Method and apparatus for in vivo blood gas analysis

• US 3,983,864 A
• Filed: 07/07/1975
• Issued: 10/05/1976
• Est. Priority Date: 08/01/1974
• Status: Expired due to Term

• Current Assignee: Airco, Inc. (Linde Plc)
• Original Assignee: Airco, Inc. (Linde Plc)
• Inventors: Peickert, Wilfried R., Sielaff, Ulrich, Brinkman, Dale A.
• Primary Examiner(s): Howell, Kyle L.
• Application Number:
  US05/593,606
• Time in Patent Office: 456 Days
• Field of Search: 128/2 G, 128/L, 128/F, 128/E, 128/214.4, 128/348, 421/5 R, 421/23 R, 421/23.1, 23/230 B, 23/232 C
• US Class Current: 600/364
• CPC Class Codes: A61B 5/145 Measuring characteristics of blood in vivo, e.g. gas concentration, pH value; Measuring characteristics of body fluids or tissues, e.g. interstitial fluid, cerebral tissuemeasuring of blood pressure or blood flow A61B5/02; non-radiation detecting or locating of foreign bodies in blood A61B5/06
• CPC Class Codes: A61B 5/14542 for measuring blood gases A61B5/14551 takes precedence
• CPC Class Codes: A61B 5/1473 invasive, e.g. introduced into the body by a catheter A61B5/1482 takes precedence
• CPC Class Codes: Y10T 436/255 including use of a solid sorbent, semipermeable membrane, or liquid extraction

Abstract

Method and apparatus for withdrawing and analyzing gases dissolved in liquid, more specifically, equilibrated blood gas samples in vivo. A catheter including a semipermeable membrane, connected to include a volume of carrier gas at atmospheric pressure, is introduced percutaneousluy into the bloodstream. After a predetermined period, equilibratin occurs between the blood gases and the carrier gas. By means of displacement in the volume or reduction in the pressure, the carrier gas including the equilibrated gas is then removed from the semipermeable membrane to another area for analysis. A corresponding volume of carrier gas is replaced in the semipermeable membrane from an inlet supply.

Claims

1. A method of sampling gases dissolved in a liquid comprising the steps of:

introducing a catheter into the liquid, at least a portion of said catheter comprising a membrane being permeable to said gases but substantially impermeable to said liquid, said permeable portion directly contacting said liquid;

admitting carrier gas at about atmospheric pressure into said catheter to contact said membrane;

permitting said carrier gas to equilibrate with the gases dissolved in said liquid whereby said dissolved gases pass into said catheter through said membrane and are mixed with said carrier gas; and

removing at least a portion of said mixed gases from said catheter.

2. A method of intermittently sampling and subsequently analyzing gases dissolved in the bloodstream of a living organism comprising the steps of:

introducing a member comprising a semipermeable membrane into said bloodstream, said membrane being permeable to gases but substantially impermeable to blood;

admitting carrier gas at about atmospheric pressure into said semipermeable membrane member within the bloodstream;

allowing equilibration between a volume of said carrier gas and said dissolved blood gases through the lateral walls of said semipermeable membrane member for a predetermined time;

removing at least a portion of said volume of carrier gas containing said equilibrated blood gases from said semipermeable membrane member; and

isolating and analyzing said removed equilibrated gases in said portion of carrier gas.

3. A method in accordance with claim 2 wherein said carrier gas is characterized relative to said dissolved blood gases by either a slow rate of diffusion through said membrane or a low solubility in blood, or both.

4. The method in accordance with claim 2 wherein said volume of carrier gas containing said equilibrated blood gases substantially exceeds the portion analyzed.

5. The method in accordance with claim 4 wherein said volume of carrier gas including said equilibrated blood gas exceeds the portion analyzed by at least a factor of ten.

6. The method is accordance with claim 2 in which the steps of removing and isolating a portion of the volume of said carrier gas containing said equilibrated gases from the remaining carrier gas is carried out by first reducing the pressure in means connected to said membrane member for sampling a discrete portion of said volume, thereby causing the said portion to move from said member to said sampling means, connecting said sampling means to a gas analyzer and subsequently forcing the said portion containing said equilibrated gases from said sampling means to said gas analyzer by introducing into said sampling means carrier gas from an auxilliary source.

7. The method in accordance with claim 6 which comprises the steps of detecting the peak amount of said equilibrated gas distributed in said portion of carrier gas as said portion moves from the membrane member to said sampling means, and actuating valve means to admit a discreet amount of said portion including said equilibrated gases to said gas analyzer when said peak is positioned in said sampling means in a preselected position in relation to the intake of said gas analyzer.

8. The method in accordance with claim 7 wherein said peak generates a signal, detecting and utilizing said signal to actuate said valve means.

9. The method in accordance with claim 7 wherein said carrier gas is characterized by a thermal conductivity which is substantially different from that of the blood gas to be measured.

10. The method in accordance with claim 9 wherein helium is employed as a carrier gas.

11. The method in accordance with claim 9 wherein the space rate of change to thermal conductivity in said portion of carrier gas including said equilibrated blood gases is represented by a "bell shaped" curve, detecting a signal corresponding to the space rate of change in said thermal conductivity represented by the change in slope of said curve, and utilizing said signal to actuate said valve means to receive said portion including said equilibrated blood gases at a position represented by the flat top portion of said curve.

