rt rate, blood pressure and electroencephalogram (EEG) wavaforms to lndicate depth of anaesthesia. No one of these measurements alone has proved to be a 05 su~lclently reliable lndex of anaesthesiaO
An artlcle by P. Suppan in the Bri~ish Journal of Anaesthesia, (1972~ 44, p.l263 describes the use of pulse rate as an indicator of depth of anaesthesia, and describes furthermore the use of a feed-back system to automatically control anaesthetic administration. Tbe article also describes the possibility of using blood pressure as an indicator of the depth of anaest-hesia, but there is no suggestion of the combined use of the parameters, or any suggestlon that combining two or more measurements to produce a "score" can provide a more reliable indication of depth of anaesthesia.
~ . Dubuis, D.E. Scott, and T.M. Save~e, in an article in Annals Anaesthesia, France (1979) 3, p215 describe the use of EEG as an indicator of the after ffects of anaesthesia.
Electronically processed EEG signals have been employed to monitor the level of electrical activity in the braln during anaesthesia. A review of this and otber applications o~ EEG monitoring is given in Nonltorlng Cerebral Function ~author P~F. Prior, X
published by Elsevoir (North-Holland Biomedical Press, 1979, Amsterdam).
Finally J.S. Stewart in The Lancet (1969) 1, pl305 describes a monitoring system for drawing the 05 attention o~ a clinician to a deteriorating condition o~ a patient, using a combination of various parameters, such as heart rate, blood pressure, and o~ygen tension. There is, however, no suggestion in the Stewart article of the use of a similar system to measure depth of anaesthesia.
We have dlscovered that the muscular activity in the oesophagus is related to the depth o~ anaesthesia.
During light anaesthesia there is a great deal of smooth muscle activity in the form of periodic contractions. During deep anaesthesia there is little oesopha~eal smooth muscle activity. We h~ve consis-tently observed this relationship between oesophageal activity and depth of anaesthesia with most common anaesthetic agents. Changes in oesophageal muscle activity cause corresponding changes in intra-lumenal oesophageal pressure. Thus, by insertion o~ a balloon-type cathetar, or some other suita~le pressure probe, into the oesophagus, and me~suring the internal pres~ure ln the oesophagus, it ls possible to obtaln an indication oi the depth of anaesthesia.
The pressure changes produced by oesophageal contraction generally last 2 - 4 seconds and occur at frequencies of up to 4 or 5 per minute during light anaesthesia. Occasionally there are short periods of 05 rapid contractions at rates of up to 15 per minute accompanied by high resting pressures between contrac-tions.
Oesophageal activity has in the past been observed for a variety of purposes, for example N.E.
Leatherman in an article in Critical Care Medicine (19?8) Vol 6, No 3 pl89 describes the use of an oesophageal balloon for measuring intra-pleural pressure in the monitoring of acutely ill patients.
However, we are not aware of any proposals for using 15 -measurements of oesophageal activity to monitor depth of anaesthesia.
We have also discovered that, whether or not oesophageal contractions are used as a measure of the degree of anaesthesia, increased reliabilitY in the quantification by the anaesthetist of depth of anaesthesia can be obtained if a plurality of di~ferent bodily ~unctions are observed, and a score value assigned to each in accordance ~ith certain parameters. The scors values may then be summed to produce a total score indicative o~ the degree of anaesthesia oi' the patlent.
%
In accordance with one aspec-t of -the method of moni-toring anaesthesia defined in the parent appllcation, signals are produced indicative of the contractions in the oesophagus of a patient, and an output is derived from the signal indicative of the degree of anaesthesia of the patien-t.
According to a first aspect of the invention defined in the parent application, there is provided patient monitoring apparatus, comprising a sensor for providing signals indicative of smooth muscle contractions in the oesopnagus of a patient, and means for deriving from the said signals an output indicative of the depth of anaes-thesia of the patient.
Preferabl~, the output is clerived from the rate of generation of signals produced by oesophageal contraction.
Accordingly, in one embodiment of this aspect of the invention of the parent application, there is provided patient monitoring apparatus comprising a sensor for producing signals indicative of smooth muscle contractions in the oesophagus of a patient, and means for producing an output indicative of the rate of occurrence of such contractions. Alternatively, an output may be derived from the amplitude of such signals.
The changes in pressure that occur and which are picked up by the sensor will be not only pressure changes due to oesophageal contraction but also pressure changes resulting from movement of the heart adjacent to the oesophagus and changes in intrathoracic pressure due to ventilation of the lungs. The pressure changes produced by ventilatlon and movement o-E the heart are rela-tively small and are usually less than 20 mm Hg, typically abou-t 10 mm Hg, when measured with a balloon--type catheter of the type hereinafter described. In contrast oesophageal contractions produce changes in intra-lumenal pressure which may be as high as 100 mm Hg ~nd are usually in e~cess of 20 mm Hg. In order therefore to eliminate signals arising out oi activity not due ~o oesophageal contractions it is desirable to set a threshold value of pressure below which no signals are utilised for monitoring purposes. This can be done by providing the apparatus with discriminating means for rejecting signals of less than a desired threshold magnitude.
The threshold magnitude is preferably substantially greater than, for exampl~- twice as great as the magnitude of signals produced by forced ventilation of the lungs of the patient.
In a ~urther embodiment of this aspec-t of the invention of the parent application, there is therefore provided patien-t monitoriny appara-tus, comprising a sensor for producing signals indicative of smooth muscle contractions in the oesophagus of a patient, and discriminating means for accepting only signals of greater than a predetermined magnitude.
Furt~ermore in order to ~inimise spurious signals arising ~rom irregularities in the pressure waveform, an inhibition period may be provided immediately following each contraction in excess of the threshold.
In the inhibition period no con~ractions are recognised. A convenient value for chreshold pressure is 20 - 25 mm Hg and for the inhibition period a time of from 5 to 10 seconds may be suitable.
The rate of generation of contraction signals can be derived from a measurement of the ti~e intervals between successive contractions. The contractions may not occur at regular intervals and a rate derived directl~ in this way would fluctuate frequently. A
measurement of such time interval could be stored and averaged to overcome this instability. A more stable and representative rate is ob-tained by providing means for counting the number of oesopha~eal contractions over a period of time and indicating the mean or a~erage rate. --_ In carrying out the invention of the parent applica-tion, therefore, it is convenient to make the period of time over which the contractions are averaged a moving and adjus-table time "window". A convenient value for such a time "window" is up to nine minutes, pre-ferably from 3 to 9 minutes.
It ls possible to provoke oesophageal contrac-tio~s. Thes~ provoked contractions are similar to sponta~eous contractions but can ~e provoked at a 25 depth oi anaesthesia su~lcient to suppress spontaneous contractions. As anaesthesia is deepened the oesophageal response to provocation diminishes~
Thus the provision of means for provoking oesophageal 1/~
contractions allows deeper levels of anaesthesia to be moni-tored.
According to yet a further embodiment of this aspect of the invention of the parent application, there is there-fore provided patient monitoring apparatus, comprising means for stimulating smooth muscle contractions in the oesophagus of a patient and a sensor for producing signals indicative of contractions in the oesophagus of the patient.
The amplitude of the provoked oesophageal response is, in part, related to the depth of anaes-thesia. Thus in addition to the rate of oesophageal contractions, the amplitude of the provoked response ma~ be used as a guide to the depth o~ anaesthesia.
Oesophageal co~tractions may be provoked by the 15 appllcatlon o~ a mechani~l or electrical stimulus to the oesophagus or contiguous structures for e~ample th~ pharyn~, lary~x or trachea. A convenlent me~ns of provo~lng oesophageal contractions is an air or llquid filled in~latable balloon inserted into the trachea or more preferably, the oesophagus.
Since the equipment described above provides an indication of the depth of anaesthesia it is possible to use the indicatlon obtained to control a drug delivery system to achieve a desired depth of anaes-thesia, >~
Anaes-thetic control equipment may comprise a sensor for providing signals indicative o-f contractions in the oesopha-gus of a patient, for example a probe adapted to be inserted into the oesophagus of the patient and means for controlling the delivery of anaesthetic drugs to the patient in accor-dance with a parameter of the signals so ob-tained to achieve a desired depth of anaesthesia.
A suitable parameter is the rate of generation of such signals, preferably averaged over a period of time, However, an amplitude measurement of such signals may be used, par~icularly where provoked conkractions are being measured~
It will be appreciated that the anaesthetic control equipment set out above operates as an lS automatic closed-loop control system.
As mentioned above ~e have also discovered that, whether or not oesophageal contractions are used as a measure of the degree of anaesthesia, increased reliability in the quantification by the an~esthetist o~ depth of anaesthesia can be obtained if a plural1ty o~ di~erent bodily functions are observed, and a score value assigned to each in accordance with certain parameters, the score values then being be summed to produce a total score indicative of the degree of anaesthesia of the patient.
According to a fur-ther aspect of the inven-tion defined in the parent application, there is provided a method of monitoring the degree of anaesthesia or sedation of a X
pa~ient, which method comprises assigni~g a score value to each of a plurality of diferent bodily functions, the said ~core values bein~ indicative o~ a depth of anaes-thesia or sedation, and summing the score values to obtain a total score indlca~ive of the degree of anaes-thesia or sedation o~ the patlent.
The invention of the pare~t application also provides a patient monitoring appara-tus, which comprises means for assigning a score value to each of a plurality of differ-ent bodily ~unctions of a patient, the said score valuesbeing indicative of a depth of anaesthesia or sedation, means for summing the score values, and means ~or produ-cing an output ~rom the summed score values indicative of the amount of anaesthetic to be given to the patien~.
Means may be provided for measuring one or more of the said bodily functions and for automatically genera-ting a score value from the measured value. This is particularly suitable for func~ions such as heart rate and blood pressure. Alternatively the means ~or assigning a score value to a bodily function may take the form of a keypaA, for entering a score value in accordance with a clinical assessment of a selected bodily function. The apparatus of the invention preferably includes means for displaying the resultant score.
