JP3623096B2 - Calibration method for transdermal blood gas monitor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a calibration method for a transcutaneous blood gas monitor that measures oxygen partial pressure and carbon dioxide partial pressure in blood from the surface of the skin.
[0002]
[Prior art]
This type of monitor is used for respiratory management of neonates and critically ill patients who require artificial respiration. In measuring each gas partial pressure, an amount of gas proportional to the gas partial pressure outside the sensor enters the sensor through the permeation membrane of the sensor, and the amount of gas that has entered the current value or potential generated at each measurement electrode. Utilizing correlation.
[0003]
By the way, since this electrical signal is weak due to electrochemical principles, it is easy to cause deviations in measurement values and fluctuations over time, and there are large variations from sensor to sensor. Must be done. As this calibration method, a so-called two-point calibration method is known (Japanese Utility Model Publication No. 64-31713).
[0004]
This is a method of calibrating a high range value and a low range value using two kinds of standard gases with known gas partial pressures and different mixing ratios. Here, the CO ₂ partial pressure and the O ₂ are obtained using the first gas (for example, O ₂ : 20%, CO ₂ : 10% containing gas) and the second gas (for example, O ₂ : 0%, CO ₂ : 5% containing gas). ₂ partial pressure will be described as an example a case of calibrating.
[0005]
First, as shown in FIG. 4, the sensor connector portion 10A is connected to the sensor connection portion 11B of the monitor, and the electrode portion 10B of the sensor is fixed to the sensor placement portion 11A. Next, the first gas is supplied to the sensor placement unit 11 via the flow rate control unit 12, and the signal value of the sensor 10 at that time is obtained. In the case of CO ₂ partial pressure, if the sensor is initially exposed to the atmosphere, as shown in FIG. 5 (A), the signal value rises steeply at first, becomes sluggish in the middle, and becomes a substantially constant value. Therefore, it is assumed that the CO ₂ partial pressure corresponds to a CO ₂ concentration of 10%. In the case of the O ₂ partial pressure, as shown in FIG. 5B, a constant signal value is observed from the beginning, and gradually increases (or decreases) to reach a substantially constant value.
[0006]
Subsequently, the cylinders 13 and 14 are switched to supply the second gas to the sensor mounting unit 11, and the signal value is similarly obtained. In the case of the CO ₂ partial pressure, since the second gas has a lower CO ₂ partial pressure than the first gas, the signal value decreases and reaches a certain value (FIG. 5A). In the case of the O ₂ partial pressure, since the second gas does not contain O ₂ , the signal value rapidly decreases and settles to a substantially constant value (FIG. 5B). Then, the values of these two points and the difference between the two points are obtained, the difference is stored as calibration data in the memory 15 (see FIG. 4) of the measurement unit, and the calibration result is displayed on the display unit 16.
[0007]
[Problems to be solved by the invention]
However, since the above calibration method is always a two-point calibration using both the first gas and the second gas, the time required for calibration is long (for example, 5 to 8 minutes). Moreover, since both the first gas and the second gas are always used, the amount of gas consumption is also large.
[0008]
Furthermore, when two-point calibration is performed, as shown in FIG. 5 (A), it may take time for the CO ₂ partial pressure to stabilize during calibration of the first gas. A value at the time when the absolute value of the slope of the fluctuation of the signal value becomes equal to or less than a certain value is used as the calibration value. However, when the calibration of the second gas is completed, the value may fluctuate. Therefore, there is a problem that the difference between the value at the time of completion of calibration of the first gas and the value at the time of completion of calibration of the second gas deviates from the true value and involves an error.
[0009]
Accordingly, a main object of the present invention is to provide a calibration method for a transdermal blood gas monitor having a short calibration time and excellent calibration accuracy.
