Device and system for supporting the separation of gas bubbles from a medical fluid

Abstract

Device (100) for assisting the separation of gas bubbles (B) from a medical fluid (L) which circulates in a fluid circuit (C) comprising a gas separator (X), the medical fluid (L) for extracorporeal blood treatment; ◯ comprising the device (100): ▪ at least one ultrasonic transducer (10) for generating ultrasonic vibrations; ▪ a control unit (20) configured to control the ultrasonic transducer (10) so that it generates ultrasonic vibrations; ▪ and means (50) for arranging the device (100) on a section of a liquid circuit (C); ◯ wherein the device (100) is designed such that it can be arranged upstream of the gas separator (X) on a section of the liquid circuit (C) or on the gas separator (X) itself; ◯ wherein the device (100) is configured such that the ultrasonic transducer (10) can couple ultrasonic vibrations into the medical fluid (L) which is in the fluid circuit, ◯ wherein ultrasound transducer (10) and control unit (20) are matched such that the ultrasound transducer (10) can generate a standing wave in the medical fluid (L) at least temporarily with the generated ultrasound vibrations, such that at least one node and / or an antinode of the standing wave forms inside the fluid (L) which is located in the fluid circuit (C), ◯ wherein the device (100) is configured such that the ultrasonic vibrations generated by the ultrasonic transducer (10) do not produce hard cavitation in the medical fluid (L), ◯ wherein the device (100) is designed such that it can be arranged on the fluid circuit (C) such that the nodes and antinodes of the standing wave are arranged along a line which is substantially perpendicular to the flow direction of the fluid (L) in the section of the fluid circuit (US).

Description

Technical area

[0001] The invention relates to the field of fluid circuits for medical fluids and gas separation from medical fluids in circuits. background

[0002] In the context of extracorporeal blood circuits in which a medical fluid circulates, such as hemodialysis, gas bubbles contained in the extracorporeal blood are usually at least partially removed before the blood is returned to the patient. Gas separators are used to remove the gas bubbles. For this purpose, for example, a venous chamber in a blood tubing set is provided as a gas separator. In a venous chamber, the cross-section of the extracorporeal circuit expands compared to other sections because a venous chamber generally has a larger free internal cross-section than a blood tubing. As a result, a venous chamber contains a slightly larger volume of blood per path length through the extracorporeal circuit, and a given volume of blood thus has more interaction partners while moving through the venous chamber than while moving through, for example, a section of tubing.In addition, venous chambers are often designed so that an inflowing volume element of blood moves along a cyclonic path, i.e. a helical path in which the diameter of the screw continuously tapers along the distance traveled. For this purpose, venous chambers can have a conically tapered shape. Movement along the cyclonic path can be supported by aligning the venous chamber in the Earth's gravitational field so that the tapered end has the outlet and is located at the bottom (i.e. closer to the Earth's core), while the wider end has the inflow connection and is located at the top (i.e. further away from the Earth's core). The venous chamber is sometimes also called a venous drip chamber, although the fluid level is actually always above the inlet opening, preventing dripping.Overall, the design results in gas bubbles, such as air, being separated from the blood in the venous chamber. Gas bubbles contained in the blood that are buoyant enough to rise against the downward flow in the drip chamber remain on the surface. The bubbles form a foam and eventually burst. In this way, the gas from the bubbles that rise to the surface of the liquid in the drip chamber is removed from the liquid. However, there are also bubbles whose buoyancy is too low to be removed from the blood in this way. Gas bubbles with lower buoyancy are often smaller because their volume-to-surface ratio is less buoyant. In other words, larger bubbles are generally easier to separate because they generally have greater buoyancy.However, smaller air bubbles can still adversely affect patient safety.

[0003] Even in the area of ​​heart and lung support such as ECMO, there may be a need to remove gas bubbles from the blood circulating in an extracorporeal circuit.

[0004] But even in the context of other medical fluids circulating in an extracorporeal circuit, it is desirable to remove gas bubbles from the fluids used for dialysis as renal replacement therapy. Examples of such medical fluids include dialysate, on the one hand, and dialysate concentrate, on the other. Dialysate concentrate is diluted with dialysis water to a concentration level low enough for dialysis treatment. Removing gas bubbles is desirable for both dialysate and dialysate concentrate. The reasons for this are different. When preparing dialysate concentrate in mixing devices, the progress of the mixing process and the quality of the mixed concentrate are determined by measuring the density of the mixture. During the mixing process, undissolved components pass into the mixture with dialysis water, thus increasing the density of the mixture.Gas bubbles in the medical fluid can interfere with density measurements and lead to measurement errors at any stage, from pure dialysis water to the finished concentrate. Gas bubble removal is also desirable for dialysate to prevent gas bubbles from entering the dialyzer, where they can adhere to filter fibers and disrupt dialysis treatment or, at the very least, reduce the effectiveness of the treatment because the section of a filter fiber covered by an adhering gas bubble is no longer available for the desired mass transfer.

[0005] It is therefore an object of the invention to mitigate the existing problems with gas bubbles in medical fluids and to provide improved separation of gas bubbles from medical fluids. Brief description of the invention

[0006] The object is achieved by a device according to the invention for supporting the separation of gas bubbles from a medical fluid circulating in a fluid circuit, the fluid circuit comprising a gas separator. The fluid is a fluid for extracorporeal blood treatment. The device comprises: - at least one ultrasonic transducer for generating ultrasonic vibrations, - a control device configured to control the ultrasonic transducer to generate ultrasonic vibrations; - an electrical power supply which supplies the ultrasonic transducer and the control unit with electrical energy; - and means for arranging the device at the section of the fluid circuit.