E~amples of bodily functions that may be measured are EEG activity, cardiac outpu and o~ygen consump~
tion. Specific cardlac function indices that may be measured include blood pressure (normally sys-tolic blood pressure, although diastolic or mean blood pressure may alternatlvely be used) and heart beat rate. ~unctions in which clinical assessments may be made and a score value assigned via ~he keypad are the degree o~ sweating and the formation of tears.
Values of bodily functlons which are readily measured by lnstruments, such as systollc blood pressure and heart bsat rate may of course be measured by conventional methods, and score values assigned using the keypad-Alternatively, or additionally to theabove-listed functions, other bodily functions may be measured or assessed.
We have ~ound that because the summed score value relates to a plurality o~ different bodily functions the score is a much more reliable indication of the depth of anaesthesia than measurement of any one individual function by itself.
Means may be included ~or recording the total score and if desired the individual score values. It may be convenient to record other associated informa-tion, ~or e~ample the time at which the measurements are takenO
l'he displayed score can be compared wi-th a desired score in a comparator to derive a score error and the rate of administration of appropriate drugs may then be determined in accordance with the score error to achieve a desired depth of an~esthesia. By providlng means for entering ~n initial rate of administration into the e~uipment and then modif~lng this rate by the score error a requlred rate of administratlon of a drug may be obtained, dlsplayed and automatlcally co~trolled.
As indicated above the score o~tained ma~ be used to automatically control the delivery of drugs to a patient.
It is desirable to provide a clock which provides control signals to the measuring means to update the score values at regular intervals and where on~ or mor~ score value asse~sments are included lt may be deslrable ~o include means for prompting the clinician or anaesthetist to enter his curren~ assessments.
In accordance with-o~e aspect of the invention of this application, there is provided an elongate probe for measur-ing oesophageal contractions, having a distal end adapted to pass downwardly through the oesophagus of the patient, and a proximal end adapted in use to lie externally of the mouth, the probe including stimulating means adapted in use to lie within the oesophagus of a patient and operable by means external to the patient for stimulating the oesophagus, to cause contractions therein, pressure sensing means adapted in use to lie within the oesophagus of the patient for enabling the measurement of pressure wi-thin the oesophagus, thereby t,o sense contractions of the oesophagus.
In accordance with a fur-ther aspect of the invention of this application, there is provided a probe for measuring oesophageal contractions, comprising an elongate body por-tion for insertion into the oesophagus and having at least first and second lumens sealed with respect to each other, the first lumen being in communication at its distal end with a sensing balloon -for sensing oesophageal pressure, and being provided at its proximal end with means for connection to a pressure measuring device, and -the second lumen being adapted to receive a fluid under pressure to sti~ulate the oesophagus to cause contractions therein.
A number of particularly preferred embodiments of the invention will now be described with reference to the accompanying drawings in which:-~ igure 1 illustrates a probe adapted to be inserted into the oesophagus together with associatedequipment;
Figure 2 illu~trates monitoring and control equipment suitable for use with the probe of Figure 1;
Figures 3 to 5b illustrate alternative construc-tions o~ oesophageal probes which may be used with the apparatus of Figure ~;
Flgure 6 shows a typical trace obtained with apparatufi a~ illustrated ln Figures 1 ~nd 2 sho~ing pro~oked oesophageal contractions;
Figure 7 is a block diagram of apparatus in accordance with the second aspect of the invention of the parent application;
Figure 8 illustrates yet a further alternative construction of an oesophageal probe, and Figure 9 is a block schematlc diagram o~ an elec~ronic circuit suitable for use with the probe of 05 Flgure 8.
Referring now to Figure 1 there is shown therein a probe which is adapted to be inserted into an oesophagus. The probe comprises a hollow flexible stem l which contains two passageways 2 and 3. At the end of the probe there is provided a balloon 4 which ls connected to passageway 2 and adjacent to balloon 4 ls a ~urther balloon 5 coupled to passageway 3.
BQ1100n 4 is liquid-filled and passageway ~ is coupled to a pressure transducer so that the external pressure applied to balloon 4 can be monitored. Balloon 5 is connected to passageway 3. A suitable length for stem 1 is about 100 cm while the total length of the two balloons 4 and 5 can be about 10 cms. The two balloons each have a ma~imum diameter of appro~imately
This invention relates to patient monitoring equipment, It has application in monitoring the depth 05 oi anaesthesia o~ patients to whom anaesthetic or sedatlve drugs are administered. The term anaesthesia is used herein in its broadest sense and is intended to include not only anaesthesia for surgery, but also ~he lighter levels o~ anaesthesia or sedation used in ~ritically ill patients receiving intensive care. The term anaesthetic is to be understood accordingly.
This application is a division of our copending Cana-dian patent application Serial No. 388,712 filed October 26, 1981.
The response of individual patients to drugs is highly variable~ Especially in the case of anaes-thetic drugs an anaesthetlst is required to employ a considerable degree of clinical judgement in order to obtain an optimum effect~ Clinical anaesthesia is not an "on-off" state but a state of unconsciousness and variable reflex suppression produced by one or more drugs. It is traditional to describe the degree of refle~ suppression as the depth of anaesthesia. At present the depth of anaesthesia is judged by the ch~nge in various clinical slgns produced ln response to surglc~l stimulus. It would be o~ great assistance 1~ some obJectlve ln~ormatlon were av~ ble l~dlcatin~ the depth o~ annesthesia. Attempts have b~en made to us~ indirect me~surement~ o~ ~ patient's ~,, vltal physiologlcal functions such as he~rt rate, blood pressure and electroencephalogram (EEG) wavaforms to lndicate depth of anaesthesia. No one of these measurements alone has proved to be a 05 su~lclently reliable lndex of anaesthesiaO
An artlcle by P. Suppan in the Bri~ish Journal of Anaesthesia, (1972~ 44, p.l263 describes the use of pulse rate as an indicator of depth of anaesthesia, and describes furthermore the use of a feed-back system to automatically control anaesthetic administration. Tbe article also describes the possibility of using blood pressure as an indicator of the depth of anaest-hesia, but there is no suggestion of the combined use of the parameters, or any suggestlon that combining two or more measurements to produce a "score" can provide a more reliable indication of depth of anaesthesia.
~ . Dubuis, D.E. Scott, and T.M. Save~e, in an article in Annals Anaesthesia, France (1979) 3, p215 describe the use of EEG as an indicator of the after ffects of anaesthesia.
Electronically processed EEG signals have been employed to monitor the level of electrical activity in the braln during anaesthesia. A review of this and otber applications o~ EEG monitoring is given in Nonltorlng Cerebral Function ~author P~F. Prior, X
published by Elsevoir (North-Holland Biomedical Press, 1979, Amsterdam).
Finally J.S. Stewart in The Lancet (1969) 1, pl305 describes a monitoring system for drawing the 05 attention o~ a clinician to a deteriorating condition o~ a patient, using a combination of various parameters, such as heart rate, blood pressure, and o~ygen tension. There is, however, no suggestion in the Stewart article of the use of a similar system to measure depth of anaesthesia.
We have dlscovered that the muscular activity in the oesophagus is related to the depth o~ anaesthesia.
During light anaesthesia there is a great deal of smooth muscle activity in the form of periodic contractions. During deep anaesthesia there is little oesopha~eal smooth muscle activity. We h~ve consis-tently observed this relationship between oesophageal activity and depth of anaesthesia with most common anaesthetic agents. Changes in oesophageal muscle activity cause corresponding changes in intra-lumenal oesophageal pressure. Thus, by insertion o~ a balloon-type cathetar, or some other suita~le pressure probe, into the oesophagus, and me~suring the internal pres~ure ln the oesophagus, it ls possible to obtaln an indication oi the depth of anaesthesia.
The pressure changes produced by oesophageal contraction generally last 2 - 4 seconds and occur at frequencies of up to 4 or 5 per minute during light anaesthesia. Occasionally there are short periods of 05 rapid contractions at rates of up to 15 per minute accompanied by high resting pressures between contrac-tions.
Oesophageal activity has in the past been observed for a variety of purposes, for example N.E.
Leatherman in an article in Critical Care Medicine (19?8) Vol 6, No 3 pl89 describes the use of an oesophageal balloon for measuring intra-pleural pressure in the monitoring of acutely ill patients.
However, we are not aware of any proposals for using 15 -measurements of oesophageal activity to monitor depth of anaesthesia.
We have also discovered that, whether or not oesophageal contractions are used as a measure of the degree of anaesthesia, increased reliabilitY in the quantification by the anaesthetist of depth of anaesthesia can be obtained if a plurality of di~ferent bodily ~unctions are observed, and a score value assigned to each in accordance ~ith certain parameters. The scors values may then be summed to produce a total score indicative o~ the degree of anaesthesia oi' the patlent.
%
In accordance with one aspec-t of -the method of moni-toring anaesthesia defined in the parent appllcation, signals are produced indicative of the contractions in the oesophagus of a patient, and an output is derived from the signal indicative of the degree of anaesthesia of the patien-t.
According to a first aspect of the invention defined in the parent application, there is provided patient monitoring apparatus, comprising a sensor for providing signals indicative of smooth muscle contractions in the oesopnagus of a patient, and means for deriving from the said signals an output indicative of the depth of anaes-thesia of the patient.
Preferabl~, the output is clerived from the rate of generation of signals produced by oesophageal contraction.
Accordingly, in one embodiment of this aspect of the invention of the parent application, there is provided patient monitoring apparatus comprising a sensor for producing signals indicative of smooth muscle contractions in the oesophagus of a patient, and means for producing an output indicative of the rate of occurrence of such contractions. Alternatively, an output may be derived from the amplitude of such signals.
The changes in pressure that occur and which are picked up by the sensor will be not only pressure changes due to oesophageal contraction but also pressure changes resulting from movement of the heart adjacent to the oesophagus and changes in intrathoracic pressure due to ventilation of the lungs. The pressure changes produced by ventilatlon and movement o-E the heart are rela-tively small and are usually less than 20 mm Hg, typically abou-t 10 mm Hg, when measured with a balloon--type catheter of the type hereinafter described. In contrast oesophageal contractions produce changes in intra-lumenal pressure which may be as high as 100 mm Hg ~nd are usually in e~cess of 20 mm Hg. In order therefore to eliminate signals arising out oi activity not due ~o oesophageal contractions it is desirable to set a threshold value of pressure below which no signals are utilised for monitoring purposes. This can be done by providing the apparatus with discriminating means for rejecting signals of less than a desired threshold magnitude.