[0010]
[Means for Solving the Problems]
The present invention solves the above-mentioned problems, and the first feature thereof is a calibration method for a transcutaneous blood gas monitor that calibrates a gas partial pressure measurement sensor using a standard gas, wherein the sensor is identification information for each sensor. When the sensor is unstable, two-point calibration is performed with two types of standard gases, the first gas and the second gas, and the calibration result is stored in the monitor for each sensor according to the identification information of the sensor. In normal times, only one point calibration with the first gas is performed, and another one point of calibration value is obtained from the calibration result stored in the two point calibration. When the sensor is unstable, it can be determined that the sensor is used for the first time, or that a certain period of time has passed since the previous two-point calibration of the same sensor, and the output signal of the sensor fluctuates to an extent that affects the measurement accuracy. Time is given.
[0011]
Here, as means for holding the identification information (ID) in the sensor, a resistance having a different value is provided for each sensor, or an identification memory is provided for each sensor, and the identification information is stored in the identification memory. .
[0012]
A second feature of the present invention is a calibration method for a transcutaneous blood gas monitor in which a gas partial pressure measurement sensor is calibrated using two kinds of standard gases consisting of a first gas and a second gas. Two-point calibration with the second gas, and further recalibration with the first gas is performed continuously, and the calibration is performed from the calibration result of the first gas, the second gas, and the recalibration result of the first gas. . This method is effective not only in the calibration method in which the two-point calibration is always performed, but also in the first feature when applied to the two-point calibration performed when the sensor is unstable.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below.
FIG. 1 is a schematic configuration diagram of a monitor used in the method of the present invention. This monitor is a sensor that detects currents and potentials according to the cylinders 1 and 2 of two kinds of standard gases (first gas and second gas) and the O ₂ partial pressure and CO ₂ partial pressure in blood from the skin surface. 31 and 32, and a sensor mounting portion 4 </ b> A that holds the sensors 31 and 32 in the gas atmosphere supplied from the cylinders 1 and 2. The structure of this monitor has many parts in common with the conventional monitor shown in FIG. 4, and displays the measurement unit 7 for performing calibration and measurement based on data from the sensors 31 and 32, the measurement result, and the like. Although the display portion 8 is common, the main difference is that the sensors 31 and 32 have identification information (ID) and the calibration data for each sensor can be stored in the monitor. It is.
[0014]
Here, a gas containing O ₂ : 20% and CO ₂ : 10% is used as the first gas, and a gas containing O ₂ : 0% and CO ₂ : 5% is used as the second gas. The cylinders 1 and 2 and the sensor mounting part 4A are connected by a gas circuit, and one of the gases is supplied to the sensor mounting part 4A by a switching device (not shown) on the way through the flow rate control part 6. It is configured as follows.
[0015]
Specific examples of the sensor structure include those described in Japanese Patent Publication No. 56-33094. The sensors 31 and 32 of this monitor can measure the O ₂ partial pressure and the CO ₂ partial pressure with a single sensor, but may be capable of measuring only the O ₂ partial pressure or only the CO ₂ partial pressure. . These sensors 31 and 32 include connector portions 31A and 32A connected to the monitor connection portion 4B and electrode portions 31B and 32B held by the sensor mounting portion 4A, and the connector portions 31A and 32A or the electrode portions 31B. , 32B possess identification information (ID). The identification information is for making the monitor recognize that the sensor has changed when replacing the sensor. For example, a resistor having a different value is provided for each sensor, and when the electrode portions 31B and 32B are fixed to the sensor mounting portion 4A, the resistor is energized, and the current is different, so that the sensor is determined. In addition, an identification memory may be provided in the connector portions 31A and 32A themselves, and sensor identification information may be stored in this memory.
[0016]
On the other hand, the monitor is provided with a memory 5 for storing calibration data for each of the sensors 31 and 32. That is, when the sensor mounting portion 4A holds the electrode portion 31B (32B) of the sensor, the monitor determines sensor identification information, and stores calibration data corresponding to each sensor. The contents of the calibration data include two calibration values obtained by the two-point calibration with the standard gas or their difference, and the latest date and time when the two-point calibration was performed. The recorded calibration data is displayed on the display unit 8.
[0017]
(Example 1)
A calibration procedure using such an apparatus is shown in FIG.
When the sensor is used for the first time, or when a certain period of time has passed since the previous two-point calibration of the same sensor, the calibration value data does not exist or the sensor signal level fluctuates and the previous data is used. Since it may not be suitable, two-point calibration is performed, and only one-point calibration is performed at other normal times.
