JPS5931325B2 - Electrode device for transcutaneous oxygen measurement - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electrode device for percutaneously measuring oxygen concentration (or partial pressure) in arterial blood.

Knowing the oxygen concentration in blood, especially in arterial blood, is extremely important for respiratory management of newborns and severely injured patients requiring artificial respiration.

Conventionally, the concentration of oxygen in blood (or oxygen partial pressure, Pa02
) The most commonly used method is to draw blood from the artery and directly measure it, but this method has the problems of not being able to measure continuously over time and of causing pain to the patient. Met.

Particularly in newborn infants who require respiratory management, it is necessary to constantly measure the arterial blood oxygen partial pressure and take appropriate measures to prevent brain damage and other fatal disorders caused by hypoxia and retinal damage caused by hyperoxia. However, the conventional method of collecting arterial blood is extremely difficult and burdens the patient.

Although it is not impossible to perform continuous measurements by placing an oxygen electrode in the blood vessel, it requires skill and is accompanied by significant risks, so it cannot be used as a general method.

The transcutaneous oxygen electrode method differs from the above-mentioned direct method in that oxygen diffused from blood through tissues is captured on the surface of the skin and can be measured continuously over time without causing pain to the patient.

The mechanism of this electrode is a special Lark-type compound oxygen electrode with a constant temperature heating mechanism added. When it is applied to the subject's skin surface, oxygen in the subcutaneous tissue diffuses from the skin and passes through the electrode membrane to the precious metal. It reaches the cathode where it is reduced to produce water.

The PO2 value in the tissue can be obtained from this electrolytic current. At this time, if the skin in contact with the electrode or the skin around it is heated to an appropriate temperature while avoiding the electrode membrane, the subcutaneous tissue near the electrode will be locally stimulated into the arteries. Therefore, if the electrode structure and measurement conditions are appropriate, the oxygen partial pressure measured by the electrode will be substantially equal to that of arterial blood.

To date, there are two types of percutaneous arterial blood oxygen measuring electrodes, excluding those by the present inventors, but both have inherent defects in their electrode structure and are difficult to handle. , measured values are also unstable and unreliable.

The first type was developed by Huch et al.
Reports of defeat since 973 (A, Huch.

R, Huch, B, Arner and C1, Ro.
oth, 5cand, J.

Cl1n, Lab, Invest,, 31, 26
9-275 (1973) s R, Huch, D, W
, Lubbers and A.

Huch, Archives of Diseases
e in Chi 1dhood 249.

21:3-218 (1974); R, Hueh, A.

Huch, M., Albani, M., Gabriel.
, F, J-5chulte.

H, Wolf, G, Rvpprath,
P, Emmrich, U, 5techele
.

G, Due, and H, Bucher, Pediat.
rics, 5 7.

681-690 (1976), and as shown in Fig. 1, a fine platinum wire of about 0.015M was used as the cathode 1, and this was used together with the silver anode 2 to support the electrolyte as an oxygen permeable thin film 4 (12 This electrode film is fixed to the electrode holder 7 with Q and IJ songs.

This electrode is used by being attached to the skin 13 with double-sided tape 12 as shown in the figure.

Since the electrodes of this type are small, the signal-to-noise ratio (S/N ratio) is extremely poor, and the flat membrane is
Because the song is wrapped around and fixed, wrinkles tend to form in the fixing part, making it difficult to maintain constant adhesion between the electrode surface and the membrane, resulting in drawbacks such as unstable electrode activity.

Furthermore, with this electrode, the subcutaneous tissue sacrifice is arterialized and the measured value is Pa.
In order to reflect O2, a method is used in which the heating of the silver anode is controlled and the skin is thereby heated, but the heating area is not large enough.

Perhaps because of these deficiencies, this type of electrode has not yet been widely put into practical use in Japan, even though it has been planned for a long time.

Next, the principle of transcutaneous measurement of arterial blood oxygen concentration using the apparatus shown in FIG. 1 will be explained.

