WO2005028002A1

WO2005028002A1 - Blood oxygenation system with single lumen catheter

Info

Publication number: WO2005028002A1
Application number: PCT/IL2004/000880
Authority: WO
Inventors: Dudu Haimovich; Dan Rottenberg
Original assignee: Dudu Haimovich; Dan Rottenberg
Priority date: 2003-09-22
Filing date: 2004-09-22
Publication date: 2005-03-31

Abstract

A system for blood oxygenation. The system comprises a blood oxygenator in which a blood compartment and a gas compartment are separated by a gas permeable barrier so as to allow exchange of carbon dioxide in blood in the blood compartment with oxygen in the gas compartment. The proximal end of a catheter is connected to the blood oxygenator, while the distal end of the catheter is inserted into a blood vessel. A pump alternates between causing blood to flow in the catheter lumen from the blood vessel to the oxygenator and causing blood to flow in the catheter lumen from the oxygenator to the blood vessel.

Description

BLOOD OXYGENATION SYSTEM WITH SINGLE LUMEN CATHETER

FIELD OF THE INVENTION This invention relates to medical devices, and more specifically to such devices for oxygenating blood.

BACKGROUND OF THE INVENTION Acute Respiratory Distress Syndrome (ARDS) is an acute, severe injury to most or all of the lungs. Patients with ARDS experience severe shortness of breath and often require mechanical ventilation or Extra-Corporeal Membrane Oxygenation (ECMO) due to respiratory failure. ARDS is not a specific disease. Rather, it refers to severe, acute lung dysfunction that is associated with a verity of diseases and chest trauma, such as pneumonia, emphysema, shock, sepsis, smoke aspiration, drowning, and chemical warfare. Current Extra-Corporeal Membrane Oxygenation (ECMO) systems comprise a hollow fiber membrane oxygenator that exchanges oxygen for carbon dioxide (CO₂) in the blood. A catheter is used to conduct oxygen-poor, CO₂ rich blood from the body to the oxygenator, while a second catheter is used to conduct oxygen-rich, CO₂ poor blood from the oxygenator to the body. The two catheters are inserted into the cardiovascular system by either an incision or by percutaneous insertion into peripheral venous and/or arterial blood vessels, usually the femoral vein and artery. A pump, usually a roller or centrifugal pump, is used to circulate blood from the body to the oxygenator via the first catheter, and from the oxygenator back to the body via the second catheter. Insertion of the catheters into the body is traumatic because it obstructs normal blood flow through the blood vessel, (especially through small arteries), and the insertion point is exposed to infection. Many types of membrane and silicone sheet oxygenators are known. All of them have a separate blood inlet and blood outlet, as well as a gas inlet and a gas outlet. Most of the blood pumps available today are roller or centrifugal pumps. These pumps are steady flow pumps that have one blood inlet and a separate blood outlet. Single catheter axial pumps, that can reduce the number of blood vessels that need to be punctured by half, like the Hemopump™, are also known in the art, but are used only as heart assist devices. They cannot be integrated with a standard oxygenator having a separate blood inlet and blood outlet. The Hattler respiratory catheter described in patent WO 03/061727 is positioned in the vena-cava (the major vein returning blood to the heart). This catheter consists of a cylinder of hollow fiber membranes. Oxygen is forced to flow through the interior lumen of the fibers while blood flows around the fibers. The cylinder of fibers surrounds a central balloon that inflates and deflates at a rate of 300 cycles per minutes to move the fibers in the blood so as to mix the blood and enhance blood oxygenation.