[0007] The means for arranging the device can be, for example, mechanical—such as a clamp, a cuff, a clamping cuff, a partial circle or a partial ring (e.g., a 3 / 4 ring or 5 / 6 ring)—or chemical (such as an adhesive). The device is designed such that it can be arranged upstream of the gas separator at a section of the fluid circuit or at the gas separator itself. Furthermore, the device is configured such that the ultrasonic transducer can couple ultrasonic vibrations into the medical fluid present in the fluid circuit.In addition, the ultrasonic transducer and control unit are coordinated in such a way that the ultrasonic transducer can generate a standing wave in the medical fluid with the generated ultrasonic vibrations, at least temporarily, so that at least one node and / or one antinode of the standing wave forms inside the fluid, which are then located in the fluid circuit.

[0008] The invention advantageously improves the separation of gas bubbles at downstream gas separators.

[0009] The device according to the invention for assisting the separation of gas bubbles from a medical fluid is configured such that the ultrasonic vibrations generated by the ultrasonic transducer do not cause hard cavitation in the medical fluid. Hard cavitation can cause damage to the fluid circuit and the medical fluid. This design advantageously prevents such damage.

[0010] In addition, the device according to the invention for supporting the separation of gas bubbles from a medical liquid is designed such that it can be arranged on a liquid circuit such that the nodes and antinodes of the standing wave are arranged along a line which runs essentially perpendicular to the flow direction of the liquid in the section of the liquid circuit. For this purpose, for example, the ultrasonic transducer can be designed and aligned such that the wavefront of the ultrasonic oscillation propagates through the liquid in sections essentially parallel to the flow direction. In the case of a plane wave, for example, the nodes and antinodes are located one behind the other along the path. This design advantageously ensures that the entire cross-section of the liquid is captured by the ultrasonic oscillation and is not accelerated in the flow direction by the oscillation.

[0011] A further development of the device according to the invention for assisting in the separation of gas bubbles from a medical fluid is designed for installation in a straight section upstream of a gas separator in a medical fluid circuit. This particularly advantageously enables a simple installation in typical circuits with little effort and few modifications.

[0012] A further development of the device according to the invention for assisting in the separation of gas bubbles from a medical fluid is designed as a clamping sleeve for placement on a section of the fluid circuit. This particularly advantageously enables simple installation on typical circuits with little effort and few modifications.

[0013] A further development of the device according to the invention for supporting the separation of gas bubbles from a medical liquid is designed such that it can be arranged on a straight section, e.g. a section of a hose line, of a liquid circuit, wherein the straight section has exactly two openings which are flowed through as an inlet opening and an outlet opening in a normal operating situation, and wherein the line section is arranged upstream of a gas separator in a circuit of a medical liquid, in particular in a circuit in the context of extracorporeal blood treatment, in particular in the context of renal replacement therapy dialysis, in particular in the context of hemodialysis or hemodiafiltration.

[0014] A further development of the device according to the invention for assisting in the separation of gas bubbles from a medical fluid is adapted to be arranged in a section of an extracorporeal blood circuit. This advantageously enables the use of the device in extracorporeal blood circuits for their gas separation.

[0015] In a further development of the device according to the invention for supporting the separation of gas bubbles from a medical fluid, which is adapted to be arranged in a section of an extracorporeal blood circuit, the control unit and ultrasonic transducer are configured to couple ultrasonic waves into blood in a frequency range suitable for concentrating gas bubbles contained in the blood in a predetermined spatial region of the blood volume. This advantageously enables the support of the separation of gas bubbles from blood. A further development of this device according to the invention for supporting the separation of gas bubbles from a medical fluid, which is adapted to be arranged in a section of an extracorporeal blood circuit, is further adapted for use in an extracorporeal blood circuit having a gas separator designed as a venous chamber.This advantageously allows the invention to separate gas bubbles from blood in conjunction with a venous chamber. In yet another refinement of this embodiment, the device is configured so that it can be arranged directly on a substantially conically shaped venous drip chamber. This results in a particularly advantageous, compact design.

[0016] A further development of the invention relates to a system for dialysis treatment comprising a blood tubing set with a gas separator and a device for assisting gas separation, which is arranged upstream of the gas separator or on the gas separator.

[0017] A further development of the invention relates to a system for extracorporeal lung support comprising an ECMO blood tubing set with a gas separator and a device for assisting gas separation, which is arranged upstream of the gas separator (X) or on the gas separator.

[0018] When "medical fluid" is mentioned in the context of this application, it generally refers to a fluid that is predominantly liquid by mass at room temperature. In the context of this application, the application concerns the removal of gas bubbles from a medical fluid. Consequently, however, the term "medical fluid" refers to a mixture of a purely liquid fluid and other admixtures such as gas bubbles, foams, gels, or solids, etc. However, it does not refer to the separation of gases from an essentially gaseous fluid.