When the electrode device is brought into close contact with the skin surface 13 with double-sided tape 12 and the temperature of the anode 2 is heated to 43 to 44°C, the skin in the area in contact with the anode while avoiding the membrane and the surrounding area is heated. The subcutaneous tissue becomes arterialized.

Therefore, the oxygen concentration (partial pressure) in the tissue becomes substantially equal to that contained in arterial blood, and this oxygen diffuses through the skin tissue, permeates the membrane, and reaches the cathode 1.

At this time, if a voltage of -0.5 to 0.8 volts is applied between the cathode and the anode 2, oxygen is reduced at the cathode and silver is oxidized at the anode.

Note that the cathode and anode are connected by an electrolytic solution (mainly HOl) existing as a thin layer between the membrane and the electrode.

On the surface of the cathode 1 (platinum or gold), electrons are consumed according to the amount of 02 as follows: 0□+4H+4e → 4H20 (in acidic case) 02+ 2H20+ 4 e → 40H- (in neutral or alkaline case) 4kg+401-"4AIC1+4e (at any pH), and as a result, an electrolytic current flows between the two electrodes, but this current depends on the number of oxygen molecules passing through the membrane, and therefore the membrane Since it is proportional to the concentration of oxygen gas at the surface, by measuring this current it is possible to approximately measure the oxygen concentration in the subcutaneous tissue and therefore in the arterial blood.

A second type of transcutaneous oxygen electrode was developed by the Swiss company R8che (Japanese Patent Publication No. 51-12199) and is currently commercially available, and its structure is shown in FIG.

In this device, an extremely large total cathode 1 (diameter 3M) is used, and an electrode film 3 (6 micron Mylar) to be covered with the silver cathode 2 is sandwiched between an electrode holder 7 and a fixing collar 8. held in a manner.

In this case, an attempt is made to warm the skin by heating the cathode, but no matter how large the cathode is, it cannot provide a sufficient heating area.

In this method, the area of the cathode is large because it serves both as an electrode and a heating part, which results in an excessive amount of electrolytic reaction, and the electrolyte is consumed rapidly. Not only is the use time for one use extremely short at about 2 days, but also during use. The drift in sensitivity is also large.

In addition, since the cathode surface is circular, the distance from the anode and the exchangeability of the electrolyte are different between the periphery and the center, so the reactivity for the same oxygen concentration is different, and this causes the oxygen partial pressure does not show an accurate response course to changes in

In addition, a major drawback of this electrode is that the cathode surface is huge and its oxygen consumption is large, which increases the oxygen flux in the skin layer, which affects the oxygen measurement value and increases the PO2 in the tissue.
There is a risk that it may be undermeasured.

For this reason, attempts have been made to reduce this error by using a membrane (6 micron Mylar) with extremely poor oxygen permeability as the electrode membrane, but this has the disadvantage of slow response.

In addition, in the case of this electrode, as with the first type, the adhesion between the electrode membrane and the electrode surface is unstable, and the electrode activity fluctuates due to the contact pressure between the electrode membrane and the skin, resulting in inaccurate measured values. Be accurate.

Furthermore, in any of the above types, the electrolyte is sealed in a thin layer between the electrode membrane and the electrode system holder, and the opening of the membrane fixing collar is wide, so that the electrode membrane is pressed directly onto the skin over a wide area. Because of this, the distance between the electrode membrane and the electrode surface changes due to the influence of internal pressure changes due to slight temperature changes of the electrodes or the pressure conditions between the electrode membrane and the skin, and this causes the measured values to become extremely unstable. have weaknesses.

3 and 4 show one embodiment of the electrode device according to the present invention, and this device is similar to FIGS.
The structure is fundamentally different from the existing electrode device shown in the figure, and the various deficiencies mentioned above in the former are eliminated, resulting in a significantly superior function.

Next, I will point out the important points. (1) Overall structure: The electrode device of the present invention includes an upper lid part with built-in cathode and both electrodes,
It is composed of three independent parts: a membrane holder to which the electrode membrane is fixed, and a heating part in which a heating element and a heat-sensitive element are embedded.The membrane and a part of the membrane holder are installed between the upper lid part and the body part. It is assembled and used and is a completely new type of skin electrode.