SUMMARY OF THE IN ENTION

The present invention provides a single catheter pulsatile pump system. The system of the invention comprises a pump, a catheter having a single lumen, and an oxygenator. The oxygenator comprises a blood compartment and a gas compartment. The blood and gas compartments are separated by a gas permeable barrier. When oxygen poor, Co2 rich blood is present in the blood compartment, a concentration gradient of gases is established across the barrier with the concentration of oxygen higher inside the gas compartment and the concentration of CO₂ higher in the blood compartment. This allows an exchange of oxygen and carbon dioxide in blood in the blood compartment with oxygen in the gas compartment by diffusion. The catheter is connected to the blood compartment of the oxygenator. In accordance with the invention, blood is conducted in the catheter lmnen from a blood vessel to the oxygenator as well as from the oxygenator back to the blood vessel. The pump is adapted to alternately and cyclically cause the flow of blood through the catheter's single lumen from the blood vessel to the oxygenator blood compartment and to cause the flow of blood through the same catheter lumen from the blood compartment to the blood vessel. In use, the distal end of the catheter is inserted into a blood vessel such as the femoral or jugular vein via a single puncture, and is then delivered to a large blood vessel carrying oxygen poor blood, such as a vena cava. In accordance with the invention, the catheter is used to conduct oxygen-poor, CO2-rich blood from the blood vessel to the blood compartment as well as to conduct oxygen- rich, CO₂ poor blood from the blood compartment to the to the blood vessel. While the blood is in the blood compartment, carbon dioxide in the blood is exchanged by diffusion through the gas permeable barrier with oxygen in the gas compartment.

BRIEF DESCRIPTION OF THE DRAWINGS In order to understand the invention and to see how it may be carried out in practice, a preferred embodiment will now be described, by way of non- limiting example only, with reference to the accompanying drawings, in which: Fig. 1 shows a single catheter blood oxygenator system in accordance with one embodiment of the invention; Fig. 2 shows one embodiment of the pump of the blood oxygenator of Fig. 1; Fig. 3 shows a second embodiment of the pump of the blood oxygenator of Fig. 1; and Fig. 4 shows an embodiment of the invention having a bypass tube.

