Patent Application
20130237897
Hemodialysis is the diffusive transfer of small solutes out of blood plasma by diffusion across a selectively permeable membrane. Hemodialysis proceeds due to a concentration gradient across the selectively permeable membrane such that solutes diffuse from a liquid having a higher concentration to a liquid having a lower concentration. Hemodialysis removes toxic substances, metabolic waste, and excess fluid from the bloodstream using an extracorporeal circuit with components designed to perform ultrafiltration and diffusion on the blood. Before the blood is returned to the body, air bubbles are removed from the blood to inhibit embolisms.
Gas venting chambers for hemodialysis systems have been disclosed in the art. For example, a conventional system is disclosed in U.S. Pat. No. 7,871,391, which describes a chamber for use in an extracorporeal liquid system. The conventional system includes a semipermeable membrane at the top of the gas vent chamber that allows gas in the liquid to vent from the chamber. In such a system, it is important to minimize contact between the liquid (e.g., blood) and the semipermeable membrane. Should the blood contact the membrane, proteins present within the blood can be deposited on the membrane, thus clogging the membrane and decreasing the ability of gas (e.g., air) to exit through the membrane.
Despite the fact that there are existing systems for venting a gas from a liquid, there is a need for improved systems that are reliable, affordable, and simple to use in either a clinical setting or in the home. In particular, there is a need for an apparatus and method for venting gas from a liquid that prevents the liquid in the gas collection chamber from contacting a semipermeable membrane covering the outlet where the gas vents to the atmosphere.
In addition, normal operation of a hemodialysis machine results in gas build-up in a gas collection chamber that is vented through a semipermeable membrane. The continual release of gas through the semipermeable membrane can tend to degrade the membrane due to the pressure applied across the membrane by the gas. Thus there is also a need for an apparatus and method for prolonging the lifetime of the semipermeable membrane.
Aspects of the present invention relate to a gas venting apparatus and a method for venting gas, which are applicable to a wide variety of medical liquid delivery systems. The embodiments discussed below, however, are directed generally to dialysis, such as hemodialysis (“HD”).
In one embodiment of this invention, an apparatus for venting gas contained in a liquid flowing in a liquid flow circuit includes a gas collection chamber located within the liquid flow circuit so that liquid flows through the chamber allowing gas to separate from the liquid and establish a gas-liquid interface within the chamber. A gas vent chamber is provided at the top of the gas collection chamber through which gas within the chamber can be released. The gas collection chamber and the gas vent chamber can be a single unit. A lower detector located at either the gas collection chamber or the gas vent chamber, and an upper detector located at either the gas collection chamber or the gas vent chamber are provided. The lower detector is located below the upper detector. The lower and upper detectors are capable of detecting gas and liquid. A clamp is provided in the gas vent chamber either between the lower and the upper level detectors or above both level detectors. The apparatus also includes a control apparatus for opening and closing the clamp in response to whether the lower and upper detectors detect gas or liquid.
In another embodiment of this invention, an automated method for venting a gas contained in a liquid flowing in a liquid flow circuit includes flowing liquid into a gas collection chamber located within the liquid flow circuit so that liquid flows through the gas collection chamber allowing gas to separate from the liquid and establish a gas-liquid interface within the gas collection chamber, detecting whether liquid is present at a lower position in either the gas collection chamber or a gas vent chamber by a lower level detector for detecting gas and liquid, opening a clamp if a liquid is not present at the lower position, detecting whether liquid is present at an upper position in either the gas collection chamber or the gas vent chamber by an upper level detector for detecting gas and liquid, and closing the clamp if liquid is present at the upper position. The clamp can be located in the gas vent chamber either between the lower level detector and the upper level detector or above both level detectors.
