How to purge a blood pump
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Patents
- Current Assignee / Owner
- ABIOMED INC
- Filing Date
- 2021-04-22
- Publication Date
- 2026-08-05
Smart Images
Figure 0007901022000001 
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Abstract
Description
Technical Field
[0001] Cross - reference to Related Applications This application claims the benefit of U.S. Provisional Patent Application No. 63 / 017,445, filed Apr. 29, 2020, which is incorporated herein by reference.
[0002] Technical Field The present invention relates to blood pumps, particularly intravascular blood pumps for supporting blood flow within a patient's blood vessels, and a method of purging such a pump while it is in operation while inserted into a patient.
Background Art
[0003] Background Different types of blood pumps are known, such as axial - flow blood pumps, centrifugal blood pumps, or hybrid - type blood pumps where blood flow is caused by both axial and radial forces. An example of a blood pump is the Impella line of blood pumps from Abiomed of Danvers, MA (e.g., Impella 2.5®, Impella CP®, Impella 5.5®, etc.). Intravascular blood pumps are inserted into a patient's vasculature, such as the aorta, by a catheter.
[0004] In some pump designs, a purge fluid is placed to prevent blood from entering the mechanism and to reduce the effect of blood on the pump mechanism; an anticoagulant such as heparin (typically the sodium salt of heparin). Heparin is thought to prevent blood from clotting within the gaps between pump components such as the impeller shaft and the housing. Heparin is a widely used anticoagulant and is typically administered in a controlled dosage.
[0005] In one example, the purge fluid is delivered by a purge cassette that enters the blood pump catheter through a filter assembly, and by an internal purge lumen that carries the purge fluid through the catheter to a purge channel in the motor assembly. The flow of the purge fluid is regulated by an automated controller. [Overview of the project]
[0006] overview A method for purging a blood pump is described herein. The method described herein provides a blood pump which may include a motor section and a pump section. At least a portion of the blood pump is inserted into a patient. The method also includes the step of operating the blood pump such that (i) a purging fluid is supplied to the motor section, where the purging fluid flows into the gap between bearings in the motor housing of the motor section, and (ii) an impeller in the pump section is rotated based on the rotation of a shaft in the motor section by a motor in the motor section. The purging fluid may include a pH-controlling buffer.
[0007] Previously, such purging fluids contained heparin. However, physicians often do not want heparin to be administered to patients' blood via purging fluids. For example, in any type of surgical procedure, heparin administration during the procedure can be counterproductive, as it interferes with blood clotting and therefore hinders healing or hemostasis. The amount of heparin administered to the patient's blood along with the purging fluid is also difficult to control for various reasons. In particular, the amount of heparin is often more than what is desirable for the physician, and it is difficult to precisely control the amount of heparin administered to the patient. Therefore, physicians often prefer to supply heparin to the patient separately from the operation of the blood pump, if necessary (and in that case, only in the necessary amount). Furthermore, some patients are heparin intolerant because they are prone to heparin-induced thrombocytopenia (HIT). Therefore, heparin-containing purging is not suitable for these patients at all. Heparin salts can also cause undesirable wear on metal pump bearings. Therefore, there is a need for intravascular blood pumps that can operate with a purging fluid that, if possible, does not contain heparin or at least has a reduced amount of heparin.
[0008] In one aspect, the purging fluid further contains an aqueous dextrose solution. In another aspect, the purging fluid also contains a reduced amount of heparin. The amount of heparin in the purging fluid is approximately zero to approximately 12.5 units per milliliter. In another aspect, the amount of heparin in the purging fluid is approximately zero to approximately 6.25 units per milliliter. In yet another aspect, the amount of heparin in the purging fluid is approximately 1 unit to approximately 6.25 units per milliliter. In one aspect, the pH-controlling buffer is one of sodium bicarbonate, citrate, lactate, gluconate, acetate, and pyruvate. In the embodiment where the pH-controlling buffer is sodium bicarbonate, the amount of pH-controlling agent in the purging fluid is approximately 1.5 milliequivalents (meq / l) to approximately 50 meq / l per liter. The pH of the pH-controlling buffer is approximately 7.5 to approximately 9.1. [Brief explanation of the drawing]
[0009] The present invention will be described below by illustration with reference to the accompanying drawings. The accompanying drawings are not intended to be drawn to a uniform scale. In the accompanying drawings, identical or nearly identical components shown in various drawings are represented by similar numbers. For clarity, not all components may be labeled in all drawings.