[0019] A further development of the invention relates to a mixing machine for preparing dialysate or dialysate concentrate for renal replacement therapy, comprising a device for assisting gas separation. The device for assisting gas separation can advantageously be used in dialysate, dialysate concentrate, and precursor fluids. A mixing machine for dialysate or dialysate concentrate can, for example, have circulation lines with a diameter of 20, 25, or 32 mm (DN 20 / DN 25 / DN32). A line for a density measurement can, for example, have an inner diameter of 6 mm or an outer diameter of 6 mm. In the context of such devices, there can be gas separators designed as filter elements. Retained gas bubbles collect there during a density measurement, and in another operating cycle, the bubbles are removed from the filter in a rinse. However, there are also other gas separators as described in the context of dialysis machines.A further development of such a mixing machine has a density measuring device for measuring the mass density of the mixture during the mixing process, and the device according to the invention for assisting gas separation and the gas separator are arranged upstream of the density measuring device. This advantageously improves the removal of gas bubbles from the mixture before the mixture reaches the density measuring device, where gas bubbles would lead to measurement errors. Measurement errors can advantageously be avoided. In a further development of this mixing machine, the density measuring device and the device for assisting gas separation are located in a bypass line parallel to the main mixing line. This advantageously allows the density measurement to be carried out on a reduced liquid volume, but without unnecessarily slowing down the mixing process by measuring the total volume.

[0020] According to a preferred embodiment of the device according to the invention, the ultrasonic transducer is designed as a piezoelectric element or the device comprises a piezoelectric element. Piezoelectric elements are particularly advantageous for the reliable and cost-effective generation of ultrasonic vibrations.

[0021] Two gas bubbles in a liquid can combine and subsequently form a larger single gas bubble that contains the gas from both original gas bubbles. Everyone has probably observed this as a child in the foam on top of their bathwater, where the liquid is bathwater and the gas bubbles are filled with air. The longer the foam persists, the more small bubbles combine to form fewer and fewer large bubbles. The invention makes use of this effect by using ultrasound excitation to specifically push the gas bubbles contained in a given volume of a medicinal liquid, which can be used in extracorporeal blood treatment, into certain, compact spatial sections, i.e. transporting the gas bubbles using longitudinal waves, and collecting them there. The ultrasonic vibrations cause the gas bubbles contained in the medicinal liquid to be transported from some regions of the space to others.As a result, the bubble density decreases in the spatial regions where the bubbles are removed, and the bubble density, in turn, increases in those spatial regions to which the gas bubbles were transported. In the context of the present teaching, air bubbles in liquids are often discussed, but the advantageous effects of the invention generally apply to other gas bubbles in liquids. When air or air bubbles are mentioned, this also includes other gases or their bubbles in liquids. As a result, the gas bubbles brought together by ultrasonic vibrations are largely in close proximity, partially touching one another, and can combine to form fewer bubbles with a larger volume.Thus, although the gas density increases in the spatial regions to which the gas bubbles are transported, the bubble density does not necessarily increase there: As bubbles merge, the number of bubbles decreases, whereas the transport initially increases the number of bubbles in the target region. The larger gas bubbles, in turn, have greater buoyancy. This makes gas bubbles easier to separate. The coupled ultrasonic vibrations create standing waves in the medical liquid. If ultrasound is used to assist gas separation from a liquid as described above, the acoustic pressure causes the transport of gas bubbles on the one hand, and the accumulation and concentration of gas bubbles in certain locations on the other hand causes the gas bubbles to coalesce and subsequently intensify separation due to the increased buoyancy of the larger bubbles.

[0022] In classical standing waves, the spatial regions where the bubbles are collected or transported away are fixed over time. Depending on the dimensions of the vessel region into which the ultrasonic vibrations are coupled, the frequency of the coupled ultrasonic vibration, the wall thickness, and the distance through the liquid, there can be a varying number of spatial regions in which the gas bubbles collect. It is crucial that the frequency is selected such that, for a given geometry, the ultrasonic excitation creates at least one spatial region in the liquid in which the gas bubbles are brought together by the ultrasonic vibration.

[0023] In a preferred embodiment of the invention, the section of the fluid circuit where the ultrasonic transducer can be arranged is a flow-through vessel of the circuit, such as a blood tube or a dialysate line or a dialysate concentrate line section or a gas separator (such as a venous chamber). It is preferred if the at least one ultrasonic transducer is arranged such that at least one spatial region in which gas bubbles are collected by means of ultrasonic vibrations runs at least partially along the flow direction or parallel to it.For this purpose, the coupling of the ultrasonic vibrations must generally not be oriented in such a way that the propagation direction of the waves is parallel to the flow direction of the medical fluid, but a coupling in which the propagation direction of the waves in the fluid is oriented essentially perpendicular to the flow direction of the fluid, at least in sections, is preferred in many cases.

[0024] In addition to continuous, uniform ultrasonic excitation at a fixed frequency, excitation with an ultrasonic burst can also be used as an alternative. It has been shown that this can further improve gas separation because the speed of the ultrasound-induced transport of the gas bubbles through the liquid is increased. According to the invention, the burst length is selected so that a standing wave forms in the liquid, at least for a short period of time. Bursts typically have a fixed frequency. When exciting using bursts, it must be taken into account that the acoustic intensity and sound pressure during a burst can temporarily reach a peak, which has a higher sound pressure than would be achieved with uniform, continuous excitation without bursts. Furthermore, burst excitation can advantageously cover frequency ranges that would otherwise be unattainable with a specific ultrasonic transducer, e.g.Lower frequencies than the natural frequency of the ultrasonic transducer can be achieved. For example, using several short bursts, with the amplitude deliberately varied between bursts, an enveloping oscillation can be achieved around the bursts, which has the form of a much lower frequency than the natural frequency of an oscillator.

