JPH0477573B2 - - Google Patents

Description

[Detailed description of the invention]

(Field of Industrial Application) The present invention relates to an oxygen sensor that measures the partial pressure of oxygen gas in body fluids such as blood or biological tissues, and particularly to a small oxygen sensor suitable for combination with a carbon dioxide sensor, PH sensor, etc. It is. (Prior Art) The partial pressure of oxygen in body fluids such as blood or in living tissues is one of the important indicators representing the state of respiration and circulation. This oxygen partial pressure is frequently measured especially for respiratory management of critically ill patients and patients undergoing surgery. Oxygen partial pressure is measured by installing a pair of cathode and anode electrodes (Clarke type oxygen sensor) in the electrolytic solution and measuring the current flowing through the cathode. However, the above method has problems such as the current value being disturbed due to stirring of the electrolytic solution and the electrical contact between the cathode and the anode becoming unstable. In order to solve this problem, attempts have been made in recent years to immobilize the electrolyte with hydrophilic polymers. Cellulose, collodion, cellulose acetate, polyhydroxyethyl methacrylate, etc. are used as hydrophilic polymers for immobilizing the electrolyte, and these can be coated directly on the cathode and anode, or coated directly on the cathode and anode. The gap was covered with a membrane. (Problems to be Solved by the Invention) However, with the latter method, it is impossible to fabricate a small elongated sensor suitable for blood monitoring, and with the former method, it is especially difficult to produce a sensor at both poles. There were drawbacks such as uneven coating at the tip and easy peeling of the coating during assembly. In order to solve this problem, the present inventors proposed a sensor in which the cathode and anode are covered with hydrophilic hollow fibers in Japanese Patent Application No. 59-225033. However, this sensor had the disadvantage of shortening its lifespan due to its large cathode area. (Means for Solving the Problems) An object of the present invention is to eliminate the drawbacks of the oxygen sensor proposed in the above-mentioned Japanese Patent Application No. 59-225033 and to provide a sensor with a long life. The sensor of the present invention has an anode housed in a hydrophilic hollow fiber, and a cathode coated with a hydrophilic polymer gel. In other words, an anode whose tip portion is coated at least with a hydrophilic hollow fiber containing an electrolytic solution and a cathode whose tip portion is coated with a hydrophilic polymer gel are electrically connected (conducted).
This oxygen sensor is characterized in that the surface of the oxygen sensor is coated with a gas-permeable membrane. (Example) Next, an example of the oxygen sensor of the present invention will be described with reference to the drawings. Figures 1 and 2 A and B (A-A' and B-B' sectional views in Figure 1) show an anode wire 1 and a cathode wire 2 insulated in a catheter 6 having two holes (double lumen catheter). An example of encapsulation with resins 7 and 8 is shown. The sensitive part of this sensor is provided to protrude from the distal end of the catheter. The anode wire 1 of this sensor is housed in a hydrophilic hollow fiber 3, the cathode wire 2 is covered with a gelled hydrophilic polymer gel 4, and both are electrically connected through an electrolyte 5. . These electrodes are covered on the outside with an oxygen permeable membrane 9. Oxygen therefore diffuses through the membrane 9 and the hydrophilic gel 4 to the cathode 2. The oxygen that has reached the cathode 2 is reduced here, and a current corresponding to the amount of oxygen that has reached the cathode 2 flows. The amount of oxygen that has reached the cathode 2 is proportional to the external oxygen concentration and the oxygen permeability coefficients of the oxygen permeable membrane 9 and the hydrophilic gel 4. Therefore, the thickness of the membrane 9 and the hydrophilic gel 4 and the oxygen permeability must be kept constant during the measurement. The hydrophilic gel 4 does not deform during measurement, and its thickness and water absorption do not change even after autoclave sterilization. Furthermore, the hydrophilic gel 4 needs to have a high water content. This is because as the water content decreases, the electrical resistance of the solution increases, and the current is determined not by the amount of oxygen but by the resistance of the electrolytic solution contained in the hydrophilic gel. In order to prevent such resistance of the electrolytic solution, the water content of the hydrophilic gel is usually preferably 20% or more. When the water content is lower than this, the response speed becomes slower.
Furthermore, the conductivity of the film deteriorates, making measurement unstable. The water content mentioned above is calculated by cutting a hydrophilic gel in half vertically, soaking it in water, wiping off the water adhering to the surface with paper, and measuring the weight as W ₁ , and the dry weight of this gel as W 1 .
When W ₀ , it is expressed as W ₁ −W ₀ /W ₀ . When the gel is porous, even if the material of the gel is hydrophobic, it can be used as long as it satisfies the above water content by treating the surface to make it hydrophilic. The thickness of the gel is usually preferably 5 to 100 .mu.m, since too thick a gel will increase the response time.
As this hydrophilic gel 4, polymer gels such as cellulose, polyhydroxyethyl methacrylate, and ethylene vinyl alcohol copolymer can be used. Items that can be autoclaved include:
The above polymers and water-soluble polymers such as polyvinyl alcohol (PVA) and polyacrylamide made insolubilized by crosslinking are used.