(2) Cathode shape: A major feature is that the cathode surface, which reacts with oxygen, is ring-shaped.

In addition, in the case of Huch, sensitivity is insufficient at minute points, and in the conventional example, sensitivity is uneven at large circles and oxygen consumption is excessive.

The ring shape allows it to respond to a wide range of skin surfaces while providing an appropriate level of reactivity that is neither too much nor too little, so S/
The N ratio is good and the drift is small.

Furthermore, since both the negative and positive electrodes are arranged concentrically in a ring, the reactivity over the entire surface of the cathode is uniform and the response to changes in the 02 concentration is accurate.

Compatibility with a wide range of skin is necessary for stable measurements, but
If a circular electrode was used, the reactivity would be uneven between the center and the periphery, so a ring shape was used.

(3) Electrode membrane attachment method: The electrode membrane was attached by fitting a cylinder to which the membrane was fixed in advance.

In conventional examples, the flat membrane is fixed with an O-ring or sandwiched between sleeves.

This method allows the film to adhere uniformly to the cathode without creating wrinkles, and the strength of adhesion can be easily adjusted according to the tension of the film.

Therefore, no skill was required to attach the membrane, and the electrode reactivity was significantly stabilized.

(4) Skin heating method: Arterialization of the skin was performed with high precision and efficiency by installing a separate large heating device, rather than by heating from electrodes (Huch
(heated with a silver anode; Roche heated with a gold cathode).

This increased the heat capacity of the heating element and improved the accuracy of temperature control.

Another major advantage is that the heating area of the skin is significantly increased.

In order to arterialize subcutaneous tissue, it is extremely desirable to heat not only the skin surface immediately below the electrode, but also a much wider area evenly and with high precision.

(5) Installation of devolatilization pressure plate: An electrode membrane press plate was provided with a small hole slightly larger than the diameter of the cathode ring.

In the conventional example, the entire surface of the electrode membrane is brought into direct contact with the skin.

This electrode uses a thin, elastic metal plate to press the membrane around the cathode, which protrudes from the anode, so the thickness of the gap between the membrane and the electrode is kept constant, and the small holes in the electrode membrane pressing plate keep the membrane from touching the skin. Since the area under pressure can be minimized, the stability of electrode sensitivity has been significantly improved.

Furthermore, since this suppression plate forms part of the heating section and is made of metal, it also serves to heat the skin near the cathode.

(6) Others: The silver anode surface is set back from the cathode surface so that the film stretches and comes into close contact with the cathode surface.

One side of the electrode membrane is surface-treated to increase the amount of electrolyte retained.

A small vent groove was provided to prevent the electrode membrane from being exposed to internal pressure.

FIG. 3 separately shows the structure of the three components of the electrode device of the present invention.

What is shown at the top of the figure is the structure of the electrode section (upper lid section).

Reference numeral 1 denotes a cylindrical cathode with an extremely thin wall (thus a thin ring-shaped cross section) made of platinum or gold.

2 is a cylindrical silver anode, and both electrodes are separated by an insulator 3.

Glass or epoxy is used as the material 3, and the inside of the cathode is also filled with this.

The end face of the ring-shaped anode is slightly set back from the cathode and insulator surfaces in order to provide tension to the electrode film when assembled.

Reference numeral 7 designates an electrode holder made of insulating plastic, which is made of engineering resin such as fluororesin or polycarbonate, and has a structure in which the electrode is fixed.

Reference numeral 19 indicates lead wires from the cathode and anode, and reference numeral 20 indicates the simplest connection using screws as an example for fixing the upper lid part (electrode part) and the body side (heating part).

The most important of the electrode parts mentioned above is the cathode that reacts with oxygen, and one of the outstanding features of the present invention is that this is made into a cylindrical shape.

Figure 2 shows that the electrode device uses a cylindrical electrode, but with a disk-shaped cross section, too much oxygen is consumed due to the electrode reaction on the electrode surface, making it difficult to accurately measure the gas concentration in the blood. Not only is it difficult to use, but the electrolyte solution is consumed too much, and changes over time are large, making continuous use over a long period of time impossible.

