NZ601028B - Carbon Dioxide Gas Removal From a Fluid Circuit of a Dialysis Device - Google Patents

Abstract

Patent 601028 A dialysate regeneration system is disclosed with urease, a dialyzer, and a housing with an external wall, where the external wall is exposed to atmosphere and comprises a material that passes gas but does not pass liquid and where the housing is positioned between the urease and dialyzer. dialyzer.

Description

CARBON DIOXIDE GAS REMOVAL FROM A FLUID CIRCUIT OF A DIALYSIS DEVICE CROSS-REFERENCE The present application relies on US. Provisional Application No. 61/021,965, filed on y 18, 2008, for priority and is herein incorporated by reference.

FIELD OF THE INVENTION The present invention generally relates to the field of alysis, and more specifically to a method and system of efficiently removing carbon e, or any gas, from the dialysatc circuit of a dialysis System without mising the solute-removal performance of a hemodialysis device.

OUND OF THE INVENTION Closed loop multi-pass sorbent based hemodialyzers have the advantage of being portable and compact while being able to rate dialysatc using a plurality of sorbents.

Typically these sorbents are used in disposable cartridges/canisters and comprise sorbent ition layers similar to those used in prior systems, Such as urease, zirconium phOSphate, s zirconium oxide and activated carbon. As spent dialysatc sing urea, diffused from impure blood in the dialyzer, passes through prior art sorbent cartridges, carbon dioxide and ammonia are produced as two unwanted byproducts of the chemical reactions. While ammonia is adsorbed in zirconium-based cartridges, carbon dioxide is not captured, mixes in the dialysate, and manifests as carbon dioxide bubbles in the dialysate circuit. Large amounts of carbon dioxide leave the liquid phase and interfere with the smooth g of dialysatc. In addition other dissolved gases may exit from the liquid phase during processing adding to the volume of gas in the system.

Accordingly, there is a need for a degassing device that can remove unwanted carbon dioxide, and other gases, from the dialysate circuit. The degassing device needs to be particularly suitable for a le hemodialyzer, where the orientation ofthe dialyzer should not disrupt or degrade the efficiency of the degassing device. At the same time, the degassing device needs to be small in size, light and low cost so that it can be a disposable component.

SUMMARY OF THE ION It is an object of the present ion to provide a degassing device that efficiently vents or removes carbon-dioxide, and other gas, bubbles, from dialysate t, that are produced from urea split by urease in the sorbent system of a is device.

It is also an object of the present ion to have a degassing device that is particularly le for a portable hemodialyzer, such as one configured as a portable artificial kidney (PAK), where the orientation of the dialyzer should not disrupt or degrade the efficiency of the degassing device.

Accordingly, it is another object of the present invention the degassing device needs to be small in size, light and low cost so that it can be a disposable component.

In one embodiment, the degassing device of the present invention comprises two annular concentric rings that make up inner and outer gs. While the upper end of the inner housing is open, the upper end of‘ the outer housing is sealed with a microporous, hydrophobic membrane that allows gases to pass through but does not allow liquids to pass. A gap is maintained between the open upper end of the inner housing and the membrane. The annular concentric housings define an inner first chamber and an outer second chamber. During dialysis, dialysate mixed with carbon-dioxide enters into and moves up the outer second chamber causing carbon dioxide to be automatically separated from the dialysate thereby forming small carbon dioxide bubbles that are vented out through the microporous hobic membrane, while the dialysate overflows into the inner first chamber and moves out of the degassing device.

In one embodiment, the present ion is directed to a degassing device comprising a) a first inner chamber, b) a a first housing having an inlet, a first length and an inner wall defining second housing oned within said first inner chamber in an annular relation to the first housing wherein the second housing has an outer wall, an outlet, at second length and an inner wall defining a second inner chamber, wherein the second length is less than the first length, and wherein a space between the first length and second length defines a gap, c) a flowpath through said degassing device wherein said flowpath is defined by the inlet, the gap, and the outlet, and d) a hydrophobic membrane oned proximate to said gap.

Optionally, the degassing device has a gap between about 0.02 inches and 0.1 inches, has the second housing a space between said inner wall of the first housing and outer wall of between about 0.04 to 0.24 inches, and is capable of removing substantially all gas from dialysate at flow rates between 20 ml/min and 450 ml/min. Optionally, the second housing includes a filter, the filter is approximately 0.1 to 0.4 inches thick, and the hydrophobic membrane is oned a distance from the second housing wherein the distance is equal to the gap.

