WO1989002594A1

WO1989002594A1 - pH MONITOR

Info

Publication number: WO1989002594A1
Application number: PCT/AU1988/000366
Authority: WO
Inventors: Alan John Lindrea
Original assignee: Thornborough Investments Ltd.
Priority date: 1987-09-18
Filing date: 1988-09-19
Publication date: 1989-03-23

Abstract

A pH sensing element is provided having a tubular shaft portion (11) containing a glass bulb (13). The tubular shaft is provided with a window (18) formed in the side wall of the shaft (11), exposing a portion of the glass bulb (13). The glass bulb (13) has an aperture (16) closed by an ion permeable membrane (17) and is filled with a sampling fluid. The membrane (17) is exposed to the medium to be tested through the window (18). Electrodes (15) are provided within the bulb (13), which are connected via connecting leads (14) to a signal amplifier (20) which is in turn connected to a meter (21), calibrated to give a direct reading which correlates to the pH of a liquid in which the shaft is inserted.

Description

pH MONITOR This invention relates to monitoring devices and to methods for monitoring pH.

This invention has particular application to monitorin≤ specific physiological conditions which vary with pH. Such conditions which correlate to pH will hereinafter be referred to as "correlated conditions". However this invention can be used in other applications such as for monitoring changes in conditions of manufactured commercial or industrial liquids or absorbent materials which vary with changes in pH and it is to be understood that such conditions are also embraced by the expression "a correlated condition" .

For illustrative purposes, particular reference will be made to the application of this invention to monitoring physiological "correlated conditions". During surgical and other medical applications, blood or other body fluids are drawn, is taken from patients and analysed to determine, inter alia, pH values, as these values provide indications as to the state of the patient's biochemical structure. The samples are taken to a biochemistry department where blood gas analysis and other testing is used to provide the necessary pH readings. Unfortunately, due to temperature changes and possible exposure of the sample to air. the pH readings obtained are often inaccurate. Furthermore, this is a time consuming and cumbersome task and requires reference solutions for calibration purposes. Unfortunately while it is known that a patient's pH reading sampled at selected body locations may provide almost instantaneous indications of changes in the patient's condition, the currently available laborious techniques for monitoring pH do not permit adequate monitoring whereby such readings can be used to best advantage. For example, the monitored pH of a foetus will

provide an indication of inadequate oxygen supply to the brain during birth.

At present, during childbirth a cardio-tocograph (CTG) machine may be arranged to monitor the heart rate of the foetus and the pressure within the mother's abdomen.

Normally, if a constriction occurs to the blood supply from the mother to the foetus, an oxygen depletion Chypoxic) situation occurs in the brain and after fifteen minutes the heart goes into bradycardia and is signalled to slow down. This bradycardia is monitored by the CTG machine and an alarm is sounded. If the bradycardia does not occur momentarily with contraction, remedial action is taken. However. it is believed that any oxygen depletion within the brain will cause some degree of irreversible brain damage. Accordingly if the pH could be monitored progressively or continuously during labour, then steps could be taken for remedial action to hypoxic episodes when necessary to substantially eliminate oxygen starvation of an infant ^:s brain. Burns patients often develop localized infections which cause local variations in pH. Thus, tissue pH sampling of a burns patient at various burns locations would enable infected areas to be readily located. If such pH sampling could be carried out wάthout disturbing the patient's bandages, the infected areas could be treated without disturbing the remainder of the burns. Furthermore, many industrial liquid processing systems could be made more efficient if it were possible either to accurately and more readily determine the pH of the liquid than is presently possible, or to constantly monitor variations in pH.

This invention aims to alleviate the abovementioned disadvantages and to provide a method of and apparatus for monitoring a correlated condition which will be reliable and efficient in use. Other objects and advantages of this invention will hereinafter become apparent.

With the foregoing and other objects in view, this invention in one aspect resides broadly in a method of monitoring pH or a correlated condition in a liquid, tissue or other absorbent material, including:- providing an apertured non-electrically conductive enclosure for sampling fluid; covering the aperture of said apertured enclosure with a membrane; arranging sampling fluid in said enclosure, said sampling fluid being a fluid which exhibits or may be induced to exhibit electrical characteristics when in contact with a further liquid or absorbent material through a membrane and which characteristics vary predictably with variations in a correlated condition of said absorbent material, and providing monitoring means for monitoring said electrical characteristics.

