JPS6143450Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a calibration device for calibrating the measured value of a sensor that continuously measures oxygen concentration in arterial blood transcutaneously.

Knowing the oxygen concentration (or partial pressure) in blood, especially in arterial blood, is extremely important for respiratory management of newborns and severely injured patients requiring artificial respiration. Unlike the method of measuring oxygen concentration in arterial blood, which involves drawing blood from the artery and directly measuring it, this method captures oxygen that diffuses from the blood through the subcutaneous tissue on the surface of the skin, causing no pain to the patient. A transcutaneous blood oxygen concentration measurement method that allows continuous measurement over time is already known.

The present invention relates to a calibration device for calibrating the measured value of such a sensor for transcutaneous blood oxygen concentration measurement. Figure 1 shows the structure of a typical transcutaneous blood oxygen partial pressure sensor to which this calibration method is applied. An electrode part consisting of an anode 3 made of silver or the like placed on the skin and an electrode membrane 4 fixedly supported so as to hold an electrolyte 6 on one end face of the electrode, a heater wire 8, and a temperature detection element 9 are built into the skin. It is composed of a heating section 10.

Figures 2 and 3 show the principle of the conventionally used calibration method.
The figure shows a calibration curve.

In Fig. 2, 11 is a container made of transparent material such as acrylic resin or glass, 12 is a heater for heating the water in the container to a constant temperature, 13 is a temperature detection element (for example, a thermistor), and 14 is a pressure feeder. 15 is distilled water, 16 is a presser spring for fixing the sensor, 17 is piping from the air pump, 18 is N ₂ Piping from the gas cylinder, 19 a three-way stopper for gas switching, and 20 a sensor to be calibrated. The conventional calibration method will be explained step by step below. The water temperature in the calibration container is set to the temperature measured by the sensor, for example 44°C, and a small amount of air is pumped in using an air pump. When the pressure-fed air passes through the porous plate 14 in the calibration container, it becomes fine bubbles and passes through the water 15 heated to 44°C. At this time, the air becomes approximately the same temperature as the water, and The so-called humid air containing saturated water vapor comes into contact with the electrode membrane surface of the sensor 20, and is subsequently discharged to the outside of the calibration container.
Therefore, the electrode membrane surface of the sensor is constantly in contact with a constant oxygen partial pressure expressed as (Po - P _H2p ) × 0.21 Po: atmospheric pressure P _H2p : saturated water vapor pressure at the measurement temperature 0.21: molar fraction of oxygen in the air Pair the electrolytic current value of the sensor at this time.
If this is determined, the upper limit of the two-point calibration has been successfully calibrated. Next, switch the three-way stopper 19 and tighten N ₂
When N ₂ gas is pumped from a bomb, the air in the calibration container is replaced by the N ₂ gas, and the electrode membrane surface becomes in a state where the oxygen partial pressure is 0. Therefore, by setting the electrolytic current value at this time to be zero oxygen partial pressure, the lower limit of the two-point calibration method can be calibrated.

FIG. 3 is a calibration curve obtained by the method described above,
By using this calibration curve, the oxygen concentration in gas or liquid can be determined.

The conventional method is extremely accurate in terms of the accuracy of calibration values, and is an excellent calibration method in this respect;
It is necessary to bring N ₂ cylinders, air pumps, etc. to the clinical site, and there are various complications such as adjusting the N ₂ gas pressure and air pressure, controlling the temperature of the calibration container, and finding a place to store the calibration container. These matters are not a problem in a normal laboratory, but in general, clinical sites are small and have a variety of equipment, so the complexity described above becomes a major drawback, and in clinical settings, it is considered an extremely serious problem. be done.

The present invention improves the above-mentioned drawbacks and allows easy and accurate calibration in clinical settings. The present invention provides a calibration device for a sensor for transcutaneous blood oxygen partial pressure measurement.