DETAILED DESCRIPTION OF THE INVENTION Fig. 1 shows a blood oxygenation system 1 in accordance with one embodiment of the invention. The system 1 comprises a pump assembly 10, a catheter 20 having a lumen 50, and a blood oxygenator 30. The oxygenator 30 comprises a cylindrical bundle of hollow microporous fibers 31 inside a cylindrical casing 37. The fibers 31 are permeable to gases but not to liquids. For example, hollow polypropylene fibers may be used. Alternatively, microporous sheets, such as silicon sheets (not shown), may be used, as known in the art. The casing 37 is provided with a gas inlet 34 and a gas outlet 35. The fibers 31 are bonded together other near their ends with an adhesive 32, as known in the art, so that oxygen or air entering the oxygenator 30 through the inlet 34 is prevented from flowing between the fibers 31 and, instead, is forced to flow through the lumen in the interiors of the hollow fibers before exiting the oxygenator 30 through the outlet 35. The lumens of the fibers 31 thus form a gas compartment, while the space between the fibers 31 and the casing 37 form a blood compartment. The gas and blood compartments are separated by the walls of the fibers 31 which thus form a gas permeable barrier between the gas and blood chambers. The casing 37 is also provided with blood ports 36a and 36b. The blood port 36a is connected to the proximal end 26 of the catheter 20, while the blood port 36b is connected to the pump assembly 10 via a connecting tube 51. In use, the distal end 25 of the catheter 20 is inserted into a blood vessel such as the femoral or jugular vein via a single puncture, and is then delivered to a blood vessel 41 carrying oxygen poor blood, such as a vena cava. In accordance with the invention, the catheter 20 is used to conduct oxygen poor, C0₂ rich, blood from the blood vessel 41 to the blood compartment as well as to conduct oxygen rich, CO₂ poor blood from the blood compartment to the blood vessel 41. The blood vessel 41 must be sufficiently wide to allow blood to be drawn from the blood vessel 41 into the catheter without collapsing the blood vessel. Similarly, the blood vessel 41 must be sufficiently wide so as to allow blood to be ejected from the catheter into the same blood vessel 41 without distending the blood vessel 41. The vessel 41 may be, for example, a vena-cave or right heart atrium. The pump assembly 10 pumps oxygen poor, CO₂ rich, blood from the blood vessel 41 through the catheter 20 to the blood compartment located in the space between the casing 37 and the fibers 31 in the oxygenator 30. In the oxygenator 30, carbon dioxide diffuses through the walls of the fibers 31 from the blood in the blood compartment into the gas compartment located in the interior of the fibers 31 due to the relatively high concentration of CO₂ in the blood compartment and the relatively low concentration of CO₂ in the gas compartment. Simultaneously, oxygen diffuses through the walls of the fibers 31 from the gas compartment into the blood in the blood compartment due to the relatively high concentration of oxygen in the gas compartment and the relatively low concentration of oxygen in the blood in the blood compartment. The pump assembly 10 then pumps the oxygenated blood in the blood compartment back to the blood vessel 41. Referring again to Fig. 1, a regulator valve 39 is inserted between a gas source 40 of a pressurized gas that is either oxygen or a mixture of gasses containing oxygen, such as air, and the gas inlet port 34. A vacuum pump 38 is connected to the gas outlet port 35. The regulator 39 valve is adjusted to a flow resistance, causing the gas pressure in the oxygenator gas port 34 to be lower then the blood pressure in the oxygenator during blood suction. The pressure in the oxygen port is preferably between -200nτmHg to -500mmHg (Gage), and more preferably about -350rnmHg to - 50mmHg (Gage). Fig. 2 shows one embodiment of the pump-head assembly 10. The pump- assembly 10 includes a distal chamber 12 and a proximal chamber 13 separated by a flexible diaphragm 14. The walls of the chambers 12 and 13 are made from a hard plastic material such as medical grade polycarbonate. The diaphragm 14 is made from a flexible plastic material such as medical grade polyurethane or silicon. The distal chamber 12 is connected to the blood chamber at the blood port 36b via the connecting tube 41. A piston servo driving system 22 cycles a piston 16 within a casing 21 between a retracted position shown in Fig. 2a and an extended position shown in Fig. 2b. The proximal chamber 13, the connecting tube 51 and the volume 23 of the casing 21 above the piston are filled with a fluid 15. As the piston 16 moves from the retracted position shown in Fig. 2a to the extended position shown in Fig. 2b, the fluid 15 is extruded from the casing 21 into the connecting tube 41 and into the proximal chamber 13. As the volume of the fluid 15 in the chamber 13 increases, the diaphragm 14 deflects from the downward curved shape shown in Fig. 2a to the upward curved shape shown in Fig. 2b. This deflection of the diaphragm 14 causes blood in the distal chamber 12 to be forced out from the distal chamber 12 into the connecting tube 41. This generates a flow of blood in the connecting tube 41, the blood compartment and the catheter 20 towards the distal end 25 of the catheter 20 so as to deliver oxygen rich blood from the blood compartment to