GB2100859A

GB2100859A - Method of and apparatus for determining and controlling the gas content of the blood

Info

Publication number: GB2100859A
Application number: GB08217698A
Authority: GB
Inventors: Robert Gylling
Original assignee: Instrumentarium Oyj
Current assignee: Instrumentarium Oyj
Priority date: 1981-06-18
Filing date: 1982-06-18
Publication date: 1983-01-06
Also published as: JPS5815850A; IT8221921A0; DE3222617A1; FI811936L; FR2508175B3; FR2508175A1; IT1152415B

Abstract

An arrangement for measuring and controlling the partial pressure of gases, especially carbon dioxide and/or oxygen, dissolved in the blood of a patient comprises unit (1) including a first space element (2), arranged to be supplied with a gaseous medium serving as carrier gas, and a second space element (3), arranged to be connected to the arterial or venous circulation of a patient for continuous blood flow through the second space element (3). Unit (1) is also provided with a gas- permeable, membrane (4) which separates the space elements (2, 3) from each other. Space elements (2 and 3) and membrane (4) are dimensioned and selected so as to produce in the first space element (2) a sample that represents the gas contents of a patients' blood. Means (9) provides for the determination of the contents of the desired gases in space element (2). The arrangement may be connected into a blood flow line in oxygenator or hemodialysis equipment. <IMAGE>

Description

SPECIFICATION Method of and apparatus for determining and controlling gas contents of the blood The present invention relates to a method of measuring and controlling the partial pressure of gas dissolved in the blood and to an apparatus for applying this method.

Several methods of measuring the partial pressure of gases dissolved in the blood of a patient are already known traditionally, a catheter is used to take blood samples from a patient and the samples are transferred to the laboratory for analysis of the blood gases, although the analysis itself, with the modern, highly automated equipment, can be effected in as little as 2-3 minutes, for a complete blood gas analysis, the entire process from the sampling to the analysis result being available is inevitably often too slow and only represents the situation at the actual moment of sampling. In addition, such automatic analyzers are sophisticated and expensive devices.

One way of analyzing a blood sample is a socalled bubble method, in which a blood sample from a patient is contacted with a gas bubble or bubbles, so that each bubble provides a sample which represents the content of gases in the blood, and from which the gas concentration content isdetermined e.g. by means of infrared spectrometry. In addition to being somewhat inaccurate, the method is complicated and rather slow.

Since in surgical operations, intensive care or the like treatment of a patient, the concentration of gases, especially CO, dissolved in the blood is an important and useful indicator of metabolism as well as the efficiency of circulation and respiration, which indicator reacts quite rapidly to any variations, the demand for more rapid and simple methods and equipment for determining the gas contents of blood has been substantial.

One device for determining the CO, content of blood is disclosed in US patent No. 3 987 303.

The determination is effected directly through the skin by letting the gases of the blood in the cutaneous capillary systems diffuse through a gas-permeable membrane into a chamber containing some appropriate gaseous medium.

Thus, the CO, dissolved in blood reaches in a manner known as such the same content on either side of the membrane, whereby the CO, content can be determined from the sample provided in said chamber. Determination is not continuous in this case either, but is based on separate samplings by always scratching away some of the top layer of the skin. It is obvious that such directly transcutaneous determination is quite susceptible to various inaccuracy inducing factors, such as skin impurities. It can also be difficult to apply the device tightly to a determination area defined on the skin.

One practical approach applied in operating rooms and intensive care wards is to determine the CO, content of blood from the exhaust gases of an oxygenator connected to the circulation of a patient. Since a gas-permeable membrane is used in an oxygenator to separate from each other spaces through which, on one hand, is led some of the circulation of a patient and, on the other hand, CO2 gas or O2"CO2 gaseous mixture, this is a way of achieving as such continuous determination of CO, content. However, since the purpose of an oxygenator is to oxygenize a patient's blood and to remove excessive CO, from the blood, it is necessary to supply into the circulation substantial amounts of the above alternative gases. This is why the chambers of an oxygenator are substantially equal in size.As the O2 and CO, contents of a patient's blood must be kept within a rather strict range, the diffusion taking place over the membrane must be accurately under control which sets strict requirements for the membrane itself. The surface area of such a membrane is typically of the order of 1 m2. As the consequence of all this, and further considering that there may be considerable local gradients in the gas concentrations in the blood flowing through an oxygenator, determination of the gas concentrations in blood from the exhaust gases of an oxygenator can give fairly inaccurate results.