The electrode in Figure 1 has an extremely small circular cross section (15μ
) A needle-shaped electrode is used, but in this case, oxygen consumption is small and there is no problem, but the sampling range of tissue oxygen to be measured is limited to the peripheral area of the needle cross section, so the average that corresponds to a wide skin area is It is difficult to measure the converted arterial blood oxygen concentration.

What is more important is that this type of point electrode surface has a low reaction amount, resulting in a poor signal-to-noise ratio, resulting in inaccurate and unstable measurements.

When using a cylindrical cathode for these, the cross-sectional area of the electrode can be arbitrarily selected within a wide range by changing the ring thickness and diameter, and because it is annular, the measurement site on the skin is unevenly distributed. There is no risk of this happening, and since the measured values obtained by this method are averaged values, extremely reliable results can be obtained.

Furthermore, since it is a ring, the total area of the cathode is approximately the same as that of the anode, which has the advantage that the uniformity of the reaction is maintained.

The thing shown in the center of Fig. 3 is the electrode membrane fixing part, 4 is the electrode membrane made of an oxygen-permeable synthetic resin thin film, and 16 is a cylindrical membrane holder made of a suitable plastic. The membrane is fixed, and the upper lid is pressed against it by an 0-IJ song 5 made of an elastic material (for example, silicone rubber). At this time, a thin groove 21 is formed at the top of the cylinder to allow air to escape.
is attached.

Furthermore, a groove 22 is provided on the inside of this cylindrical portion, and this is to prevent the electrolyte from seeping out to the outside of the cylinder.

Immediately before assembling the three parts of the electrode device, a small amount of the electrolyte should be deposited on the center of the electrode membrane 4. After assembly, it will spread over the surfaces of the cathode and anode, and some of it will also be deposited on the anode. Adheres to the surrounding area.

The groove 22 prevents the electrolyte in this portion from coming out from the air vent groove 21 due to shock.

Note that the small grooves 21 are necessary to prevent the electrode film from separating from the electrode surface due to internal pressure.

Note that a hydrophobic oxygen-permeable membrane is used as the electrode membrane, which does not allow the electrolyte to pass through at all, but allows oxygen molecules to pass through.

These include polyvinylidene chloride film (Saran film), fluororesin film (Tetron film), polypropylene film, and polyester film (Mylar film).

In order to fix these films to the membrane holder cylinder 16, materials that can be heat-sealed such as polypropylene are heat-sealed, and other materials are bonded as is or after surface treatment with an adhesive.

If the material is particularly difficult to adhere, it is possible to use the membrane and the membrane holder by adhering them together using double-sided adhesive tape.

When the membrane is bonded to a membrane holder in this way, the tension on the membrane surface is kept constant, so depending on the individual who handles it, the sensitivity may become unstable due to wrinkles, excessive stretching or loosening of the membrane surface. No defects will occur.

The conventional method shown in Figures 1 and 2 has the disadvantage that it is necessary to replace the membrane each time it is used, and the tension on the membrane surface varies depending on the tension, resulting in variations in gas permeation performance. However, this method of applying the electrodes was a problem that required a lot of skill.

In addition, in the membrane holder according to the present invention, this also serves as a storage container for the electrolyte solution.

inside this holder. Excess electrolyte solution is stored around the silver anode 2, and when the electrolyte solution is consumed in the electrode section, it is replenished from the surroundings, and the reaction characteristics are maintained constant.

The membrane used in the present invention is a polymer film that is permeable to oxygen and impervious to water and electrolyte, but the material and thickness vary depending on the area of the electrode (cathode) used.

With a cathode that has a large area, the amount of oxygen consumed by the electrode reaction is large, making it difficult to obtain a measurement value that reflects the oxygen concentration in the tissue. To compensate for this, a membrane with low permeability is used, but this reduces the response. This has the disadvantage of being slow.

On the contrary, a dot-like cathode with a small cross-sectional area allows the use of a membrane with good gas permeability, so the response is generally fast.

