JPS5931327B2 - Carbon dioxide transcutaneous measurement electrode device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electrode device for percutaneously measuring the concentration (or partial pressure) of carbon dioxide in tissue or blood.

Knowing the carbon dioxide concentration in the blood is extremely important in clinical tests for determining the quality of the respiratory and metabolic functions of a living body and the approximate value of the pH concentration in the blood. Conventionally, the main method used to measure the concentration (or partial pressure) of carbon dioxide in blood is to draw blood, especially blood from the arteries, and directly measure it, but this method requires continuous measurement over time. The problem was that it was impossible to perform this procedure and that it caused pain to the patient.In particular, in the case of premature infants and newborns, blood sampling was highly invasive, making it extremely difficult to implement. Unlike the above-mentioned direct method, the transcutaneous electrode method captures carbon dioxide gas diffused from blood through tissues on the skin surface, and can continuously measure it over time without causing pain to the patient.

Prior to explaining the transcutaneous carbon dioxide measuring electrode according to the present invention, the carbon dioxide gas electrode will be explained in general.

An electrode for electrochemically measuring CO2 in a gas or solution basically consists of the following four parts, as shown in FIG. (1) pH detection electrode in the center, consisting of an internal standard electrode 1 made of Ag/AICI or the like, an internal electrolyte 2, a glass tube wall 3 made of lead glass or the like, and a thin film 4 made of soda glass or lithium glass. :
(2) CO2-permeable electrode membrane 5; (3) A spacer 6 such as a thin cloth, which exists as a thin layer between the electrode membrane 5 and the lower surface of the pH electrode, and further extends to the outer surface of the electrode, and a NaHCO3 (4) An external standard electrode 8 in contact with the external electrolyte T containing the external electrolyte T. The electrode membrane 5 is tightened and tensioned with a suitable rubber ring against the plastic membrane support tube 9. That is, the above PH electrode has a glass thin film 4 with good H+ permeability (for example, Na2O26%, B
The internal electrolyte 2 (
KCI, etc.) and standard electrode 1 (A9-Af!) into this.
Cl system or H9-H92Cl2 system), and the magnitude of H+ in the liquid outside the glass thin film 4 (PH
By changing the potential between the external standard electrode and the external standard electrode that contacts the outer liquid depending on the
Measure.

For the electrode membrane 5, a membrane such as Teflon that does not permeate water (and therefore the electrolyte) but permeates CO2 is used, and a spacer 6 (thin cloth or thin paper) is used to separate the membrane and the glass thin membrane of the internal electrode. A thin electrolyte layer of a certain thickness is created between the two.

This external electrolyte contains NaCl or K for electrode reactions.
In addition to CI, NaHCO3 is included, but all of this dissociates into HCO3-)HendersOnHa
According to Sselbalch's equation, the pH of the external liquid is determined by the ratio of this to H2CO3 generated by CO2 entering through the membrane. As is clear from the following equation, when CO2 is low,
CO2 is released from this electrolyte through the membrane and the pH increases. When CO2 outside the membrane (measurement object) is high, HCO3:H2CO3 decreases (PH decreases), and when CO2 outside the membrane (measurement object) is low, HCO3-:H2CO3 increases (PH increases).

That is, the external electrolyte between the electrode film and the glass thin film is Na.
By containing HCO3, it becomes a buffer solution whose pH changes with CO2, and at the same time, by containing NaCl (or KCI), it becomes an electrolyte solution which reacts with the external standard electrode 8.