[0010] [Figure 1] The blood flow and purge flow through the gap between the shaft and housing inside the pump are illustrated. [Figure 2] This is a schematic diagram of an intravascular blood pump, which is inserted in front of the left ventricle, with its inflow cannula positioned inside the left ventricle. [Figure 3] This is a schematic longitudinal cross-section of an exemplary prior art blood pump. [Figure 4] This is an enlarged view of a portion of the blood pump in Figure 3, based on the second embodiment. [Modes for carrying out the invention]
[0011] Detailed explanation Blood pumps are deployed in patients requiring critical and life-saving care. Therefore, it is crucial to correct any aspects of the device that could potentially have adverse effects on pump operation. This specification discloses a blood pump operation in which the purging fluid contains sodium bicarbonate in addition to or instead of heparin.
[0012] The aforementioned type of blood pump is known, for example, from EP 0 961 621 B1. Referring to Figure 1, the pump 100 comprises: a drive section 110; a catheter 115 attached to the proximal end 120 of the drive section 110 (the end of the drive section closer to the physician, or the “rear end” of the drive section) and having a line extending through it for supplying power to the drive section 110; and a pump section 130 fastened to the distal end 125 of the drive section. The drive section 110 includes a motor housing 150 having an electric motor 151 disposed therein, the motor shaft 160 of the electric motor protruding distally from the drive section 110 and reaching into the pump section 130. The pump section 130 includes a tubular pump housing 165 having an impeller 170 rotating inside; the impeller 170 is seated on the end of the motor shaft 160 protruding from the motor housing 150. The motor shaft 160 is mounted within the motor housing in two bearings 171 and 172; the two bearings 171 and 172 are spaced as far apart as possible from each other to ensure that the impeller 170 is truly and accurately centered and guided within the pump housing 150. Different pump designs use different bearing types. As shown in Figure 1, bearing 171 is a radial ball bearing, and bearing 172 is an axial-radial sliding bearing. As shown in Figure 1, blood 140 exits from the outlet cage of the pump housing 165. The blood would otherwise enter the motor housing 150, but is further offset by the purge fluid 135 passing through the motor housing and the shaft seal bearing on the impeller side. Therefore, to prevent blood from entering the housing, the purge fluid passes through the gap in the radial sliding bearing on the impeller side. This is done by a purge fluid pressure higher than the pressure present in the blood.
[0013] As shown in Figure 1, the purge fluid 135 fills the motor housing 150 of the pump, forming a lubricating film within the pump bearings 171 and 172. As described in U.S. Patent Publication No. 20150051436, the purge fluid 135 may also form a lubricating film within the bearing gap 180 of the axial sliding bearing of the pump. The purge fluid is described as being fed through a purge fluid feed line, flowing through the radial bearing 171 located at the distal end of the motor housing 150, and then also flowing through the bearing gap 180 of the axial sliding bearing. The purge fluid fed in this manner is responsible for blood dilution and reducing the blood residence time under the impeller 170.
[0014] To ensure that the purge fluid 135 reaches the distal radial bearing 172 at a pressure higher than the blood pressure present, a channel is provided in at least one of the surfaces forming the bearing gap of the axial sliding bearing, penetrating the bearing gap 180 from the radially outside to the radially inside, so that the purge fluid can flow through this channel to the distal radial bearing. This channel does not necessarily have to be present on the bearing gap surface and can also be realized as a separate channel or bore. However, providing a channel on one of the bearing gap surfaces has the advantage of less heating of the smooth film in the bearing gap because a portion of the lubricating film is continuously replaced by the subsequently flowing purge fluid. Preferably, to minimize radial transport capacity, the channel is located within the stationary bearing gap surface.
[0015] A common problem arises with heparin, which is typically mixed with purging fluid. That is, although the purging fluid flows through the gap formed between the shaft and the housing opening, thereby pushing back blood that tends to enter the housing through such gaps, it cannot completely prevent blood from entering the gaps. In particular, some blood or blood components can always enter, at least in the distal section of such gaps. Heparin helps prevent blood clotting or blood adhesion to the surface within the gaps, thus preventing obstruction of shaft rotation.