[0025] In aqueous solutions (including saline water, dialysate, and dialysate concentrate) and water, it has been shown that gas bubbles with a diameter of 10–100 µm can be effectively removed by the invention. In particular, in dialysate and dialysate concentrate, which are aqueous solutions, carbon dioxide gas bubbles can also occur. The invention is also designed to remove carbon dioxide gas bubbles.

[0026] Preferably, the invention is designed so that it can be installed in an existing liquid circuit to improve gas separation without requiring modifications to the liquid circuit or to a device comprising the liquid circuit. This allows the invention to be advantageously combined and used with existing systems at particularly low additional costs.

[0027] In blood, it has been shown that relevant bubbles with a diameter of less than 1000 µm, typically 10-500 µm in diameter, can be better removed by the invention. Embodiments of the invention adapted for use in an extracorporeal blood circuit are also designed such that the effective power coupled into the blood is less than 50 mW per cm 2 is.

[0028] Depending on frequency, geometry, coupling, liquid medium, hose wall, etc., the ultrasonic transducer (e.g. piezo oscillator) is supplied with an electrical power in the range of 0.1 W to 50 W.

[0029] In the context of the invention, a ceramic piezoelectric oscillator is preferably used as an ultrasonic transducer to generate the ultrasonic vibrations. A preferred material for the piezoelectric oscillator is PZT ceramic (lead zirconium titanate) with a material thickness in the range of 1 to 10 mm. In an exemplary design for a planar ultrasonic oscillator, the resonator surfaces are 50 × 50 mm. 2 up to 50×100 mm 2 .

[0030] The device according to the invention is configured such that the excitation frequency emitted by the ultrasonic oscillators is in the range of 16 kHz to 1 GHz. Preferably, the frequency is in the range of 100 kHz to 700 kHz. This range advantageously provides a significant improvement in gas separation. Even more preferred are the frequency ranges of 200 kHz to 250 kHz and 500 kHz to 550 kHz. These ranges advantageously provide an even greater improvement in gas separation.

[0031] In an exemplary embodiment, the device according to the invention for supporting the separation of gas bubbles from a medical fluid for extracorporeal blood treatment, the medical fluid circulating in a fluid circuit comprising a gas separator, is adapted for use in a section of an extracorporeal blood circuit, as occurs in hemodialysis or hemodiafiltration for renal replacement therapy. The section of the fluid circuit can be a blood tube, a cuvette, or a chamber that is integrated into the course of, for example, a blood tubing set. The fluid circuit comprises a gas separator. When hemodialysis is mentioned, similar, closely related extracorporeal blood treatment methods such as hemodiafiltration are always also meant.In an example extracorporeal blood circuit for hemodialysis, there is a blood line that runs from an arterial vascular access to a venous vascular access. Blood flows from the patient through the arterial vascular access into the extracorporeal blood circuit, and the blood flows back to the patient through the venous vascular access. Downstream of the arterial vascular access, there is a section of blood line that can be inserted into a blood pump designed as a roller pump. Downstream of the pump, a dialyzer is connected to the circuit for mass transfer. Downstream of the dialyzer, there is a gas separator in the extracorporeal blood circuit. This is where air contained in the blood, in particular, but also other gases, are separated. Downstream of the gas separator is a valve, and downstream of it is the venous vascular access. Optionally, there can be an air bubble detector between the gas separator and the valve.Optionally, the gas separator can be designed as a gas separation chamber. In one embodiment, the device according to the invention is arranged between the dialyzer and the gas separator to support the improved separation of gas bubbles from a medical fluid during dialysis for renal replacement therapy. Preferably, it is arranged, for example, approximately 20 cm of the tubing length upstream of the gas separator on a straight piece of tubing. This advantageously ensures good coupling by ensuring that the tubing runs straight in the coupling area, and at the same time the blood tubing set can retain the usual curve radii on the blood tubing that typically occur when inserted into a dialysis machine - e.g., a route of the blood tubing between the dialyzer and the gas separator in which at least two curves occur.Another advantage is the arrangement in a section of the blood line that is only a short distance and has only a few elements separating it from the return point, the venous patient access. However, the device according to the invention should be located either upstream of the gas separator or arranged on the gas separator itself in order to advantageously improve the separation of gas bubbles by the gas separator. The removal of gas bubbles from the blood before it is returned to the patient. Other advantages of such an arrangement are ergonomic advantages and the fact that no or only minor adjustments to the blood line set or treatment machine are required to enable the device to be arranged in this way. Another, alternative preferred embodiment is designed such that it is arranged on the blood line immediately upstream of the gas separator. The above-mentioned advantages apply in the same way.A blood tube for hemodialysis typically has an outer diameter of 6.8 mm and an inner diameter of 4.3 mm. The device is preferably designed as a so-called clamp-on device. This means that the device can be placed around a blood tube or another section of a fluid circuit (such as a chamber, a cuvette, or a section of pipe) like a cuff that completely or partially encloses the tube, whereby coupling of the ultrasound signal is enabled by pressing it against the section of the circuit. The device according to the invention is therefore designed as a clamping cuff for arranging the device on a section of a fluid circuit. Alternatively, the device in the clamp-on design can also be designed like a clamp or a partial ring.A clamp-on device according to the invention can be designed as a component of a blood treatment machine, such as a dialysis machine, with the clamp-on element preferably protruding from the front of the machine housing, for example, where other elements for connecting to the blood tubing set—such as clamps, air bubble detectors, or pressure sensors—are also arranged. In an alternative embodiment, a clamp-on device according to the invention is designed as a separate device from a blood treatment device. Particularly advantageously, no adaptation of the blood treatment device is required.A clamp-on device designed as a small, portable device can be simply arranged on the tube upstream of a gas separator, allowing the inventive combination of numerous small gas bubbles into significantly fewer but larger gas bubbles, thus advantageously increasing the gas separation effect of the gas separator. This mode of operation requires no further connection between the fluid-conveying device, a blood tubing set, and the device according to the invention. In particular, no data communication is required. The effect of the device according to the invention in improving the removal of gas bubbles from the fluid is due to the coupling of ultrasonic vibrations into the fluid.A clamp-on device can also be designed as a separate device in such a way that it has an electrical energy storage device such as an electrical accumulator, i.e. a rechargeable electrical storage battery, or a battery compartment for arranging, for example, commercially available electrical batteries - rechargeable and / or non-rechargeable. This makes retrofitting particularly advantageous and very simple because, without any annoying cables, the clamp-on device can be easily attached to a section of a circuit for a medical fluid that is to be freed of gas bubbles. In a further development, the device is configured so that the rechargeable battery can be charged via wireless charging. As an alternative to designing the device with an energy storage device, it is also conceivable to create an energy supply via a wired external power supply.