Since a material with good CO2 permeability and permeability (such as Teflon film) is selected for the electrode membrane, the test solution outside the membrane (
Since the partial pressure of CO2 in the thin outer electrolyte layer (or gas) reaches equilibrium relatively quickly (1 to 2 minutes), the pH of this electrode solution can be measured. The external CO2 partial pressure will be measured. The percutaneous arterial blood carbon dioxide gas partial pressure measuring device by the present inventor has been developed by modifying the above-mentioned CO2 measuring electrode into a shape convenient for installation on the skin surface, and by arterializing the subcutaneous tissue to measure arterial blood carbon dioxide gas. This device is equipped with a constant temperature heating mechanism to reflect the pressure. When applied to the subject's skin surface, carbon dioxide gas in the subcutaneous tissue diffuses from the skin, causing the electrode film (which is permeable to carbon dioxide gas) to diffuse through the skin. The liquid enters the liquid outside the glass electrode through the hydrophobic membrane (hydrophobic membrane), and a potential difference is generated between the liquid inside the glass electrode and the liquid outside in proportion to the concentration of permeated carbon dioxide. By measuring this potential difference, the PCO2 value in the tissue can be obtained.In this case, when the skin in contact with the electrode across the electrode membrane or the skin in the vicinity is heated to an appropriate temperature, the skin tissue in the vicinity of the electrode is locally heated. If the electrode structure and measurement conditions are appropriate, the carbon dioxide partial pressure measured by the electrode will be substantially equal to that of arterial blood. DESCRIPTION OF THE PREFERRED EMBODIMENTS The configuration and effects of the present invention will be explained below with reference to the accompanying drawings showing examples. FIG. 2 shows an assembled diagram of the electrode device according to the present invention.
31 is an H+ permeable glass thin film, which can be made of ordinary soda glass, but it has high electrical conductivity and is susceptible to acid errors, alkali errors,
A thin glass with a wall thickness of about 0.02 to 0.1 mm is used because it has a small salt error, a quick response time, and is highly safe.

32 is a space for maintaining the external liquid of the glass electrode at a constant thickness, and is preferably made of a porous hydrophilic thin film, such as Joseph paper.

33 is preferably a polymer film that is permeable to carbon dioxide gas but hydrophobic and impermeable to water or electrolyte, such as a polymer film made of tetrafluoroethylene resin, polyethylene, polypropylene, or the like.

Reference numeral 34 denotes a glass electrode internal solution, for example, an electrolyte solution such as KCI is used.

35 is an internal electrode in a glass electrode, and is preferably a silver wire whose surface is coated with A9Cl.

Reference numeral 36 designates the wall portion of the glass electrode tube, which is made of glass having a melting point lower than that of the H+ transparent glass 31 and having good fusion properties, such as a tube made of lead glass.

Reference numeral 37 indicates an external electrolyte solution for the glass electrode, which is preferably a mixed solution of NaHCO3 and NaCl whose pH changes depending on the CO2 partial pressure and which serves as a chloride ion source for the external reference electrode.

This external electrolyte solution also exists as a thin layer between the glass thin film 31 and the electrode film 33. 38 is preferably a silver tube with an A9C2 surface and an external reference electrode.

Reference numeral 39 denotes an electrode membrane support tube, which fixes the electrode membrane to the bottom surface, facilitates the attachment and detachment of this membrane, and serves as a storage tank for holding the external liquid of the glass electrode.

As the material, an electrically insulating material suitable for fixing the electrode film is used. Reference numerals 10 and 11 designate cushion members for fixing the electrode membrane support tube, and each uses an 80'' ring and a flat ring made of silicone rubber or the like.

13 is a lead wire fixing tube for fixing the lead wires 40 and 41 of both the inner and outer electrodes, and a metal tube such as stainless steel is used.
is a shielded mesh tube with both inner and outer electrode lead wires 40 and 41.

Reference numeral 15 denotes the body of the skin heating part of the electrode, which is made of a metal with good thermal conductivity, such as copper, brass, aluminum, etc.

16 is a skin warming/electrode membrane pressing thin plate with good heat conduction.
It is preferred to use a resilient metal plate, for example a 0.1+ thick bronze plate.

Reference numeral 17 denotes a resistance wire for a heater, preferably an enamel-coated manganin wire, a CU-N2 wire, or the like.

18 is a temperature sensing element, for example a thermistor.