[0016] EP 3 542 837 A2 describes a pump that limits, at least intermittently, the use of purge fluid to mitigate the consequences of heparin administration to a patient through the purge fluid of a blood pump. To achieve this, EP 3 542 837 A2 proposes using a material with relatively high thermal conductivity for the gap surface for at least one surface of the sliding bearing. Examples of such materials include silicon carbide. The opposing surface may be made of a ceramic material with low thermal conductivity (e.g., alumina-reinforced zirconia). As described, the shaft is made of alumina-reinforced zirconia, and the sleeve into which the shaft is journaled is made of silicon carbide. Thus, using special materials for the pump components is one solution to limit or even eliminate the use of heparin-containing purge fluid.
[0017] However, there is still a need for more universal solutions to the difficulties of using heparin in the purge fluid for cardiac pumps.
[0018] Figure 2 illustrates the use of a blood pump to support the left ventricle in this particular example. The blood pump includes a catheter 14 and a pumping device 10 attached to the catheter 14. The pumping device 10 has a motor section 11 and a pump section 12, which are arranged coaxially behind each other to form a rod-shaped structure. The pump section 12 has an extension that is in the form of a flexible suction hose 13, often called a "cannula." An impeller is provided within the pump section 12 to generate blood flow from the blood flow inlet to the blood flow outlet, and the rotation of the impeller is caused by an electric motor located in the motor section 11. The blood pump is positioned to be primarily located within the ascending aorta 15b, which leads to the aortic arch 15a. The aortic valve 18, in the closed state, leans either outside the pump section 12 or substantially within the suction hose 13 located within the left ventricle 17. By advancing the catheter 14 using a guidewire as needed, the blood pump with the suction hose 13 is advanced to the position shown in the figure. At this time, the suction hose 13 passes retrogradely through the aortic valve 18, so blood is drawn in through the suction hose 13 and pumped into the aorta 16.
[0019] Figure 2 only includes typical examples of applications, and the use of blood pumps is not limited to those shown in Figure 2. Therefore, the pump may also be inserted through other peripheral vessels, such as the subclavian artery. Alternatively, the reverse application to the right ventricle can also be envisioned.
[0020] Figure 3 shows an exemplary embodiment of a blood pump described in U.S. Patent Publication No. 2015 / 0051436 A1; that blood pump is equally suitable for use in the context of the present invention, except that the front end, circled and labeled "I", may be modified, such modification is shown in Figure 4. Accordingly, the motor section 11 has an elongated housing 20 in which an electric motor 21 may be housed. The stator 24 of the electric motor 21 may have a number of windings distributed circumferentially and a longitudinal magnetic return path 28, as is typical. The magnetic return path 28 may form a cylindrical sleeve on the outside of the elongated housing 20. The stator 24 may surround a rotor 26, which is connected to a motor shaft 25 and consists of permanent magnets magnetized in the direction of action. The motor shaft 25 may extend beyond the entire length of the motor housing 20 and may project distally from the motor housing 20 through an opening 35. An impeller 34 is attached there, with pump vanes 36 protruding from it, and the impeller 34 may rotate inside a tubular pump housing 32, which may be securely connected to the motor housing 20.
[0021] The proximal end of the motor housing 20 has a flexible catheter 14 sealed therein. An electrical cable 23 for powering and controlling an electric motor 21 may extend through the catheter 14. In addition, a purge fluid line 29 may extend through the catheter 14 and penetrate the proximal end wall 22 of the motor housing 20. The purge fluid may be fed into the interior of the motor housing 20 through the purge fluid line 29 and exit through the end wall 30 at the distal end of the motor housing 20. The purge pressure is selected to be higher than the existing blood pressure to prevent blood from entering the motor housing, and is 300 to 1400 mmHg depending on the case applied.
[0022] As described above, the same seal by purge may be combined with a pump driven by a flexible drive shaft and a remote motor.
[0023] When the impeller 34 rotates, blood is sucked through the distal opening 37 of the pump housing 32 and is transported axially in the opposite direction within the pump housing 32. The blood flows out of the pump section 12 through the radial outlet opening 38 in the pump housing 32 and further flows along the motor housing 20. This ensures that the heat generated within the motor is carried away. It is also possible to operate the pump section in the reverse transport direction, in which case blood is sucked along the motor housing 20 and exits through the distal opening 37 of the pump housing 32.