[0018]
First, when the connector part 31A (32A) of the sensor is connected to the sensor connection part 4B of the monitor, the electrode part 31B (32B) is fixed to the sensor mounting part 4A and the connection of the sensor is confirmed, calibration with the first gas is performed. That is, the first gas is supplied from the cylinder to the sensor placement unit 4A, and the signal value of the sensor at that time is obtained. When the sensor was initially exposed to the atmosphere, with CO ₂ partial pressure, the signal value rises steeply at first as shown in FIG. 5 (A), slows down in the middle, and reaches a substantially constant value. , a value of CO ₂ partial pressure at this time is a value corresponding to CO ₂ concentration of 10%. In O ₂ , the signal value shows a certain high value from the beginning as shown in FIG. 5B, and gradually increases to reach a constant value. Therefore, the O ₂ partial pressure is the O ₂ concentration at this time. It is assumed that the value corresponds to 20%.
[0019]
Next, sensor identification information (ID) is read from the identification memory, and it is confirmed whether or not the sensor has calibration data registered in the monitor memory. When the sensor is used for the first time, naturally, calibration data is not registered in the memory, so two-point calibration is performed.
[0020]
In order to perform two-point calibration, the cylinder is switched and the second gas is supplied to the sensor mounting portion, and the signal value is obtained in the same manner as described above. In the case of CO ₂ partial pressure, since the second gas has a lower CO ₂ partial pressure than the first gas, the signal value decreases and reaches a certain lower limit value. In the case of the O ₂ partial pressure, since the second gas does not contain O ₂ , the signal value rapidly decreases and reaches a substantially constant value. These calibration data are registered in the monitor memory.
[0021]
On the other hand, if the calibration data is already registered, the registered data is read. Then, the date and time when the two-point calibration was performed last time is used among the registered data, and it is determined whether or not a predetermined period has elapsed from the date and time. If this specified period has been exceeded, it is determined that the calibration data obtained by the calibration of the sensor with the second gas may have fluctuated greatly, and two-point calibration is performed according to the above-described procedure. The specified period may be selected as appropriate, and in this example, it is one month. However, if it is within the specified period, it is determined that the calibration data obtained by the previous two-point calibration is usable, and only one-point calibration is performed, and only one calibration value (high range value) is obtained.
[0022]
As described above, the one-point calibration is usually sufficient in the case of the CO ₂ partial pressure, the difference between the signal value for the first gas and the signal value for the second gas is relatively small, and in the case of the O ₂ partial pressure, _This is because the signal value when the partial pressure is 0 is almost stable, so that the other calibration value can be obtained based on the calibration data obtained by the two-point calibration described above. That is, in the case of CO ₂ partial pressure, the calibration value for the second gas can be obtained by subtracting from the calibration value for the first gas by an amount corresponding to the difference between the two calibration values obtained by the two-point calibration. Also, if the partial pressure of O _2, to obtain a calibration data at two points from the signal value when the O ₂ partial pressure which is registered in the memory is 0. determined by calibration data obtained with two points at one point calibration be able to.
[0023]
In this way, the time required for calibration can be reduced to about half by making the normal calibration one-point calibration. On the other hand, when the sensor is used for the first time, or when a certain period has elapsed after the two-point calibration, high calibration accuracy can be ensured by performing the two-point calibration.
[0024]
Further, since only the identification information can be held in the sensor and the calibration data can be stored in the memory of the monitor, calibration with high accuracy can be performed for each sensor without complicating the sensor structure.
[0025]
Further, since the second gas used for the two-point calibration is not used in the normal calibration, the amount of the standard gas used for the calibration can be saved in the long term. This also makes it possible to reduce the size of the second gas cylinder, and to reduce the size of the monitor to which the cylinder is attached.
[0026]
(Example 2)
Next, a method for further improving the calibration accuracy when performing two-point calibration will be described with reference to FIG. In this method, after performing two-point calibration with the first gas and the second gas, recalibration with the first gas is subsequently performed.