According to one method, the sampling fluid is an amniotic fluid, a constituent thereof, or a synthesised constituent thereof which is or may be induced, by maintaining the sampling fluid at a substantially constant temperature to provide electrical characteristics which vary predictably with variations in a correlated condition. Preferably the amniotic fluid is maintained substantially at body temperature. This may be achieved by immersins' the enclosure in the body or by arranging the enclosure in a passageway externally of the body through which blood or bod'* fluids may be diverted and held at 37 degrees celsius. A heating element and thermostat control may be provided to maintain the necessary temperature range. Preferably, the amniotic fluid is sterilized or treated to destroy the DN^'A of any cells therein, such that the risk of infection to the patient is minimised in the event that the sampling liquid enters the patient's body. This sterilization may be

_SUBSTITUTE SHEET achⁱeved by gamma radiation of the sampling liquid. _υ, course other treatment methods may be used to destro_y or ma contamⁱnating cells ineffective. It is also preferred that when the sampling fluid is a fluid extracted from an animal, the membrane is so formed as to prevent passage of cells therethrough but permit flow of ions therethrough. For this purpose the membrane may a permeable substance. Of course non-ⁱon permeable membranes which exhibit monitorable characteristics other than ion flow when in contact with a solutⁱon to be monitored may be utilised if suitable

According to a further aspect, this invention resides ^broadly m a probe including an apertured enclosure_' a membrane sealing said apertured enclosure; sampling _fluid , saⁱd enclosure; an electrode assembly in said enclosure and adapted for interacting with the sampling fluid whereb_y an electrical potential is produced when said membrane is^' in contact with a liquid or other absorbent material monitoring -ans for monitoring charges in said electrical potential and mountⁱng means for supporting said enclosure.

In one embodiment the mounting means is a needle whereb_v the enclosure may be carried therewith into a patient's bodv^'. Alternatively, the mounting means may be a catheter or a ^' temperature controlled reservoir through which li_{quid to be} onⁱtored ma^y pass or be delivered. The mountin_g means mav be a hard piece so that the probe assembly can be selec_tivel- xnserted in a liquid or operative!, held against an absorbent or tⁱssue like material.

It is also preferred that sterile storage means be provⁱded for the probe whereby the membrane is maintained in a moist condition.

If desired the membrane may be separated from the I qu d, tissue or absorbent material to be monitored b_{y a} further membrane and a suitable interposed electrol_yte^" ±n D one form the sampling fluid is amniotic fluid extracted from the cavity of the uterus and in particular the uterus of a sheep.

In a preferred embodiment of the invention the apertured enclosure is a glass enclosure supported within the free end portion of a hypodermic needle. In such arrangements the aperture may be coincident with the open end of the needle or with a window in the side wall of the needle. Alternatively the enclosure may be a glass bulb supported at the end of a probe which may be in the form of a flexible conduit so as to convey the leads for the monitoring means to a position remote from a patient being treated.

The monitoring means may comprise an electrode assembly disposed within the sampling liquid. The electrode assembly may be a single electrode or a pair or electrodes adapted for interacting with the sampling fluid whereby an electrical potential is produced. The electrodes may be polarized and one may be earthed so as to provide a grounded reference for one electrode. The electrodes may be connected through an amplifier to an indicator gauge such that a constant visual indication of the monitored pH or a correlated condition may be displayed to give a constant display of pH values . Of course this display may be a digital or an analogue display. Other types of displays such as audible displays may be provided as required.

In order that this invention may be more readily understood and put into practical effect, reference will no be made to the accompanying drawings which illustrate a typical embodiment of the present invention. The probe 9 is in the form of a hypodermic needle assembly 10 having a tubular shaft portion 11 extending from a hand grip portion 12. The tubular shaft 11 contains a glass bulb 13 which encapsulates the sampling fluid and a

SUBSTITUTE SHEET pair of platinum electrodes 15 provided with connections 14 which extend rearwardly through the bore of the shaft 11' and exit from the remote end of the handle 12. The glass bulb

13 is apertured at 16 and a membrane 17 extends sealably across the aperture 16. The membrane 17 is exposed through an open window 18 formed in the side wall of the shaft 11.

