Coaxial cannula for extracorporeal membrane oxygenation systems

Abstract

The present invention relates to a coaxial cannula assembly comprising a perfusion tube defining a backflow lumen and having a proximal end and a distal end. The distal end of the perfusion tube comprises a plurality of perfusion openings and a flow restriction member located between the plurality of perfusion openings and a distal tip of the perfusion tube. The cannula assembly further comprises a drainage tube coaxially aligned with the perfusion tube and having a proximal end and a distal end. The distal end of the drainage tube comprises a plurality of drainage openings and the length of the drainage tube is less than the length of the perfusion tube. The cannula assembly further comprises a drainage lumen defined by the space between the perfusion tube and the drainage tube.

Description

[0001] Cross-references to related applications

[0002] This application claims priority to U.S. Provisional Patent Application Serial No. 63 / 133,995, filed January 5, 2021, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This invention generally relates to extracorporeal membrane oxygenation systems, and more specifically, to coaxial cannulas for bidirectional blood flow in extracorporeal membrane oxygenation systems. Background Technology

[0004] Various types of cardiac assist devices have been developed for use in patients whose hearts are unable to provide sufficient blood circulation (commonly referred to as arrhythmia or heart failure). For example, patients with chronic arrhythmias may use an implantable ventricular assist device (VAD) while awaiting a heart transplant or during long-term targeted therapy. As another example, patients with acute arrhythmias may use an external pump or circulatory support system that pumps blood out and back into the patient. External circulatory support systems can also be used perioperatively, for example, to guide blood flow through the patient during cardiac surgery.

[0005] At least some extracorporeal blood circulation support systems temporarily replace a patient's cardiopulmonary function by pumping blood around or around the patient's heart and lungs. Such extracorporeal blood circulation support systems typically include an oxygenator, such as an extracorporeal membrane oxygenator or ECMO, to provide oxygen to the blood passing through the extracorporeal blood circulation support system.

[0006] At least some known extracorporeal blood circulation support systems use multiple cannulas, including multiple single-lumen cannulas at multiple insertion sites, high-volume circuits, and multiple cannulas that cannot be used for extended periods. Multiple sites increase the risk of bleeding, vascular injury, infection, and patient pain and discomfort. Furthermore, at least some known extracorporeal blood circulation support system cannulas are prone to kinking or may cause blood flow injury.

[0007] Therefore, there is a need for extracorporeal blood circulation support systems that provide coaxial lumen cannulas with improved blood flow. Summary of the Invention

[0008] This invention relates to a coaxial cannula assembly. The coaxial cannula assembly includes an infusion tube defining a reflux chamber and having a proximal and distal end, wherein the distal end of the infusion tube includes a plurality of infusion openings. The coaxial cannula also includes a drainage tube coaxially aligned with the infusion tube and having a proximal and distal end, wherein the distal end of the drainage tube includes a plurality of drainage openings and the length of the drainage tube is less than the length of the infusion tube. The drainage chamber is defined by a space between the infusion tube and the drainage tube. The coaxial cannula also includes a distributor extending into and attaching to the proximal end of the drainage tube, and having a reservoir for receiving fluid from the proximal end of the drainage tube. The infusion tube extends through the distributor, and wherein the diameter of the infusion tube remains constant on the distributor as the infusion tube extends from the proximal end of the distributor through the distributor to the distal end of the distributor, and wherein the diameter of the infusion tube gradually decreases proximally to the distributor. Attached Figure Description

[0009] Figure 1 This is a schematic diagram of an extracorporeal blood circulation support system connected to the patient's body.

[0010] Figure 2 This is a top perspective view of an embodiment of the coaxial cannula of the present invention.

[0011] Figure 3A yes Figure 2 The cross-sectional view shown is of a portion of the coaxial cannula, illustrating the distributor connected to various tubes.

[0012] Figure 3B yes Figure 3A An enlarged view of the far end of the distributor shown.

[0013] Figure 3C yes Figure 3A An enlarged view of the near end of the distributor shown.

[0014] Figure 4 yes Figure 3A The diagram shows a cross-sectional end view of the distributor, illustrating the infusion tube within the drainage tube.

