JPS5931329B2 - Transcutaneous blood carbon dioxide sensor - 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 and caused pain to the patient. Particularly in the case of premature infants and newborns, blood sampling is highly invasive, making implementation extremely difficult. 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.

The present invention relates to the improvement of a transcutaneous blood carbon dioxide sensor, and in particular relates to the structure of a glass electrode for detecting pH changes and the skin heating mechanism.

Figure 1 shows the basic structure of a transcutaneous blood carbon dioxide sensor. KCt or NaCt, etc. An upper lid part 7 in which an internal electrolyte 3 mainly composed of an aqueous solution, a glass electrode 5 containing a silver wire 4 whose surface is abrasive with AgcA, and an external reference electrode 6 such as silver/silver chloride are built in, and an electrode film. A heating part 1 in which a membrane holder 9, a heating element 10, and a heat sensitive element 11 are embedded, to which a membrane holder 8 is attached in advance;
It is constructed of three independent parts (2), and has a structure in which the membrane holder part can be easily installed between the upper lid part and the heating part.

Note: NaHCO3 is used between the electrode film and the glass thin film.
, an electrolytic solution 1 consisting of a mixed aqueous solution of NaCι or KCt, etc.
3, and if necessary, a spacer such as paper or nylon cloth is interposed.

However, the sensor with the above basic structure is
Since the internal electrolyte is sealed in an H-responsive glass container, l) If the sensor is overturned,
The internal electrolyte on the surface of the pH-responsive glass thin film moves and runs out, causing the sensor to lose its function.

1i) When used in a cold region, the internal electrolyte may freeze, causing problems such as glass breakage.

111) When the sensor is heated during transdermal measurement, a portion of the internal electrolyte evaporates and condenses in the glass container, resulting in abnormal sensor response.

1) Internal electrolyte leaks easily, causing insulation failure. V) The glass thin film part is easily damaged.

The D glass electrode has a large temperature effect on its electromotive force;
Although it is necessary to increase the temperature within ±0.2° C., it is difficult to keep the temperature of the glass electrode portion constant, and therefore the stability of the measured values is poor.

There are other problems. The present invention eliminates the various problems that occur when using the glass electrode filled with an internal electrolyte, and provides a transdermal blood carbon dioxide sensor that is stable, robust, and has good workability.

FIG. 2 shows the structure of a sensor according to the present invention, and the structure of the glass electrode and heating mechanism are completely different.

In the figure, 16 is a glass thin film responsive to H± ions, and 17 is a toric body made of a highly insulating material such as glass, ceramic, plastic, rubber, etc. The glass thin film 16 is attached to the end by welding, bonding, etc. A container with a glass thin film is constructed by fixing the glass thin film. 18 is A formed on the entire surface of the glass thin film 16 and a part or the entire surface of the toric body 17.
The conductive film is made of a metal such as silver, Pt, or Ag, or a salt such as AgCt, and is formed by a vacuum evaporation method, an ion blating method, or the like.

In addition, in the case of salts having a melting point lower than that of the glass used, a film can be formed on the glass surface by a hot melting method. Reference numeral 19 shows a heating element which is a particularly important component of the present invention, and is made of a metal with good thermal conductivity such as silver, copper, or aluminum, and has a built-in heater 20 and a temperature detection element 21. It is configured to be able to control the temperature to a constant temperature.

In this explanatory drawing, the heating body is assembled using a conductive adhesive if necessary so that it comes into close contact with the conductive film 18 formed on the inner surface of the glass thin film, and the potential on the surface of the conductive film is adjusted via the heating body. , which shows a glass electrode with a heating mechanism that can be read by a lead wire 22 connected to one end.
Of course, it is also possible to use a heating element whose surface is insulated by connecting lead wires directly to the conductive film 18 provided on the inner surface of the glass thin film. Reference numeral 23 denotes an annular external comparison electrode made of silver/silver chloride or the like, which is provided on the outer periphery of the glass electrode with a heating mechanism according to the present invention.

The glass electrode with heating mechanism and the external electrode are fixed to an electrode holder 24 made of an insulating material such as plastic or rubber.

26 is a carbon dioxide permeable and hydrophobic polymer film;
Electrode film 2 made of, for example, Teflon, silicone rubber, etc.
5 is attached to the end, and it is a disposable part along with the electrode membrane.

An aqueous solution containing KCt, NaHCO3, etc. is placed between the end surface of the electrode and the electrode film to increase carbon dioxide response (depending on the concentration of CO2).
It is the same as the conventional method to use it as an electrolyte (H changes). 27 is a fixed support plate for fixing the membrane holder to the electrode surface and the sensor to the skin surface, and is connected to the electrode holder by a screw mechanism.

FIG. 2 shows a cross-sectional view showing the structure of the transcutaneous blood carbon dioxide sensor according to the present invention. Next, the features and effects of the present invention will be explained.

