JPH0368691B2 - - 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 tissue, and in particular to a small oxygen sensor suitable for combination with a carbon dioxide sensor, PH sensor, etc. be. (Prior Art) Oxygen partial pressure in body fluids such as blood and living tissues is one of important indicators representing respiratory and circulatory conditions. This oxygen partial pressure is particularly important for respiratory management of critically ill patients and patients undergoing surgery, and is frequently measured. The oxygen partial pressure is measured by a Clark-type oxygen sensor that includes a pair of electrodes, a cathode and an anode, in the electrolytic solution and measures 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 connection 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. Cellophane, 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 between the cathode and the anode. It was covered with a flat membrane. (Problems to be Solved by the Invention) However, the latter method makes it impossible to produce a small, elongated sensor suitable for blood monitoring, and the former method requires coating on both poles of the sensor, especially at its tip. There were drawbacks such as uneven coating and easy peeling of the coating during assembly. (Means for Solving the Problems) The present invention solves the above drawbacks by accommodating the cathode and the anode in a hydrophilic hollow fiber. That is, the present invention accommodates a cathode ray and an anode ray whose tips are coated at least with hydrophilic hollow fibers containing an electrolyte in an oxygen-permeable tube, and makes the hollow fibers protrude from the tip of the tube. This oxygen sensor is characterized in that a hollow fiber coated with an anode wire and an anode wire are brought into contact with each other, and the surface thereof 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. 1 and 2 (A-A sectional view in FIG. 1) show an example in which an anode ray 1 and a cathode ray 2 are sealed in a catheter having two holes with insulating resins 7 and 8. The sensitive part of this sensor is provided in a protruding manner at the distal end of the catheter, and has an anode ray 1 and a cathode ray 2.
are housed in hydrophilic hollow fibers 3 and 4, respectively. These hollow fibers are in contact with each other, and the two electrodes are electrically connected by an electrolytic solution contained in the hollow fibers. These hollow fibers are further integrally covered with a gas permeable membrane 6. Oxygen gas moves through the gas permeable membrane and the hollow fibers 4 by diffusion and is electrolytically consumed by the cathode rays 2. The current flowing at this time is proportional to the amount of oxygen diffusing into the cathode, and thus to the external oxygen partial pressure, so the oxygen partial pressure can be measured by measuring the current. The cathode housed in the catheter is gold, platinum,
A noble metal wire such as silver is used, and silver, lead wire, etc. are used for the anode. Usually, a platinum wire is used as the cathode, and a silver wire is used as the anode. These electrodes are housed in hydrophilic hollow fibers 3 and 4, respectively.
This hydrophilic hollow fiber may be a homogeneous membrane such as cellulose or polyhydroxyethyl methacrylate (PHEMA), or a porous membrane such as polyvinyl alcohol or vinyl alcohol ethylene copolymer. The affinity of the membrane used in the present invention can be expressed by the water content. A low water content in the membrane increases the electrical resistance of the membrane such that the current is dominated by the resistance of the membrane rather than the amount of oxygen that diffuses to the cathode. The water content of the membrane is measured by cutting the hollow fiber in half lengthwise, exposing the inner surface, immersing it in water, and wiping off the water adhering to the surface with paper. W ₁
If the dry weight of this hollow fiber is W ₀ , then W ₁ − _{W 0} /
It is expressed as W ₀ . It is desirable that the hollow fiber used in the present invention has a moisture content of 20% or more as measured in this manner. When the hollow fiber is a porous membrane, even if the material of the membrane is hydrophobic, it can be used in the present invention as long as it satisfies the above water content by treatment to make the surface hydrophilic. In addition to such hydrophilicity, hollow fibers must also have strength to the extent that they do not break during measurement or fabrication, and resistance to liquid bacteria.Membranes that meet these conditions include cellulose and its derivatives, glutaric, etc. Particularly preferred are polyvinyl alcohol and ethylene vinyl alcohol copolymers crosslinked with aldehydes. If the wall thickness of a hollow fiber-sized cathode is too large, the amount of oxygen diffusion will decrease, causing a decrease in current value and an increase in response time.
Preferably, the wall thickness is 100μ. In the anode, the hollow fiber also plays the role of holding the electrolyte, so