[0015] Figure 5A This is a three-dimensional cross-sectional view of the distributor, illustrating one embodiment of the fixture within the distributor.

[0016] Figure 5B This is a three-dimensional cross-sectional view of the distributor, illustrating another embodiment of the fixture within the distributor.

[0017] Figure 6 This is a top view of the bend-eliminating component surrounding the injection pipe.

[0018] Figure 7A yes Figure 2 The top view of the coaxial cannula shown illustrates an embodiment of the stabilizing sleeve near the distributor.

[0019] Figure 7B yes Figure 2 The top view of the coaxial cannula shown illustrates a second embodiment of the stabilizing sleeve near the distributor.

[0020] Figure 7C yes Figure 2 The top view of the coaxial cannula shown illustrates a third embodiment of the stabilizing sleeve near the distributor.

[0021] Figure 8 This is a perspective view of one embodiment of the infusion tube.

[0022] Figure 9 This is a perspective view of the second embodiment of the infusion tube.

[0023] Figure 10 This is a perspective view of the third embodiment of the infusion tube.

[0024] Figure 11 This is a perspective view of the fourth embodiment of the infusion tube.

[0025] Figure 12A yes Figure 2 The diagram shown is a three-dimensional representation of the coaxial cannula, illustrating the drainage groove at the distal end of the drainage tube.

[0026] Figure 12B yes Figure 12A The diagram shows a cross-sectional end view of the drainage channel. Detailed Implementation

[0027] Please refer to the attached diagram. Figure 1 This is a schematic diagram of an extracorporeal mechanical blood circulation support system 10 connected to the vascular system of patient 12. The extracorporeal mechanical blood circulation support system 10 includes a blood pump assembly 14, an inflow conduit or first conduit 16, an outflow conduit or second conduit 18, a coaxial cannula 20, a controller (not shown), and a power supply (not shown).

[0028] The blood pump assembly 14 includes a blood pump 24, an extracorporeal membrane oxygenator (ECMO) 26, and an inlet 28 and an outlet 30 for connecting to it via flexible tubing. The blood pump assembly 14 may include any suitable type of pump capable of functioning as described herein, including, for example, but not limited to, axial rotary pumps and centrifugal rotary pumps. The ECMO 26 includes an oxygenator membrane (not shown) configured to increase the oxygen concentration and / or decrease the carbon dioxide concentration of blood pumped through the blood pump assembly 14. The oxygenator membrane may include any suitable type of oxygenator membrane capable of functioning the blood pump assembly 14 as described herein, including, for example, but not limited to, fiber bundles. In some embodiments, the extracorporeal mechanical circulatory support system 10 also includes a vent valve (not shown) to release air or other gases present within the extracorporeal mechanical circulatory support system 10. The vent valve may be connected to, for example, an outflow tubing 18, or may be integrated within the ECMO 26 (e.g., at the outlet of the ECMO 26).

[0029] The blood pump assembly 14 is connected to the patient's vascular system via an inflow conduit 16 and an outflow conduit 18. More specifically, the inlet 28 of the blood pump assembly 14 is connected to the inflow conduit 16, and the outlet 30 of the blood pump assembly 14 is connected to the outflow conduit 18. Furthermore, the inflow conduit 16 is connected to the outlet 32 ​​of the coaxial cannula 20, and the outflow conduit 18 is connected to the inlet 34 of the coaxial cannula 20. The coaxial cannula 20 offers considerable placement flexibility, allowing it to be placed at different vascular insertion sites and depths within the patient's body. The coaxial cannula 20 is designed for insertion into the internal jugular vein 36 and placement above or below the right atrium, thus generally not traversing the heart. Therefore, the coaxial cannula 20 is less invasive than transcutaneous cannulas. However, in some applications, the coaxial cannula 20 may be used transcutaneously. The coaxial cannula 20 is adapted for use with a guide (not shown) that extends through the cannula and assists the user in properly placing the coaxial cannula 20 at the correct site and depth within the patient's body.

[0030] It should be understood that the illustrated connection to the patient's vascular system is for illustrative purposes only, and the blood pump assembly 14 may be connected to the patient's vascular system in any other suitable manner that enables the extracorporeal mechanical blood circulation support system 10 to function as described herein, including, for example, but not limited to, vein-to-vein (VV) connections and vein-to-artery (VA) connections.