According to the present invention, changes in H+ ion concentration (PH changes) can be measured without using an internal electrolyte. Even if the vehicle rolls over, the sensor function will not be impaired. mouth. There is no problem of the internal electrolyte freezing and damaging the glass electrode in cold regions. C. When the sensor is heated, a portion of the internal electrolyte evaporates and there is no abnormal behavior in potential caused by condensation in the space of the glass electrode.

two. There is no risk of trouble occurring due to internal electrolyte leaking from the glass electrode.

Ho. Since the heating element is in close contact with the inner surface of the glass thin film through the conductive film, the glass thin film part is reinforced.
Much more resistant to external pressure and impact.

As described above, the present invention not only eliminates the drawbacks caused by glass electrodes, but also allows the heating element to be brought into close contact with the inner surface of the glass thin film via the conductive layer, resulting in less problems compared to conventional products. The following effects can be obtained. That is, (1) Since the PH-responsive glass thin film is in direct contact with the heating element made of a metal with good thermal conductivity, the temperature of the electrode part rises to the measurement temperature in an extremely short time, and the measurement temperature can be accurately measured from then on. maintained.

Therefore, there is no drift in the generated potential due to temperature changes in the electrode section, which was seen in conventional products. (2) Conventional products have a structure in which an annular heating mechanism is attached around the glass electrode, so if the diameter of the glass electrode is increased, the skin temperature at the measurement site will not rise, so the diameter of the glass electrode must be increased. However, according to the present invention, since the glass electrode itself heats the skin, the diameter of the glass electrode can be adjusted to any size according to the required characteristics. I can do it.

(3) Since the conventional product uses an annular skin heating element placed around the outer periphery of the glass electrode, the heating area of the skin is inevitably large, and if a burn occurs on the heated part, the scar may become large. However, according to the present invention, the area of the skin heated is the same as the cross-sectional area of the glass electrode, so the scar caused by a burn is much smaller than with conventional products, making it clinically safe. It can be used.

(4) Glass electrodes have a large temperature effect on their electromotive force, and it is necessary to warm the glass electrode temperature to within ±0.2°C. This is achieved by the heating method of the present invention. As explained above. According to the present invention, the drawbacks of conventionally used transcutaneous blood carbon dioxide sensors can be eliminated and it is possible to provide a transcutaneous blood carbon dioxide sensor that is extremely superior in terms of performance and handling.

Examples will be described below.

The composition of the glass thin film is Na2O25O by weight! ), C
Using glass with aOlO% and 65% SiO2, a glass thin film with a diameter of 8 mm and a thickness of 0.15 mm is welded to the end of a lead glass cylinder using glass solder, and platinum is applied to the inner surface of the glass container. was vacuum deposited.

A heating element inscribed inside the glass container on which platinum is vapor-deposited is made of copper, and a heater for heating is attached to this heating element.
After attaching a thermistor for temperature detection and a lead wire for potential measurement, the heating body was adhered to the inner wall of a glass container with a conductive adhesive and used as a glass electrode. A silver ring whose surface was silver chloride-treated by electrolytic method at 0.1 NHC was adhered and fixed to the outer periphery of the glass electrode as an external reference electrode using an epoxy resin.

As external electrolyte, 0.02m0tNaCt+0.0
05m0tNaHC02 was used. 20 as an electrode film
A μ-thick Teflon film was used. It was confirmed that the sensor according to the present invention manufactured under the above manufacturing conditions had excellent characteristics and operability as shown in Table 1.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram of the structure of a conventionally used sensor for measuring transcutaneous blood carbon dioxide concentration, and Fig. 2 is an explanatory diagram of a sensor for transcutaneous blood carbon dioxide concentration measurement according to the present invention. indicates the following members. 1...H+ ion responsive glass thin film, 2...
...Glass container, 3...Internal electrolyte, 4...
...Silver wire with AgCt surface, 5...Glass electrode, 6...External electrode, 7...Top cover, 8...Electrode Membrane, 9... Membrane holder, 10... Heating element, 11... Heat sensitive element, 12... Heating section, 13... Electrolysis liquid,
14...Potential measurement cord, 15...
Cord from heating body, 16... H+ ion responsive glass thin film, 17... Highly insulating toric body, 1
8... Conductive layer, 19... Heating body, 20
... Heater, 21 ... Temperature detection element, 22 ... Lead wire, 23 ... External electrode, 24 ... Electrode holder 25・・・・・・
...Electrode membrane, 26...Membrane holder 27...
...Fixed support plate.

Claims (1)

[Claims] 1. A carbon dioxide permeable polymer membrane is placed on the patient's skin, and an electrolyte solution is held on the side of the polymer membrane facing the skin, allowing carbon dioxide gas to diffuse from the skin into the electrolyte solution through the polymer membrane. In a transcutaneous blood carbon dioxide sensor, the pH of the electrolyte solution changes according to changes in blood carbon dioxide partial pressure, and this pH change is detected as a potential difference between a glass electrode and an external reference electrode. Metals such as silver, gold, platinum, copper, aluminum, AgCl, A
Transcutaneous blood carbon dioxide, characterized by having a heating element with a built-in heating heater and a temperature detection element inside a glass electrode formed with a conductive film made of a metal salt such as GL and used as an internal electrode. sensor.