[0024] The motor shaft 25 is mounted within the radial bearings 27, 31 at the proximal end of the motor housing 20 on the one hand and at the distal end of the motor housing 20 on the other hand. The radial bearings, particularly the radial bearing 31 at the opening 35 at the distal end of the motor housing, are configured as sliding bearings. Further, the motor shaft 25 is also axially mounted within the motor housing 20, and the axial bearing 40 is likewise configured as a sliding bearing. The axial sliding bearing 40 serves to receive the axial force of the motor shaft 25 that acts in the distal direction when the impeller 34 transports blood from the distal side to the proximal side. If the blood pump is used to transport blood in the reverse direction as well or for that purpose only, a corresponding axial sliding bearing 40 may be provided at the proximal end of the motor housing 20 (at the proximal end as well or at the proximal end only) in a corresponding manner.
[0025] Figure 4 shows in more detail a structurally modified version of the part indicated as "I" in Figure 3, based on a preferred embodiment of the present invention. In particular, the radial sliding bearing 31 and the axial sliding bearing 40 are visible. The bearing gap of the radial sliding bearing 31 is formed on the one hand by the circumferential surface 25A of the motor shaft 25, and on the other hand by the surface 33A of the through bore in the bushing or sleeve 33 of the end wall 30 of the motor housing 20; the end wall 30 defines an outer gap diameter of about 1 mm, although the outer gap diameter may also be larger. In one example, the bearing gap of the radial sliding bearing 31 has a gap width of 2 μm or less along its entire length, not just at the front end or impeller side of the gap. Preferably, the gap width is 1 μm to 2 μm. The length of the bearing gap may be in the range of 1 mm to 2 mm, preferably 1.3 mm to 1.7 mm, for example 1.5 mm. The surface forming the gap of the radial sliding bearing 31 has a surface roughness of 0.1 μm or less. These dimensions are likely to vary depending on the type of pump and are presented as examples, not limitations.
[0026] The bearing gap of the axial sliding bearing 40 is formed on one hand by the axial inner surface 41 of the end wall 30 and the opposing surface 42. This opposing surface 42 is part of the ceramic disc 44 that sits on the motor shaft 25 distal to the rotor 26 and rotates with the rotor 26. A channel 43 in the bearing gap surface 41 of the end wall 30 allows the purging fluid to flow through the bearing gap surfaces 41 and 42 of the axial sliding bearing 40 to the radial sliding bearing 31 and then distally out of the motor housing 20. The axial sliding bearing 40 presented in Figure 3 is a normal sliding bearing. Unlike the presentation, the axial gap of the axial sliding bearing 40 is very small, only a few micrometers.
[0027] Instead of the axial sliding bearing 40 and the radial sliding bearing 31, a composite radial-axial sliding bearing 40 can also be realized, having a concave bearing shell in which a convex bearing surface operates. Such a variant is presented in Figure 4 by a spherical sliding bearing 40. The bearing gap surface 41 is designed as a spherical concave surface, and the opposing bearing gap surface 42 is designed as a corresponding spherical convex surface. Here again, the channel 43 is present in the bearing gap surface 41 on the stationary side of the end wall 30. Alternatively, the bearing gap surface 41 on the stationary side of the end wall 30 may be convex, and the opposing bearing gap surface 42 may be concave. Surfaces 42 and 43 may also be conical instead of spherical. Preferably, corresponding radial-axial sliding bearings are provided on both sides of the motor housing 20 to prevent radial offset when the shaft 25 moves axially. The advantage of the composite axial-radial sliding bearing is its higher load capacity. However, the disadvantage is its larger friction diameter.
[0028] During operation, the blood pump is attached to a source of purge fluid, and the fluid enters the motor housing through the purge fluid line. The purge fluid then flows through the axial sliding bearing and further through the distal radial bearing. In the axial sliding bearing, the purge fluid forms a lubricating film within the bearing gap. However, the pressure of the purge fluid as it flows through the motor housing has a detrimental effect on the width of the bearing gap. Specifically, higher purge fluid pressure requires a smaller bearing gap width, resulting in a thinner lubricating film between the sliding surfaces.
[0029] The viscosity of the purging fluid is controlled by the concentration of dextrose in the purging fluid. Aqueous solutions of dextrose are widely administered to patients for various reasons. The amount of dextrose in an aqueous solution is approximately 5% to 50%. In one embodiment, the purging fluid contains a 5% aqueous dextrose solution (i.e., 252 mmol / liter). Viscosity can be increased by including a higher concentration of aqueous dextrose solution (e.g., D20W, D40W, etc.). When a high-viscosity purging fluid is used, the fluid film is maintained even at high pressures, and therefore the friction of the axial sliding bearing does not depend on the pressure of the purging fluid. In some embodiments, when the purging fluid has a viscosity of approximately 1.2 mPas or higher at 37°C, the axial sliding bearing may be configured as a simple sliding bearing or not as a hydrodynamic sliding bearing. Therefore, even when considering purging fluids that do not contain heparin or contain less heparin, the viscosity of such purging fluids must be considered.