the blood vessel 41. As the piston 16 moves from the extended position shown in Fig. 2b to the retracted position shown in Fig. 2a, the fluid 15 is drawn from the proximal chamber into 13 the casing 21 the connecting tube 41 and into. As the volume of the fluid 15 in the chamber 13 decreases, the diaphragm 14 deflects from the upward curved shape shown in Fig. 2b to the downward curved shape shown in Fig. 2a. This deflection of the diaphragm 14 causes blood in the connecting tube 41 to be forced into the distal chamber 12. This generates a flow of blood in the connecting tube 41, the oxygenator 30 and the catheter 20 away from the distal end 25 of the catheter 20 so as to deliver oxygen poor blood from the blood vessel to 41 the oxygenator 30. A pressure transducer 19 may be used to control the fluid pressure of the fluid 16. In another embodiment of the invention shown in Fig. 3, the piston 16 is attached directly to the diaphragm 14 so that cycling of the piston 16 causes the cyclic deflection of the diaphragm, as explained above with reference to the embodiment of Fig. 2. In another embodiment (not shown), a direct electro-mechanical driving system is used in stead of a pneumatic or hydraulic mechanism to drive the piston 16. In this embodiment, a load cell may be used to control the pressures applied by the system. In another embodiment of the invention (not shown), a peristaltic roller pump configured to alternate between forward and reverse rotational movement is used to conduct oxygen rich blood from the blood compartment to the blood vessel 41 and oxygen poor blood from the blood vessel 41 to the blood compartment. In this case, blood flows from the vessel 41 to the oxygenator 30 through the peristaltic pump into a blood reservoir in the form of a flexible bag made from a bio-compatible material, and back again. Oxygen flowing inside the fibers from gas inlet port 34 to gas outlet port 35 is kept all the time under high negative pressure, by means of a vacuum pump 38. The pressure is always kept more negative then the pressure in the blood around the fibers, even during blood suction, in order to prevent air or gas from entering the blood compartment through the fibers against the concentration gradient as a result of a static pressure difference. The negative oxygen pressure may be used for quick priming of the system, by connecting a priming solution bag (such as saline solution) to one of the oxygenator ports 36. The negative pressure in the gas side sucks all the air from the system through the oxygenator fibers, eliminating the need to rotate and knock on the system components to verify removal of all air from the blood circuit. Fig. 4 shows another embodiment of the invention. In the embodiment of Fig. 4, the system includes an inlet valve 21 and an outlet valve 22 and inlet and outlet ports 23 and 24, respectively. A bypass tube 27 bypasses the oxygenator 30, and connects with a "Y" shaped connector 28 to the catheter 20. In this embodiment, when the diaphragm 14 deflects from the upward curved shape shown in Fig. 2b to the downward curved shape shown in Fig. 2a, oxygen poor blood flows in the catheter 20, the "Y" shaped connector 28 and the bypass tube 27 from the blood vessel 41 to the distal chamber 12 through the inlet valve 21. The outlet valve 22 prevents oxygen poor blood from flowing from the "Y" shaped connector 28 into the oxygenator 20. When the diaphragm 14 deflects from the downward curved shape shown in Fig. 2a to the upward curved shape shown in Fig. 2b, oxygen rich blood flows in the catheter 20, and the "Y" shaped connector 28 from the distal chamber 12 through the outlet valve 22 to the blood vessel 41. The inlet outlet valve 21 prevents oxygen rich blood from bypassing the oxygenator 20 by preventing oxygen rich blood from flowing from the "Y" shaped connector 28 into the by pass tube 27. In the embodiment of Fig. 4, the negative pressure inside the oxygenator blood path, and the risk of the fibers collapsing and air penetration into the blood are reduced, since blood suction is not done through the oxygenator. The pump system preferably works at a slow rate and large stroke- volumes, rather then high rates and small stroke-volumes, in order to assure good oxygenation of venous blood, good blood mixing in the oxygenator and an adequate supply of oxygenated blood into the blood vessel 41. The pump rate may be, for example, between 5 to 50 cycles per minute, and more preferably between 10 to 15 cycles per minute. The pump stroke volume must exceed the volume of the catheter 20. For example, with a pump stroke volume between 100 to 250 cc, and more preferably between 150 to 200cc, only a small fraction of the blood removed from the blood vessel 41 is returned to the blood vessel without passing through the oxygenator 20. A large stroke volume and slow pump rate, thus provides a good supply of oxygenated blood to the vessel 41. A flow rate of blood flow can be achieved as high as 2.5 liters per minute in a catheter 7 mm in diameter. Small stroke volumes and high pump rates can provide the same blood flow, but may not provide an adequate supply of oxygenated blood to the vessel 41 due to the volume of the catheter 20 which is a dead-space volume. With small stroke volumes and high pump rates, a significant portion of the blood removed from the blood vessel 41 is returned to the vessel 41 without entering the oxygenator 20.