19 is a fixed tube for the heater lead wire 42 and the thermistor lead wire 43.

20 is an electrode section shown in an independent form in FIG. 3A and a third
This is a fixing screw for the heating unit shown in an independent form in Figure C.

21 is a highly insulating embedding resin, preferably epoxy resin or silicone resin.

Reference numeral 22 denotes a metal plate for shielding the electrode portion, which is a thin plate made of stainless steel or the like.

23 is a double-sided adhesive tape for adhering the skin and the electrode;
24 is the skin, but there is no adhesive tape near the center opening corresponding to the glass electrode of the electrode, and a contact liquid 25 such as distilled water or saline solution is inserted into this part to remove the CO2 of the electrode.
Intervening in order to improve responsiveness to

The measurement principle, procedure, etc. will be explained step by step with reference to FIG.

The electrode device according to the present invention is attached to a double-sided adhesive tape 23 for adhesion to the skin.
and attach it to the subject.

At this time, it is necessary to appropriately bring the skin surface 24 and the electrode surface into close contact using a contact liquid 25 so as not to create a gap between the skin surface 24 and the electrode surface.
When the temperature of the skin heating section body 15 is heated to 43 to 44 DEG C. after being brought into close contact with the skin surface 24, the skin in the contact area and the surrounding area is heated and the subcutaneous tissue is arterialized. Therefore, the carbon dioxide concentration (partial pressure) in the tissue becomes substantially equal to that contained in arterial blood, and this carbon dioxide diffuses through the skin tissue and reaches the carbon dioxide permeable electrode membrane 33. It passes through this and reaches the external electrolyte layer 37 between the glass electrode and the electrode membrane. The carbon dioxide gas that reaches the external liquid of the glass electrode produces carbonic acid through the reaction CO2+H2O2H2CO3, but the external electrolyte contains Na.
Since HCO3 is included, NaHCO3/H2CO3
A system buffer system is formed whose mass changes depending on the CO2 concentration.

When a difference in hydrogen ion concentration occurs between the internal liquid of the glass electrode and the external liquid, a potential difference corresponding to the theoretical equation occurs, but the H+ activity a'H+ of the internal liquid of the glass electrode is the H+ that passes through the glass thin film. Since it is extremely small, it can be considered to be a fixed value. Combining the second and third terms of the above equation, this is Ef! Then, the measured potential difference indicates the hydrogen ion concentration in the external liquid.

The relationship between this value and pH is actually determined experimentally using two to three types of standard pH solutions. When the hydrogen ion concentration value is determined in this way, this value is HandersOn-
Based on the Hasselb-Alch equation, PK depends on the concentration of carbon dioxide gas, so PK is H2CO32H+1°-HCO
The antilogarithm of the dissociation constant of 3.

When the concentration and temperature of NaHCO3 in the external electrolyte become constant, the first and second terms above become constant, and the PCO2 in the external electrolyte therefore balances with the PCO2 outside the membrane (
Transcutaneous measurement allows the carbon dioxide concentration in arterial blood to be determined closely. The relationship between this carbon dioxide concentration and PH is based on the temperature of the external liquid and the concentration of NaHCO3 (usually 0.005
Once m01 or 0.01m01) is determined, it can be determined from a table, or it can be determined experimentally using a standard partial pressure gas of CO2. Figures 3A, 3B, and 3C show the structure of each part of the electrode to clarify the main points of the present invention.

The important points, features, effects, etc. of the present invention will be pointed out below.