[0032] As an alternative to a clamp-on device, the device according to the invention can also be designed, according to preferred embodiments, such that it is a firmly connected part of a device which is operated in conjunction with a circuit of a medical fluid, such as a hemodialysis machine or a mixing device for dialysis concentrate.

[0033] A device according to the invention can, for example, be adapted to be arranged on a section of a fluid circuit, wherein the section is designed as a tube or blood line and has an inner diameter in the range of 3 mm to 15 mm. Furthermore, a device according to the invention can be adapted, for example, to be arranged on a section of a fluid circuit that is designed as a venous chamber with a diameter of up to approximately 30 mm.

[0034] For the functioning of the invention, it is not crucial how far upstream of the gas separator the device with ultrasonic transducer is arranged, since the gas bubbles brought together in the section of the liquid circuit where the device is arranged do not break down into individual small bubbles again, but are transported further through the liquid circuit as fewer but larger bubbles.

[0035] A device according to the invention can, for example, be adapted to be arranged on a section of a liquid circuit which is part of a dialysate circuit or a circuit in a dialysate mixing system or a dialysate concentrate mixing system, wherein the section is designed as a hose or as a gas separator.

[0036] In one embodiment of the device, the fluid circuit is an extracorporeal blood circuit used in ECMO therapy. Blood tube diameters of up to approximately 12 mm are typically used, to which the device can be adapted.

[0037] As an alternative to being arranged on a venous chamber (with or without a cyclone), the device according to the invention can also be adapted to be arranged on a gas separator in a blood cassette with a venous chamber, or to be adapted to be arranged on a gas separator with a blood level chamber, as is known from hemodialysis applications. The device according to the invention can also be adapted to be provided on a gas separator with a flow edge over which the gas separator is flowing during operation. The invention can be combined with all of these gas separator principles.

[0038] An embodiment of the invention is adapted so that the device according to the invention can be arranged on a section of a circuit of a medical fluid which is designed with a hemodialysis blood tubing set, and the ultrasonic vibrations can be coupled into the medical fluid in the blood tubing set.

[0039] One embodiment of the invention is adapted so that the ultrasonic vibration according to the invention can be coupled into the medical fluid at a section of the fluid circuit designed as a rectangular cuvette. With such a rectangular design, additionally with plane-parallel ultrasonic transducers, it is particularly advantageous to easily calculate where standing waves develop in the interior depending on the exciting ultrasonic frequency, because the approximation of the calculation under the assumption that the ultrasonic vibrations propagate like plane waves yields good results. Suitable materials for the rectangular cuvette include quartz glass or plastic.

[0040] One embodiment of the invention is adapted so that the ultrasonic vibration according to the invention can be coupled into the medical fluid at a section of the fluid circuit which is designed as a cylindrical jacket-shaped tube. The tube can be made of borosilicate, for example, and have an outer diameter of 6 mm and an inner diameter of 4 mm. Unlike with a rectangular cuvette, standing waves arise in a cylindrical almond-shaped section which are not plane waves, but rather - due to the curvilinear geometry and the fact that the tube also oscillates as a whole - standing waves of a non-plane shape. Gas bubbles to be separated advantageously collect centrally in the region of the longitudinal axis or concentric cylinder jacket regions.

[0041] In all embodiments of the invention, an ultrasound gel for transmitting the ultrasound can optionally be arranged between the ultrasound transducer, for example, a piezoelectric ultrasonic oscillator, and the wall at the section of the fluid circuit. This particularly advantageously enables the ultrasonic vibrations to be better transmitted or coupled into the fluid.

[0042] Preferred embodiments with a fixed excitation frequency for the ultrasonic vibrations, adapted to a fluid circuit of a medical fluid, which may be dialysis water, blood, dialysate, dialysate concentrate, saline solution or water with other salts such as sodium sulfate, can be adapted as follows: • Adapted to the arrangement of the ultrasonic transducer on a rectangular cuvette made of quartz glass and the control unit configured for an ultrasonic frequency of 535 kHz, • Adapted to the arrangement of the ultrasonic transducer on a cylindrical tube made of borosilicate and the control unit configured for an ultrasonic frequency of 233 kHz, • Adapted to the arrangement of the ultrasonic transducer on a plastic chamber with a rectangular profile and the control unit configured for an ultrasonic frequency of 519kHz.