[0030] The pump impeller imposes shear stress on the blood passing through the pump. This shear stress is primarily caused by the gap between the impeller and the outer surface of the ceramic bearing, and the gap between the impeller shaft and the inner race of the bearing (e.g., ceramic bearing, ball bearing, etc.). Due to the shear stress on the blood, blood proteins denature and polymerize as the blood passes through the pump. The deposition of denatured and aggregated proteins triggers the activation of the coagulation cascade, which leads to the accumulation of biological deposits on the pump mechanism (e.g., impeller, outflow cage, etc.). Small gaps between components (i.e., purge gaps) are particularly vulnerable to blockage by biological deposits. The accumulation of biological deposits increases the motor current required to operate the pump. Increased motor current or biological deposits can degrade pump performance or even cause the pump to shut down.
[0031] As mentioned above, to mitigate the harmful effects of shear stress on the blood flowing through the pump, the purge fluid used in a purging blood pump typically contains the anticoagulant heparin (e.g., 50 units / ml) in 5% dextrose (D5W). The dextrose concentration determines the viscosity of the purge fluid and therefore affects the purge flow rate. A purge fluid with a lower dextrose concentration has lower viscosity and flows faster through the purge system at lower pressure. A purge fluid with a higher dextrose concentration (higher viscosity) results in a lower purge flow rate and requires a higher purge pressure. Reducing the dextrose concentration from 20% to 5% increases the purge flow rate by approximately 30% to 40%.
[0032] Purge flow rates typically range from approximately 2 mL / hour to approximately 30 mL / hour. This results in purge pressures of approximately 1100 mmHg to approximately 300 mmHg. For the blood pumps described herein, such as Impella CP, Impella 2.5, Impella 5.0 / LD, and RP, typical purge flow rates are approximately 5 mL / hour to approximately 20 mL / hour. All of these pumps have ball bearing rotor / stator systems with similar tolerances, which leads to similar purge operating ranges. A typical purge flow rate for Impella 5.5 is approximately 2 to approximately 10 mL / hour. This lower flow rate is due to the placement of a ceramic bearing rotor / stator system designed with a smaller (radial) purge gap to reduce or eliminate the amount of heparin delivered to the patient. Surgeons prefer not to administer heparin to surgical patients during the first few days post-operatively. If so, a heparin-free purge fluid is preferred for these patients.
[0033] A consistent purge flow is used to keep two critical areas debris-free: 1) the gap between the rotor shaft and the sleeve bearing, and 2) the gap between the sleeve bearing and the impeller. Co-mixing of diffusion and flow means that some blood components may potentially reach these gaps. Heparin in the purge solution enhances protection against the entry, adsorption, deposition, and coagulation of blood components. Heparin in the purge solution also improves the practical life of the bearings, at least for reasons described below.
[0034] Specifically, the sustained and dynamic physical adsorption (physicoadsorption) of heparin onto the surfaces around the purge path reduces the adsorption of blood components, thus preventing the biological deposition of blood debris onto the bearings and other pump components. Heparin also partially neutralizes the slightly acidic D5W solution, which helps maintain the physiological pH within the aforementioned gap, thus reducing the risk of blood protein denaturation. Localized increases in heparin concentration both under the impeller and inside the sleeve bearing gap may also reduce the risk of blood coagulation in these areas. The addition of heparin increases the conductivity of the purge fluid, thus reducing the negative impact of electrostatic discharge on the practical life of the bearings.
[0035] Therefore, heparin is provided in the purge fluid to prevent the formation of shear-induced biological material or biological deposits, and consequently, to prevent undesirable deposition / accumulation of biological material in the pump in high-shear areas, such as between the impeller shaft and the inner race of the bearing. However, as mentioned above, there are challenges associated with the addition of heparin to the purge fluid. Specifically, heparin a) complicates the systemic management of anticoagulants (i.e., the amount of heparin the patient is receiving via the purge fluid must be considered); b) as an anticoagulant, heparin increases the patient's bleeding tendency; c) heparin makes it more difficult to control bleeding in postoperative patients, especially if surgical devices are used in such patients; and d) heparin cannot be used in patients with heparin-induced thrombocytopenia (HIT). Heparin may also be administered systemically to some patients, which makes it difficult to coordinate two sources of heparin administration.
