JPS61154540A - Apparatus for measuring concentration of gas in blood - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention relates to partial pressure of carbon dioxide in blood (hereinafter referred to as PCO2).
This relates to a device for measuring or monitoring. More specifically, the present invention relates to a device for measuring partial pressure of carbon dioxide in blood that can be inserted into a blood vessel and has particular utility in in-vivo monitoring applications.

(Prior Art) Carbon dioxide partial pressure, oxygen partial pressure, and aqueous ion concentration in blood are collectively referred to as blood gases, and are extremely important as measures of the respiratory and metabolic functions of living organisms. Conventionally, blood gas measurements have been carried out using a blood gas analyzer after blood collection.

However, with this method, it takes a long time from blood collection to completion of measurement.
There were problems such as the inability to perform continuous measurements, and loss of blood from the patient. In order to solve these problems, the present inventors disclosed a so-called infusion type blood gas measuring device in Japanese Patent Application Laid-Open No. 155240/1983.

In this device, a gas partial pressure sensor is installed in a catheter inserted into a blood vessel or a measurement chamber connected to the catheter, the catheter or measurement chamber and an infusion reservoir are connected with a conduit, and a gas partial pressure sensor is installed in the catheter or measurement chamber. Cap e'5r containing a gas component at a certain concentration: At the same time as supplying blood, appropriate blood is sucked into the catheter/V or/and the measurement chamber by the means for sucking the infusion in the catheter/I/or the measurement chamber, and the above gas is This device is configured so that at least the detection part of the partial pressure sensor comes into contact with blood. The aim of the device was to calibrate the gas sensor with an infusion fluid having a gas partial pressure equal to the gas partial pressure in the blood. Also, a special application for 1982-22
No. 5216, we proposed a device using a cap fluid reservoir made of a gas-impermeable metal-laminated organic polymer film. However, subsequent studies revealed that the device had the following problems.

(1) Metal laminate film has a high gas barrier property, making it suitable as a container for storing infusions containing a certain amount of gas, but because it is opaque, even if foreign matter is mixed inside, it cannot be detected from the outside. , it is also impossible to see the internal liquid level. These points are major problems in terms of medical safety.

(2) Manufacturing an infusion reservoir (infusion bag) using a metal laminate film requires considerable molding technology and is costly.

(Problems to be solved by the present invention) In general blood (7) PCO2 is 30 to 100 mmK
g, this (on the other hand, PCO2 in the air is 0.2 mmM
It's around g.

Severinghaus type) PCO2 (c y f
The O output voltage is proportional to the logarithm of the construction PCO2, and its sensitivity is around somV71og PCO2. Therefore, P.C.O.
230 to 100 mm f1g has a width of only about 2 s mV when considered as the output of the PCO2 sensor. On the other hand, 0.
2 to a o mmm1 (about 110 mV is a joke. In this way, there is a large difference in the output of the PCO2 sensor between air and blood. Furthermore, as a general characteristic of the PCO2 sensor, PCO2tk0 mmf ( It takes a long time, from several tens of minutes to several hours, to stabilize from a level μ of more than 1 mmHg to a level μ of less than 1 mmHg.For these two reasons, the zero point calibration of the Severinghaus POO2 (! It has been conventional wisdom that it is impossible to use air itself or an aqueous solution that is in equilibrium with air.

However, as mentioned above, it is difficult to adopt a metal fuminate flexible infusion bag, and furthermore, the method of bringing a standard carbon dioxide gas cylinder into the clinical site and creating the carbon dioxide calibration solution within the device makes it inconvenient to replace the standard carbon dioxide gas cylinder. However, it is difficult to sterilize the calibration solution, making it impractical.

Judging from the above points, I decided to consider the possibility of an infusion type pco2 monitor that uses an aqueous solution in equilibrium with air as a calibration fluid, although this is contrary to conventional wisdom. If this method becomes possible, it would be possible to use already commercially available infusion solutions (for example, lactated Ringer's solution as is).
It can be used as a calibration solution for sensors, making it possible to significantly simplify the commercialization of measurement systems.

(Means and effects for solving the problem) As a result of intensive research on a PCO2 monitoring system that uses an infusion solution in vapor-liquid equilibrium with air as a calibration fluid, it was discovered that the system described below makes it possible 1. The present invention reached. This system has a function in which a Beveringhaus type POO2say+ is installed in a measurement chamber connected to a catheter, and a measurement liquid and an infusion liquid equilibrated with air can be introduced into the measurement chamber alternately at predetermined intervals. , the PCO2
This system has a calculation function that converts the amplitude (V) of the periodic response of the sensor into the PCO2 value (P) of the measurement liquid.

More preferably, it is a system having a function of calculating V into P using equation (1).

P = v-10 (a ma2 + by + C)
, l) where a, b, c are unique constants determined in advance for each PCO2 sensor.

Next, the experimental results that formed the basis of the present invention will be explained.