[0031] The controller is communicatively coupled to the blood pump assembly 14 and configured to control its operation. For example, the controller is configured to control the operation (e.g., speed) of the blood pump 24. The controller may generally include any suitable computer and / or other processing unit, including any suitable combination of computers, processing units, and / or similar entities that can communicatively couple with each other (e.g., the controller may form all or part of a controller network). Therefore, the controller may include one or more processors and associated storage devices configured to perform various computer-implemented functions (e.g., performing the methods, steps, calculations, and / or similar functions disclosed herein). As used herein, the term "processor" refers not only to an integrated circuit known in the art as being contained within a computer, but also to a controller, microcontroller, microcomputer, programmable logic controller (PLC), application-specific integrated circuit (ASIC), digital signal processor (DSP), field-programmable gate array (FPGA), and other programmable circuits. Furthermore, the controller's storage devices may generally include storage elements, including but not limited to non-transitory computer-readable media (e.g., random access memory (RAM)), computer-readable non-volatile media (e.g., flash memory), floppy disks, optical disc read-only memory (CD-ROM), magneto-optical disk (MOD), digital versatile optical disc (DVD), and / or other suitable storage elements. Such storage devices can typically be configured to store suitable computer-readable instructions such that, when executed by a processor, these instructions configure the controller to perform various functions, including but not limited to controlling components such as the blood pump assembly 14 described herein.

[0032] The power supply provides power to the blood pump 24, the controller, and other electrical components of the blood pump assembly 14, and may generally include any suitable power source that enables the extracorporeal mechanical blood circulation support system 10 to function as described herein. In other embodiments, the controller and power supply may be external to the blood pump assembly 14, or all or part of the controller and / or power supply 22 may be incorporated into the blood pump assembly 14.

[0033] Figure 2 This is a top perspective view of one embodiment of the coaxial cannula 20. Figure 3A This is a cross-sectional view of a portion of the coaxial cannula 20, illustrating the distributor 62 connected to various tubes. Figure 3B This is an enlarged view of the far end of the distributor 62. Figure 3C This is an enlarged view of the near end of the distributor 62. Figure 4 This is a cross-sectional end view of the distributor 62, which shows the infusion tube 40 inside the drainage tube 52. Figure 5A This is a three-dimensional cross-sectional view of the distributor 62, illustrating one embodiment of the fixture 78 within the distributor 62. Figure 5B This is a three-dimensional cross-sectional view of the distributor 62, illustrating another embodiment of the fixture 78 within the distributor 62.

[0034] The coaxial cannula 20 includes an irrigation tube 40 having a proximal end 42, a distal end 44, and an internal lumen or reflux chamber 46 defined extending between the two ends 42 and 44. The distal end 44 includes an end reflux opening 48 and a plurality of irrigation openings 50 defined for fluid communication through the irrigation tube 40 and with the reflux chamber 46. The coaxial cannula 20 also includes a drainage tube 52 coaxial with the irrigation tube 40 and including a proximal end 54, a distal end 56, and a drainage chamber 58 extending between the two ends 54 and 56. The distal end 56 of the drainage tube 52 is securely attached to the irrigation tube 40 and includes a plurality of drainage openings 60 defined for fluid communication through the drainage tube 52 and with the drainage chamber 58. Figure 3A Ideally, the infusion tube 40 is located within the drainage cavity 58 of the drainage tube 52, such that blood flowing through the drainage cavity 58 surrounds the infusion tube 40. Specifically, the diameter of the reflux cavity 46 is smaller than the first cross-section of the drainage cavity 58, thereby defining a predetermined ratio of the reflux cavity 46 to the drainage cavity 58. More specifically, compared to at least some known coaxial cannulas, this ratio is designed to reduce the pressure within the drainage cavity 58 by increasing the cross-sectional area of ​​the drainage cavity 58 relative to the reflux cavity 46.