(1) Overall structure: The electrode device of the present invention consists of an upper lid part with a built-in glass electrode (Fig. 3A), an electrode membrane support tube to which a membrane is fixed (Fig. 3B), a heating element and a heat sensitive element embedded. The electrode skin heating section main body (Fig. 3C) is composed of three independent parts, and the entire structure includes a membrane 33 and an electrode membrane support tube section 39 having a U-shaped cross section between the soil cover section and the electrode skin heating section main body. It is assembled so that it can be inserted into the

According to this method, not only can the electrode membrane and the glass electrode external liquid be exchanged extremely easily, but also the electrode membrane surface can always maintain a constant degree of elongation without wrinkles or sagging (
The commonly used method shown in FIG. 1 requires skill and has poor reproducibility). This allows the thickness of the external electrolyte layer to be kept constant, allows for assembly and disassembly without requiring any skill, and allows the skin surface to be accurately heated to a predetermined temperature over a wide area. It has a great feature of being able to do it. (2) Glass electrode: Glass electrode Carbon dioxide gas permeates through the lower part and outer periphery of the glass thin film 33 through an electrode external liquid containing chlorine ions and a component (HaHCO3) that creates a buffer system with carbon dioxide gas near neutral pH. (water vapor,
It is covered with a membrane (which does not allow moisture, electrolytes, etc. to permeate through it), and the carbon dioxide that diffuses from the skin surface and passes through this membrane is trapped in the thin layer of the external liquid, and the increase in H+ within this thin layer causes approximately CO2 is quantified.

In particular, by heating the carbon dioxide gas diffusing from the skin surface and the CO2 in the external liquid thin layer through the carbon dioxide gas-permeable thin film to bring them into equilibrium, the arterial blood PCO2 is brought into equilibrium with the tissue. A major feature of the carbon dioxide transcutaneous measuring electrode device according to the present invention is that it measures PCO2. 3) Electrode membrane: As the electrode membrane used in the present invention, a polymer membrane that is permeable to carbon dioxide gas and impermeable to water and electrolyte is used.

Films used for this purpose include fluororesin films (Teflon films), polyethylene films, polypropylene films, and polyester films (Mylar films), which can be selected depending on the required response speed and strength. In the electrode device of the present invention, tetrafluoroethylene (Teflon), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), polypropylene, etc. having a thickness of 10 to 20 μm were suitable. Among the membranes mentioned above, fluororesin films have excellent properties as they do not absorb water, but on the other hand, they have extremely strong water wicking properties, so they have poor wettability with the electrolyte on the membrane surface, and they repel the electrolyte, resulting in poor electrode safety. may cause damage.

As a result of various studies on how to improve this drawback,
When one side of the film was subjected to corona discharge or etching treatment with a naphthalene solution of metallic sodium, the affinity of the electrolyte was significantly improved and the electrode reaction was stabilized. It has been found that it is effective to perform similar etching or surface roughening treatment on one side of other films as well. If these treatments are carried out appropriately, the spacer for keeping the thickness of the external electrolyte layer constant can also be removed. 1) Method of attaching the electrode membrane: The electrode membrane 33 is attached by fitting a cylindrical electrode membrane support tube 39 to which the membrane is fixed in advance into the main body of the heating section.

According to this method, it is possible to attach the membrane without requiring any skill and without applying wrinkles or excessive tension to the membrane surface, thereby significantly stabilizing the electrode reaction. Note that the electrode membrane support tube used for this purpose is preferably provided with a groove 39 on its inner surface, and this groove serves as a storage container for the electrolyte solution. Very narrow grooves or holes may also be provided to provide air vents to prevent pressure changes to the electrolyte during assembly and use. ])
Skin heating: Arterialization of the skin is caused not by heating from electrodes;
Separately, a heating device with an independent main body as shown in FIG. 3C was provided to perform the heating over a wide area and with high precision. This increased the heat capacity of the heating element and improved the accuracy of temperature control. For arterialization of the subcutaneous tissue to a degree that faithfully reflects arterial blood composition,
The skin surface directly under the electrode is not enough, and it is required to heat a much wider area evenly and with high precision.However, the skin heating unit body according to the present invention has a wide heating surface and is capable of heat transfer. The arterialization is also excellent, and extremely precise arterialization can be achieved. (
6) Installation of membrane pressing plate 16: In the electrode according to the present invention, the electrode membrane pressing plate 16 is provided with an inner hole extending portion 16', and the thin and elastic metal plate presses the membrane around the glass electrode. Since the thickness of the gap between the membrane and the electrode is kept constant, and the area where the membrane is directly pressed against the skin can be minimized, the stability of electrode sensitivity has been significantly improved.