Figure 1 shows a part of the apparatus used in this experiment. In FIG. 1, 1 is a constant temperature bath, 2 is a container placed therein, and a measuring liquid 3 is placed therein. A measuring chamber 5 connected to an indwelling needle (catheter) 4 is immersed in the measuring liquid, and both the measuring liquid and the measuring chamber reach Km! It is maintained at a constant temperature by the rod 1. A PCO2 sensor 6 is fixed in the measurement chamber with an O-ring 7 and screws 8. The output of the senna is taken out by connecting a monitor to the connector 9. A tube 10 is connected to the measurement chamber 5, and a roller pump 1 is connected to the measurement chamber 5.
A flexible bag 12 is connected via 1. A mixed gas of carbon dioxide/nitrogen having a predetermined PCO2 is bubbled into the measurement liquid 3 through a bubbler 13. We used an indwelling needle and a lactic acid ringer solution containing cetylvac in the measurement chamber. Since this flexible bag was made of a gas-permeable polymer film, the lactate Lisge/I/liquid was in equilibrium with carbon dioxide gas in the atmosphere. Carbon dioxide sensor 6
As for Japanese Patent Application Publication No. 59-155240 and Japanese Patent Application No. 58-6
120, based on PfI mechanistic field effect transistors. roller pump 11
The rotation speed of the infusion is 0 in both the forward direction (from the infusion bag to the measurement chamber) and the reverse direction (from the measurement chamber to the infusion bag).
．． It was set to be 35 Cc for 7 minutes. The rotation time of the roller pump was 4.5 minutes in the forward direction and i and s minutes in the reverse direction. Output voltage of the PCO2 sensor (source potential of PH-sensitive field effect transistor) obtained when the temperature of the thermostatic chamber is 37°C and the volume ratio of blown carbon dioxide/nitrogen is 5795
Figure 2 shows the changes in . A (dashed line portion) and F<* line portion) on the time axis in FIG. 2 indicate the rotation time periods of the pump in the reverse direction and in the forward direction, respectively. As is clear from this figure, when the pump starts to rotate in reverse and the measurement liquid containing dissolved carbon dioxide enters the measurement chamber, the source potential of the PCO2 sensor increases (moves downward in the figure).

When the rotation of the pump is switched in the forward direction, lactated Ringer's solution balanced with air enters the measurement chamber, so the source potential of the rcu2 sensor decreases. By repeating these steps, a periodic waveform as shown in FIG. 2 is obtained. There are several possible ways to determine the amplitude of this waveform. FIG. 2 illustrates two of them.

The first method uses the straight line AB connecting the pump reversal start points A and B as the baseline, and the amplitude α■) as the base line.The second method uses the straight line EF connecting the troughs E and F of the waveform as the base line. The GH, which is a line, is the amplitude (V weight). Here, the first method was adopted and the relationship between P 002 of the measurement liquid and the amplitude vI was investigated. The results are shown in Figure 3. Third
In the figure, the solid line connects the measured values (black circles) with a smooth curve.

On the other hand, white circles indicate values calculated using equation (1). In this case, the parameters a, b, and o were calculated using the actual measured values of the three cross marks in FIG. That is, the three fruits [, a
Koff ;b Vt,! = PCO2t (Vi,
Px), (V2.P2).

(V3.P3) then aVi"-)-bVi+o=log(Pi/Vi)
(i=i ~3) (2) holds true. By solving this, a, b, and c can be found using the following formula.

It is.

As is clear from Figure 2, the value of PCO2 calculated from the actually measured PCO2 and equation (1) is PCO2 = O ~ 200.
Very good agreement is shown in the mmHg' range. That is, it has been experimentally found that the relationship expressed by equation (1) holds between the output amplitude V of the infusion type PCO2 sensor and PCO2.

Generally, PCO2, iron P) is a function of amplitude V (V)
It is expressed as

P = f (V) +
7) The present inventors arrived at formula (1) through trial and error, but
In order to arrive at equation (1), simulations using several functions such as those described below were attempted.

P = V-(av2-)-by-1-c)
+8) P = V -10"+b(9) P = V・(10"+bv+c)
(IQ, = v, (10(av2+l)1')
+c) ”) However, both functions (1
) formula did not give any good results.

In the apparatus of the present invention, an aqueous solution in equilibrium with air can be used as the calibration liquid. In this device, since the calibration fluid is injected into the patient's blood vessel, it is preferable to use an infusion fluid that is determined according to the patient's condition. Commonly used infusion solutions include lactate lv solution, physiological saline, glucose lactate lv solution, glucose electrolyte solution, and amino acid solution. The partial pressure of carbon dioxide in the calibration solution is that of the atmosphere (P■2
= 0. zmmHg), but PCO2 does not necessarily have to be equal to 2 mmHg, as long as PCO2 is between 0 and 2 mmHg. When PCO2 exceeds 2 mmHg, the amplitude deviates from the calculated value. Regarding the flow rate of the calibration garment and measurement solution, it is necessary to determine the optimal conditions based on the indwelling needle and the dead volume of the measurement chamber. For example, when the total dead volume between the indwelling needle and the measurement chamber is 0.3 cc, the flow rate of the measurement liquid back into the measurement chamber is 0.3 to 0.5 cc.
degree is necessary. On the other hand, the amount of calibration liquid injected into the measurement chamber must be sufficient to push the measurement liquid out of the measurement chamber (into the blood vessels). Usually this is 1.1 to 5 of the backflow amount.
About twice as much, preferably about 1.5 to 3 times. Furthermore, it is necessary to determine the optimum program for the forward rotation, reverse rotation, and, if necessary, stoppage of the pump, depending mainly on the response time of the senna. Generally 8everin
The 90% response time of ghaus type PCO2 is 0.
It takes about 5 to 3 minutes. Therefore, if the forward/reverse cycle of the pump is a few seconds, the sensor cannot fully respond, and if the cycle is 10 minutes or more, it is too long to be useful for monitoring. Usually, the cycle of bonding is preferably about 0.5 to 10 minutes. Here, the period of the pump means the time from the start of reverse rotation through (stop) → normal rotation → (stop) to the start of the next reverse rotation.