12. A device for the sampling of gases dissolved in liquid characterized by a catheter, a portion of which comprises a membrane permeable to gas diffusion but substantially impermeable to diffusion by said liquid, said catheter being designed for introduction into the liquid to be analyzed, a carrier gas source connected to the gas permeable membrane portion of said catheter comprising means to supply carrier gas thereto at substantially atmospheric pressure, said supply means being adapted to retain a volume of carrier gas contacting the gas-permeable membrane portion for a preselected period of time to permit the establishment of an equilibrium between the carrier gas and said dissolved gases causing mixing thereof within the catheter, and means connected to the catheter to remove therefrom at least a portion of the carrier gas including the mixed equilibrated gases.

13. A system for intermittently sampling and subsequently analyzing gases dissolved in the blood which comprises in combination:

a catheter comprising intake and exhaust terminals at its proximal end connected by a continuous passage formed in a semipermeable membrane member constructed for insertion at the distal end of said catheter into the bloodstream of a subject to be analyzed, said membrane being permeable to gases but substantially impermeable to blood;

a source of carrier gas connected to the intake terminal of said catheter and comprising means for supplying carrier gas to the passage formed in said membrane member at about atmospheric pressure;

means for retaining a volume of said carrier gas in said passage for a preselected interval to allow equilibration between said carrier gas and said dissolved blood gases;

means connected to the exhaust terminal of said catheter for removing said volume of carrier gas including said equilibrated blood gases from said passage;

means connected to said last-named means for analyzing at least a portion of said removed equilibrated blood gases.

14. In a system in accordance with claim 13 wherein said means connected to the exhaust terminal of said catheter for removing said volume of carrier gas including said equilibrated blood gas from said passage to said means for analyzing the blood gases comprises:

an auxilliary source of carrier gas,

pumping means constructed and arranged to induce evacuation and exhaust cycles in said system,

a gas purging valve connected to said pumping means;

a conduit system including a sampling valve having at least two positions for transmission therethrough;

during the evacuation cycle of said system;

said sampling valve operable in a first position for connecting the exhaust terminal of said catheter to said pumping means to receive at least a portion of said volume of said carrier gas including said equilibrated blood gas in said sampling valve, and in a second position for connecting said auxilliary carrier source through said sampling valve to said means for analyzing said equilibrated blood gas, whereby said portion is forced into said blood gas analyzing means; and

during the exhaust cycle of said system;

said purging valve connectable for purging said pumping means of gas in preparation for the next evacuation cycle.

15. A system in accordance with claim 14 wherein said pumping means comprises automatic vacuum pumping means, and said system comprises detecting means connected adjacent one terminal of said sampling valve and responsive to detect the peak of equilibrated blood gases in said volume of carrier gas passing from said semipermeable membrane member to said sampling valve, and to generate a signal in response to the passage of said peak, and means responsive to said detecting means and actuated by said signal for operating said sampling valve to connect said auxilliary carrier source through said sampling valve to said gas analysis means.

16. A system in accordance with claim 15 wherein the space rate of change of the thermal conductivity of said volume of equilibrated blood gas varies as a function of the distribution of dissolved blood gas therein, and wherein said detecting means is sensitive to the space rate of change of thermal conductivity in said volume.

17. A system in accordance with claim 16 wherein said function is a "bell shaped" curve having a flattened peak, and wherein said defecting means is responsive to a change of slope of said "bell shaped" curve to actuate said sampling valve to introduce a portion of said volume including said equilibrated blood gases represented by the flat portion of said peak into said means for analyzing blood gas.

18. A system in accordance with claim 13 wherein said means for analyzing the blood gases comprises a gas chromatograph.

19. A system in accordance with claim 13 wherein the membrane member comprising said catheter comprises tubular means constructed for insertion percutaneously into the blood vessel in a direction extending along the principal axis thereof and simultaneously providing a continuous gas permeable conduit in contact with the blood of said subject between said input and output terminals,

said input and output terminals both the the proximal end of said tubular means, and

connecting means to said input and output terminals comprising a housing including input and output gas receptacles respectively constructed and arranged for connection in circuit relation to said source of carrier gas at said input receptacle and to said means for analyzing the blood gases at said output receptacle.

20. The combustion in accordance with claim 19 wherein said semipermeable tubular membrane member consists essentially of a polysiloxane polymer.

21. A system in accordance with claim 19 wherein said gas permeable conduit has a substantially uniform cross-section and permeability along its length between said terminals.

22. The combination in accordance with claim 19 wherein said semipermeable tubular membrane member comprises a plurality of lumens interconnected to provide a continuous uniform gas permeable conduit between said input and output terminals having a length in contact with the blood which substantially exceeds the length of said membrane member.

23. The combination in accordance with claim 22 wherein said semipermeable tubular membrane member comprises at least two parallel lumens of substantially uniform cross-section and permeability forming a gas permeable conduit substantially double the length of said tubular membrane member and joined together by connecting means at their distal ends to provide a reversal of gas flow from one to the other, the proximal ends of said lumens respectively connected to said input and output terminals.

24. The combination in accordance with claim 22 wherein each of said lumens has a cross-sectional dimension not exceeding about 0.011 inch and said membrane has an overall cross-sectional dimension not exceeding about 0.028 inch.

25. The combination in accordance with claim 19 wherein said membrane member comprises an external membrane tube coaxial with another tube, said tubes being inter-connected at their distal ends.