[0035] The distributor 62 includes a distal end 64, a drainage proximal end 66, and an infusion proximal end 68. The distal end 64 is attached to the proximal end 54 of the drainage tube 52, the drainage proximal end 66 is connected to the proximal drainage tube 70, and the infusion tube 40 extends through the distributor 62 and exits the infusion proximal end 68. The distributor 62 also includes a reservoir 72 for receiving fluid from the proximal end 54 of the drainage tube 52, wherein the infusion tube 40 extends through the distributor 62 and is not connected to the drainage tube 52 at the distributor 62, and wherein the infusion tube 40 remains substantially coaxial with the drainage tube 52 along its entire length.

[0036] For reference Figure 3B and Figure 3C The distal end 64 of the distributor 62 includes a transition portion 74 located at the transition from the drainage tube 52 to the distributor 62. Similarly, the proximal end 66 of the drainage includes a transition portion 76 located at the transition from the distributor 62 to the proximal drainage tube 70. Transition portions 74 and 76 improve hemodynamics and blood compatibility by allowing a smooth transition between multiple components without a stepped transition, which could lead to turbulence within the blood flow. As shown, transition portions 74 and 76 are rounded or inclined surfaces that cause the thickness of the distributor 62 to gradually decrease at the distal end 64 and the proximal end 66.

[0037] Still referencing Figure 3A and Figure 3CAs can be seen, the injection pipe 40 has a constant cross-sectional diameter along the entire length of the drainage pipe 52 and the entire length of the distributor 62. When the injection pipe 40 flows out of the distributor 62, the injection pipe 40 gradually becomes larger outward to match the diameter of the outflow pipe 18.

[0038] For reference Figure 4 , Figure 5A and Figure 5B The distributor 62 includes a retainer 78 for smoothly guiding blood flow from the drainage tube 52 around the infusion tube 40 within the reservoir 72 of the distributor 62. Specifically, the distributor 62 includes an inner surface 80 defining the reservoir 72, and the retainer 78 extends from the inner surface 80 into the reservoir 72. The retainer 78 includes a top surface 82, a distal end 84, and a pair of sidewalls 86 that gradually extend outward from the end 84 in a proximal direction. The sidewalls 86 may have any constant or varying height that allows the retainer 78 to operate as described herein. Furthermore, the pair of sidewalls 86 converge at the end 84 at any angle that allows the retainer 78 to operate as described herein.

[0039] During operation, the infusion tube 40 is fixed to the top surface 82, and the end 84 and sidewall 86 guide blood to flow around the infusion tube 40 and into the proximal drainage tube 70. Furthermore, although only a single retainer 78 is shown, the distributor 62 may include multiple retainers 78 circumferentially spaced around the inner surface 80. Thus, the retainers 78 guide blood to flow around the infusion tube 40 and into the proximal drainage tube 70, reducing recirculation within the reservoir 72. Additionally, the retainers 78 are positioned within the distributor 62, where the infusion tube 40 is turned laterally and the cross-section of the reservoir 72 available for drainage is increased. Thus, the retainers 78 occupy space within the reservoir 72 to maintain a relatively constant pressure. Figure 5A An embodiment of the fastener 78a is illustrated, wherein the distal portions of the sidewall 86a and the top surface 82a are integrated into the inner surface 80 of the distributor 62. Figure 5B An embodiment of the fastener 78b is illustrated, wherein the sidewalls 86b and the top surface 82b are not integrated into the inner surface 80.

[0040] Figure 6This is a top view of the bend-eliminating member 90 surrounding the infusion tube 40. The infusion tube 40 includes a distal portion 92 having a first diameter, a proximal portion 94 having a second diameter greater than the first diameter, and a taper 96 between the proximal portion 94 and the distal portion 92. As described herein, the distal portion 92 extends through the distributor 62 and exits from the proximal infusion end 68 of the distributor 62, such that the taper 96 originates proximal to the distributor 62. The bend-eliminating member 90 may be positioned at least around the taper 96 of the infusion tube 40 to prevent or reduce bending and kinking (reduction of cross-sectional area) of the infusion tube 40 at the transition between the distal portion 92 and the taper 96. The bend-eliminating member 90 is a flexible material and may include a metal braid for additional structural support. Furthermore, the infusion tube 40 in… Figure 6 The diagram shows a braid 98 for additional structural support. This braid 98 is not limited to embodiments including a bend-eliminating member 90, but can be included in all embodiments described herein. Furthermore, the distal end 100 of the bend-eliminating member 90 can be connected to the infusion proximal end 68 of the distributor 62 to ensure that the bend-eliminating member covers the transition between the distal portion 92 and the taper 96 of the infusion tube 40. The infusion proximal end 68 of the distributor 62 may include a coupling structure (not shown) to secure the bend-eliminating member 90 in place.