[0036] However, purging fluids / purging fluid additives that can mitigate pump performance problems caused by pump operation are still needed. Protein unfolding exposes the hydrophobic regions of the protein, and it has been observed that denatured proteins are more prone to aggregation. This leads to undesirable biological deposition. In the absence of denaturation and aggregation, the hydrophobic segments are shielded, and the electrostatically charged chemical groups of the protein repel each other.
[0037] It is known that soluble calcium ions mediate coagulation. Serum albumin in the blood regulates calcium ions. At higher pH values, albumin retains calcium ions more strongly. This mechanism reduces the effective concentration of calcium available for coagulation. Therefore, providing additives that increase the pH of the purge fluid is thought to reduce the amount of calcium that supports coagulation in high-shear areas. High-pH buffers for use in purge fluids that increase the pH of blood and thus reduce blood clotting are described herein.
[0038] What is anticipated herein is a pH-controlling buffer to be added to a purging fluid that avoids the problems of heparin but is suitable for other purposes of the purging fluid (reduction of biological deposits; reduction of bearing wear; pressure higher than blood pressure, etc.). One example of a suitable pH-controlling buffer is sodium bicarbonate. However, pH-controlling buffers other than sodium bicarbonate are also anticipated. These pH-controlling buffers include, for example, salts of small organic acids, such as citrates, lactates, glucons, acetates, pyruvates, etc. In one example, the pH of sodium bicarbonate is approximately 7.4 to approximately 9.1. In one example, the pH of the purging fluid with bicarbonate is approximately 8.4. Other ranges are also expected, including, but not limited to, approximately 7.5–9.1, 7.6–9.1, 7.7–9.1, 7.8–9.1, 7.9–9.1, 8.0–9.1, 8.1–9.1, 8.2–9.1, 8.3–9.1, 8.4–9.1, 8.5–9.1, 8.6–9.1, 8.7–9.1, 8.8–9.1, 8.9–9.1, and 9.0–9.1. The pH of blood is approximately 7.3–7.4. Adding sodium bicarbonate to the purging fluid increases the pH of the blood in contact with the purging fluid. The increased pH reduces biological deposits resulting from blood coagulation caused by the high-shear pump environment. Because of this effect, the presence of sodium bicarbonate reduces the formation of insoluble biological deposits, even if coagulation proceeds toward the formation of individual fibrin molecules.
[0039] In one embodiment, adding a bicarbonate-containing solution mixed with a dextrose solution, such as a 5% dextrose aqueous solution (D5W), a 20% dextrose aqueous solution (D20W), or a 40% dextrose aqueous solution (D40W), to blood increases the local pH of the blood in gaps (areas of higher shear), preventing protein aggregation by increasing the electrostatic charge of serum proteins and thus reducing the formation of biological deposits. The amount of bicarbonate in the bicarbonate solution mixed with the dextrose solution is approximately 1.5 milliequivalents (mEq / L) to approximately 50 mEq / L per liter. Other pH-controlling buffers besides sodium bicarbonate are also expected. These pH-controlling buffers include, for example, salts of small organic acids, such as citrates, lactates, glucons, acetates, and pyruvates. The concentration of such other pH-controlling buffers in the solution with the dextrose aqueous solution is selected to result in a solution with a pH within the range specified above. The concentrations of these pH-controlling buffers are selected such that their concentrations in the solution do not significantly exceed the natural physiological limits of these buffers in the blood (i.e., within the range where such organic acids are present in the blood). Such concentrations can be readily determined by those skilled in the art.
[0040] The purge solutions anticipated herein cause less bearing wear on the blood pump than purge solutions containing reduced heparin but without the pH-controlling buffer described herein. It is expected that bearing wear will increase as the amount of heparin is reduced. While the applicants do not wish to be bound by any particular theory, they suggest that solutions with higher concentrations of heparin have higher conductivity. A conductive purge solution provides better charge dissipation, thereby reducing charge accumulation on the pump's metal bearings. Therefore, a more conductive purge solution reduces wear on the metal bearings. Reducing the amount of heparin in the purge solution also reduces the conductivity of the purge solution. Surprisingly, however, when the amount of heparin in the purge fluid is reduced or absent, and a pH-controlling buffer is added to the purge fluid, bearing wear does not increase because the pH-controlling buffer also increases the conductivity of the purge fluid. The purge solutions described herein also maintain the patency of the purge line that delivers the purge solution to the pump.