In another embodiment of this invention, an apparatus for controlling pressure differential across a semipermeable membrane sealing an exit pathway from a gas venting chamber is disclosed. The apparatus includes a first pressure sensor that senses the pressure along an exit pathway from a gas venting chamber, a valve operably connected to a gas source, the exit pathway from the gas collection chamber, and the atmosphere, and a control apparatus connected to the first pressure sensor and the valve. The control apparatus can vary the gas source in order to vary the amount of backpressure applied across the semipermeable membrane. A gas pump or pressurized gas, such as pressurized air or nitrogen, can provide the gas source. The apparatus can further include a second pressure sensor that senses the inlet or outlet pressure. The control apparatus can compare the pressure measured by the first pressure sensor and the second pressure sensor and control the gas source so that the amount of pressure along the exit pathway is less than the pressure measured by the second pressure sensor. The pressure sensed by the second pressure sensor can be approximately 100 mmHg to approximately 500 mmHg, or approximately 100 mmHg to approximately 200 mmHg. The apparatus can further include a lower level detector located in either the gas collection chamber or the gas vent chamber, and an upper level detector located in either the gas collection chamber or the gas vent chamber. The lower level detector can be located below the upper level detector, and the lower and upper level detectors can be capable of detecting gas or liquid. The control apparatus can open the valve connection to the atmosphere when the lower level detector detects gas and close the valve connection to the atmosphere when the upper level detector detects liquid.
In another embodiment, an apparatus for controlling the pressure differential across a semipermeable membrane sealing an exit pathway from a gas venting chamber that receives liquid-releasing gas is disclosed. The apparatus includes a gas source for applying pressure to the exit pathway side of the semipermeable membrane, a valve operably connected to the gas source, the exit pathway, and the atmosphere, a first pressure sensor that senses the pressure along the exit pathway side, a second pressure sensor that detects the pressure in the gas venting chamber, and a control means connected to the first and second pressure sensors and the valve. The control means can vary the gas source in order to vary the amount of backpressure applied across the semipermeable membrane.
In another embodiment, an automated method for controlling pressure differential across a semipermeable membrane includes detecting an inlet or outlet pressure, detecting a pressure along an exit pathway, comparing the inlet or outlet pressure to the exit pathway pressure with a control apparatus, increasing the amount of pressure supplied by a gas source if the inlet pressure exceeds the exit pathway pressure by a first predetermined amount, and decreasing the amount of pressure supplied by the gas source if the inlet pressure is too close to the exit pathway pressure by a second predetermined amount.
In another embodiment, an automated method for controlling pressure differential across a semipermeable membrane includes detecting an inlet or outlet pressure, detecting a pressure along an exit pathway, comparing the inlet or outlet pressure to the exit pathway pressure with a control apparatus, opening a valve connection to the atmosphere if the inlet pressure exceeds the exit pathway pressure by a first predetermined amount, and closing the valve connection to the atmosphere if the inlet pressure is too close to the exit pathway pressure by a second predetermined amount.
In another embodiment, an automated method for controlling pressure differential across a semipermeable membrane includes detecting whether liquid is present at a lower level detector, opening a valve connection to the atmosphere if liquid is not present at the lower level detector, detecting whether liquid is present at an upper level detector, and closing the valve connection to the atmosphere if liquid is present at the upper level detector.
In another embodiment of this invention, an extracorporeal hemodialysis circuit includes arterial tubing for receiving unfiltered blood from a patient, venous tubing for providing filtered blood to a patient, a dialyzer, and an apparatus for venting gas contained in a liquid. The dialyzer and apparatus for venting gas are located within the extracorporeal hemodialysis circuit so that blood flows from the patient, through the arterial tubing, through the dialyzer, through the apparatus for venting gas, and towards the venous tubing.
In another embodiment of this invention, an extracorporeal hemodialysis circuit includes arterial tubing for receiving unfiltered blood from a patient, venous tubing for providing filtered blood to a patient, a dialyzer, and an apparatus for controlling pressure differential. The dialyzer and apparatus for venting gas are located within the extracorporeal hemodialysis circuit so that blood flows from the patient, through the arterial tubing, through the dialyzer, through the apparatus for controlling pressure differential, and towards the venous tubing.
Embodiments described herein can provide advantages in operating a hemodialysis machine. By opening and closing a clamp to control the height of a gas-liquid interface in the gas collection chamber, liquid (such as blood or saline) can be prevented from contacting the semipermeable membrane positioned at the upper portion of the gas vent chamber. By reducing the pressure differential across the semipermeable membrane, the lifetime of the semipermeable membrane can be prolonged. These advantages result in decreased operator supervision, maintenance, and operating costs, as well as improved sterility.
The foregoing will be apparent from the following more particular description of example embodiments of the invention, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating embodiments of the present invention.