[0041] Figure 7A This is a top view of the coaxial cannula 20, illustrating one embodiment of a stabilizing sleeve 102a proximal to the distributor 62. The stabilizing sleeve 102a includes a first sleeve 104a positioned around the infusion tube 40 at the transition from the taper 96 to the proximal portion 94. The stabilizing sleeve 102a also includes a second sleeve 106a positioned around the proximal drainage tube 70 and spaced apart from the distributor 62. A bridging member 108a extends between these sleeves 104a and 106a and restricts movement of the infusion tube 40 relative to the proximal drainage tube 70. The stabilizing sleeve 102a provides support for the infusion tube 40 proximal to the distributor 62 and can be used in place of the bend-eliminating member 90. Specifically, the stabilizing sleeve 102a is made of a rigid material and prevents or reduces bending and kinking (reduction of cross-sectional area) of the infusion tube 40. In addition, the stabilizing sleeve 102a can be used to maintain a predetermined angle between the infusion tube 40 and the proximal drainage tube 70 on the proximal side of the distributor 62.

[0042] Figure 7BThis is a top view of the coaxial cannula 20, illustrating a second embodiment of the stabilizing sleeve 102b proximal to the distributor 62. The stabilizing sleeve 102b includes a first sleeve 104b positioned around the infusion tube 40 at the transition from the taper 96 to the proximal portion 94. The stabilizing sleeve 102b also includes a second sleeve 106b positioned around the distributor 62 and / or a portion of the proximal drainage tube 70 adjacent to the distributor 62. Thus, the first sleeve 104b and the second sleeve 106b are offset from each other. A bridging member 108b extends between these sleeves 104b and 106b and restricts movement of the infusion tube 40 relative to the proximal drainage tube 70. The stabilizing sleeve 102b provides support to the infusion tube 40 proximal to the distributor 62 and can be used in place of the bend-eliminating member 90. Specifically, the stabilizing sleeve 102b is made of a rigid material and prevents or reduces bending and kinking (reduction of cross-sectional area) of the infusion tube 40. In addition, the stabilizing sleeve 102b can be used to maintain a predetermined angle between the infusion tube 40 and the proximal drainage tube 70 on the proximal side of the distributor 62.

[0043] Figure 7C This is a top view of the coaxial cannula 20, illustrating a third embodiment of the stabilizing sleeve 120c proximal to the distributor 62. The stabilizing sleeve 102c includes a first sleeve 104c positioned around the infusion tube 40 at the transition from the taper 96 to the proximal portion 94. The stabilizing sleeve 102c also includes a second sleeve 106c positioned around the distributor 62 and / or a portion of the proximal drainage tube 70 adjacent to the distributor 62. Thus, the first sleeve 104c and the second sleeve 106c are offset from each other. Furthermore, the second sleeve 106c is longer than the first cuff 104c to provide additional support. A bridging member 108c extends between the sleeves 104c and 106c and restricts movement of the infusion tube 40 relative to the proximal drainage tube 70. The stabilizing sleeve 102c provides support for the infusion tube 40 proximal to the distributor 62 and can be used in place of the bend-eliminating member 90. Specifically, the stabilizing sleeve 102c is made of a rigid material and prevents or reduces bending and kinking (reduction of cross-sectional area) of the infusion tube 40. In addition, the stabilizing sleeve 102c can be used to maintain a predetermined angle between the infusion tube 40 and the proximal drainage tube 70 of the distributor 62.

[0044] In another embodiment, a mesh (not shown) extends between the infusion tube 40 and the proximal drainage tube 70. This mesh may be an extension of the distributor 62, integral with the distributor 62 and secured around the infusion tube 40 and the proximal drainage tube 70. Alternatively, the mesh may be made of the same material as the infusion tube 40 and the proximal drainage tube 70.