Although the ring-shaped cathode of the present invention has a considerably large total cross-sectional area,
A membrane with good permeability can be used.

In any case, it is necessary to select it empirically depending on the electrode device used.

In the case of the device of the present invention, 15-30μ thick tetrafluoroethylene (Teflon), 10-20μ tetrafluoroethylene-trifluoropropylene copolymer (FEP), 10-20μ polypropylene, or 5-10μ thick polypropylene Vinylidene chloride films (Saran or Flehalon films) were suitable.

Among the membranes mentioned above, Teflon film has excellent water absorption properties, but on the other hand, because it has extremely strong water retention properties, it has poor wettability with the electrolyte solution on the membrane surface, and it repels the electrolyte solution, resulting in poor electrode stability. 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 an ammonium solution of sodium metal, the affinity or water retention 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.

According to FIG. 3C, the main body or body 16 of the heating section of this device is made of copper, aluminum, brass, etc. with good thermal conductivity, and the lower surface is made of elastic material such as stainless steel phosphor bronze. A thin plate 18 with good properties is fixed to the body by solder or adhesive.

Reference numeral 5 denotes a heater, which is made by providing a groove on the outer periphery of the body, and wrapping therein a resistance wire with a small resistance change due to temperature, such as an insulating coated manganin wire or a Cu--Ni wire.

Reference numeral 6 denotes a heat sensitive body or temperature detection device, such as a thermistor, embedded in the body to detect the temperature of a part of the body.

23 is a lead wire from the heater and the heat sensitive body, and 24 is a protective tube fixed to a part of the body to protect these, and a thin stainless steel pipe or the like is used.

To assemble the three parts above, place the electrolyte in the center of the electrode membrane, align the three parts, and then tighten the three screws on the electrode part.

The structure of the product assembled in this way is shown in FIG.

The assembled electrode device is used by applying a small amount of water (contact liquid) 14 to the exposed part of the electrode membrane and attaching it to the skin 13 with double-sided tape 12, as in the case of FIG.

When adhering to the skin in this manner, it is preferable that the skin surface be as close to the electrode film as possible.

However, when the membrane is subjected to pressure from the skin, the thickness of the electrode liquid layer between the membrane and the cathode surface is subtly affected, making the measured values unstable.

The device of the present invention solves this difficult problem by fixing a thin stainless steel plate 18 about 0.05M thick with a small hole in the center to the bottom of the heating body.

Furthermore, since this thin stainless steel plate is in close contact with the electrode film, it also eliminates the problem of oxygen gas from inside the body penetrating between the skin and the electrode film on the cathode and distorting the measured values.

FIGS. 5, 6, and 7 show measurement examples using the electrode device of the present invention.

FIG. 5 is a test curve when a 50μ Teflon film etched by IJum treatment is used as the electrode film for the transcutaneous oxygen electrode of the present invention.

After placing the electrode on the assay container, air is first passed through it and its current value is recorded (84.5 nA).

Next, when nitrogen gas is passed through the test container at the arrow on the right, the current value rapidly decreases as shown in the figure and reaches a constant value near the current value O (1.5 nA).

Next, when air is passed at the second (left) arrow, the current value rises rapidly and reaches the air value when re-stringing (84 nA).
.

According to this test, an 80% response is approximately 20 seconds, a 90% response is 30 seconds, and a 96% response is approximately 50 seconds.

Figure 6 shows electrode 2 under the same conditions as those used in the experiment in Figure 5.
This device is attached to the upper and lower right chest of a newborn baby, and the oxygen partial pressure (electrolytic current value calibrated with a certified value) is recorded.

It can be seen that the measured values rise rapidly when oxygen is inhaled, and then decrease when air is breathed, before returning to the original level.

You can see that even when breathing air, the oxygen level fluctuates slightly throughout the newborn due to differences in physiological conditions.

For example, breastfeeding causes a slight decrease, and crying causes an even greater decrease.

In addition, it was found from a comparison of the arterial blood oxygen measurement values obtained by blood sampling that the degree of reflection of the percutaneous measurement value on the arterial blood oxygen concentration at this time was about 95%.