The threshold magnitude is preferably substantially greater than, for exampl~- twice as great as the magnitude of signals produced by forced ventilation of the lungs of the patient.
In a ~urther embodiment of this aspec-t of the invention of the parent application, there is therefore provided patien-t monitoriny appara-tus, comprising a sensor for producing signals indicative of smooth muscle contractions in the oesophagus of a patient, and discriminating means for accepting only signals of greater than a predetermined magnitude.
Furt~ermore in order to ~inimise spurious signals arising ~rom irregularities in the pressure waveform, an inhibition period may be provided immediately following each contraction in excess of the threshold.
In the inhibition period no con~ractions are recognised. A convenient value for chreshold pressure is 20 - 25 mm Hg and for the inhibition period a time of from 5 to 10 seconds may be suitable.
The rate of generation of contraction signals can be derived from a measurement of the ti~e intervals between successive contractions. The contractions may not occur at regular intervals and a rate derived directl~ in this way would fluctuate frequently. A
measurement of such time interval could be stored and averaged to overcome this instability. A more stable and representative rate is ob-tained by providing means for counting the number of oesopha~eal contractions over a period of time and indicating the mean or a~erage rate. --_ In carrying out the invention of the parent applica-tion, therefore, it is convenient to make the period of time over which the contractions are averaged a moving and adjus-table time "window". A convenient value for such a time "window" is up to nine minutes, pre-ferably from 3 to 9 minutes.
It ls possible to provoke oesophageal contrac-tio~s. Thes~ provoked contractions are similar to sponta~eous contractions but can ~e provoked at a 25 depth oi anaesthesia su~lcient to suppress spontaneous contractions. As anaesthesia is deepened the oesophageal response to provocation diminishes~
Thus the provision of means for provoking oesophageal 1/~
contractions allows deeper levels of anaesthesia to be moni-tored.
According to yet a further embodiment of this aspect of the invention of the parent application, there is there-fore provided patient monitoring apparatus, comprising means for stimulating smooth muscle contractions in the oesophagus of a patient and a sensor for producing signals indicative of contractions in the oesophagus of the patient.
The amplitude of the provoked oesophageal response is, in part, related to the depth of anaes-thesia. Thus in addition to the rate of oesophageal contractions, the amplitude of the provoked response ma~ be used as a guide to the depth o~ anaesthesia.
Oesophageal co~tractions may be provoked by the 15 appllcatlon o~ a mechani~l or electrical stimulus to the oesophagus or contiguous structures for e~ample th~ pharyn~, lary~x or trachea. A convenlent me~ns of provo~lng oesophageal contractions is an air or llquid filled in~latable balloon inserted into the trachea or more preferably, the oesophagus.
Since the equipment described above provides an indication of the depth of anaesthesia it is possible to use the indicatlon obtained to control a drug delivery system to achieve a desired depth of anaes-thesia, >~
Anaes-thetic control equipment may comprise a sensor for providing signals indicative o-f contractions in the oesopha-gus of a patient, for example a probe adapted to be inserted into the oesophagus of the patient and means for controlling the delivery of anaesthetic drugs to the patient in accor-dance with a parameter of the signals so ob-tained to achieve a desired depth of anaesthesia.
A suitable parameter is the rate of generation of such signals, preferably averaged over a period of time, However, an amplitude measurement of such signals may be used, par~icularly where provoked conkractions are being measured~
It will be appreciated that the anaesthetic control equipment set out above operates as an lS automatic closed-loop control system.
As mentioned above ~e have also discovered that, whether or not oesophageal contractions are used as a measure of the degree of anaesthesia, increased reliability in the quantification by the an~esthetist o~ depth of anaesthesia can be obtained if a plural1ty o~ di~erent bodily functions are observed, and a score value assigned to each in accordance with certain parameters, the score values then being be summed to produce a total score indicative of the degree of anaesthesia of the patient.
According to a fur-ther aspect of the inven-tion defined in the parent application, there is provided a method of monitoring the degree of anaesthesia or sedation of a X
pa~ient, which method comprises assigni~g a score value to each of a plurality of diferent bodily functions, the said ~core values bein~ indicative o~ a depth of anaes-thesia or sedation, and summing the score values to obtain a total score indlca~ive of the degree of anaes-thesia or sedation o~ the patlent.
The invention of the pare~t application also provides a patient monitoring appara-tus, which comprises means for assigning a score value to each of a plurality of differ-ent bodily ~unctions of a patient, the said score valuesbeing indicative of a depth of anaesthesia or sedation, means for summing the score values, and means ~or produ-cing an output ~rom the summed score values indicative of the amount of anaesthetic to be given to the patien~.
Means may be provided for measuring one or more of the said bodily functions and for automatically genera-ting a score value from the measured value. This is particularly suitable for func~ions such as heart rate and blood pressure. Alternatively the means ~or assigning a score value to a bodily function may take the form of a keypaA, for entering a score value in accordance with a clinical assessment of a selected bodily function. The apparatus of the invention preferably includes means for displaying the resultant score.
E~amples of bodily functions that may be measured are EEG activity, cardiac outpu and o~ygen consump~
tion. Specific cardlac function indices that may be measured include blood pressure (normally sys-tolic blood pressure, although diastolic or mean blood pressure may alternatlvely be used) and heart beat rate. ~unctions in which clinical assessments may be made and a score value assigned via ~he keypad are the degree o~ sweating and the formation of tears.
Values of bodily functlons which are readily measured by lnstruments, such as systollc blood pressure and heart bsat rate may of course be measured by conventional methods, and score values assigned using the keypad-Alternatively, or additionally to theabove-listed functions, other bodily functions may be measured or assessed.
We have ~ound that because the summed score value relates to a plurality o~ different bodily functions the score is a much more reliable indication of the depth of anaesthesia than measurement of any one individual function by itself.
Means may be included ~or recording the total score and if desired the individual score values. It may be convenient to record other associated informa-tion, ~or e~ample the time at which the measurements are takenO
l'he displayed score can be compared wi-th a desired score in a comparator to derive a score error and the rate of administration of appropriate drugs may then be determined in accordance with the score error to achieve a desired depth of an~esthesia. By providlng means for entering ~n initial rate of administration into the e~uipment and then modif~lng this rate by the score error a requlred rate of administratlon of a drug may be obtained, dlsplayed and automatlcally co~trolled.
As indicated above the score o~tained ma~ be used to automatically control the delivery of drugs to a patient.
It is desirable to provide a clock which provides control signals to the measuring means to update the score values at regular intervals and where on~ or mor~ score value asse~sments are included lt may be deslrable ~o include means for prompting the clinician or anaesthetist to enter his curren~ assessments.
In accordance with-o~e aspect of the invention of this application, there is provided an elongate probe for measur-ing oesophageal contractions, having a distal end adapted to pass downwardly through the oesophagus of the patient, and a proximal end adapted in use to lie externally of the mouth, the probe including stimulating means adapted in use to lie within the oesophagus of a patient and operable by means external to the patient for stimulating the oesophagus, to cause contractions therein, pressure sensing means adapted in use to lie within the oesophagus of the patient for enabling the measurement of pressure wi-thin the oesophagus, thereby t,o sense contractions of the oesophagus.
In accordance with a fur-ther aspect of the invention of this application, there is provided a probe for measuring oesophageal contractions, comprising an elongate body por-tion for insertion into the oesophagus and having at least first and second lumens sealed with respect to each other, the first lumen being in communication at its distal end with a sensing balloon -for sensing oesophageal pressure, and being provided at its proximal end with means for connection to a pressure measuring device, and -the second lumen being adapted to receive a fluid under pressure to sti~ulate the oesophagus to cause contractions therein.
A number of particularly preferred embodiments of the invention will now be described with reference to the accompanying drawings in which:-~ igure 1 illustrates a probe adapted to be inserted into the oesophagus together with associatedequipment;
Figure 2 illu~trates monitoring and control equipment suitable for use with the probe of Figure 1;
Figures 3 to 5b illustrate alternative construc-tions o~ oesophageal probes which may be used with the apparatus of Figure ~;
Flgure 6 shows a typical trace obtained with apparatufi a~ illustrated ln Figures 1 ~nd 2 sho~ing pro~oked oesophageal contractions;
Figure 7 is a block diagram of apparatus in accordance with the second aspect of the invention of the parent application;
Figure 8 illustrates yet a further alternative construction of an oesophageal probe, and Figure 9 is a block schematlc diagram o~ an elec~ronic circuit suitable for use with the probe of 05 Flgure 8.
Referring now to Figure 1 there is shown therein a probe which is adapted to be inserted into an oesophagus. The probe comprises a hollow flexible stem l which contains two passageways 2 and 3. At the end of the probe there is provided a balloon 4 which ls connected to passageway 2 and adjacent to balloon 4 ls a ~urther balloon 5 coupled to passageway 3.
BQ1100n 4 is liquid-filled and passageway ~ is coupled to a pressure transducer so that the external pressure applied to balloon 4 can be monitored. Balloon 5 is connected to passageway 3. A suitable length for stem 1 is about 100 cm while the total length of the two balloons 4 and 5 can be about 10 cms. The two balloons each have a ma~imum diameter of appro~imately
2 cms.
Passageway 3 is connected to an air supply line 9. An air-pump 6 supplles a reservoir 7 ~hlcb ~eeds supply line ~ t~rough a valve 8. A pressure gauge 10 i~ coupled to reservolr 7. In an alternative and pre~erred embodiment, gauge 10 is coupled to line 9 so a3 ko measure directly the provoking pressure.
L~ ~
Reservoir 7 also has a regulating valve 11 which can be ad~usted to prevent excessive rise in ths pressure in reservoir 7. Valve 8 is controlled by a timing u~it 12.