[0043] Preferably, the device according to the invention is designed so that it is non-invasive, ie nothing from the device other than the ultrasonic vibrations penetrates into the fluid circuit, does not damage the walls of the fluid circuit, does not require any changes to the fluid circuit.

[0044] According to a preferred embodiment, the device according to the invention is configured such that the cavitation number cannot be reached, i.e. in particular no hard cavitation occurs. The ultrasonic transducer and control unit are coordinated such that, at the given temperature, the given liquid and the given geometry, the coupled power does not reach the cavitation number and, in particular, the ultrasonic transducer with the generated ultrasonic oscillations does not cause hard cavitation in the medical liquid. The frequency of the ultrasonic excitation is a decisive factor for the occurrence of hard cavitation. In a simple embodiment of the device according to the invention, configured to prevent the occurrence of hard cavitation, the control unit has a circuit for frequency-dependent power limitation.Cavitation is harmful not only to technical components but can also damage components of the fluid. Especially with vibration excitation in burst mode, care must be taken to ensure that cavitation does not occur, even at the moment of the most intense coupling during a burst. In a further development of this embodiment, the heating of the ultrasonic transducer during operation is taken into account with regard to how this locally changes the temperature of the fluid. This temperature change is taken into account in the design so that cavitation does not occur. The cavitation threshold for higher frequencies is higher. Therefore, increasing the minimum frequency of the device can be a suitable way to avoid reaching the cavitation number at higher temperatures.

[0045] The device according to the invention is preferably configured such that the frequency of the ultrasonic oscillations is limited such that at least one node or antinode of the standing wave forms inside the liquid in the liquid circuit. The frequency of the ultrasonic oscillations is set such that a lower limit for an ultrasonic oscillation frequency is determined depending on the geometric shape of the section of the liquid circuit where the ultrasonic transducer is arranged, the depth of the section behind the ultrasonic transducer, and the propagation speed in the liquid, so that at least one antinode / node of a standing wave of the ultrasonic oscillation forms inside the liquid. Nodes form at positions where a wave has a zero crossing. Antinodes form at positions of amplitude maxima.The positions of zero crossings and amplitude maxima can be determined using the wavelength of the oscillation. The following relationship applies between wavelength, frequency, and phase velocity of wave propagation in the medium—here, the speed of sound in the liquid: The wavelength is determined by dividing the phase velocity by the frequency. By determining a lower limit for an exciting ultrasonic oscillation, it is advantageously ensured that the inventive accumulation and concentration of gas bubbles has a concentration region in the liquid.

[0046] Preferably, the device according to the invention is designed such that it can be arranged in the liquid circuit such that the nodes and antinodes of the standing wave are arranged along a line that runs essentially perpendicular to the direction of flow of the liquid in the section of the liquid circuit. It has been shown that this advantageously better supports gas separation.

[0047] The gas to be separated with the device according to the invention can be air or, for example, CO2.

[0048] All embodiments of the device according to the invention can optionally include means for switching the device on. This advantageously allows the device to be controlled individually and autonomously.

[0049] Further preferably, the ultrasonic transducer and control unit of the device according to the invention are configured to generate a node and an antinode of a standing wave in the liquid. This ensures that if gas bubbles with different properties (such as significant size differences or composition) accumulate at the different features of the standing wave—one type at the antinodes, one type at the nodes—the removal of both types of gas bubbles can be supported. According to one aspect, the device according to the invention comprises an electrical power supply that supplies the ultrasonic transducer and the control unit with electrical power. Such a power supply is optional for all embodiments. It advantageously enables autonomous operation and simplified retrofitting to existing fluid circuits.

[0050] According to one aspect, the device according to the invention is configured such that it can be arranged externally on the wall of a fluid circuit, so that the ultrasonic transducer can couple ultrasonic vibrations through the wall of the fluid circuit into a medical fluid which is located in the fluid circuit. Short description of the drawing

[0051] Embodiments of the device are described below with reference to the drawing. The drawing shows: Fig. 1 a schematic representation of an embodiment of the device according to the invention for supporting the separation of gas bubbles from a medical fluid for dialysis circulating in a fluid circuit with a gas separator, Fig. 2 shows a section of a photographic image of the device according to the invention in action, wherein initially chaotically distributed gas bubbles have been agglomerated and concentrated in defined spatial regions in the medical fluid by the coupling of ultrasound, Fig. 3 a schematic representation of an extracorporeal blood circuit with a blood tubing set for use in hemodialysis treatment, wherein the positions for arrangement are indicated for several embodiments of the device according to the invention.