An object of the present invention is to eliminate the drawbacks of the prior art and to provide a method which in a simple and effective manner utilizes gas diffusion through a membrane for measuring and controlling the gases dissolved in the blood of a patient. An object of an embodiment of the invention is to create a continuously-operating and reliable results supplying apparatus for employing the method of the invention and for analyzing gas contents of the blood of a patient, said apparatus being economic to manufacture and operate.

Another object of an embodiment of the invention is to provide an apparatus as optimal as possible, especially suitable for the determination of CO2 or O2 contents, by means of which apparatus the determination of gas contents in blood can be accomplished and variations in contents can be detected as quickly as possible. A still further object of an embodiment of the invention is to provide a method of and apparatus for analyzing the gas contents of blood and preferably adaptable for use e.g. in connection with oxygenators or hemodialysis equipment as one member of a system to be connected with the blood circulation of a patient.

According to the present invention there is provided a method of measuring and controlling the partial pressure of one or more gases, dissolved in the blood of a patient, wherein measuring is effected by means of an operative measuring unit including a first space element, into which is supplied a gaseous medium serving as carrier gas, and a second space element separated from said first space element by a gas permeable membrane and having a substantially larger volume than the first space element, said second space element being connected to the arterial or venous circulation of a patient or to a system coupled thereto so as to produce a continuous blood stream through said second space element with having substantial effect on the composition or gas contents of blood in said second space element, the gases dissolved in blood are allowed to diffuse through said membrane into said gaseous medium acting as carrier gas for producing a sample in said first space element representing the gas content of a patient's blood, and that the content of the or each desired gas diffused from a patient's blood into said first space element is determined and variations occurring therein are monitoied.

Embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Fig. 1 is a schematic view of an apparatus embodying the present invention, Fig. 2 shows an embodiment of an operative unit which is part of an apparatus according to an embodiment of the invention, Fig. 3 is a schematic view of another embodiment of the invention, and Fig. 4 shows schematically an embodiment of the apparatus of the invention applied to a blood processing system connected with the blood circulation of a patient.

In the figures, an operative unit 1 is shown which comprises, a space element 2 into which a carrier gas, e.g. air is supplied. A space element 3 is connected with the blood circulation of a patient.

Inlet pipes 5, 7 and outlet pipes 6, 8 are connected to the space elements 2, 3, the flow directions being shown in the figures by arrows.

The operative unit 1 is also provided with a gaspermeable membrane 4 e.g. of silicone rubber separating the space elements 2 and 3 from each other. The apparatus also comprises a gas content analyzing unit 9 for CO2 and/or 02 gases or for other gases possibly dissolved in blood. By way of example, the following description deals only with CO2 and 02 gases.

According to the invention, the gases dissolved in the blood of a patient are capable of diffusing from space element 3 through membrane 4 into the carrier gas in space element 2, CO2 and O2 gases reaching the same content on either side of membrane 4. Sample gas hereby obtained represents the CO2 and O2 contents of blood and follows variations in said contents and, thus, the contents of said gases can be determinad thereafter by means of conventional means and methods, e.g. by means of an infrared gas analyzer and oxygen sensors.