Optionally, the inlet and outlet are positioned on a same side of said degassing device.

Fluid having gas flows into the first inner chamber through said inlet, flows through said gap, flows past the hydrophobic membrane, flows into said second inner r. and flows through said , n gas passes through the hobic membrane and wherein liquid does not pass through said hydrophobic membrane. Optionally, a dialysate circuit includes a dialysate regeneration system with urease, a dialyzer, and this degassing device, which is positioned between the urease and the dialyzer.

In another embodiment, the present invention is directed to a dialysate circuit including a) wherein a dialysate regeneration system including urease, b) a housing including an external wall, the external wall is exposed to atmosphere and wherein the external wall includes a material that wherein said housing is positioned between passes gas but does not pass liquid, and c) a dialyzer, the urease and dialyzer. The housing preferably is just a tube, a section of tubing, or a coil of tubing with nothing internal to the tube (the inner chamber defined by the external walls is devoid of any ures or ctions) and with the external wall exposed to atmosphere, or at least to an area external to the degassing device.

Optionally, the dialysate t es a membrane that is between 0.5 feet to 16 feet long, has an outer diameter of about 0.1 to 0.45 , or has an inner diameter of about 0.1 to 0.4 inches. Optionally, the housing (degassing ) removes substantially all gas from the dialysate at or below 10 psi. at flow rates from about 20 ml/min to 200 ml/min or at internal pressures Optionally, the dialysate regeneration system includes charcoal and the housing is positioned between the charcoal and dialyzer.

BRIEF DESCRIPTION OF THE DRAWINGS These and other features and advantages of the present invention will be appreciated, as considered they become better understood by reference to the following detailed description when in tion with the accompanying drawings, wherein: Figure 1 is a schematic illustration of an ment of an ary le dialysis system; Figure 2 is a schematic illustration of an exemplary process flow for performing dialysis; Figure 3 is a m depicting an exemplary embodiment of the degassing device of the t invention; Figure 4 is a diagram depicting another ary embodiment of the degassing device of the present invention; Figure 5a depicts a scaled up degassing device in relation to a dialyzer; and Figure 5b depicts another view of a degassing device sing material that passes gas but not liquid.

DETAILED DESCRIPTION OF THE INVENTION While the present invention may be embodied in many different forms, for the purpose of promoting an understanding of the invention, reference will now be made to the embodiments rated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended.

The present specification incorporates by reference co-pending, co-assigned US. Patent ation Nos. 12/324,924, 12/210,080, 12/238,055, 12/237,914, 12/249,090, and 12/245,397 and third party owned US. Patent No. 6,960,179, U.S. Patent Application No 10/940,862, /846,618, 1 ”427,267, 11/500,572 and PCT Application No. PCT/USO6/30923.

Closed loop multi-pass sorbent based is systems regenerate dialysate for reuse by passing spent dialysatc through a regeneration section comprising a plurality of sorbent cartridges and suitable additives. A l sorbent cartridge system comprises a urease cartridge, and an activated carbon a zirconium phosphate cartridge, a hydrous zirconium oxide cartridge cartridge. Those of ordinary skill in the art will recognize that these sorbents are similar to the sorbents employed by the commercially available REDYTM System.

As spent ate passes through the REDYTM sorbent system the conversion of urea to ammonium carbonate, the exchange of ammonium ions for en ions, and the reaction of the hydrogen ions with carbonate in the sorbent system, produces substantial amounts of carbon dioxide. These large amounts of carbon dioxide that leave the liquid phase and the ensuing bubbles interfere with smooth pumping of dialysate and therefore need to be removed from the system. In addition, other gases may leave the liquid phase and, together with the carbon dioxide, presents bubbles that need to be removed.

Accordingly, the present invention is a degassing device that functions to remove carbon dioxide or any other gas from closed circuit dialysis s. The degassing device ofthe present invention is suitable for functioning in any orientation apart from being small in size and low cost enough to be disposable thus eliminating the need for periodic cleaning and sterilization.

Figure 4 shows one ment ofthe ing device 400 of the present invention comprising two annular cylindrical housings 405, 410. The housings 405, 410 are concentric.