[0045] Figure 8This is a perspective view of one embodiment of the distal end 44 of the infusion tubing 40. As described herein, the infusion tubing 40 is designed to allow blood to be infused into the main pulmonary artery of the patient 12. The distal end 44 of the infusion tubing 40 includes a plurality of infusion openings 50 and an end return opening 48. More specifically, the distal end 44 includes an end cap 110 located distal to the infusion openings 50, and defines the end return opening 48 therein. In the illustrated embodiment, the distal end 44 including the end cap 110 includes a constant inner diameter and an outer diameter. In another embodiment, the outer diameter of the end cap 110 tapers to facilitate insertion, but the inner diameter remains constant. The end cap 110 is formed of a material softer than the infusion tubing 40 for non-invasive insertion.

[0046] Figure 9 This is a perspective view of a second embodiment of the distal end 44 of the infusion tubing 40. As described herein, the infusion tubing 40 is designed to allow blood to be infused into the main pulmonary artery of the patient 12. The distal end 44 of the infusion tubing 40 includes a plurality of infusion openings 50, a taper 112 distal to the infusion openings 50, and an end return opening 48. The taper 112 allows for a smooth transition between the cannula tip and a guide (not shown). The taper 112 also allows for greater flexibility around the distal end 44 of the cannula 20 for tracking into place. Furthermore, the distal end 44 includes an end cap 110 located distal to the taper 112, and defines the end return opening 48 therein. In the illustrated embodiment, the distal end 44, including the end cap 110 and the taper 112, includes a constant inner diameter. In another embodiment, the outer diameter of the end cap 110 tapers for easy insertion, but the inner diameter remains constant. The end cap 110 is formed of a material softer than the infusion tubing 40 for damage-free insertion.

[0047] Figure 10 This is a perspective view of a third embodiment of the distal end 44 of the infusion tube 40. The distal end 44 includes a plurality of infusion openings 50 and a plurality of elongated flexible members 114 at the distal end of the distal end 44, such that the distal end is serrated. Specifically, Figure 10 The distal end 44 shown includes a defined end return opening 48 instead of Figure 8 and Figure 9The end cap 110 is shown with an elongated member 114. A plurality of elongated members 114 are circumferentially spaced around the periphery of the perfusion tube 40 and separated by a plurality of perfusion channels 116. More specifically, adjacent elongated members 114 are separated by a single perfusion channel 116. The perfusion channels 116 are end-open, such that the distal ends 118 of the elongated members 114 are separated by the plurality of perfusion channels 116. The configuration of the channels 116 and the elongated members 114 allows blood to flow out of the distal end 44, even if the distal end abuts against a blood vessel or other structure within the patient 12. In operation, the perfusion channels 116 allow increased blood flow through the channels 116 and through the end return openings 48, which allows the size of the perfusion openings 50 to be smaller or fewer in number than if the distal end 44 did not include the perfusion channels 116. More specifically, by using the perfusion channels 116, the total cross-sectional area of ​​the plurality of perfusion openings 50 is smaller than the cross-sectional area of ​​the perfusion tube 40.

[0048] In addition, such as Figure 10 As shown, the distal end 118 of the elongated member 114 tapers distally. Specifically, each elongated member 114 includes a pair of circumferential sidewalls 120 that taper toward each other to form the distal end 118. It is important to note that the taper is circumferential, such that the cross-sectional diameter of the elongated member 114 is constant. This taper allows the elongated member 114 to bend or fold inward during insertion of the coaxial cannula 20. During insertion, the distal end 118 can engage the walls of the patient's vascular system and allow the engaged elongated member 114 to bend inward for trauma-free insertion.