[0041] In some embodiments, the purging fluid solution may contain a reduced amount of heparin along with the pH-controlling buffer described above. A reduced concentration of heparin of about 12.5 units / ml or less is expected. A reduced concentration of about 6.25 units / ml or less is also expected. A reduced concentration in the range of about 1 unit to about 6.25 units / ml per ml is also expected. Reducing the amount of heparin in the purging solution increases the amount of bearing wear, but the pH-controlling buffer in the purging solution described herein reduces the amount of bearing wear without the problems arising from the use of heparin in the purging solution as described elsewhere herein.
[0042] Surprisingly, as the applicant has been able to determine, the pH-controlling buffers described herein, when added alone or in reduced amounts with heparin to a dextrose-containing purging fluid, mitigate the problem of biological deposits on pump components; such deposits may otherwise result from blood being subjected to high shear on the pump impeller. Heparin does not need to be present in the purging solution to mitigate the formation of biological deposits and avoid pump failure.
[0043] Durability tests showed no reduction in pump durability when 25 units / mL was used in the purge solution along with a dextrose solution (e.g., 5%-20% dextrose). Clinical data were examined when 25 units / mL was used in the process, and initial findings showed no difference in performance compared to 50 units / mL. In one example, the units represent molar equivalents in the solution.
[0044] If a patient is heparin intolerant due to heparin-induced thrombocytopenia (HIT), and yet an anticoagulant needs to be added to a purge solution combining a pH-controlling buffer with dextrose aqueous solution, a direct thrombin inhibitor (DTI) may be added to the solution. When a DTI is added to the purge solution, the concentration of DTI in the purge solution should be an equivalent dose of approximately 0.01 mg / kg / hr to approximately 0.012 mg / kg / hr. The equivalent dose is selected to produce a partial thromboplastin time (PTT) of approximately 40 to 50 seconds. Examples of suitable DTIs include, but are not limited to, argatroban or bivalirudine. The concentration of DTI in the purge solution is approximately 20 mg / 500 ml to approximately 60 mg / 500 ml. For example, when the DTI in the purge solution is bivalirudine, the concentration in the dextrose solution (e.g., D5W; D10W) is approximately 20 mg / 500 ml. For example, when DTI in the purge solution is argatroban, its concentration in the dextrose solution (e.g., D5W; D10W) is approximately 30-60 mg / 500 ml. When DTI is added to the purge solution, it is added in place of heparin, not added in addition to heparin.
[0045] Because bicarbonates maintain the patency of purge lines, the presence of bicarbonates in the system reduces the effects of kinking in the purge system, in addition to damage to purge elements or the accumulation of biological deposits in the pump.
[0046] One advantage of the purge solution described herein is that the pH-controlling buffer described herein is easily miscible in dextrose aqueous solution. Furthermore, during storage, even when stored for a considerable period of time, the pH-controlling buffer remains mixed with the dextrose aqueous solution. In contrast, heparin needs to be mixed more vigorously with dextrose aqueous solution and gradually separates from it when stored for a considerable period of time. However, when heparin is added to a purge solution containing the pH-controlling buffer in combination with dextrose aqueous solution, the degree of ionization and net charge of the heparin molecule increases. As a result, heparin mixes more easily with the purge solution and remains more evenly distributed within the bag. Consequently, the current method of periodically equilibrating the contents of the bag by squeezing the bag by hand may be made easier or even eliminated.
[0047] This specification describes a system and method for using sodium bicarbonate as a substitute for heparin in a purging fluid used to maintain the patency of a purge system for a blood pump. The sodium bicarbonate is placed within the purging system and is not used for systemic anticoagulation in the patient to whom the pump is placed. Even when sodium bicarbonate is used during purging, systemic anticoagulation with heparin, bivalirudin, or argatroban is used to prevent thromboembolic events.
[0048] In this specification, the word “comprising” should be understood in its “open” meaning, that is, “including,” and therefore not limited to its “closed” meaning, that is, “consisting only of.” Where the corresponding words “comprise,” “comprised,” and “comprises” appear, those words are given their corresponding meanings.