Furthermore, since this pressing plate 16 is made of metal, it is also intended to be useful for heat transfer and heating to the skin near the cathode. Table 1 shows a comparison between the blood carbon dioxide concentration (partial pressure) measured by transcutaneous measurement for each subject using the electrode device according to the present invention and the value measured by the conventional method of blood sampling.
Although the results differed somewhat depending on the subject, a high reflection rate of 84% to 91(f) was obtained with respect to the measured value by blood sampling. Although there is a slight difference between these results and the actual measured values, when considering the superiority of transcutaneous measurement in that there is no invasion to the subject, the electrode device according to the present invention provides an extremely useful clinical testing device. and its social effects are extremely significant. FIG. 1 is a cross-sectional view showing an example of an immersion type carbon dioxide concentration measuring electrode, and FIG. 2 is an assembly diagram of an embodiment of the transcutaneous electrode device according to the present invention. is a spacer, 33 is a carbon dioxide permeable hydrophobic membrane, 34 is an internal liquid of a glass electrode, 35 is an internal electrode of a glass electrode, 36 is a tube wall of a glass electrode, 37 is an external liquid of a glass electrode, and 38 is an external control. electrode, 39 an electrode membrane support tube, 10 a lower cushion member for the electrode membrane support tube, 1
1 is an O-ring-shaped upper cushion member for the electrode membrane support tube, 12 is an electrode holder 13 is a tube for fixing both the inner and outer electrode lead wires, 14 is a shield mesh tube for both the inner and outer electrode lead wires, 15 is the main body of the electrode skin heating section, 16 17 is a heater wire, 18 is a temperature sensing element, 19 is a heater and thermistor lead wire fixing tube, 20 is a screw for fixing the electrode part and heating part, 21 is a high Insulating embedding resin, 2
2 is a metal plate for shielding the electrode portion, 23 is a double-sided adhesive tape for skin adhesion, 24 is a skin surface, 25 is a contact liquid, and 40 to 43 are lead wires.

Claims (1)

[Scope of Claims] 1. A top lid in which a glass electrode using a hydrogen ion permeable glass thin film and an external reference electrode that contacts the external liquid of the glass electrode at one end are fixed together, and a carbon dioxide gas permeable polymer membrane is used. Three independent parts, an electrode membrane support tube fixed to one end and having the external liquid adhered to the membrane, and a skin heating part main body in which a heating element and a heat sensitive element are embedded, are configured so that they can be attached to and detached from each other, An electrode device for transcutaneous measurement of carbon dioxide gas, characterized in that the membrane and the electrode membrane support tube section are assembled by being attached between an upper lid section and a main body of the electrode skin heating section. 2. The electrode membrane support tube according to claim 1, characterized in that an electrode membrane support tube is used, in which a polymer membrane of fluororesin, polyethylene, polypropylene, polyester, etc. is fixed to one end of a cylinder or a cylinder having a groove on the inner surface. Carbon dioxide transcutaneous measurement electrode device. 3. Claim No. 3 characterized in that a fluororesin film such as polytetrafluoroethylene, tetrafluoroethylene-hexafluoropropylene copolymer, etc., which has been etched on one side by corona discharge, sodium naphthalene solution, etc. The carbon dioxide transcutaneous measuring electrode device according to item 1. 4. A patent claim characterized in that a pressing plate made of a thin metal plate having a spring effect, such as phosphor bronze or stainless steel, and having a small hole in the center is tightly attached to the end surface of the heating unit main body on the side that comes into contact with human skin. The carbon dioxide transcutaneous measuring electrode device according to scope 1.