[0052] Fig. 1 shows a schematic representation of an exemplary embodiment of the device 100 according to the invention for supporting the separation of gas bubbles B from a medical fluid L circulating in a fluid circuit C with a gas separator X. The medical fluid L is intended for use in dialysis treatments for renal replacement therapy. The further design of the fluid circuit C is left open except for the device 100 according to the invention and the gas separator X arranged downstream thereof. The device 100 has at least one ultrasonic transducer 10 for generating ultrasonic vibrations. Only one ultrasonic transducer 10 is shown here, which is indicated as a plate-shaped element. However, other shaped ultrasonic transducers 10 are also conceivable, such as wedge-shaped, annular, or forming parts of rings, or even thin layers.Embodiments with two or more ultrasonic transducers 10 are also part of the invention. Between the ultrasonic transducer 10 and the wall W of the fluid circuit C, an optional layer 70 is shown for better coupling of the ultrasonic transducer 10 to the wall W, which layer can be designed, for example, as ultrasonic gel 70. There are also embodiments of the invention without a separate ultrasonic coupler 70 or with other coupling materials. Also shown is a control unit 20, which is configured to control the ultrasonic transducer 10 such that it generates ultrasonic vibrations. The device 100 comprises the control unit 20, and a cable is indicated as an exemplary connection between the control unit 20 and the ultrasonic transducer 10. Furthermore, the device 100 according to the invention has an electrical power supply 30, which supplies the ultrasonic transducer 10 and the control unit 20 with electrical power.A cable is indicated as an exemplary connection between control unit 20 and power supply 30. Furthermore, the device 100 according to the invention has means 50 for arranging the device 100 on a section of the fluid circuit C. As an example of such means 50 for arranging, a type of clamp or annular sleeve is shown here, which presses the ultrasonic transducer 10 onto the wall W of the fluid circuit C and thus effects a coupling suitable for coupling the ultrasonic vibrations generated by the ultrasonic transducer 10 into the wall W and through the wall W into the fluid L in the fluid circuit C.As described above, an inventive effect of the device 100 occurs in that the accumulation of gas bubbles B in defined spatial regions leads to improved separation of the gas bubbles B in a gas separator X, because the gas bubbles B are each larger, having arisen from several smaller bubbles B that have been in close proximity due to the concentration in certain regions. Therefore, the schematic representation shows a gas separator X downstream of the device 100 according to the invention. To visualize this technical effect of the device 100 according to the invention, gas bubbles B are indicated as circles in the section US of the liquid circuit C shown, where the ultrasonic transducer 10 is arranged. Although all bubbles B are drawn approximately the same, this is not the intended purpose of the representation.Rather, the bubbles B to the right of the hourglass-shaped symbol T*, i.e., on the inlet side D of the liquid L into the device 100, are actually smaller and more numerous. In the illustration, the liquid L flows in the circuit C from right to left through the image. Liquid here represents a fluid that, in terms of mass, essentially consists of a liquid, but which also contains gas bubbles. The hourglass-shaped symbol T* represents the transition between the disordered state on the inlet side D, where the gas bubbles B are still randomly distributed in the liquid L, and the ordered state, where the gas bubbles B are collected and concentrated in predetermined spatial regions, as can be observed on the outlet side A of section US of the liquid circuit. In reality, the concentration process and the spatial displacement occur continuously, and the hourglass symbol T* merely serves as a simplified schematic representation.The continuous course of the ordering effect of ultrasonic vibrations can be seen in . Fig. 2, where a photo of a test setup taken with a high-speed camera can be seen. Ultrasonic transducer 10 and control unit 20 are tuned such that the ultrasonic transducer 10 can at least temporarily generate a standing wave in the medical fluid L with the generated ultrasonic vibrations, so that at least one wave crest and / or one wave trough of the standing wave forms inside the fluid L in the fluid circuit C. Indicated here is a spatial region running essentially horizontally through the center of the shown section US of the circuit, where the ultrasonic transducer 10 is arranged, where gas bubbles collect when the ultrasonic transducer is active and couples ultrasonic vibrations into the fluid. For simplification, a representation has been chosen in which only one spatial region exists where the gas bubbles collect, i.e.it is only a crest / trough of a standing wave inside the fluid circuit section US.

[0053] Fig. Figure 2 shows a photograph of a section US of a circuit C of a medical fluid L, to which a device 100 according to the invention is applied to assist in the separation of gas bubbles B contained in the medical fluid L. The photograph was taken with a high-speed camera. As shown in Fig. 1, the liquid L also flows from right to left through the image. The entire image area shown lies spatially between ultrasonic transducers 10 of a device 100 according to the invention, which were active at the time of recording. The effect of the device is clearly visible in the fact that in the inlet region D of the line section US, the gas bubbles B are randomly distributed, numerous, and smaller, whereas in the outlet region A of the line section US, where they were aligned over a longer period of the standing wave of the ultrasonic oscillation of the device 100 according to the invention, they are collected in spatial regions defined by the standing wave. It is also evident that the bubbles B are generally fewer in number but individually larger. This is due to the fact that several bubbles were adjacent to one another after concentration in spatial regions with ultrasound and fused with one another.The now fewer but larger gas bubbles B are easier to remove. For illustrative purposes, a medical fluid L was shown here, which, unlike blood L, is transparent. It is a mixture of dialysis water and dissolved salts, similar to dialysate or dialysate concentrate. With such aqueous solutions, such as isotonic saline solution with dissolved sodium chloride, or a medical fluid L consisting of water and dissolved sodium sulfate, photographs can be taken of the displacement of the gas bubbles B caused by the ultrasonic vibrations due to the fluid's transparency.

[0054] Fig.3 shows a simplified schematic sketch of a circuit C of a medical fluid L with two possible positions for arranging a device 100 according to the invention for supporting the separation of gas bubbles B from the fluid L. Shown is a simplified fluid circuit C, such as is used, for example, for renal replacement treatment in hemodialysis. This means that the medical fluid L here is blood L, and a dialyzer F is connected to the circuit C for blood purification. Blood from the patient P flows via inlets into the extracorporeal blood circuit C, the flow direction of which is indicated by dotted arrows. A blood pump R designed as a roller pump R pumps the blood L in the circuit C past a section where heparin H can be administered and on to the dialyzer F.