In the embodiment shown in Figure 1, a gas sample provided by the carrier gas is transferred into the separate analyzing unit 9 by means of said carrier gas. Transfer of the sample gas can take place continuously or in pulses by using a sample suction pump (not shown in the figures) which is a part of said analyzing unit 9. For example, the supply can occur once in every 1 .5 minutes by feeding a flow for ten seconds, preferably at a rate of 50ml/min. In a continuous transfer of sample gas, the preferably flow rates are < 200ml/min. After this, the sample gas is returned to space element 2 of the operative unit 1 to serve again as the carrier gas which thus forms a closed flow system.An advantage gained by this solution is that, due to its repeated cycles, said carrier gas quite well represents a fresh gas sample to be produced, this arrangement being apt to eliminate defects of sample gas as compared with an arrangement, in which fresh carrier gas is continuously sucked or supplied into space element 2. Hence, since mixing of carrier gas to be supplied with new sample gas to be produced in space element 2 is not in the embodiment oF fig. 1 very critical for the gas contents, the operative unit 1 can accordingly be of a more simple design. On the other hand, an open system only requires one connecting line between operative unit 1 and analyzing unit 9 and the above drawbacks can be compensated by extending the distance travelled by carrier gas in said operative unit 1.

Fig. 2 illustrates one embodiment of the operative unit 1 which can be used with advantage both in a closed circulating system for the carrier gas and in an open supply system of carrier gas. As shown in Fig. 2, the operative unit 1 comprises a member 10 which defines the space element 2 designed as a duct arrangement comprising a plurality of channels or ducts, as well as a member 11 which correspondingly defines the space element 3 designed as a duct arrangement 13. Members 10 and 11 are hermetically secured to each other by means of members 27. Sealing can preferably be effected by means of membrane 4. Intermediate ribs 14 and 15 in said duct arrangements on their part provide a preferable support surface for the membrane 4.

The time spent for obtaining a representative gas sample of the contents of the CO2 and O2 gases dissolved in blood can be effected by the design, length, volume and diffusion surface of carrier gas duct arrangement 12. If there is a risk that fresh carrier gas to be supplied into space element 2 has excessive effect on produced sample gas to be analyzed, a more complicated and/or longer duct system 12 is required. On the other hand, the smaller the volume of duct system 12 and the entire carrier gas and sample gas flow system and the larger a diffusion surface, the shorter is the time required for producing sample gas and the quicker said system reacts to variations possibly occurring in the blood gas contents.

In addition to the above, an arrangement of the invention can be carried out in such a manner that, immediately adjacent space element 2, there is provided a sample gas analyzing space, e.g. a chamber which can be arranged as a part of the gas content analyzing system preferably in a manner that the analyzing means themselves form a separate unit functionally connectible to said analyzing chamber. When using infrared gas analyzing means, it is then sufficient that the analyzing chamber is fitted with suitable window surfaces. If necessary, it is also easy to provide the analyzing chamber with an oxgyen sensor.

Another advantageous solution is to combine the above alternatives, so that, on one hand, for measuring the CO2 gas, a sample flow is passed into a separate analyzer and, on the other hand, measuring of 02 gas is effected in the space element 2 or in a space preferably separated therefrom. A schematic view of this embodiment is shown in Fig. 3, according to which the space element 2 is divided into two sections 2a and 2b.

Section 2b is filled with carrier gas but is separated from the circulating system of the members 2a, 8, 9, 7 to form an independent analyzing chamber, into which the gases dissolved in blood diffuse from the space element 3 and in which they, especially 02, can be determined by one or several sensors 27.

According to this embodiment C02-content can be determined by means of the circulating system of the carrier gas and the section 2a of the space element 2 can include a duct arrangement as shown in Fig. 2. The measurement of O2-content, on the other hand, is very advantageous because as a rule O2-sensors are rather slow. As the analyzing chamber 26 includes also carrier gas, the accuracy of the measured content values is independent of the properties of the membrane 4 and e.g. of flow velocity of blood. Naturally the analyzing chamber 26 can also be used for determining of other gases dissolved in blood.

In all the above cases, the operative unit 1 can be constructed as a quite simple design, sterile and economical disposable product that can be coupled to the system separately for each patient, thus improving the applicability of the entire system. The volume of the space element 2 or the gas space is preferably chosen to be S5 cm3 in view of simple and effective measuring. The space element 3 is of substantially larger volume than space element 2, in practice up to ten times larger. This is to guarantee a sufficiently rapid sampling and short sampling intervals. This is also effected by the surface area of membrane 4 which can preferably be S250 cm2.