[0049] While specific aspects of the present technology have been described above, it will be apparent to those skilled in the art that the present technology can be embodied in other specific forms without departing from its essential characteristics. Therefore, the aspects and examples presented herein should be considered in all respects as illustrative and not restrictive. Furthermore, it should be understood that any reference herein to publicly known material in the art does not constitute an acknowledgment that such material is widely known to those skilled in the art, unless otherwise indicated.
Claims
1. The method of operating a blood pump, The blood pump includes a motor section, a pump section, and a purging fluid line. The step in which the supply source supplies purge fluid to the purge fluid line; and (i) A purge fluid line provides purge fluid to the motor section, where the purge fluid flows into the gap between the bearings in the motor housing of the motor section, and (ii) The step in which the motor in the motor section rotates the impeller in the pump section based on the rotation of the shaft in the motor section. Includes, The purging fluid contains a pH-controlling buffer. method.
2. The method according to claim 1, wherein the purging fluid further comprises an aqueous dextrose solution.
3. The method according to claim 2, wherein the purging fluid further comprises heparin.
4. The method according to claim 1 or claim 2, wherein the pH-controlling buffer is selected from the group consisting of sodium bicarbonate, citrate, lactate, gluconate, acetate, and pyruvate.
5. The method according to claim 4, wherein the pH-controlling buffer is sodium bicarbonate.
6. The method according to claim 5, wherein the amount of pH control buffer in the purging fluid is approximately 1.5 milliequivalents (mEq / L) to approximately 50 mEq / L per liter.
7. The method according to either claim 1 or claim 6, wherein the pH of the pH-controlling buffer is approximately 7.4 to approximately 9.
1.
8. The method according to claim 3, wherein the amount of heparin in the purging fluid is zero to about 12.5 units per milliliter.
9. The method according to claim 8, wherein the amount of heparin in the purging fluid is zero to about 6.25 units per milliliter.
10. The method according to claim 9, wherein the amount of heparin in the purging fluid is approximately 1 unit per milliliter to approximately 6.25 units per milliliter.
11. The method according to claim 4, wherein the purging fluid further comprises a thrombin inhibitor directly.
12. The method according to claim 11, wherein the direct thrombin inhibitor is argatroban, bivalirudin, or a mixture thereof.
13. The method according to claim 11, wherein the amount of direct thrombin inhibitor in the purging fluid is about 20 mg / 500 ml to about 60 mg / 500 ml.
14. The method according to claim 1 or claim 6, wherein the pH of the pH-controlling buffer is approximately 7.5 to approximately 9.
1.
15. The method according to either claim 1 or claim 6, wherein the pH of the pH-controlling buffer is approximately 7.6 to approximately 9.
1.
16. The method according to either claim 1 or claim 6, wherein the pH of the pH-controlling buffer is approximately 7.7 to approximately 9.
1.
17. The method according to either claim 1 or claim 6, wherein the pH of the pH-controlling buffer is approximately 7.8 to approximately 9.
1.
18. The method according to either claim 1 or claim 6, wherein the pH of the pH-controlling buffer is approximately 7.9 to approximately 9.
1.
19. The method according to either claim 1 or claim 6, wherein the pH of the pH-controlling buffer is approximately 8.0 to approximately 9.
1.
20. The method according to claim 1 or claim 6, wherein the pH of the pH-controlling buffer is approximately 8.9 to approximately 9.
1.
21. The method according to either claim 1 or claim 6, wherein the pH of the pH-controlling buffer is approximately 8.1 to approximately 9.
2.
22. The method according to either claim 1 or claim 6, wherein the pH of the pH-controlling buffer is approximately 8.2 to approximately 9.
1.
23. The method according to either claim 1 or claim 6, wherein the pH of the pH-controlling buffer is approximately 8.3 to approximately 9.
1.
24. The method according to either claim 1 or claim 6, wherein the pH of the pH-controlling buffer is approximately 8.4 to approximately 9.
1.
25. The method according to claim 1 or claim 6, wherein the pH of the pH-controlling buffer is approximately 8.5 to approximately 9.
1.
26. The method according to claim 1 or claim 6, wherein the pH of the pH-controlling buffer is approximately 8.6 to approximately 9.
1.
27. The method according to either claim 1 or claim 6, wherein the pH of the pH-controlling buffer is approximately 8.7 to approximately 9.
1.
28. The method according to either claim 1 or claim 6, wherein the pH of the pH-controlling buffer is approximately 8.8 to approximately 9.
1.
29. The method according to either claim 1 or claim 6, wherein the pH of the pH-controlling buffer is approximately 9.0 to approximately 9.1.