05 In use of the equipment shown in ~igure 1 probe 1 is inserted into the oesophagus so that the balloon 4 is in the lower part of the oesophagus, in an adult, typically 35 cm from the incisor teeth, and the timing unit 12 functions to control valve 8 to connect reservoir 7 to intermittently inflate balloon 5. At the end o~ each inflation period valve 8 connects line ~ to a vent 13 to allow balloon 5 to deflate. With reservoir 7 having a volume of approximately 200 cc and being held at a pressure of around 200 mm Hg and with balloon 5 having an inflated volume of about 5 cc the opening of valve 8 will cause full and rapid e~pansion of balloon 5 to its maximum capacity. It is convenient to hold balloon 5 inflated for periods of 5 seconds or ~here- abouts with the intervals between inflations being in the range of 1 - 10 mins.
In order to safeguard against deleterious ef,t'ects on ~ patient arlslng out of rupture o~ halloon 5 it may be desirable to provide means for limi-ting the volume or rate o~ air~low out of reservoir 7.
2S second valve may be provided, operated by the timing unit 12, between the air pump 6 and the reservoir 7 and open when valve 8 is closed, to restore pressure in the reservoir 7 only when ~he reservoir is not directly connected to balloon 5.
Any contraction of the oesophagus which is either 05 spontaneous or else is trlggered by inflation of balloon 5 is monitored by liquid-filled balloon 4 and the pressure signal therefrom fed through passageway 2 to a pressure transducer (not shown).
The monitor balloon 4 described above is liquid filled, preferably with water. It is however possible to use an air or gas filled balloon for monitoring pur.poses al~hough in such cases there ~ay be a loss of fidelity in the recording of pressure amplitude.
Alternatively in place of a balloon a catheter tip 15 ~trarsducer can be inserted into the oesophagus in a so~t balloon sleeve, in the position of balloon 4 While a separate monitoring balloon 4 and provoking balloon 5 have been described with reference to Flgure 1 it is possible to replace the two balloons by a single balloon which fulfils both functions. In such a case a switching valve is required which normally co~nects the balloon to the pressure tr~nsducer but ~hich is switched to valve 8 whenever a provoking stimulus is called for by the timing unit ~-Timing unit 12 is optionally provided with an inhibit input along a line 14~ When an inhibit pulse is received timing unit 12 does not function for a set period thereafter so that inflation of provoking 05 balloon 5 is inhibited during that period. The inhibit pulses are derived from the pressure transducer 21 to which balloon 4 is coupled as shown in Figure 2. Use of the inhibit pulses ensures that when there are spontaneous contractions operation of the provoking balloon, which is unnecessary, is prevented. A further option provides for manual triggering o~ timing unit 12 to operate valve 8.
Figure 2 shows monitoring and control equipment in block diagrammatic form. The pressure signal obtained from the balloon 4 shown in Figure 1 is fed to a transducer 21 which provides an output si~nal of magnitude proportional to the amplitude o~ the pressure signal fed to it. Transducer 21 may include of~set and gain controls.
The output signal from transducer 21 includes not only ma~or signals derived from oesophageal contrac-tions but also other signal~ which arise from heartbeats and lung ventilation as well as other background sigllals lncluding noise. The output from transducer 21 ls applied to a filter 22 to remove low level background signals and thence to an adjustable _ 18 -threshold circuit 23 to block all remaining signals below a set level. Since the oesophageal con-tractions result in pressure signals of ~uch higher level of amplitude than signals from other sources the 05 setting of an appropriate threshold level in circuit 23 ensures that the output therefrom comprises signals due to the oesophageal contractions only.
The signals from circuit 23 are utilised to provide a count o~ events in a moving time "window".
The count is made in a timer/counter circuit 24 into which the desired lengths or duration of the time "window" is entered. Conveniently circuit 24 has a plurality of registers each of which records the inputs received from circuit 23 in a ii~ed time period (e.g. one minute) in succe~sion. The number o~ the most rece~tly ~illed registers that contribute their contents to the summation is determined by the length of the time "window". Thus for one minute registers and a time "window" o~ four minutes the four last-filled registers are summed and their sum is outputted. The above e~ample of a one minute time perlod and a time ~indow of four minutes is purely to illu~trate the manner of operatlon of circuit 24 and a dl~erent time period can be provided in the circuit and the length of the time "windo~l' may be adjustable ~or greater or smaller durations than the fi~ure quoted. The summation of the register contents may be ad~usted to bias the sum in favour of some part of the window~.
It can occur that contractions of the oesophagus 05 may be stimulated, for e~ample by mo~ement of the patient during an operation. The inclusion of signals due to such stimulation may give rise to misleading estimations of degree of anaesthesia. For this reason, it is preferable to provide as a function of the apparatus means for selectively rejecting any particular signal at the discretion of the operator, such that the particular signal does not contribute to the degree of anaes~hesia indicated.
The output from circult 24 is applied to an invert0r 25 to glve a rate of contraction and this rate is displayed in an analogue display 261 for e~ample as a bar of varying length. Alternatively or in addition it ls displayed in digital form in a digital display 270 It may be desired to have a visual record of oesophageal activity. A temporary record may be shown on a cathode ray tube or similar display, A permanent ~ecord may be obtained with a chart recorder 28 which is ~ed with the signal from transducer 21. Recorder 28 can also c~rr~ indications of the input pulses to timer/counter circuit 24 by ~eeding signals ~rom circuit 23 to an event marker 29 to provide a suitable lndication on the chart of the occurrence of each supra-threshold signal. Additionally the operatlon of valve ~ may be recorded by a second event marker 34 05 triggered from a line 3S from timing unit 12~ Thus, as well-as provldin~ a record of oesophageal activity, the chart recorder may also produce a separate record of those sensed pulses greater than the preset threshold value, and the inflation of the provoking 10 balloon~
A typical trace obtained from apparatus as illustrated in Figllre 1 is shown in Figure 6, in which the lower trace 41 represents the amplitude of provoking pulses applied to balloon 5, and the upper trace 42, represents the amplitude of pressure-waveform sensed by the liquid-filled balloon 4. Upper trace 42 can be seen to consist of a regular background pattern of pressure-waves 43 approximately 10 mm Hg~ in amplitude due to forced ventilation of the lungs of the patient. On the top of this re~ular trace 43 are superimposed waveforms 45 of much greater amplitude, typically 30 to 50 mm Hg., each following a provoking pulse 44 bg a matter of some 5 to 10 seconds. The occurrence or non-occurrence of these provoked pressure waves 45, above a preset threshold magnltude, for e~ample 25 mm Hg. can be used as a simple "on-o~f" indicatlon of whether the depth of X
~ 21 -anaesthesia of the patient is greater or less than A
deslred level.
The equipment thus far described operates to ~onitor depth o~ anaesthesia. However the signal from 05 inverter 25 can be used directly to control the delivery o~ anaesthetic drugs to a patient. Drugs may be delivered to a patient by two routes depending on the type of drug usedO Certain drugs may be given as a solution administered by controlled intravenous in~usion for example by means of a syringe pump or drip controller. Where the anaesthetic drug ls a gas or volatile liquid it may be administered by inhalation of a gas or vapour mi~ture produced by controllable gas mixing valves and vapourising systems. Where drug delivery is by means of a syringe pump loaded with the appropriate drug, the plunger of the syringe may be driven by a stepper motor. The rate of drive pulses supplied to the stepper motor determLnes the rate of delivery of the drug.
Comparison o~ the rate signal from inverter 25 with a ~alue set by th~ anaesthetist enables a control signal to be obtained which elther speeds up or slows do~n the drlve pul~e rate of a syringe pump stepper motor i~ ~ccordance with whether the rate signal that is monitored ls abo~e or below the set value.
.X
The equipment required for this control function comprises a co~para~or 31 whicn is fed with the output from inverter 25. Comparator 31 also has fed to it a desired rate which is set by the anaesthetist. Comp-05 arator 31 compares the actual rate of contraction ofthe oesophagus with the desired rate and provides ~n error signal giving the magnitude and sign of the difference between the actual rate and the desired rate set by the anaesthetistO The error signal is ~0 applied to a pulse generator 32 to modify the rate of pulse generation therefrom. The pulse output from generator 32 is in the form of drive pulses to a stepper motor 33 which drives a syringe pump.
An alarm 30 is preferably included to give an audible or visual alarm or both. Trig~ering of a alarm 30 may be caused when the signal from inverter 25 falls below or rises above set safety levels.
Additional alarm trigger signals can be obtained from various parts of the circuit, for example from pulse generator 32 if the pulses similarly are above or belo~ set safety levels.
Many of the functions of the monitoring and control equipment oi Figure 2 can be incorporated in an appropriately programmed microprocessor. The Z5 inputs to the microprocessor include the signal from ~iltPr 22 as well as the various set values such as - 23 ~
pressure threshold, window length and the desired rate of contractions. The output from the microprocessor includes display information and signals to control pulse generator 32~ Conditions for operating alarm 30 05 can also be incorporated.
The pattern of oesophageal contractions, e.g. the amplltude, rate, degree of repetition of any particular sequence of contractions, may be characteristic for a particular patient. This allows the possibility of providing for the apparatus to be adaptive, in the sense that the microprocessor can be programmed to generate a response "norm" for a particular patient, based on observation over a period, and to produce an output corresponding to deviation from the norm, whether in amplitude, rate, or any other parameter of the contractions, which will indicate the degree of anaesthesia.
8efore being processed, signals from the transducer may be converted from analogue to digital forrll, and the digitised form of -the input may be connected directly to the microprocessor circuitry.
Using this technique it is possible for the micro-processor to compare the output signal directly with pre-programmed "norm", as regards for e~ample amplitude, duratlon, and profile or "shape". If the ~ignal fits the pre-set norm the ~ave~orm is X
_ 24 -recognised as a significant contraction. Clearly it may be useful to employ a threshold discriminator in combination with the above technique.
The amplitude of tbe contractions of the 05 oesophagus has been ~ound to vary along ~he length of the oesophagus, and to be greatest approximately 5 to 10 cm from the entry to ths stomach. It is therefore preferable to provide means for retaining the sensor in the appropriate position in the oesophagus, for e~ample a balloon adapted to pass into the stomach where lt is inflated to locate the sensor in the desired position.
Figures 3 to 5b show ~lternative embodiments of the oesophageal probe, the same re~erence numerals being used as in Figure 1 to deno-te corresponding parts .