Examples of the crosslinking method include a method in which a polymer is coated in solution and then crosslinked using a crosslinking agent, heat, or light, and a method in which a monomer and a crosslinking agent are applied and then polymerized. Examples of the former method include a method in which polyvinyl alcohol is crosslinked with glutaraldehyde or dichromate using light; a method in which polyhydroxyethyl methacrylate copolymerized with glycidyl ether is crosslinked by heat treatment; There is a method in which a mixed solution of methacrylate and ethylene glycol dimethacrylate is applied and then polymerized. This gel can be either a homogeneous hydrous gel or a heterogeneous porous gel, but the latter is better because it can increase oxygen permeability even in hard materials that can withstand autoclave sterilization. preferred. Such porous hydrophilic gels include cross-linked PVA, EVA, polysulfone, and acetate resins, which are essentially the same membranes used for artificial kidneys and reverse osmosis, and are similar to those used in artificial kidneys and reverse osmosis. It can be made using this method. 3 is a hydrophilic hollow fiber that covers the anode wire;
It mainly serves to fix the electrolyte. Anions in the electrolyte are consumed at the anode. Therefore, the amount of electrolyte that can be held by the hollow fiber determines the sensor's lifespan. Therefore, it is preferable for the volume and water content of the hollow fiber to be large from the viewpoint of longevity, but if the volume is increased too much, the volume of the sensor will become large.
Usually, the appropriate thickness is 50 to 1000μ. The same material as the above-mentioned hydrophilic gel 4 can be used for the hollow fibers 3. The cathode 2 housed in the catheter is a noble metal wire such as gold, platinum, silver, etc., and the anode is made of silver, lead wire, etc., but usually platinum is used for the cathode and silver is used for the anode. As shown in the drawing, these cathodes and anodes are exposed from the catheter 6 at the distal end and are electrically connected through the internal electrolyte 5. The internal electrolyte is also a hydrophilic gel containing an electrolyte like the hollow fiber 3 or hydrophilic gel 4 mentioned above, but deformation of this part does not have a big effect on the response, so it is shown in electrolyte gel 4. In addition to the material, gels that are relatively weak against heat and external forces, such as uncrosslinked PVA, can also be used. The catheter 6 also needs to have good electrical insulation, and is usually made of polyamide, polyester,
Thermoplastic resins such as polyethylene and polypropylene, thermosetting resins such as silicone resins and epoxy resins are used. The two poles may be inserted into the catheter 6 after the catheter is manufactured, or the catheter may be molded after the cathode and anode are placed. Reference numeral 9 denotes a gas permeable membrane, and a membrane having high gas permeability, such as polyethylene, polypropylene, polytetrafluoroethylene, or silicone resin, is generally used. Reference numeral 7 designates double insulation to completely insulate the cathode, and reference numeral 8 designates a core material to eliminate deflection of the sensor. The oxygen sensor of the present invention has autoclave resistance because the electrolyte is fixed with a hollow fiber made of a hydrophilic polymer. There is also a sensitive part at the tip,
Furthermore, since the sensitive part can be made short, it is suitable for measuring oxygen concentration in small parts such as blood vessels and organs. Further, by manufacturing this sensor using two holes of a catheter having three or more holes and storing another sensor in the other hole, a multiplex sensor can be easily manufactured. The present invention will be explained in detail below using Examples and Comparative Examples. Examples and Comparative Examples A platinum wire with a length of 6 cm and a diameter of 0.1 mm was embedded between a catheter made of nylon 11 with an outer diameter of 0.4 mm and an inner diameter of 0.2 mm. After filling the void inside the tube with epoxy resin, the platinum wire was Cut the tip diagonally to expose the cross section, then coat the exposed tip with a hydrophilic polymer and add 0.05M NaHCO ₃ , 0.1M NaCl.
A cathode was fabricated by absorbing an aqueous solution into a hydrophilic polymer. On the other hand, a hollow fiber impregnated with the above aqueous solution has a length of 7
cm, and a silver wire with a diameter of 0.2 mm was housed to prepare an anode.
The above cathode and anode are shown in Figure 1 with diameters of 0.5 mm and 0.3 mm.
A silicon catheter with an outer diameter of 1.2 mm and two holes is swollen with hexane, an anode and a cathode are embedded in each hole, fixed with insulating resin, and the tips of the cathode and anode are sealed. An oxygen sensor was fabricated by covering the tube with a silicon tube with a thickness of 0.1 mm and a length of 3 mm, and fixing it to the catheter with silicone adhesive. This sensor was treated in steam at 120℃ for 30 minutes.
The results of measuring the response are shown in Table 1.

【table】

[Table] (Effects of the invention) As described above, the oxygen sensor of the present invention exhibits high stability, long service life, and good response, and even when autoclaved, there are no large changes in current value or response speed. It has excellent durability and is extremely useful in practice.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of the oxygen sensor of the present invention,
FIG. 2 is a cross-sectional view taken along lines A-A' and B-B' in FIG. 1...Anode ray, 2...Cathode ray, 3...Hollow fiber,
4... Hydrophilic gel, 5... Electrolyte solution.

Claims (1)

[Claims] 1. An anode wire whose tip end is coated with a hydrophilic hollow fiber containing an electrolyte and a cathode wire whose tip end is coated with a hydrophilic gel are housed in a tube, and the hollow fiber is inserted from the tip of the tube. An oxygen sensor characterized in that a protruding hollow fiber covering an anode ray and a tip of a cathode ray are brought into electrical contact, and the surface thereof is covered with a gas permeable membrane.