A pump 160, such as a peristaltic pump, forces the blood to continue along the path through the circuit 100. After exiting the drip chamber 115, the blood then flows through tubing 117 to a dialyzer 170, which separates waste products and excess fluid from the blood. After passing through the dialyzer 170, the blood flows through venous tubing 180 towards a gas collection and venting chamber 230 in which gas (e.g., air) bubbles in the blood can separate from the blood and escape by passing across a semipermeable membrane 270 before the blood continues to the patient 105. As used herein, the term “semipermeable membrane” refers a membrane that is permeable to gas, but impermeable to liquid. Thus, the semipermeable membrane operates to inhibit liquids within the chamber 230 from escaping while allowing gas to escape from the chamber 230. After leaving the chamber 230, the blood travels through a venous line 190 and back to the patient 105. The gas collection apparatus and cassette subsequently described herein can be used with an extracorporeal hemodialysis circuit and device, as illustrated in
The lower level detector 240 and the upper level detector 260 can detect the presence of a gas or a liquid. The clamp 250 can open or close based on signals from the lower level detector 240 and the upper level detector 260. During operation, the gas collection chamber initially fills with a liquid, such as blood, if the clamp 250 is in an open position. Upon detecting the presence of liquid at the upper level detector 260, the clamp 250 can close. The liquid can contain gas bubbles. Over time, the gas bubbles rise to the surface and begin to fill the gas collection chamber with the gas, thereby creating an interface between the gas and the liquid. As gas bubbles continue to rise to the surface, the interface between the gas and the liquid moves vertically down the gas collection chamber.
When the lower level detector 240 detects the presence of a liquid, the clamp 250 remains closed. When the gas-liquid interface crosses the location where the lower level detector is positioned, the level detector can send a signal indicative of the presence of a gas. The signal can be sent from the lower level detector 240 to a control apparatus, which is described with respect to
Once the clamp 250 opens, the gas in the gas collection chamber 230 can travel through the gas venting chamber 270. The gas venting chamber 270 has a semipermeable membrane 275 positioned at the upper portion and a gas outlet 280. In some embodiments, the outlet can vent gas to the atmosphere. When the clamp 250 is open, the gas collection chamber 230 is in fluid communication with the gas vent chamber 270, which in turn is in fluid communication with the atmosphere.
Ordinarily, the pressure in the gas collection chamber is greater than atmospheric pressure. Thus when the clamp 250 is open, the gas-liquid interface moves vertically up the gas collection chamber, which releases accumulated gas to the atmosphere.
Similar to the lower level detector, the upper level detector 260 detects the presence of a gas or a liquid. When the clamp 250 is open, the gas-liquid interface can move vertically up the chamber and can cross the location where the upper level detector 260 is positioned. When the upper level detector 260 detects the presence of a gas, the clamp 250 can remain open, thus permitting further venting of gas to the atmosphere. When the upper level detector 260 detects the presence of a liquid, the clamp 250 can close, thus preventing the liquid from reaching the gas outlet 280. In some embodiments, the upper level detector can send a signal indicative of the presence of a gas or a liquid to the control apparatus, which is described with respect to
The term “clamp” is used in its broadest sense, meaning that it is an element that is capable of opening and closing the gas vent chamber. In one embodiment, the clamps (250 and 350) can be pinch clamps that, in a closed position, exert pressure on a tube to prevent the passage of gas or liquid. In another embodiment, the clamps (250 and 350) can be balloon clamps. A wide variety of suitable devices that can open and close the gas vent chamber in response to a signal can be used. The clamp can completely close and completely open the gas vent chamber, or the clamp can partially close and partially open the gas vent chamber.
In one embodiment, the level detectors (240, 260, 340, and 360) can detect the density of a fluid. For example, the level detectors can be ultrasonic level detectors. Liquids have a higher density than gasses. Thus, the level detector can send a signal indicative of the density of a fluid, wherein the density is indicative of the presence of a gas or a liquid. In some embodiments, the liquid can be blood. In some embodiments, the gas can be air.
The gas bubbles can be dissolved in the liquid, or the gas bubbles can be too large to be considered dissolved in the liquid. In some cases, the gas bubbles can be observable with the naked eye. In other cases, the gas bubbles can on the order of magnitude of a millimeter or less.