Figures 3a and 3b show respectively a schematic side and end view of an oesophageal probe, in which A
provoking balloon 5 and a measuring balloon 4 are arranged in a parallel, rather than a series configuration. In use, the lumens 2 and 3 are connected as in Figure lo In the arrangement shown in Figure 4, two provokirlg ball~ons, 5a and 5b are used. Thus, the oesophagus may be provoked in two positions 6imultaneou~1y. By provlding communicating holes o~
.X
- ~5 -dif~erellt sizes from the balloons shown ln 5a and 5b to the outer lumen 3, the rate of expansion of the balloons 5a and 5b may be made to differ from each other, so as to give a peristaltic-like efiect.
05 Multiple balloons of this kind may be ut~lised with any o~ the probe designs proposed herein.
Figures 5a and 5b show side and end schematic views respectively of a probe in which a provoking balloon 5 is provided concentric with a sensing balloon 4. The sensing balloon continues to be sensitive to pressure changes, provided tha~ the provoking balloon is deflated. During the application of brief provoking pressure pulses to the provoking balloon 5, ths sensing balloon ~ is not responsive to changes in oesophageal activity, but sensitivty returns to normal, when the provoking pulse has ceased.
A number of other modifications may be used with the probes described above. For example, the sensing balloon may be provided with a foam insert, to maintain the balloon volume. This is particularly usei'ul when the sensing balloon is gas filled, since a co~traction of the oesophagus will ~ive rise to a greater pressure slgnal.
X
When the sensing balloon is gas filled, progressive drift in the system pressure is likely to occur, due to both temperature change of gas within the balloon, and by the diffusion of anaesthetic 05 gases, for example, nitrous oxide, from the body tissues through t~e balloon wall. It is therefore desirable when a gas ~illed sensing balloon is used to incorporate a small controlled leak into the gas line connected to the monitor balloon, ~o allow very slow equalisation of any progressive pressure drifto The leak is not, of course, so large as to interfere significantly with the transmission of transient high pressure signals. Instead of a fluid-filled balloon for pressure sensing, a pressure transducer may be inserted into a soft sleeve in place of balloon 4.
This may be combined ~ith means for provoking the oesophagus ~o contraction, for example, a pressure balloon of the kind described above.
As an alternative to a balloon ~or provoking the oesophagus to contraction, a pair of spaced stimu-lating electrodes may be provided, and these may be spaced along the length of a balloon type catheter used ~or sensing oesophageal pressure.
In yet a ~urther alternatlve embodiment, provocation of the oesophagus may be carrled out by a suitable balloon inserted into the tr~chea of the patient.
Any of the oesophageal probes discussed above may have incorporated therein a microphone, a temperature 05 prob~ or electrodes ~or recording an electrocardio-gram. The microphone mQy be either incorporated ln the region of $he probe tip, or else connected either to the provoking lumen 3, or sensing lumen 2, sound from the oesophagus belng transmit~ed by the inter-medlate fluid. Thus, a stethoscope function m~y beprovided.
Similarly, a temperature probe, for example a thermistor, may be provided in the probe tip to record body temperatureO
A particularly preferred embodiment of an oesophageal probe ~or use in the method of the invention is illustrated in Figure 8. The probe of Figure 8 includes two sensing balloons, 84a and 84b each connected to separate transducers via passage-ways 82a and 82b respectively. The two sensing balloons each have a length of appro~imately 3 to 5 cm, and a ma~imum diameter o~ appro~imately 2 cm.
Appro~imately 1 cm ~rom the distal sensing balloon~ 84a; i3 a single provoking balloon 85. The provoking balloon 85 is in communication via holes 86 ~ith a passageway 83, through which provoking pulses X
ca~ be applied, in the same way as described above, The dlstance between the provoking balloon 85 and the monitoring balloon 84b is approximately 5 cm.
The provision of two transducers linked to 05 passageways 82a and 82b enables oesophageal pressure to be monitored at two points in the oesphagus spaced by appro~imately 10 - 15 cm.
The human oesophagus is unusual in that it has a nervous control mechanism which controls the whole of the oesophagus, despite the fact that the lower part is made of involuntary or "smooth" muscle, and the upper part of voluntary or "skeletal" muscle. The ability to measure oesopha.geal contractions at two po~nts spaced in the oesophagus, using a probe as illustrated in Figure 8, is a useful one, since there ~re certain drugs, for e~ample curare-like muscle rela~ants, which selectively paralyse "skeletal", but not "smooth" muscle.
Wben muscle relaxants have been given to a patient9 oesophageal con~ractions can only be elicited in the lower part of the oesophagus. As the mu~cle rela~ant wears off (the half-life of many rela~nts is around 15 to 20 minutes) an increasing amount o~ activity can be recorded in the upper oeæophagus. Thus, the rel~tive smplitude of contrac-X
Passageway 3 is connected to an air supply line 9. An air-pump 6 supplles a reservoir 7 ~hlcb ~eeds supply line ~ t~rough a valve 8. A pressure gauge 10 i~ coupled to reservolr 7. In an alternative and pre~erred embodiment, gauge 10 is coupled to line 9 so a3 ko measure directly the provoking pressure.
L~ ~
Reservoir 7 also has a regulating valve 11 which can be ad~usted to prevent excessive rise in ths pressure in reservoir 7. Valve 8 is controlled by a timing u~it 12.
05 In use of the equipment shown in ~igure 1 probe 1 is inserted into the oesophagus so that the balloon 4 is in the lower part of the oesophagus, in an adult, typically 35 cm from the incisor teeth, and the timing unit 12 functions to control valve 8 to connect reservoir 7 to intermittently inflate balloon 5. At the end o~ each inflation period valve 8 connects line ~ to a vent 13 to allow balloon 5 to deflate. With reservoir 7 having a volume of approximately 200 cc and being held at a pressure of around 200 mm Hg and with balloon 5 having an inflated volume of about 5 cc the opening of valve 8 will cause full and rapid e~pansion of balloon 5 to its maximum capacity. It is convenient to hold balloon 5 inflated for periods of 5 seconds or ~here- abouts with the intervals between inflations being in the range of 1 - 10 mins.
In order to safeguard against deleterious ef,t'ects on ~ patient arlslng out of rupture o~ halloon 5 it may be desirable to provide means for limi-ting the volume or rate o~ air~low out of reservoir 7.
2S second valve may be provided, operated by the timing unit 12, between the air pump 6 and the reservoir 7 and open when valve 8 is closed, to restore pressure in the reservoir 7 only when ~he reservoir is not directly connected to balloon 5.
Any contraction of the oesophagus which is either 05 spontaneous or else is trlggered by inflation of balloon 5 is monitored by liquid-filled balloon 4 and the pressure signal therefrom fed through passageway 2 to a pressure transducer (not shown).
The monitor balloon 4 described above is liquid filled, preferably with water. It is however possible to use an air or gas filled balloon for monitoring pur.poses al~hough in such cases there ~ay be a loss of fidelity in the recording of pressure amplitude.
Alternatively in place of a balloon a catheter tip 15 ~trarsducer can be inserted into the oesophagus in a so~t balloon sleeve, in the position of balloon 4 While a separate monitoring balloon 4 and provoking balloon 5 have been described with reference to Flgure 1 it is possible to replace the two balloons by a single balloon which fulfils both functions. In such a case a switching valve is required which normally co~nects the balloon to the pressure tr~nsducer but ~hich is switched to valve 8 whenever a provoking stimulus is called for by the timing unit ~-Timing unit 12 is optionally provided with an inhibit input along a line 14~ When an inhibit pulse is received timing unit 12 does not function for a set period thereafter so that inflation of provoking 05 balloon 5 is inhibited during that period. The inhibit pulses are derived from the pressure transducer 21 to which balloon 4 is coupled as shown in Figure 2. Use of the inhibit pulses ensures that when there are spontaneous contractions operation of the provoking balloon, which is unnecessary, is prevented. A further option provides for manual triggering o~ timing unit 12 to operate valve 8.
Figure 2 shows monitoring and control equipment in block diagrammatic form. The pressure signal obtained from the balloon 4 shown in Figure 1 is fed to a transducer 21 which provides an output si~nal of magnitude proportional to the amplitude o~ the pressure signal fed to it. Transducer 21 may include of~set and gain controls.
The output signal from transducer 21 includes not only ma~or signals derived from oesophageal contrac-tions but also other signal~ which arise from heartbeats and lung ventilation as well as other background sigllals lncluding noise. The output from transducer 21 ls applied to a filter 22 to remove low level background signals and thence to an adjustable _ 18 -threshold circuit 23 to block all remaining signals below a set level. Since the oesophageal con-tractions result in pressure signals of ~uch higher level of amplitude than signals from other sources the 05 setting of an appropriate threshold level in circuit 23 ensures that the output therefrom comprises signals due to the oesophageal contractions only.
The signals from circuit 23 are utilised to provide a count o~ events in a moving time "window".
The count is made in a timer/counter circuit 24 into which the desired lengths or duration of the time "window" is entered. Conveniently circuit 24 has a plurality of registers each of which records the inputs received from circuit 23 in a ii~ed time period (e.g. one minute) in succe~sion. The number o~ the most rece~tly ~illed registers that contribute their contents to the summation is determined by the length of the time "window". Thus for one minute registers and a time "window" o~ four minutes the four last-filled registers are summed and their sum is outputted. The above e~ample of a one minute time perlod and a time ~indow of four minutes is purely to illu~trate the manner of operatlon of circuit 24 and a dl~erent time period can be provided in the circuit and the length of the time "windo~l' may be adjustable ~or greater or smaller durations than the fi~ure quoted. The summation of the register contents may be ad~usted to bias the sum in favour of some part of the window~.
It can occur that contractions of the oesophagus 05 may be stimulated, for e~ample by mo~ement of the patient during an operation. The inclusion of signals due to such stimulation may give rise to misleading estimations of degree of anaesthesia. For this reason, it is preferable to provide as a function of the apparatus means for selectively rejecting any particular signal at the discretion of the operator, such that the particular signal does not contribute to the degree of anaes~hesia indicated.