The upper end of the inner housing 405 is Open and forms a circular rim 404. The upper end of the outer h0using 410 is sealed with a microporous, hydrophobic membrane 415 that allows The hydrophobic membrane can be of gases to pass through but does not allow s to pass.

GoreTM hydrophobic any suitable type, including a PALLTM hydrophobic membrane, a membrane, including model numbers SMPL-MMT317, MMT-RD-OOl, -OOZB and MMT-RD-OOZA. A gap exists between the upper end of the inner housing 405 and the hydrophobic membrane sealed upper end of the outer g 410. The gap is sized to allow gas bubble passage within the gap. Typical dimensions from .002” to .025”, and more particularly defines from 0.05” to 0.15”, have been used in the preferred embodiment. The inner housing 405 inner and the outer housings an inner first chamber 401 while the concentric region between the orifice at 405, 410 constitutes a second chamber 411. An inlet tube 420 is connected to an inlet the first the second chamber 411 while an outlet tube 425 is connected to an outlet orifice at chamber 401.

In one embodiment, the inner first housing 405 has a discontinuous internal surface to provide areas upon which gas within the liquid can nucleate, collect, form bubbles, and migrate In one embodiment, the inner first housing up and h the top hydrophobic membrane. comprises a filter membrane which is approximately 0.1 to 0.4 inches thick (more particularly 0.25 inches). has an inner diameter of 0.5 to 1.5 inches (more particularly 1 inch), and an outer diameter of 0.5 inches to 2.5 inches (more ularly 1.5 inches). In another embodiment, the 405 and hydrophobic ne 415 is about 0.02 gap at the top, n the inner first housing first housing 405 to 0.1 inches (more particularly 0.064), the gap n the outside of the inner and the inner wall of the outer housing 410 is about 0.04 to 0.24 inches (more particularly 0.141 inches), and there is no gap between the inner first housing 405 and the base ofthe degassing device 400. In one embodiment, the degassing device 400 has a height of l to 5 inches (more particularly three inches) and an outer diameter of .5 to 3 inches (and more ularly 1.75 inches). The degassing device is able to substantially remove all gas from the dialysate at a flow of 20 ml/min to 450 mein (more particularly 250 ml/min).

During hemodialysis, dialysate mixed with carbon dioxide enters the inlet tube 420 and overflows into the inner first chamber 401 passes into the concentric second chamber 411, through the gap and flows out the outlet tube 425 connected to the first chamber 401. During this mixture is fed h the inlet tube 420, the mixture process as the dialysate and carbon dioxide small moves upwards causing carbon dioxide to be ted from the dialysate thereby forming carbon dioxide bubbles that are vented out through the microporous hydrophobic membrane 415.

The ate-free carbon e moves through and out the outlet tube 425. The ing chamber can be placed at various locations in the dialysis flow, but preferably in the flow stream immediately after the dialysate is subjected to filtration in sorbcnt canisters, depicted as 520 in Figures 5a and 5b. It should be appreciated that, regardless of where the degassing chamber is placed in the system, it should be vertically ined, with ne 415 at the top of the device, in order to properly direct air bubbles h and out of the device 400.

Figure 1 shows a closed multi-pass hemodialyzer configured as a wearable dialysis device 100 that, in one embodiment comprises a shuttle pump or dual-channel pulsatile pump 105 to propel both blood and dialysate h the device 100, a high flux, polysulfonc er 110 with 0.6 square meter membrane surface, a dialysate regeneration system 1 15 consisting of three specially designed canisters containing a plurality of sorbcnts, such as 122, zirconium, phosphate, 123, activated charcoal, and 121 urease, as well as reservoirs of electrolyte additives 1 16 and a pH-control t (not ; micro-pumps (not shown) for delivering heparin and a reservoir to the blood circuit, additives including Mg, Ca, K and sodium bicarbonate 118, for excess ultrafiltrate 1 19, all at pre-specified flow rates; and a blood-leak/bubble detector and 120. pump power~up and alarm/shutoff system The main pump 105 uses a 3-Watt DC micro motor. The gear-head accommodates an oscillating mechanism, which in conjunction with a dual-channel flow cartridge, allows simultaneous pulsatile flows of both blood and the dialysate at controllable rates of 40-100 ml/min per channel. The cartridge allows both blood and dialysate to flow either in the same direction or in opposite directions, depending on the configuration/location of the other system components. It is preferred, however, that, when one channel propels fluid out of its compressible chamber, the other l fills its ssible chamber, allowing for peak pressure in one channel at the same time the pressure in the other channel is at its lowest level.