[0049] Figure 11 This is a perspective view of a fourth embodiment of the distal end 44 of the infusion tubing 40. The illustrated distal end 44 includes a plurality of infusion openings 50 and a flow-limiting member 122 located between the infusion openings 50 and the end return opening 48. The flow-limiting member 122 defines an inner cavity 124 with a cross-sectional area smaller than that of the end return opening 48. Thus, during operation, a region of higher pressure will be formed proximal to the flow-limiting member 122. This high-pressure region forces more blood to flow through the infusion openings 50 compared to the absence of the flow-limiting member 122. The higher pressure and higher flow rate allow for a smaller size or fewer number of infusion openings 50 compared to the distal end 44 without the flow-limiting member 122. More specifically, by using the flow-limiting member 122, the total cross-sectional area of ​​the plurality of infusion openings 50 is smaller than the cross-sectional area of ​​the infusion tubing 40.

[0050] Figure 12A This is a three-dimensional view of the coaxial cannula 20, which shows the distal end 56 of the drainage tube 52. Figure 12BThis is a cross-sectional end view of the distal end 56 of the drainage tube 52. The distal end 56 includes a tapered portion 126 connected to the outer surface of the infusion tube 40. The tapered portion 126 is located distal to the plurality of drainage openings 60 formed in the drainage tube 52. Furthermore, the tapered portion 126 includes a plurality of circumferentially spaced slots 128 through which blood can flow. Although only four slots 128 are shown, the tapered portion 126 may include any number of slots 128 to facilitate manipulation of the cannula 20 as described herein. Figure 12A and Figure 12B As shown, the slot 128 is oriented parallel to the axis of the drainage tube 52, such that blood enters through the slot 128 in an axial direction rather than radially as blood flows through the opening 60. The axially oriented slot 128 allows blood to flow more efficiently because the blood does not need to change direction as it flows through the drainage opening 60. This higher efficiency results in a higher flow velocity through the slot, which allows for a smaller size and / or fewer number of drainage openings 60 compared to the case where the distal end 56 does not include the slot 128. More specifically, by using the slot 128, the total cross-sectional area of ​​the multiple drainage openings 60 plus the cross-sectional area of ​​the slot 128 is smaller than the cross-sectional area of ​​the drainage tube 52.

[0051] Although the embodiments and examples disclosed herein have been described with reference to specific embodiments, it should be understood that these embodiments and examples are only for illustrating the principles and applications of the invention. Therefore, it should be understood that various modifications can be made to the illustrative embodiments and examples, and other arrangements can be designed, without departing from the spirit and scope of the invention as defined by the claims. Therefore, this application is intended to cover modifications and variations of these embodiments and their equivalents.

[0052] This written description discloses the invention using examples (including the best mode) and enables any person skilled in the art to practice the invention, including making and using any device or system, and performing any combination of methods. The patentable scope of the invention is defined by the claims, but may include other examples that would occur to a person skilled in the art. Such other examples are intended to be covered within the scope of the claims if they have structural elements that are not different from the literal language of the claims, or if they include equivalent structural elements that are not substantially different from the literal language of the claims.

Claims

1. A coaxial cannulation assembly, comprising: An infusion tube defining a reflux chamber and having a proximal end and a distal end, wherein the distal end of the infusion tube includes a plurality of infusion openings, and wherein the distal end of the infusion tube includes a flow-limiting member located between the plurality of infusion openings and an end reflux opening at the distal end of the infusion tube. The flow-limiting member includes a ring defining a central cavity, and the ring causes the pressure in the proximal region of the flow-limiting member in the return cavity to be higher than that on the distal side of the flow-limiting member, which increases the flow velocity through the plurality of injection openings without preventing fluid from flowing to the end return opening; as well as A drainage tube, which is coaxially aligned with the infusion tube and has a proximal end and a distal end, wherein the distal end of the drainage tube includes a plurality of drainage openings, and wherein the length of the drainage tube is less than the length of the infusion tube; The drainage cavity is defined by the space between the infusion tube and the drainage tube.

2. The coaxial cannulation assembly of claim 1, wherein the flow-limiting member is located distal to the distalest of the plurality of infusion openings.

3. The coaxial cannula assembly according to claim 1, wherein the cross-sectional area of ​​the central cavity is smaller than the cross-sectional area of ​​the end return opening.

4. The coaxial cannula assembly according to claim 1, wherein the total cross-sectional area of ​​the plurality of infusion openings is smaller than the cross-sectional area of ​​the infusion tube.

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