The output from circult 24 is applied to an invert0r 25 to glve a rate of contraction and this rate is displayed in an analogue display 261 for e~ample as a bar of varying length. Alternatively or in addition it ls displayed in digital form in a digital display 270 It may be desired to have a visual record of oesophageal activity. A temporary record may be shown on a cathode ray tube or similar display, A permanent ~ecord may be obtained with a chart recorder 28 which is ~ed with the signal from transducer 21. Recorder 28 can also c~rr~ indications of the input pulses to timer/counter circuit 24 by ~eeding signals ~rom circuit 23 to an event marker 29 to provide a suitable lndication on the chart of the occurrence of each supra-threshold signal. Additionally the operatlon of valve ~ may be recorded by a second event marker 34 05 triggered from a line 3S from timing unit 12~ Thus, as well-as provldin~ a record of oesophageal activity, the chart recorder may also produce a separate record of those sensed pulses greater than the preset threshold value, and the inflation of the provoking 10 balloon~
A typical trace obtained from apparatus as illustrated in Figllre 1 is shown in Figure 6, in which the lower trace 41 represents the amplitude of provoking pulses applied to balloon 5, and the upper trace 42, represents the amplitude of pressure-waveform sensed by the liquid-filled balloon 4. Upper trace 42 can be seen to consist of a regular background pattern of pressure-waves 43 approximately 10 mm Hg~ in amplitude due to forced ventilation of the lungs of the patient. On the top of this re~ular trace 43 are superimposed waveforms 45 of much greater amplitude, typically 30 to 50 mm Hg., each following a provoking pulse 44 bg a matter of some 5 to 10 seconds. The occurrence or non-occurrence of these provoked pressure waves 45, above a preset threshold magnltude, for e~ample 25 mm Hg. can be used as a simple "on-o~f" indicatlon of whether the depth of X
~ 21 -anaesthesia of the patient is greater or less than A
deslred level.
The equipment thus far described operates to ~onitor depth o~ anaesthesia. However the signal from 05 inverter 25 can be used directly to control the delivery o~ anaesthetic drugs to a patient. Drugs may be delivered to a patient by two routes depending on the type of drug usedO Certain drugs may be given as a solution administered by controlled intravenous in~usion for example by means of a syringe pump or drip controller. Where the anaesthetic drug ls a gas or volatile liquid it may be administered by inhalation of a gas or vapour mi~ture produced by controllable gas mixing valves and vapourising systems. Where drug delivery is by means of a syringe pump loaded with the appropriate drug, the plunger of the syringe may be driven by a stepper motor. The rate of drive pulses supplied to the stepper motor determLnes the rate of delivery of the drug.
Comparison o~ the rate signal from inverter 25 with a ~alue set by th~ anaesthetist enables a control signal to be obtained which elther speeds up or slows do~n the drlve pul~e rate of a syringe pump stepper motor i~ ~ccordance with whether the rate signal that is monitored ls abo~e or below the set value.
.X
The equipment required for this control function comprises a co~para~or 31 whicn is fed with the output from inverter 25. Comparator 31 also has fed to it a desired rate which is set by the anaesthetist. Comp-05 arator 31 compares the actual rate of contraction ofthe oesophagus with the desired rate and provides ~n error signal giving the magnitude and sign of the difference between the actual rate and the desired rate set by the anaesthetistO The error signal is ~0 applied to a pulse generator 32 to modify the rate of pulse generation therefrom. The pulse output from generator 32 is in the form of drive pulses to a stepper motor 33 which drives a syringe pump.
An alarm 30 is preferably included to give an audible or visual alarm or both. Trig~ering of a alarm 30 may be caused when the signal from inverter 25 falls below or rises above set safety levels.
Additional alarm trigger signals can be obtained from various parts of the circuit, for example from pulse generator 32 if the pulses similarly are above or belo~ set safety levels.
Many of the functions of the monitoring and control equipment oi Figure 2 can be incorporated in an appropriately programmed microprocessor. The Z5 inputs to the microprocessor include the signal from ~iltPr 22 as well as the various set values such as - 23 ~
pressure threshold, window length and the desired rate of contractions. The output from the microprocessor includes display information and signals to control pulse generator 32~ Conditions for operating alarm 30 05 can also be incorporated.
The pattern of oesophageal contractions, e.g. the amplltude, rate, degree of repetition of any particular sequence of contractions, may be characteristic for a particular patient. This allows the possibility of providing for the apparatus to be adaptive, in the sense that the microprocessor can be programmed to generate a response "norm" for a particular patient, based on observation over a period, and to produce an output corresponding to deviation from the norm, whether in amplitude, rate, or any other parameter of the contractions, which will indicate the degree of anaesthesia.
8efore being processed, signals from the transducer may be converted from analogue to digital forrll, and the digitised form of -the input may be connected directly to the microprocessor circuitry.
Using this technique it is possible for the micro-processor to compare the output signal directly with pre-programmed "norm", as regards for e~ample amplitude, duratlon, and profile or "shape". If the ~ignal fits the pre-set norm the ~ave~orm is X
_ 24 -recognised as a significant contraction. Clearly it may be useful to employ a threshold discriminator in combination with the above technique.
The amplitude of tbe contractions of the 05 oesophagus has been ~ound to vary along ~he length of the oesophagus, and to be greatest approximately 5 to 10 cm from the entry to ths stomach. It is therefore preferable to provide means for retaining the sensor in the appropriate position in the oesophagus, for e~ample a balloon adapted to pass into the stomach where lt is inflated to locate the sensor in the desired position.
Figures 3 to 5b show ~lternative embodiments of the oesophageal probe, the same re~erence numerals being used as in Figure 1 to deno-te corresponding parts .
Figures 3a and 3b show respectively a schematic side and end view of an oesophageal probe, in which A
provoking balloon 5 and a measuring balloon 4 are arranged in a parallel, rather than a series configuration. In use, the lumens 2 and 3 are connected as in Figure lo In the arrangement shown in Figure 4, two provokirlg ball~ons, 5a and 5b are used. Thus, the oesophagus may be provoked in two positions 6imultaneou~1y. By provlding communicating holes o~
.X
- ~5 -dif~erellt sizes from the balloons shown ln 5a and 5b to the outer lumen 3, the rate of expansion of the balloons 5a and 5b may be made to differ from each other, so as to give a peristaltic-like efiect.
05 Multiple balloons of this kind may be ut~lised with any o~ the probe designs proposed herein.
Figures 5a and 5b show side and end schematic views respectively of a probe in which a provoking balloon 5 is provided concentric with a sensing balloon 4. The sensing balloon continues to be sensitive to pressure changes, provided tha~ the provoking balloon is deflated. During the application of brief provoking pressure pulses to the provoking balloon 5, ths sensing balloon ~ is not responsive to changes in oesophageal activity, but sensitivty returns to normal, when the provoking pulse has ceased.
A number of other modifications may be used with the probes described above. For example, the sensing balloon may be provided with a foam insert, to maintain the balloon volume. This is particularly usei'ul when the sensing balloon is gas filled, since a co~traction of the oesophagus will ~ive rise to a greater pressure slgnal.
X
When the sensing balloon is gas filled, progressive drift in the system pressure is likely to occur, due to both temperature change of gas within the balloon, and by the diffusion of anaesthetic 05 gases, for example, nitrous oxide, from the body tissues through t~e balloon wall. It is therefore desirable when a gas ~illed sensing balloon is used to incorporate a small controlled leak into the gas line connected to the monitor balloon, ~o allow very slow equalisation of any progressive pressure drifto The leak is not, of course, so large as to interfere significantly with the transmission of transient high pressure signals. Instead of a fluid-filled balloon for pressure sensing, a pressure transducer may be inserted into a soft sleeve in place of balloon 4.
This may be combined ~ith means for provoking the oesophagus ~o contraction, for example, a pressure balloon of the kind described above.
As an alternative to a balloon ~or provoking the oesophagus to contraction, a pair of spaced stimu-lating electrodes may be provided, and these may be spaced along the length of a balloon type catheter used ~or sensing oesophageal pressure.
In yet a ~urther alternatlve embodiment, provocation of the oesophagus may be carrled out by a suitable balloon inserted into the tr~chea of the patient.
Any of the oesophageal probes discussed above may have incorporated therein a microphone, a temperature 05 prob~ or electrodes ~or recording an electrocardio-gram. The microphone mQy be either incorporated ln the region of $he probe tip, or else connected either to the provoking lumen 3, or sensing lumen 2, sound from the oesophagus belng transmit~ed by the inter-medlate fluid. Thus, a stethoscope function m~y beprovided.
Similarly, a temperature probe, for example a thermistor, may be provided in the probe tip to record body temperatureO
A particularly preferred embodiment of an oesophageal probe ~or use in the method of the invention is illustrated in Figure 8. The probe of Figure 8 includes two sensing balloons, 84a and 84b each connected to separate transducers via passage-ways 82a and 82b respectively. The two sensing balloons each have a length of appro~imately 3 to 5 cm, and a ma~imum diameter o~ appro~imately 2 cm.
Appro~imately 1 cm ~rom the distal sensing balloon~ 84a; i3 a single provoking balloon 85. The provoking balloon 85 is in communication via holes 86 ~ith a passageway 83, through which provoking pulses X
ca~ be applied, in the same way as described above, The dlstance between the provoking balloon 85 and the monitoring balloon 84b is approximately 5 cm.
The provision of two transducers linked to 05 passageways 82a and 82b enables oesophageal pressure to be monitored at two points in the oesphagus spaced by appro~imately 10 - 15 cm.
The human oesophagus is unusual in that it has a nervous control mechanism which controls the whole of the oesophagus, despite the fact that the lower part is made of involuntary or "smooth" muscle, and the upper part of voluntary or "skeletal" muscle. The ability to measure oesopha.geal contractions at two po~nts spaced in the oesophagus, using a probe as illustrated in Figure 8, is a useful one, since there ~re certain drugs, for e~ample curare-like muscle rela~ants, which selectively paralyse "skeletal", but not "smooth" muscle.
Wben muscle relaxants have been given to a patient9 oesophageal con~ractions can only be elicited in the lower part of the oesophagus. As the mu~cle rela~ant wears off (the half-life of many rela~nts is around 15 to 20 minutes) an increasing amount o~ activity can be recorded in the upper oeæophagus. Thus, the rel~tive smplitude of contrac-X
3~
tions in t~le upper and lo~er ot~sopha~us provide~ a means fvr ~ssessing t~le extent of sk~lt-~tal mus~L~
paralysis.