The gas collection chamber (230 and 330) and the gas vent chamber (270 and 370) are not necessarily separate pieces. Rather, the two can be an integrated component. In other words, the gas collection chamber and the gas vent chamber can be a single, integral unit. While
Typically, the gas outlet (280 and 380) is capped with a semipermeable membrane (275 and 375) made from polymers such as a polytetrafluoroethylene (PTFE) or polyethylene (PE), though other suitable semipermeable membranes can also be used. Typically, the semipermeable membrane is a hydrophobic membrane. Typically, the semipermeable membrane is a microporous membrane. Preferably, the semipermeable has a pore size between 0.1 micron to 0.22 microns. Suitable membranes are manufactured by W. L. Gore & Associates, Inc., Millipore Corporation, and Pall Corporation.
The chamber embodiment of
Typically, the liquid inlet (210 and 310) and the liquid outlet (220 and 320) connect to tubing. As shown in
While the clamp is open, gas in the gas collection chamber is in fluid communication with the atmosphere via a gas venting chamber, and gas can vent to the atmosphere. As gas vents to the atmosphere, the gas-liquid interface rises, and the upper level detector detects the presence of a liquid or a gas (step 440). If liquid is not present at the upper level detector (i.e., if gas is present), the clamp remains open (step 430), and the upper level detector continues to detect the presence of liquid or gas (step 440). If liquid is present at the upper level detector (i.e., if gas is not present), then the clamp closes (step 460). Liquid continues to flow into the gas collection chamber (step 410) and the cycle repeats.
While
While steps 420 and 440 describe detecting whether liquid is present at the level detectors, it is equivalent to detect whether gas is present at the level detectors. In such case, the relative placement of the “Yes” and “No” answers to the inquiry are reversed. In other words, if gas is present at the lower level detector (step 420), then the clamp opens (step 430), and if gas is not present, then the clamp remains closed (step 410). Similarly, if gas is present at the upper level detector (step 440), then the clamp remains open (step 430), and if gas is not present, then the clamp closes (step 460).
Another embodiment is an apparatus and method for controlling the pressure differential across a semipermeable membrane by providing backpressure to the semipermeable membrane (i.e., in the direction opposite to the direction applied by the flow of gas exiting the system). Thus, the present apparatus and method can prolong the lifetime of the semipermeable membrane as well as provide a means to actively control the level of liquid, such as blood and/or saline, in the gas venting chamber.
Near the top of the gas collection chamber is a semipermeable membrane 542 that serves as a barrier between the hemodialysis circuit, such as the extracorporeal hemodialysis circuit 100 of
During operation of a hemodialysis machine, the gas collection chamber 530 becomes increasingly filled with gas, and the gas-liquid interface 562 moves downward. Gas exits the gas collection chamber 530 by flowing across the semipermeable membrane 542 and along the exit pathway 545 and 565 into the T-connector 570. The gas vents to the atmosphere 575 via valve 572.
In a first and second mode of operation, the machine side pressure sensor 561 and the inlet pressure sensor 511 can be operably connected to a control apparatus, which is described with respect to
In a third mode of operation, the lower level detector 540 and upper level detector 560 can detect the presence of a liquid or a gas, as described above. When the lower level detector detects the presence of a gas, a signal can be sent to a control apparatus, which is described with respect to
The apparatus for controlling pressure differential can serve to reduce the pressure differential across the semipermeable membrane 542, which can reduce the damage to the membrane caused by excessive pressure differential across the membrane. In the inventors' experience, the semipermeable membrane can be fragile and can tend to leak liquid, particularly over the course of an operation of extended duration (e.g., 24 to 72 hours). By reducing or preventing the incidence of rips, tears, breaks, or other leaks in the membrane 542, the operational lifetime of the membrane can be increased, thereby reducing operating costs and improving ease of operation in a clinical or home setting. The increased reliability provided by the active venting system and method can reduce the amount of operator intervention required during a typical hemodialysis procedure.
While this invention has been particularly shown and described with references to example embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims.
This application claims the benefit of U.S. Provisional Application No. 61/609,587, filed on Mar. 12, 2012. The entire teachings of U.S. Provisional Application No. 61/609,587, filed on Mar. 12, 2012 and U.S. Provisional Application No. 61/470,680, filed on Apr. 1, 2011, are incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 61609587 | Mar 2012 | US |