FIG. 7 shows two electrodes of the present invention with a 12 μm polyvinylidene chloride film attached to the inner side of the upper arm of an adult (30-year-old male) to alternately breathe air and breathe oxygen. The current value was recorded using a two-pen recorder.

Curve A is the case when the electrode temperature is 44°C, and curve B is the case when the electrode temperature is 42°C.

Arrows indicate the point of switch to oxygen or air breathing, respectively.

It can be seen that 44°C reflects the oxygen changes within the tissue to a much greater extent than 42°C.

In addition, the reflection speed of arterial blood oxygen partial pressure at 44°C is approximately 8
It was 0%.

[Brief explanation of the drawing]

Figures 1 and 2 a and b are longitudinal sectional side views and bottom views of different conventional devices, Figure 3 a, b, and c are exploded longitudinal sectional side views of the device of the present invention, and Figures 4 a and b. FIG. 3 shows a longitudinal sectional side view and a bottom view of the device after assembly, and FIGS. 5, 6, and 7 show recording charts of measurement examples using the device of the present invention. 1... cathode, 2... anode, 16...
... Membrane holder, 5 ... Heating element, 6 ...
...Thermal sensitive body, 7...Thermal and electrical insulator (electrode holder) of the upper lid part.

Claims (1)

[Scope of Claims] An upper lid part made of a thermal and electrical insulator that holds a cathode part and an anode part composed of 11 parts, a membrane holder made of synthetic resin to which an electrode film is fixed, and the electrode part and It consists of a heating section that houses a membrane holder and is made of a good thermal conductor that is equipped with a heating element and a heat-sensitive element, and these three parts are made detachable, and the heating section is used in close contact with the skin surface of the part to be measured. An electrode device for transcutaneous oxygen measurement, characterized by: 2. A patent claim characterized in that it consists of a circular cathode part made of a precious metal such as gold or platinum, and a circular anode part made of silver and arranged concentrically with an electrically insulating material separated from the cathode part. The electrode device for transcutaneous oxygen measurement according to scope 1. 3 An insulating material such as glass or synthetic resin is interposed between a cathode and an anode that are arranged concentrically, and the end surfaces of the cathode and the insulator are made to be on the same plane, and the end surface is made to protrude from the end surface of the anode. An electrode device for transcutaneous oxygen measurement according to claim 1. 4. A patent characterized in that the heating section has an elastic electrode membrane suppressing plate provided with small holes slightly larger than the diameter of the cathode in the part where the heating section contacts the skin surface of the part to be measured. The electrode device for transcutaneous oxygen measurement according to claim 1. 5. The upper lid part, the membrane holder, and the heating part are combined together, the electrolyte is interposed as a thin layer between the electrode part and the membrane, and the membrane holder is heated so that a predetermined tension is applied by the devolatilization pressure plate of the heating part. 2. The electrode device for transcutaneous oxygen measurement according to claim 1, characterized in that the cathode is pressed against the cathode portion, and the cathode is brought into contact with the skin across the membrane through the small holes of the devolatilization plate. 6 As the electrode membrane held by the membrane holder, tetrafluoroethylene-trifluoropropylene copolymer, polypropylene,
The electrode device for transcutaneous oxygen measurement according to claim 1, characterized in that a membrane made of polyvinylidene chloride or polyvinylidene fluoride is used. 7. Claims 1, 5, and 6, characterized in that one side of the membrane, particularly the electrode side, is roughened by etching or mechanical abrasion treatment to improve water retention. The electrode device for transcutaneous oxygen measurement according to any one of the above. 8. The electrode device for transcutaneous oxygen measurement according to claim 1, characterized in that a recess for an electrolyte reservoir is provided on the inner wall surface of the cylindrical membrane holder, and a ventilation hole is further provided near the upper end surface. 9. A heating section made of copper, aluminum, or an alloy thereof with good heat conductivity, and an electric heater and a thermostat installed in the heating section to maintain the temperature of the heating section at a constant temperature suitable for measurement. An electrode for transcutaneous oxygen measurement according to claim 1.