Fig. 3 shows schematically how the arrangement of the invention can be applied with advantage to a blood processing system connected with the circulation of a patient 16, said processing system being e.g. an oxygenator or 3 hemodialysis apparatus designated in fig. 4 by referance numeral 17. The apparatus 17 is provided with two chambers 21 and 22 which in practice can be formed of complicated duct systems. The chambers are separated from each other by a membrane 23 which in an oxygenator is conventionally gas-permeable and in a hemodialysis apparatus permeable to certain liquids and materials. Chamber 21 is connected to the circulation of a patient 16 by means of a supply duct 18, and chamber 22 is accordingly fitted with a medium flow system 20.Apparatus 17 is also provided with a flow-creating pump assembly as well as with a so-called bubble trap for the blood to be fed into a patient (not shown in fig. 4). Having been processed in apparatus 17 in a desired manner, the blood is passed through a duct 24 into an operative unit 1 of the invention and from thereon through a duct 19 back into the patient. As a practical precaution, this system is also fitted with a bubble trap downstream of the operative unit 1 (not shown in fig. 4). By analyzing, according to the invention, the blood supplied into a patient 16, it is possible to make sure that said blood has proper CO2 and O2 gas contents.Unless this is the case, the information obtained frnm analyzing unit 9 can be used to control the diffusion via membrane 23 and, if necessary, to cut off the supply into the patient 16 by means of a closing valve 26 and/or by a bypass (the control symbolically depicted by arrows 24 and 25). It is also conceivable to reverse the connecting order of said operative unit 1 and unit 17, whereby information is received about the gas contents of the blood of the patient prior to the blood processing and, thus, it is possible to assess the metabolism of the patient, and the operating efficiency of the heart, circulation and respiratory organs etc.

The invention can also be applied with advantage in connection with fluid flow systems relating to body organs, e.g. kidneys, separated from a patient, whereby the circulating liquid instead of blood can also be some nutrient solution.

Claims

1. A method of measuring and controlling the partial pressure of one or more gases, dissolved in the blood of a patient, wherein measuring is effected by means of an operative measuring unit including a first space element, into which is supplied a gaseous medium serving as carrier gas, and a second space element separated from said first space element by a gas-permeable membrane and having a substantially larger volume than the first space element, said second space element being connected to the arterial or venous circulation of a patient or to a system coupled thereto so as to produce a continuous blood stream through said second space element without having substantial effect on the composition or gas contents of blood in said second space element, the gases dissolved in blood are allowed to diffuse through said membrane into said gaseous medium acting as carrier gas for producing a sample in said first space element representing the gas content of a patient's blood, and that the content of the or each desired gas diffused from a patient's blood into said first space element is determined and variations occurring therein are monitored.

2. A method as claimed in claim 1, wherein sample gas produced is passed into a separate analyzing unit and that carrier gas is correspondingly passed for the determination of the desired gas content into said first space element so that, due to diffusion, sample gas is continuously produced in said first space element.

3. A method as claimed in claim 1 or 2, wherein the desired gas content are determined from the sample gas produced in said first space element or in an analyzing chamber connected and in direct communication therewith.

4. A method as claimed in claim 1 or 2, wherein the content of one of a plurality of gases, is determined in an analyzing chamber separated from said first space element, said analyzing chamber being filled with carrier gas but being separated from the carrier gas circulating system.

5. A method as claimed in claim 4, wherein said one gas is oxygen.

6. An apparatus for measuring and controlling the partial pressure of one or more gases, dissolved in the blood of a patient, the apparatus comprising an operative unit having a first space element arranged for supply with a gaseous medium serving as carrier gas, and a second space element of substantially larger volume than said first space element and arranged for connection to the arterial or venous circulation of a patient for producing a continuous blood stream through said second space element without any substantial effect on the composition or gas content of the blood in said second space element, a gas-permeable membrane arranged to separate said space elements from each other, said space elements and said membrane being dimensioned and selected so as to optimize diffusion of the gases dissolved in blood through said membrane into said gaseous medium acting as carrier gas for producing in said first space element a sample representing the gas contents of the patient's blood, and that the apparatus is provided with means for determining the content of the or each gas diffused from a patient's blood into the carrier gas of said first space element and for monitoring variations in said gas content.