If the wall thickness is too thin, the life of the sensor will be shortened, and if it is too thick, the size of the sensor will increase, so the appropriate wall thickness is 50 to 1000 μm. The sensor shown in FIG. 1 can be made, for example, as follows. First, a catheter 5 with two holes is cut to an appropriate length, and an anode 1 covered with a hollow fiber 3 in each hole and a cathode that has been insulated with an insulating material 7 are embedded, and the insulated tip of the cathode is embedded. Cover the missing part with hollow fiber 4. The hollow fibers 3 are immersed in advance in an electrolytic solution containing chloride ions to contain an electrolyte. The hollow fibers 3 and 4 are brought into contact with each other and covered with a gas-permeable tube 6 whose tip is sealed, and the tube 6 is bonded to the catheter 5 with an adhesive 8'. Further, if necessary, the cathode and anode are fixed to the catheter 5 with an adhesive 8, and the other end of the catheter is connected to a connector for connecting the cathode and the anode to a measurement circuit. Known materials can be used for the catheter 5, the gas permeable membrane 6, and the insulating material 7. Among them, the gas permeable membrane 6 has excellent gas permeability, water resistance, and antithrombotic properties. Silicone resin is preferable from the viewpoint of properties etc. Also for the catheter 5,
From the viewpoint of adhesion to the gas permeable membrane, it is preferable to use silicone resin. When the sensor fabricated in this way is left in water, the hollow fibers 3 and 4 absorb water and an electrolyte is generated, and when a voltage of 0.5 to 1 V is applied between the anode and the cathode, the gas permeable membrane 6 and the hollow fiber Diffuse 4 to form cathode 2
A current flows corresponding to the amount of oxygen that reaches . Since this amount of oxygen is proportional to the oxygen partial pressure around the gas permeable membrane 6, the oxygen partial pressure can be measured by measuring the current value. The oxygen sensor of the present invention has the advantage that electrical leakage between the cathode and anode is unlikely to occur because the cathode and anode are housed in each of the catheters having two holes. Also, since the electrolyte is fixed with hollow fibers made of hydrophilic polymer, it has autoclape resistance. In addition, since there is a sensitive part at the tip and 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. Figures 3 and 4 (BB-B sectional view in Figure 3) are examples of multiple sensors, and the diameter
The anode 1 and cathode 2 of the oxygen sensor of the present invention were placed in two holes of a silicon catheter 12 with a diameter of 2.5 mm having five holes of 0.6 mm, and a liquid junction type reference electrode 9 and a FETPH sensor 10 were placed in the other three holes, respectively. , a composite sensor for PH, O ₂ and CO ₂ is shown in which a FET carbon dioxide sensor 11 is embedded. As the ion sensor used in the composite sensor, it is preferable to use a FET sensor because it is small and has autoreave sterilization resistance. The present invention will be explained in detail below with reference to Examples. Example: A platinum wire with a length of 6 cm and a diameter of 0.1 mm is embedded into a nylon 11 catheter with an outer diameter of 0.4 mm and an inner diameter of 0.2 mm, leaving a tip of 0.5 mm.The gap inside the tube is filled with epoxy resin, and then the tip of the platinum wire is embedded. 0.1M to
A cathode was prepared by coating the hollow fiber 4 with an aqueous solution of NaHCO ₃ and 1M NaCl. On the other hand, a silver wire having a length of 7 cm and a diameter of 0.2 mm was housed in the hollow fiber 3 impregnated with the above aqueous solution to prepare an anode. The above cathode and anode are 1.2 mm in outer diameter with two holes of 0.5 mm and 0.3 mm in diameter as shown in Figure 1.
After swelling a silicon catheter 5 with hexane, an anode and a cathode are embedded in each hole and fixed with an insulating resin, and the outer diameter of the catheter 5 is sealed with the tips of the cathode and anode.
A silicone tube 6 with a thickness of 0.7 mm, a film thickness of 0.1 mm, and a length of 3 mm was covered and fixed to the catheter with silicone adhesive to produce an oxygen sensor. This sensor at 120℃
Table 1 shows the results of measuring the response after treatment in steam for 30 minutes.

【table】

[Table] (Effects of the Invention) As described above, the oxygen sensor of the present invention exhibits high stability and responsiveness, and even when autoclaved, there is no significant change in current value or response speed.
Furthermore, it has good 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 sectional view taken along the line AA in FIG. 1. Figure 3 is a cross-sectional view of the composite sensor, and Figure 4 is B of Figure 3.
-B sectional view.

Claims (1)

[Claims] 1 A cathode ray and an anode ray whose tips are coated at least with a hydrophilic hollow fiber containing an electrolyte are accommodated in an oxygen-permeable tube, and the hollow fiber is made to protrude from the tip of the tube, and the cathode ray and anode ray are covered with a hydrophilic hollow fiber containing an electrolyte. 1. An oxygen sensor characterized in that hollow fibers coated with are brought into contact with each other, and the surfaces thereof are covered with a gas permeable membrane.