[0027]
Conventionally, the calibration value is obtained by the first supply of the first gas, but depending on the safety level of the sensor, it may take a considerable amount of time until this value is completely stabilized. When the value falls below a certain value or after a certain time has elapsed, the signal value is adopted as the calibration value (see FIG. 5). In the present invention, after the stability standard is reached by the first supply of the first gas (the calibration value at this time is Sa), the calibration value (Sb ′) is obtained by the second gas supply, The second supply of the first gas is performed, and the signal value Sc by the second first gas is obtained (see FIG. 3). Next, a signal value Sb corresponding to the first gas at Tb is calculated from these values Sa, Sc and times Ta, Tb, Tc at the time of three calibrations according to the following formula.
Sb = Sa + (Tb−Ta) × (Sc−Sa) / (Tc−Ta)
[0028]
By obtaining the difference between Sb and the signal value Sb ′ for the second gas, the difference between the calibration value of the first gas and the calibration value of the second gas that is closer to the true value can be obtained. FIG. 3A shows the relationship between time and signal value in calibration of CO ₂ partial pressure, and FIG. 3B shows the relationship between time and signal value in calibration of O ₂ partial pressure.
[0029]
In this way, if the calibration with the first gas is performed again after the two-point calibration, the difference between the value obtained by the first gas supply and the value obtained by the second gas supply is determined in consideration of the fluctuation of the signal value. Therefore, calibration with higher accuracy can be performed.
[0030]
In the above description, in each of the examples, the first gas having a high CO ₂ partial pressure and an O ₂ partial pressure was calibrated first, and the second gas having a low partial pressure was calibrated later, but this order is not particularly limited. . Contrary to this example, the second gas may be calibrated first. Moreover, when performing two-point calibration in the method of Example 1, you may use the method of Example 2 together.
[0031]
【The invention's effect】
As described above, according to the present invention, the calibration time is shortened by performing one-point calibration at all times, two-point calibration is performed only when necessary, and data serving as a reference for performing one-point calibration is stored. Therefore, high calibration accuracy can be achieved at the same time.
[0032]
Further, by performing recalibration with the first gas after the two-point calibration, the calibration value with the first gas can be brought close to a true value, and highly accurate calibration can be performed.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of a monitor used in a method of the present invention.
FIG. 2 is a flow diagram of the method of the present invention.
FIG. 3 is a graph showing the relationship between time and calibration signal value according to the method of the present invention, where (A) shows the CO ₂ partial pressure and (B) shows the O ₂ partial pressure calibration.
FIG. 4 is a schematic configuration diagram of a monitor used in a conventional method.
FIG. 5 is a graph showing the relationship between time and calibration signal value according to a conventional method, where (A) shows CO ₂ partial pressure and (B) shows O ₂ partial pressure calibration.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 1st gas cylinder 2 2nd gas cylinder 31, 32 Sensor 31A, 32A Connector part 31B, 32B Electrode part 4A Sensor mounting part 4B Sensor connection part 5 Memory 6 Flow control part 7 Measurement part 8 Display part

Claims (4)

In a calibration method for a transcutaneous blood gas monitor that calibrates a gas partial pressure measurement sensor using a standard gas, the sensor has identification information for each sensor, and when the sensor is unstable, 2 of the first gas and the second gas. Two-point calibration is performed with various types of standard gases, and the calibration result is stored in a monitor for each sensor according to the identification information of the sensor. Normally, only one-point calibration with the first gas is performed, A calibration method for a transcutaneous blood gas monitor, wherein a calibration value of another point is obtained from a calibration result stored in two-point calibration. The percutaneous blood gas monitor calibration method according to claim 1, wherein the sensor identification information is provided by providing different resistances for each sensor. 2. The method for calibrating a transdermal blood gas monitor according to claim 1, wherein each sensor includes an identification memory, and the identification information is stored in the identification memory. In the two-point calibration performed when the sensor is unstable, first, two-point calibration with the first gas and the second gas is performed, and then recalibration with the first gas is continuously performed. The calibration method for a transcutaneous blood gas monitor according to claim 1, wherein the calibration is performed based on the result of recalibration with the first gas.

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