In one embodiment, the t ers of the t invention are filled (in order of dialysate flow) with approximately the following amounts of sorbents: 121, Canister #1: 50 grams of urease, followed by thin filter paper, and then 335 grams of ium phosphate; 122, Canister #2: 335 grams of zirconium phosphate, followed by thin filter paper, and then 50 grams of s zirconium oxide; and 123, Canister #3: 150 grams of activated . chassing device 124 is located in the fluidic circuit between urease canister 12], and ium Phosphate er 122. Carbon dioxide gas generated by the urease — urea reaction in canister l2l is removed by the degassing device 124, before the dialysate fluid is passed into canister 122. Other positioning of the degassing device, within the circuit, is possible, in particular after all the sorbent canisters, ing the charcoal canister, 123 as shown in figure 5a. It should be appreciated that the degassing device 124 could be located afier canister 122 and before canister 123 or after canister 123 and before dialyzcr 110.

Another embodiment of the degassing device 124 is shown in Figures 5a and 5b. The device 520 consists of a coil of gas pcrmcablc tubing, such as that manufactured by GORE, Inc., tubing part number MMT-RD-OOZA. In Figure 5a, the degassing device 520 is connected, via tubing 522, to a dialyzcr. Figure Sb depicts the degassing device 520 connected to tubing 522.

This tube is 9 feet long, has an outside diameter of approximately 0.275” and a wall thickness of approximately .025”. The coil assembly is approximately 2.25” outside diameter and approximately 2.5” in height In this embodiment, the entire outer wall of the outside chamber is gas permeable. Because gas can now diffuse through any portion of the outer wall, not just the in nearly any top as in the embodiment disclosed in Figure 4, the device can be placed orientation, making it well suited for use with a wearable dialysis system such as that depicted in Figure 1. In one embodiment of the device the total tube length is 9 feet. This size is designed to yield an adequate surface area to provide gas l capability for a typical wearable artificial kidney operating around the 24 hours a day, seven days a week with a dialysate and blood flow rate at or below 100 ml/min. Shorter lengths of tubing (therefore possessing lower surface area) can be used for removing less gas, such as if flow rates were lowered or longer lengths can be used for increased gas removal capacity.

In operation, gas collects in a self generated pocket on the top of the many coils of the gas ble tubing in device 520. This location of the gas pocket s depending on orientation of the device. y dictating that the gas collects on whatever surface is “up” in varying orientations. Since the entire length of the device is composed of gas permeable tubing, no matter where the gas pocket collects it is able to escape. ate packaging of the lube may include long serpentine shaped runs accommodating the shape of a belt wom around the waist of a patient using a wearable artificial kidney. Thus the embodiment pictured in Figure 5b is not exclusive to the functionality of the degassing device.

The key factor is that whatever shape the device takes the fluid path be composed of a gas permeable tube of sufficient length, and therefore surface area, to remove the amount of gas desired.

In another embodiment, shown in Figure 3, the degassing device 300 is a section of a tube, a housing, a coil oftubing, or any other shape 310 that defines a chamber 325 and a flowpath 305 therein. The external wall ofthe housing 310 comprises any material 315 that will be sized so that the amount of gas passed equals or pass gas but not fluid. The material 315 must exceeds the amount of gas generated. Gas tion is a t of urea level in the patient and dialysatc flow rate. Gas passed by the ing device 300 is a product of the wall area and the of the fluid in the tube relative to the gas permeability of the tube plus the internal pressure external pressure on the tube. One ofordinary skill in the art would be able to select the appropriate material for a given application based upon the given parameters.