Fig. 4 shows a calibration device and a calibration method according to the present invention, where 21 is a main body of the calibration device made of a heat insulating material such as rubber, plastic, or foam, and 22 is a moisture absorbent material made of sponge, paper, nonwoven fabric, etc. 23 indicates a magnet for fixing the sensor on the mount or on the surface of the measuring instrument while the sensor is attached to the calibration instrument. In FIG. 4, a shows the sensor 24 attached to the calibration tool and calibration is being performed, and b and b' show a plan view and a sectional view of the calibration tool.

Figure 5 shows the zero point calibration method according to this calibration method, where 24 is the sensor with the membrane surface facing up, 26
27 is a dropper for dropping an aqueous solution containing a reducing agent such as sodium sulfite, sodium nitrite, or pyrogallol hydrosulfide, and 27 is an aqueous solution containing the reducing agent dropped onto the membrane surface of the sensor.

Next, a method of calibrating the transcutaneous blood oxygen concentration sensor using the calibration device according to the present invention will be described. That is, a small amount of distilled water is dropped onto the water-absorbing agent of the calibration device shown in FIG. 4, and then the sensor is attached as shown in FIG. 4a. As a result, the cavity 25 in the calibration device is brought to a constant temperature by the heat from the sensor's heating device, and is filled with air containing saturated water vapor at this temperature and thus having a constant oxygen partial pressure. Therefore, the electrode surface will be in contact with the known oxygen partial pressure, and the upper limit value of the sensor can be correctly calibrated.

As shown in Figure 5, zero point calibration is performed by dropping an aqueous solution containing a reducing agent onto the electrode membrane surface, which creates a state of zero oxygen concentration on the membrane surface, making it possible to calibrate the sensor zero point. .

In this way, since the calibration is carried out using a small space, the present calibration instrument only needs to be one size larger than the sensor and can be made very compact. For example, in this example, the diameter of the sensor is 16 mm, and the diameter of the calibration tool is 22 mm.
It is.

However, because it is small, it has drawbacks such as being dragged by the sensor and falling when the sensor is attached. There is no point in miniaturizing it if it is embedded in a large holding object. The magnet 23 shown in FIG. 4 is used to fix the calibration instrument to the main body of the measuring instrument, a steel mount near the measurement site, or the surface of another measuring instrument.

This allows the calibration instrument to be fixed in a convenient location when in use, improving maneuverability in confined clinical settings.

As mentioned above, according to this calibration method, it was previously necessary to bring _N2 gas cylinders, air pumps, etc. to the clinical site, but these complications are no longer necessary, and transcutaneous blood oxygen partial pressure can be measured extremely easily and quickly. It is possible to calibrate the sensor for use.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram of a sensor for measuring transcutaneous blood oxygen partial pressure, and includes 1...cathode, 2...insulating material, 3...anode, 4...
... Electrode membrane, 5 ... Membrane holder, 6 ... Electrolyte, 7
... Electrode holder, 8 ... Heater wire, 9 ... Heat sensitive element, 10 ... Skin heating body. Figure 2 shows a conventionally used calibrator, 11...melter, 12...heater, 13...temperature detection element, 14...porous body, 15...distilled water, 16...presser spring, 17...Air pump piping, 18...Piping from _N2 gas cylinder, 19...
...Three-way stopper, 20...Sensor, etc. are shown. Figure 3 is a calibration curve diagram. Fig. 4 shows a calibration instrument according to the present invention, 21...calibration instrument main body, 22...water absorbing agent, 2
3...Magnet, 24...Sensor, 25...Gap, etc. are shown. Figure 5 shows a simple calibration method for 0 points.
4 is a sensor, 26 is a dropper, and 27 is an aqueous solution containing a reducing agent.

Claims (1)

[Scope of utility model registration request] Covering the outer periphery of the sensor except for the upper end side with a covering made of a thermally insulating material such as rubber, plastic, or foam, and providing a gap on the inner surface of the covering on the side of the electrode film,
A calibration device for a sensor for transcutaneous blood oxygen partial pressure measurement, characterized in that a water-absorbing material such as sponge, paper, or non-woven fabric is interposed in the gap, and a magnet is embedded in the bottom of the outer periphery of the sensor covering.