In the apparatus of the present invention, a blood φ blood flow monitor is installed with a multi-sensor system including other sensors in addition to the Pco2 sensor in the measurement chamber, and furthermore, N&+.

Examples include blood gas/electrolyte monitors with Oa2+ sensors added. In blood gas/electrolyte monitors, the infusion fluid that is the calibration solution has a constant pH and Na".

The concentration of K'', Ca'+ ions is constant, and P
CO2 and PO2 are in equilibrium with those of air,
For example, lactic acid ring A/liquid is used.

(Example) Example 1 An infusion type PC0,2 measuring device as shown in FIG. 4 was manufactured. Frekinpur infusion bag 21 is bonded to 22t.
Pass through the tube body 23 (silicone rubber tube) to the measurement chamber 2
It is connected to 4. Lactated Ringer's solution was used as the infusion. An indwelling needle 25 is connected to the measurement chamber, and a PCO2 sensor 26 is installed.

The pco2 senna described in Japanese Patent Application No. 58-6120 was used. The sensor is operated by a sensor circuit 27, and its signal is processed by a CPU 29 via a unit 28, and the measurement results are output to a display 30, a printer 31, and a recorder 32.

The pump is operated by CPU29. I10 unit 28. This is done by the pump control circuit 33. The measurement chamber shown in FIG. 1 was used. The dead volume of the indwelling needle and measurement chamber was 0.3 cc.

Both the measurement chamber and the measurement solution were set at 37°C.
The parameters a, b, and C of the PCO2 sensor were determined using an aqueous solution having 2. That is, PUO2=36.72
and V in an aqueous solution of 214 mmHg.

The results were 25.0 and 40.5, respectively. and 57.
It was 5mV. From now on (3), 14), (5)
Calculating aIbIG using the formula: 8=0.000399
b=-0,02020=0.415 was obtained. The pump runs for 1.5 minutes in reverse, 4.5 minutes in forward rotation,
The stoppage was 0 minutes, the total period was 6.0 minutes, and the flow rate was 0.35 cc/min in both forward and reverse directions.

Next, under the same operating conditions, an aqueous solution with an unknown Pco2 was subjected to vIt- measurements, and this and a determined above.

Using b and c, PCO2 was calculated from formula (1) and compared with the PCO2 value measured with a commercially available PCO2 analyzer (■Kuraray PR/PCO2 monitor 500).The results are shown in Table s1. As is clear from this, the rcoz value obtained by the device of the present invention is y
Exact match.

Table 1 (Effects) As described above, in the device of the present invention, the inherent parameters of the PC sensor (a, b in the above example).

If C) is required by the manufacturer, it is possible to use a commercially available infusion solution as a calibration solution without using a specially prepared calibration solution or standard gas cylinder in a clinical setting.
can be determined easily and with high accuracy. Furthermore, since the blood after the measurement is completed is returned to the patient together with the blood, no blood from the patient is lost.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an experimental apparatus used in experiments of the present invention. FIG. 2 shows the sensor output curve of the cap fluid type PCO2 monitor. Figure 3 shows the amplitude of the PCO2 sensor output and the PCO
This shows the relationship between the two. FIG. 4 is a block diagram of the apparatus of the present invention.

Claims (2)

[Claims] (1) A Severinghaus type carbon dioxide partial pressure sensor is installed in a measurement chamber connected to a catheter inserted into a blood vessel, and the measurement chamber and an infusion reservoir are connected with a conduit, so that the temperature within the measurement chamber is 2 mmHg or less. In addition to supplying an infusion having a carbon dioxide partial pressure of blood by means of detecting the potential of the sensor by contacting the sensors alternately and at regular intervals, and converting the amplitude (V) of the periodic response of the detected value into the partial pressure of carbon dioxide gas (P) in the blood. A device for measuring the partial pressure of carbon dioxide in blood, characterized in that it is configured to convert the partial pressure of carbon dioxide into the partial pressure of carbon dioxide in the blood. (2) The device according to claim 1, wherein the means for converting the amplitude (V) of the periodic response of the measured value into the carbon dioxide partial pressure (P) in the blood is converted according to the following calculation formula. P=V・10^(^a^v^^2^+^b^v^+^c
^) Here, a, b, and c are constants specific to each carbon dioxide gas partial pressure sensor.