FigUI`e 9 lS a bloclc schematic diagram 05 illuscratLng a clrcuit suitable for use with the probe of Figure 8 to make use of this effect.
Balloons 84a and ~4b are connected to transducer a and ~ransducer b respectively, and the amplitude of the signals is compared in a comparator. The comparator may ~unction continuously, activated b~
contractions in excess of a threshold value, or by any of the other identification methods outlined above, as monitoreti by the distal monitorin~ balloon 84a.
Alternatively, the system may operate only when enabled by a si~nal from the provoking unit.
When the provoking balloon 85 is inflated, provoked contractions will be observed in both sensing balloons 84a and 84b within 5 to 10 seconds. Thus, the urran~ement will normally provide for the comparator to be enabled for a period of from 5 to 10 secor.ds. The display provides an output corresponding to the ratio o~ amplitudes of pressure senst?d hy oalloons 84b and 84~. \Yhen this r~tio i~ near unity, there is little muscle paralysi~s. when the ratio is ~5 close to zero, skeletal muscle iS paralysetl fully.
Thus, according to yet a further embodiment of the inventlon, there is provided a method for determining the degrse of skelet~l muscle relaxation of a patient, which method comprises providing signals indicative of ~5 contractions at two spaced points in the oesophagus of a patient, and comparing the signals to derive therefrom an output indicative of the degree of skeletal muscle rela~ation of the patient. The invention includes ~ithin its scope apparatus for carrying out the above method.
A number o~ the probes described above are in themselves novel, and such probes should be considered as lying within the scope of ~his aspect of the inventton.
A preferred embodiment of the second aspect of the invention discussed above, involving allocating a "score" for various bodily functions is illustrated in more detail with reference to ~igure 7, a~d ~he following table. The table illustrates a sultable scoring system for the four parameters systolic blood pressure, heart rate, sweat, and tears.
X
T A B L E
INDEX CONDITION SCORE
SYSTOLIC ~LOOD LESS THAN CONTROL ~ 15 O
PRESSURE LESS THAN CONTROL ~ 30 (mm Hg) ~ORE THAN CONTROL ~ 30 2 HEART RATE LESS THAN CONTROL + 15 O
(beats/min) LESS THAN CONTROL + 30 MORE THAN CONTROL + 30 2 SWEAT NIL O
SKIN MOIST TO TOUCH
TEARS OR NO EXCESS TEARS WIT~ EYE-LACRIMATION LIDS OPEN O
EXCESS TEARS VISIBLE
WITH ~YELIDS OPEN
TEAR OVERFLOW FROM CLOSED
EYELIDS
In the illustrated embodiment each of these ~unctiQns is assigned one of three score values O, 1 or 2. Clearly, a different number of values and a dl~erent value system can be used if desired. The total score of the ~our iunctions in the above system c~ thus vary ~rom O to 8. A lo~ score would be ch~racteristlc o~ deep anaesthesia and a high ~core of light anaesthesla. The ~our ~unc~ions that are selected are systolic blood pressure, heart beat rate, s~sating and tears. The first two are obtained by direct measurements of the patient while the last two functions are assessed by a clinician. In the 05 embodiment illustrated the measured or assessed values are entered by the clinician via a keypad, ~lthough in an alternative embodiment, suitable electrical transducers may be used to measure one or more of the functions directly, the transducers providing the appropriate electrical input to the apparatus.
In the case of blood pressure Qnd heart beat it is the deviation from control values that is used in determining a score value and these control values are obtained from the patient by measurement beforehand.
15 The scoring system shown in the table of Fig 6 may be modified to include additional or alternative ~unctions. Clearly a different set of score values can b~ used giving a smaller or greater number of ranges.
Suitable equipment incorporating the scoring system shown in the table is shown in Fig f. The equipment provides ~or the input o~ parameters of ~our bodlly ~unction~ These are systolic blood pressure (indlc~ted by BP~, heart beat rate Sindicated by HR), s~eating (indicated by SW) and tear~ or lacrimination (indicated by T~. Initlally ~uitabl~ thumbwheel X
s~i~ches 51 are set to give control values of BP and HR. These values are fed to a comparator 52 to which the current measured values of BP and HR are also fed.
These values may be measured by suitable ~ransducers.
05 Comparator 52 carries out the appropriate calculation ~or determining in which of the three ran~es of measurement set out in Fig 8 the ~easured values lie and provides outputs of numerical values 0, 1 or 2 as appropriate. These values are fed to a summing circuit 53. There are also further inputs to summing circuit 53. These are the score values of the functlons SW and TE as assessed by the clinician.
Summing circuit 53 adds all the score values and displays the total score in a display unit 54 which may be analogue or digital, or both if desired.
An alarm circuit 55 may be provided to give an audible or visual alarm or a combination thereof if the ,,otal score is above or below preset limits. The maximum and minimum score limits may be entered by thumb~heel switches 56 and the output of circuit 53 may be compared in a comparator 57 with the score limits set by switches 56 to determine whether alarm 55 needs to b~ actlvated.
To e~able the requlred rate of administrQtion of a drug to be displayed a ~urther comparator 58 is provided whlch has as one input a de5ired score level - ~4 -set by a thumbwheel switch 59 and as its other input the total score output from circuit 53. The output of comparator 58 is an error function which is a measure of the difference between the desired or required 05 level of anaesthesia and the level which is obtained ~rom ~easurement and assessment. This error function is ~ed to a drug rate calculator 60 which has as a preset input an initial drug rate obtained from a thumbwheel switch 61 which is set by the clinician.
Calculator 60 modifies the value of the initial drug rate held in switch 61 in accordance with the error function obtained from comparator 58 and displays the required drug rate in a display 62. This calculation ma~ be carried out at intervals as controlled by a clock 63.
The equipment thus far described enables the depth of anaesthesia of a patient to be monitored and additionally displays information as to the required rate of administration of drugs to achieve a desired dPpth of anaesthesia. Since the equipment provides such in~ormation it can also include means for automatically delivering drugs at the required rate.
Drugs may be delivered to patients by two routes depending on the type o~ drug used. Some drugs are given as a solution adminstered by controlled intra-venous infusion ~rom for example a syringe pump or drip controller. Where the anaesthetic drug is a gas or volatile liquid it may be administered by inhalation of a gas or vapour mixture produced by controllable gas mi~ing valves and vaporising systems.
05 ~here drug delivery is by means of a syringe pump loaded ~ith the appropriate drug, the plunger o~ the syringe may be driven by a stepper motor. The rate of drive pulse supplied to the stepper motor de~ermines the rate of delivery of the drug. Comparison of the current total score with the desired score set by the anaesthetist enables a control signal to be obtained which either speeds up or slows down the drive pulse rate to the syringe pump stepper motor in accordance with whether the score value that is monitored is ~ove or below the set value.
An e~ample of additional item~ of equipment to control the administration of drugs is also shown in Fig 7. The output from calculator 60 giving the required drug rate is switched through a switch 64 if automatic control is desired to a comparator 65.
Comparator 65 has inputs irom thumbwheel switches 66 wbich give the ma~imum and minimum limits oi drug rates. If the input from drug rate calculator 60 is ; outside the limits set b~ switches ~6 then an alarm 67 ls energi~ed. I~ the output from calculator 60 is within the set limits then thi~ value ls ~ed to a X
variable frequency oscillator 68 to control the frequency thereof in accordance with the value of the output of calculator 60. Oscillator 68 controls the speed of operation of a stepper motor 69 which 05 operates a suitable syringe pump or the like for drug infusion. A drug rate setting circuit 70 may be interposed in the input path to oscillator 68 to enable the rate of drug supply to be changed manually.
The total amount of drug supplied is displayed in a display 71 fed ~rom oscillator 68.
Nhilst the above description relates primarily to patients undergoing anaesthesia for surgery, the apparatus described herein can readily be used for patients to whom sedative, muscle rela~ant and/or analgesic drugs may be adm:inistered, for e~ample in intenslve care units, and the terms "anaesthetic" and "anaesthesia" in the following claims should be unders~ood accordin~ly.
tions in t~le upper and lo~er ot~sopha~us provide~ a means fvr ~ssessing t~le extent of sk~lt-~tal mus~L~
paralysis.
FigUI`e 9 lS a bloclc schematic diagram 05 illuscratLng a clrcuit suitable for use with the probe of Figure 8 to make use of this effect.
Balloons 84a and ~4b are connected to transducer a and ~ransducer b respectively, and the amplitude of the signals is compared in a comparator. The comparator may ~unction continuously, activated b~
contractions in excess of a threshold value, or by any of the other identification methods outlined above, as monitoreti by the distal monitorin~ balloon 84a.
Alternatively, the system may operate only when enabled by a si~nal from the provoking unit.
When the provoking balloon 85 is inflated, provoked contractions will be observed in both sensing balloons 84a and 84b within 5 to 10 seconds. Thus, the urran~ement will normally provide for the comparator to be enabled for a period of from 5 to 10 secor.ds. The display provides an output corresponding to the ratio o~ amplitudes of pressure senst?d hy oalloons 84b and 84~. \Yhen this r~tio i~ near unity, there is little muscle paralysi~s. when the ratio is ~5 close to zero, skeletal muscle iS paralysetl fully.
Thus, according to yet a further embodiment of the inventlon, there is provided a method for determining the degrse of skelet~l muscle relaxation of a patient, which method comprises providing signals indicative of ~5 contractions at two spaced points in the oesophagus of a patient, and comparing the signals to derive therefrom an output indicative of the degree of skeletal muscle rela~ation of the patient. The invention includes ~ithin its scope apparatus for carrying out the above method.
A number o~ the probes described above are in themselves novel, and such probes should be considered as lying within the scope of ~his aspect of the inventton.
A preferred embodiment of the second aspect of the invention discussed above, involving allocating a "score" for various bodily functions is illustrated in more detail with reference to ~igure 7, a~d ~he following table. The table illustrates a sultable scoring system for the four parameters systolic blood pressure, heart rate, sweat, and tears.