7. An apparatus as claimed in claim 6, wherein for determining the desired gas content, means are provided to pass sample gas produced from said carrier gas in said first space element by diffusion into a separate analyzing unit, and to pass carrier gas into said first space element so that, due to diffusion sample gas is continuously produced so as to be passed into said analyzing unit.

8. An apparatus as claimed in claim 7, a continuous, closed flow system is provided for the carrier gas flow and the sample gas flow obtained therefrom.

9. An apparatus as claimed in claim 7 or 8, wherein the passing of said sample gas into said analyzing unit is arranged to be effected in pulses as the content of the or each gas to be determined have reached sufficient equilibrum through said membrane.

10. An apparatus as claimed in claim 7 or 8, the passing of said sample gas into said analyzing unit is arranged to be effected as a continuous flow the rate of which is selected so that the gas content of the or each gas to be determined have reached sufficient equilibrium through said membrane.

1 An apparatus as claimed in claim 10, wherein the rate of said gas flow is 1200my per minute.

12. An apparatus as claimed in any of the claims 6 to 11, wherein said operative unit is a replaceable and sterilized member removably connected to the rest of the apparatus.

13. An apparatus as claimed in claim 12, wherein said operative unit is disposable.

14. An apparatus as claimed in claim 6 or 7, wherein for the determination of the content of one of a plurality of desired gases from sample gas produced from said carrier gas in said first space element by diffusion, said operative unit comprises an analyzing space which preferably forms part of said first space element.

15. An apparatus as claimed in claim 6 or 7, wherein for the determination of the content of one of a plurality of desired gases from sample gas produced by diffusion from the carrier gas said first space element is divided to include at least two sections, one of which being separated from the circulating system of carrier gas to form an independent analyzing chamber.

1 6. An apparatus as claimed in any of the claims 6 to 15, wherein said operative unit is divided into two members hermetically secured to each other, one of the members being arranged to define said first space element and the other being arranged to define said second space element, and said members of the operative unit separated and sealed to each other by means of said gas-permeable membrane.

1 7. An apparatus as claimed in any of the claims 6-1 6, wherein each of said space elements comprises a duct arrangement, that the duct arrangements are so dimensioned that the distance travelled by said carrier gas and sample gas produced therefrom is substantially longer than the distance travelled by said blood flow, and that the duct system for carrier gas is of considerably smaller volume than the duct system for coupling to the blood circulation, the amount of carrier gas being optimized for producing a sufficient amount of sample gas.

18. An apparatus as claimed in claim 17, wherein the ducts of said first space element are arranged substantially transversely relative to the ducts of said second space element, and intermediate ribs are provided between the ducts to support said membrane.

1 9. An apparatus as claimed in any of the claims 6 to 18, wherein the area of said membrane is < 250 cm2.

20. An apparatus as claimed in any of the claims 6 to 19, wherein the volume of said first space element is < 5 cm3.

21. An apparatus as claimed in any of the claims 6 to 20, wherein said carrier gas is air.

22. An apparatus as claimed in any of the claims 6 to 21, wherein said operative unit and means for the determination of gas content are connected as part of the oxygenator or hemodialysis system, coupled to the circulation of a patient for controlling the oxygenizing or hemodialysis process by means of the gas content information obtained and determined from the blood.

23. An apparatus as claimed in any of claims 6 to 22, for measuring and controlling of the partial pressure of carbon dioxide and/or oxygen.

24. A method as claimed in any of claims 1 to 5 for measuring and controlling the partial pressure of carbon dioxide and/or oxygen.

25. An apparatus for measuring and controlling the partial pressures of gases substantially as herein described with reference to figure 1 with or without reference to any of figures 2 to 4 of the accompanying drawings.

26. A method of measuring and controlling the partial pressures of gases substantially as herein described with reference to figure 1 with or without reference to any of figures 2 to 4 of the accompanying drawings.