Claims

CLAJJVIS: 1. A system for blood oxygenation comprising: (a) a blood oxygenator having a blood compartment and a gas compartment, the blood and gas compartments being separated by a gas permeable barrier so as to allow exchange of carbon dioxide in blood in the blood compartment with oxygen in the gas compartment; (b) A catheter having a lumen, a proximal end and a distal end, the proximal end being connected to the blood oxygenator; and (c) A pump configured to alternate between causing blood to flow in the catheter lumen from a blood vessel to the oxygenator and causing blood to flow in the catheter lumen from the oxygenator to the blood vessel when the distal end of the catheter is inserted into the blood vessel.

2. The system according to Claim 1 comprising a bundle of hollow fibers made from a gas permeable material, the hollow fibers having a lumen serving as the gas compartment, the fibers being enclosed within a casing defining the blood compartment outside the fibers and inside the casing.

3. The system according to Claim 1 or 2 wherein the pump comprises: (a) a distal chamber and a proximal chamber, the distal chamber containing blood and being connected to the blood chamber of the oxygenator by a first tube; the distal and proximal chambers being separated by a flexible diaphragm; and (b) a piston contained within a piston chamber, the piston chamber containing a fluid and being connected to the proximal chamber by a second tube, the piston configured to cycle between a retracted position and an extended position, movement of the piston from the retracted position to the extended position causing the fluid to flow from the piston chamber into the proximal chamber via the second tube so as to cause the diaphragm to deflect towards the distal chamber and to cause blood to flow from the blood compartment through the catheter lumen to the blood vessel, and movement of the piston from the extended position to the retracted position causing the fluid to flow from the proximal chamber into the piston chamber via the second tube so as to cause the diaphragm to deflect towards the proximal chamber and cause blood to flow in the catheter lumen from the blood vessel to the oxygenator blood compartment.

4. The system according to Claim 1 or 2 wherein the pump comprises: (a) a distal chamber containing blood and being connected to the blood chamber of the oxygenator by a first tube; the distal chamber having a flexible diaphragm; and (b) a piston connected to the diaphragm, the piston configured to cycle between a retracted position and an extended position, movement of the piston from the retracted position to the extended position causing the diaphragm to deflect towards the distal chamber and cause blood to flow in the catheter lumen from the blood compartment to the blood vessel and movement of the piston from the extended position to the retracted position causing the diaphragm to deflect away from the distal chamber and cause blood to flow in the catheter lumen from the blood vessel to the blood compartment

5. The system according to any one of the previous claims, further comprising a bypass tube having a first end connected to the catheter and a second lumen connected to the distal chamber.

6. The system according to Claim 5 further comprising a first valve located on the first tube so as to prevent blood flow from the blood compartment into the distal chamber; and a second valve located on the bypass tube so as to prevent blood flow from the distal chamber into the bypass tube.

7. The system according to any one of the previous claims further comprising means for causing a gas to flow through the gas compartment.

8. The system according to Claim 7 wherein the gas is air or oxygen.

9. The system according to any one of the previous claims in which oxygen in the gas compartment is at a pressure that is more negative than the blood pressure in the blood compartment.

10. The system according to Claim 3 wherein the piston has a stroke volume between 100 and 250 milliliter.

11. The system according to Claim 3 or Claim 4 wherein the piston has a stroke rate of between 5 and 50 beats per minutes.

12. A method for blood oxygenation comprising: (a) Delivering the distal end of the catheter of the system according to any one of the previous claims into a blood vessel; (b) Causing a flow of oxygen or a gas mixture containing oxygen through the gas compartment; and (c) Causing the pump to alternate between causing blood to flow in the catheter lumen from the blood vessel to the oxygenator and causing blood to flow in the catheter lumen from the oxygenator to the blood vessel so as to allow exchange of carbon dioxide in blood in the blood compartment with oxygen in the gas compartment.