[0055] Downstream of the dialyzer F, a first possible alternative for arranging the device 100 according to the invention is provided as a dashed box 100 on a straight line section of the blood tubing set. The means 50 for arranging the device 100 can be, for example, a clamp, a cuff, a ring part with an open section, a hose baffle, or even an adhesive. Downstream of the dashed box 100 for arranging the device 100 is a gas separator X. Here, the gas separator X is designed as a conically tapered venous drip chamber X. As a further embodiment of the invention, the device 100 can be applied to the venous drip chamber X like a conically shaped ring 100 or partial ring 100, or a cuff 100, again shown in dashed lines as a conical ring 100.The inventive effect of supporting gas separation also occurs when the ultrasonic vibrations are coupled into the liquid L in the gas separator X. Downstream of the gas separator X is a valve V and finally the second access to the patient P, where the blood L circulating in the circuit C is returned. A sensor for detecting gas bubbles can be arranged between the gas separator X and the valve V. Such a sensor is also called an air bubble detector or air detector because in many applications the primarily detected gas is air. The arrangement of such an optional sensor downstream of the gas separator is conceivable for the invention not only in the context of hemodialysis but also for all other embodiments of the invention.With the air bubble sensor, it can also be demonstrated that the presence of ultrasonic vibrations generated by the device according to the invention improves gas separation because significantly fewer gas bubbles then reach the detector.

Claims

[1] Device (100) for assisting the separation of gas bubbles (B) from a medical fluid (L) which circulates in a fluid circuit (C) comprising a gas separator (X), the medical fluid (L) for extracorporeal blood treatment; ◯ the device (100) comprising: ▪ at least one ultrasonic transducer (10) for generating ultrasonic vibrations; ▪ a control device (20) configured to control the ultrasonic transducer (10) to generate ultrasonic vibrations; ▪ and means (50) for arranging the device (100) on a portion of a fluid circuit (C); ◯ wherein the device (100) is designed so that it can be arranged upstream of the gas separator (X) on a section of the liquid circuit (C) or on the gas separator (X) itself; ◯ wherein the device (100) is configured such that the ultrasonic transducer (10) can couple ultrasonic vibrations into the medical fluid (L) located in the fluid circuit, ◯ wherein the ultrasonic transducer (10) and the control unit (20) are tuned such that the ultrasonic transducer (10) can at least temporarily generate a standing wave in the medical liquid (L) with the generated ultrasonic oscillations, so that at least one node and / or one antinode of the standing wave forms inside the liquid (L) which is located in the liquid circuit (C), ◯ wherein the device (100) is configured such that the ultrasonic vibrations generated by the ultrasonic transducer (10) do not generate hard cavitation in the medical liquid (L), ◯ wherein the device (100) is designed such that it can be arranged on the liquid circuit (C) such that the nodes and antinodes of the standing wave are arranged along a line which is substantially perpendicular to the flow direction of the liquid (L) in the section of the liquid circuit (US). [2] Device (100) according to claim 1, wherein antinodes and nodes of the standing waves are stationary and thus allow accumulation of air bubbles at a fixed distance from the wall of the section. [3] Device (100) according to claim 1, designed to be arranged on a straight section (US) upstream of a gas separator (X) in a circuit (C) of a medical liquid (L). [4] Device (100) according to claim 1, designed to be arranged on a straight section (US) with only one inlet opening and one outlet opening upstream of a gas separator (X) in a circuit (C) of a medical liquid (L). [5] Device (100) according to one of claims 1 to 4, which is designed as a clamping sleeve for arrangement on a section of the liquid circuit (C). [6] Device (100) according to one of claims 1 to 5 adapted to be arranged on a section (US) of an extracorporeal blood circuit (C). [7] Device (100) according to claim 6, wherein the control unit (20) and the ultrasonic transducer (10) are configured to couple ultrasonic waves into blood in a frequency range which is suitable for concentrating gas bubbles (B) contained in the blood in a predetermined spatial region of the blood volume. [8] Device (100) according to claim 6 or 7, adapted for use in an extracorporeal blood circuit (C) comprising a gas separator (X) designed as a venous chamber. [9] Device (100) according to one of claims 8, configured for arrangement on a substantially conically shaped venous drip chamber (X). [10] System for dialysis treatment comprising a blood tubing set with a gas separator (X) and a device (100) for assisting gas separation according to one of claims 1 to 9, which is arranged upstream of the gas separator (X) or on the gas separator (X). [11] A system for extracorporeal lung support comprising an ECMO blood tubing set with a gas separator (X) and a device (100) for assisting gas separation according to one of claims 1 to 9, which is arranged upstream of the gas separator (X) or on the gas separator (X). [12] Mixing machine for preparing dialysate or dialysate concentrate for renal replacement therapy, comprising a device (100) for assisting gas separation according to one of claims 1 to 5. [13] Mixing machine according to claim 12, comprising a density measuring device for measuring the mixture during the mixing process, wherein the device (100) according to the invention for assisting gas separation and the gas separator (X) are arranged upstream of the density measuring device. [14] Mixing machine according to claim 13, wherein the density measuring device and the device (100) for assisting gas separation are located in a bypass line parallel to the main mixing line.

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