X
T A B L E
INDEX CONDITION SCORE
SYSTOLIC ~LOOD LESS THAN CONTROL ~ 15 O
PRESSURE LESS THAN CONTROL ~ 30 (mm Hg) ~ORE THAN CONTROL ~ 30 2 HEART RATE LESS THAN CONTROL + 15 O
(beats/min) LESS THAN CONTROL + 30 MORE THAN CONTROL + 30 2 SWEAT NIL O
SKIN MOIST TO TOUCH
TEARS OR NO EXCESS TEARS WIT~ EYE-LACRIMATION LIDS OPEN O
EXCESS TEARS VISIBLE
WITH ~YELIDS OPEN
TEAR OVERFLOW FROM CLOSED
EYELIDS
In the illustrated embodiment each of these ~unctiQns is assigned one of three score values O, 1 or 2. Clearly, a different number of values and a dl~erent value system can be used if desired. The total score of the ~our iunctions in the above system c~ thus vary ~rom O to 8. A lo~ score would be ch~racteristlc o~ deep anaesthesia and a high ~core of light anaesthesla. The ~our ~unc~ions that are selected are systolic blood pressure, heart beat rate, s~sating and tears. The first two are obtained by direct measurements of the patient while the last two functions are assessed by a clinician. In the 05 embodiment illustrated the measured or assessed values are entered by the clinician via a keypad, ~lthough in an alternative embodiment, suitable electrical transducers may be used to measure one or more of the functions directly, the transducers providing the appropriate electrical input to the apparatus.
In the case of blood pressure Qnd heart beat it is the deviation from control values that is used in determining a score value and these control values are obtained from the patient by measurement beforehand.
15 The scoring system shown in the table of Fig 6 may be modified to include additional or alternative ~unctions. Clearly a different set of score values can b~ used giving a smaller or greater number of ranges.
Suitable equipment incorporating the scoring system shown in the table is shown in Fig f. The equipment provides ~or the input o~ parameters of ~our bodlly ~unction~ These are systolic blood pressure (indlc~ted by BP~, heart beat rate Sindicated by HR), s~eating (indicated by SW) and tear~ or lacrimination (indicated by T~. Initlally ~uitabl~ thumbwheel X
s~i~ches 51 are set to give control values of BP and HR. These values are fed to a comparator 52 to which the current measured values of BP and HR are also fed.
These values may be measured by suitable ~ransducers.
05 Comparator 52 carries out the appropriate calculation ~or determining in which of the three ran~es of measurement set out in Fig 8 the ~easured values lie and provides outputs of numerical values 0, 1 or 2 as appropriate. These values are fed to a summing circuit 53. There are also further inputs to summing circuit 53. These are the score values of the functlons SW and TE as assessed by the clinician.
Summing circuit 53 adds all the score values and displays the total score in a display unit 54 which may be analogue or digital, or both if desired.
An alarm circuit 55 may be provided to give an audible or visual alarm or a combination thereof if the ,,otal score is above or below preset limits. The maximum and minimum score limits may be entered by thumb~heel switches 56 and the output of circuit 53 may be compared in a comparator 57 with the score limits set by switches 56 to determine whether alarm 55 needs to b~ actlvated.
To e~able the requlred rate of administrQtion of a drug to be displayed a ~urther comparator 58 is provided whlch has as one input a de5ired score level - ~4 -set by a thumbwheel switch 59 and as its other input the total score output from circuit 53. The output of comparator 58 is an error function which is a measure of the difference between the desired or required 05 level of anaesthesia and the level which is obtained ~rom ~easurement and assessment. This error function is ~ed to a drug rate calculator 60 which has as a preset input an initial drug rate obtained from a thumbwheel switch 61 which is set by the clinician.
Calculator 60 modifies the value of the initial drug rate held in switch 61 in accordance with the error function obtained from comparator 58 and displays the required drug rate in a display 62. This calculation ma~ be carried out at intervals as controlled by a clock 63.
The equipment thus far described enables the depth of anaesthesia of a patient to be monitored and additionally displays information as to the required rate of administration of drugs to achieve a desired dPpth of anaesthesia. Since the equipment provides such in~ormation it can also include means for automatically delivering drugs at the required rate.
Drugs may be delivered to patients by two routes depending on the type o~ drug used. Some drugs are given as a solution adminstered by controlled intra-venous infusion ~rom for example a syringe pump or drip controller. Where the anaesthetic drug is a gas or volatile liquid it may be administered by inhalation of a gas or vapour mixture produced by controllable gas mi~ing valves and vaporising systems.
05 ~here drug delivery is by means of a syringe pump loaded ~ith the appropriate drug, the plunger o~ the syringe may be driven by a stepper motor. The rate of drive pulse supplied to the stepper motor de~ermines the rate of delivery of the drug. Comparison of the current total score with the desired score set by the anaesthetist enables a control signal to be obtained which either speeds up or slows down the drive pulse rate to the syringe pump stepper motor in accordance with whether the score value that is monitored is ~ove or below the set value.
An e~ample of additional item~ of equipment to control the administration of drugs is also shown in Fig 7. The output from calculator 60 giving the required drug rate is switched through a switch 64 if automatic control is desired to a comparator 65.
Comparator 65 has inputs irom thumbwheel switches 66 wbich give the ma~imum and minimum limits oi drug rates. If the input from drug rate calculator 60 is ; outside the limits set b~ switches ~6 then an alarm 67 ls energi~ed. I~ the output from calculator 60 is within the set limits then thi~ value ls ~ed to a X
variable frequency oscillator 68 to control the frequency thereof in accordance with the value of the output of calculator 60. Oscillator 68 controls the speed of operation of a stepper motor 69 which 05 operates a suitable syringe pump or the like for drug infusion. A drug rate setting circuit 70 may be interposed in the input path to oscillator 68 to enable the rate of drug supply to be changed manually.
The total amount of drug supplied is displayed in a display 71 fed ~rom oscillator 68.
Nhilst the above description relates primarily to patients undergoing anaesthesia for surgery, the apparatus described herein can readily be used for patients to whom sedative, muscle rela~ant and/or analgesic drugs may be adm:inistered, for e~ample in intenslve care units, and the terms "anaesthetic" and "anaesthesia" in the following claims should be unders~ood accordin~ly.
Claims (19)
1. An elongate probe for measuring oesophogeal contrac-tions, having a distal end adapted to pass downwardly through the oesophagus of the patient, and a proximal end adapted in use to lie externally of the mouth of the patient, the probe including stimulating means adapted in use to lie within the oesophagus of a patient and operable by means external to the patient for stimulating the oesophagus, to cause contractions therein, pressure sensing means adapted in use to lie within the oesophagus of the patient for enabling the measurement of pressure within the oesophagus, thereby to sense contractions of the oesophagus.
2. A probe as claimed in claim 1, wherein the stimulating means comprises a sealed inflatable balloon, and the probe comprises a lumen in fluid communication between the balloon and the proximal end of the probe.
3. A probe as claimed in claim 2, wherein the maximum diameter of the inflatable balloon is about 2 cm.
4. A probe as claimed in claim 3, wherein the stimulating means comprises two inflatable balloons spaced along the probe.
5. A probe as claimed in claim 4, including means to cause the two inflatable stimulating balloons to expand at differing rates.
6. A probe as claimed in claim 1, wherein the stimulating means includes a pair of electrodes on the probe, and means for supplying an electrical voltage to the electrodes.
7. A probe as claimed in claim 1, wherein the pressure sensing means includes an inflatable sensing balloon.
8. A probe as claimed in claim 7, including a lumen in fluid communication between the said sensing balloon and means on the proximal end of the tube for the connec-tion of a pressure transducer.
9. A probe as claimed in claim 8, wherein the maximum diameter of the sensing balloon is about 2 cm.
10. A probe as claimed in claim 7, wherein the sensing balloon has a length of from 3 to 5 cm.
11. A probe as claimed in claim 7, wherein a small leak is provided to permit the equalization of permanent pressure changes in the sensing balloon.
12. A probe as claimed in claim 7, wherein the pressure sensing balloon includes a foam insert to maintain the balloon volume.
13. A probe as claimed in claim 7, which also incor-porate a sealed inflatable stimulating balloon as defined in claim 2.
14. A probe as claimed in claim 13, wherein the stimulating balloon and the sensing balloon are concentric.
15. A probe as claimed in claim 1, including a pressure transducer adapted in use to lie in the oesophagus of the patient.
16. A probe as claimed in claim 1, including means for sensing the pressure at two points spaced along the oesophagus.
17. A probe as claimed in claim 16, wherein the said points are spaced from each other by from 10 to 15 cm.
18. A probe as claimed in claim 1, including a microphone or a temperature sensor.
19. A probe for measuring oesophogeal contractions, comprising an elongate body portion for insertion into the oesophagus and having at least first and second lumens sealed with respect to each other, the first lumen being in communication at its distal end with a sensing balloon for sensing oesophageal pressure, and being provided at its proximal end with means for connection to a pressure measuring device, and the second lumen being adapted to receive a fluid under pressure to stimulate the oesophagus to cause contractions therein.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000472073A CA1199846A (en) | 1980-10-28 | 1985-01-14 | Patient monitoring apparatus |
Applications Claiming Priority (6)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB8034669 | 1980-10-28 | ||
| GB8034669 | 1980-10-28 | ||
| GB8039741 | 1980-12-11 | ||
| GB8039741 | 1980-12-11 | ||
| CA000388712A CA1193504A (en) | 1980-10-28 | 1981-10-26 | Patient monitoring apparatus |
| CA000472073A CA1199846A (en) | 1980-10-28 | 1985-01-14 | Patient monitoring apparatus |
Related Parent Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000388712A Division CA1193504A (en) | 1980-10-28 | 1981-10-26 | Patient monitoring apparatus |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1199846A true CA1199846A (en) | 1986-01-28 |
Family
ID=27167157
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000472073A Expired CA1199846A (en) | 1980-10-28 | 1985-01-14 | Patient monitoring apparatus |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1199846A (en) |
-
1985
- 1985-01-14 CA CA000472073A patent/CA1199846A/en not_active Expired
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