In one embodiment, the degassing device comprises a GORE membrane that is between 0.5 feet to 16 feet long (more ularly 9 feet long), has an outer diameter of about 0.1 to 0.45 inches (more particularly .275 inches) and an inner diameter of about 0.1 to 0.4 inches (more particularly .25 inches) and configured in any shape, including a tight coil. In one embodiment, the aforementioned degassing device 300 removes substantially all gas from the dialysate at flow tube rates from about 20 mein to 200 ml/min (more particularly 100 ml/min) and/or at internal below 5 psi). In one embodiment, the res at or below 10 psi (more particularly at or degassing device 300 is oned between a t canister (more particularly the charcoal sorbent) and the dialyzer. In one embodiment, the degassing device 300 is positioned after the urease canister and before the dialyzer.

PERFORMANCE EXAMPLE 1 Various configurations of the dialysis device 100 of Figure 1 were tested to evaluate their operational performance and, in particular, the gas removal capability of the degassing device 124 and 520. Referring to Figure 2, after priming the is device with saline, the is device 200 was connected to a large (40- to 80-litcr) reservoir 205 of properly formulated aqueous solution (referred to as “blood” here, made out of fresh zed water or spent human dialysate) accurately mimicking end stage renal disease (ESRD) typical human blood. This “blood” was designed to approximate actual human composition and contained about 50 mg/dL of BUN (Blood Urea-Nitrogen), 10 mg/dL of creatinine, 5 mmol/L of K, among other solutes.

No additives were provided and no ultrafiltration was performed; however. dialysate pH was maintained at an optimal value by a manual injection ofsodium bicarbonate in order to measure its effect on the volume of C02 produced. “Blood” and dialysatc samples were drawn every 30 s, and the samples were d for pH, BUN, and creatinine.

In one experiment, which used a Gore tube MMT-RD-OOZA, to fabricate degassing device 520, sorbent canisters were packed with 50 grams of urease, 670 grams of zirconium phosphate, 50 grams of hydrous zirconium oxide, and 150 grams of ted carbon, and operated at an e blood and dialysate flow rates of 55.6 and 43.2 mL/min, pressure reading oscillating ranges were measured to be: a) between pump and er #1: 300-400 mmHg, b) between canisters #1 and #2: 150-220 mmHg, 0) between canisters #2 and #3: 55-65 mmHg; and d) between dialyzer and pump: 2-35 1111an (rarely going below 0). The urea, measured as BUN (Blood Urea-Nitrogen) when reacted with the Urease generated C02 in amounts dictated by the flowrate and urea concentrations present. Such conditions were set up to mimic actual human dialysis. Under these test conditions the degassing device successfully removed all the C02 generated.

While there has been illustrated and described what is at present considered to be a preferred embodiment of the present ion, it will be understood by those skilled in the art that various changes and modifications may be made, and equivalents may be substituted for elements thereof without departing from the true scope of the invention. In on, many modifications may be made to adapt a particular situation or al to the teachings of the invention without departing from the central scope thereof. ore, it is intended that this invention not be d to the particular embodiment disclosed as the best mode contemplated for carrying out the invention, but that the invention will include all embodiments falling within the scope ofthe appended claims.

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Claims (9)

CLAIM :
1. l. A dialysate circuit including: a. a dialysate regeneration system including ; b. a housing including an external wall, wherein the external wall is exposed to atmosphere and n the external wall includes a al that passes gas but does not pass liquid; and c. a dialyzer, wherein said housing is positioned between the urease and dialyzer.
2. 2. The dialysate t of claim 1 or claim 2 wherein the housing includes at least one of a tube, a section of tubing, or a coil of .
3. 3. The ate circuit of claim 2 wherein the housing includes a membrane that is between 0.5 feet to 16 feet long.
4. 4. The dialysate circuit of claim 2 wherein the housing includes a membrane that has an outer diameter of about 0.1 to 0.45 inches.
5. 5. The dialysate circuit of claim 2 wherein the housing includes a membrane that has an inner diameter of about 0.1 to 0.4 inches.
6. 6. The dialysate t of any one of the preceding claims wherein the housing removes substantially all gas from the dialysate at flow rates from about 20 ml/min to 200 ml/min.
7. 7. The dialysate circuit of any one of the preceding claims wherein the housing removes substantially all gas fiom the dialysate at internal pressures at or below 10 psi.
8. 8. The dialysate circuit of any one of the preceding claims wherein the dialysate regeneration system includes charcoal and wherein said housing is positioned between the charcoal and dialyzer.
9. 9. The ate circuit as claimed in claim 1 and as substantially herein described with reference to any one of