In this embodiment, the sampling fluid is a sample of amniotic fluid taken from a pregnant sheep and the electrodes

14 are formed with bulbous silver terminals. These are connected by the connections 14 to an amplifier 20 and an associated meter 21 which is calibrated to giv.e a direct reading which correlates to the pH of sample liquids in which the needle 10 is inserted.

In use, the needle 10 may be simply inserted into a patient whereupon the temperature of the sampling fluid will stabilize at body temperature and provide a potential difference between the electrodes 15 of up to 10 millivolts which may be calibrated to correlate to pH values of liquids or tissues in contact with the membrane 17.

Accordingly in use, such as in the earlier mentioned applications, the needle 10 may be inserted subcutaneously into the scalp of a foetus so as to provide a constant monitoring of pH values of blood circulating. Any constriction in the blood oxygen supply o the foetus will immediately be detected as a result of changes in the pH of the blood and remedial action may be taken before damage occurs. Alternatively a burns patient exhibiting results of an infection may be monitored by inserting the probe 9 subcutaneously into various areas of the burn so that by detecting the change in pH characteristic, an infection can be located. Once located the burn may be treated locally. Such a probe could also be inserted through a cast to monitor- concealed parts of the body. , - In a further embodiment the active components of the probe are located on a catheter like probe whereby it may be fed to various parts of the body. For example, the probe could be inserted down the oesophagus of an infant to monitor regurgitation of stomach fluids into the oesophagus.

The probe could also be provided with internal pressure sensing means for monitoring a possible rupture of the membrane or enclosure whereby an immediate alarm could be given upon such contingency. The sampling fluid may be the active ingredient or ingredients isolated from a suitable amniotic fluid or a corresponding synthesised fluid. Further, for. use in industrial applications the probe may be mounted in a vessel provided with heating or cooling means and thermostatic temperature control through which the liquid to be monitored may be circulated or sampled.

It will of course be realised that the above has been given only by way of illustrative example of the invention and that all such modifications and variations thereto as would be apparent to persons skilled in the art are deemed x<^~, fall within the broad scope and ambit of the invention as is defined in the appended claims .

Claims

THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS : -

1. A method of monitoring pH or a correlated condition in a liquid, tissue or other absorbent material, including: - providing an apertured non-electrically conductive enclosure for sampling fluid; covering the aperture of said apertured enclosure with a membrane; arranging sampling fluid in said enclosure, said sampling fluid being a fluid which exhibits or may be induced to exhibit electrical characteristics when in contact with a further liquid or absorbent material through a membrane and which characteristics vary predictably with variations in a correlated condition of said absorbent material, and providing monitoring means for monitoring said electrical characteristics.

2. A method as claimed in claim 1, wherein said sampling fluid is selected from the group consisting of amniotic fluids, derivatives of amniotic fluids or synthetic analogues of amniotic fluids.

3. A method as claimed in claim 2, wherein said sampling fluid is sterilized ovine amniotic fluid.

4. A method as claimed in any one of the preceding claims vherein said membrane is ion permeable.

5. A probe including an apertured enclosure; a membrane sealing said apertured enclosure; sampling fluid in said enclosure; an electrode assembly in said enclosure and adapted for interacting with the sampling fluid wliereby an electrical potential is produced when said membrane is in contact with a liquid or other absorbent material monitoring means for monitoring charges in said electrical potential and

SHEET mounting means for supporting said enclosure .

6. A probe as claimed in claim 5, wherein said apertured enclosure comprises a glass envelope.

7. A probe as claimed in either of claims 5 or 6 , wherein said membrane is an ion permeable membrane.

8. A probe as claimed in any one of claims 5 to 7 , wherein said sampling fluid is sterilized ovine amniotic fluid.

9. A probe as claimed in any one of claims 5 to 8 , wherein said monitoring means comprises a single electrode or a pair of electrodes adapted for interacting with the sampling fluid whereby an electrical potential is produced.

10. A probe as claimed in claim 9, wherein said mounting means comprises a hypodermic needle, the enclosure being mounted within the needle such that the membrane is either coincident with the open free end of the needle, or coincident with a window provided in the side wall of the needle .

11. A method substantially as hereinbefore defined with reference to the example.

12. A probe substantially as hereinbefore defined with reference to the accompanying drawing.