Valve mechanism for infusion fluid systems

A method and an apparatus are provided for preventing retrograde flow of fluid, e.g., blood products, into a source of sterile substitution fluid (50). The apparatus of the present invention includes a controllable pinch valve member (110) that is placed on a section of a conduit (90) which carries sterile substitution fluid to an extracorporeal circuit (30). In one embodiment, control over the valve member (110) is based on a control unit (120) using fluid pressures that are sensed upstream and downstream of the valve member (110) by upstream sensor (121) and downstream pressure (122) respectively. The valve member (110) is preferably opened only when the upstream pressure is greater than the downstream pressure. This assures that the substitution fluid flows only in a single direction when the pinch valve member (110) completely occludes the conduit (90) when in a closed position. Therefor, blood will not contaminate the sterile fluid by being drawn into the conduit (90) due to pressure differences.

FIELD OF THE INVENTION

The present invention relates to the production of and supply of sterile fluids in general and, more particularly, to a valve mechanism intended to be used with current systems which deliver sterile fluid from an external source or from a fluid preparation section of a machine to a point of use, such as a blood and fluid mixing chamber.

BACKGROUND OF INVENTION

Therapies, including hemofiltration, hemodiafiltration, and plasma pheresis, that require significant volumes of plasma water to be filtered and discarded require an equal or slightly smaller volume of fresh replacement fluid to be directly or indirectly infused into the patient's vascular compartment. In hemodialysis, for example, the infusion fluid is generally used to prime an extracorporeal circuit of a blood-cleansing machine, prior to connecting a patient to the machine, and to rinse the patient's blood at the end of the treatment. In the practice of hemodiafiltration, plasma water is removed by filtration from the blood as it traverses through the hemodialyzer cartridge. To compensate for this loss of plasma water, sterile fluid is added either upstream or downstream of the dialyzer cartridge. The sterile fluid used in these applications is generally a normal saline solution (e.g., a solution having a sodium chloride concentration of 0.9 percent by weight) which is supplied in flexible bags having predetermined volumes. In some cases, a Ringer's Lactate Solution may be used. In peritoneal dialysis, sterile peritoneal dialysis fluid packaged in flexible bags is typically infused into and subsequently emptied from the patient's peritoneal cavity.

The current state of the art employs one of two basic schemes for meeting the replacement infusion fluid requirements of such treatments. A commercially prepared solution intended for intravenous infusion is contained in a suitable reservoir, such as a flexible bag or a non-flexible vented bottle. The reservoir is connected to a fluid delivery assembly that includes a pump, such as a peristaltic pump and sterile tubing with appropriate connectors. The pump is used to create the required pressure differential between the fluid reservoir and a point of use (e.g., a blood and fluid mixing chamber) to assure the infusion fluid flow moves in a direction toward the point of use.

If an occlusive type pump is used, such as a peristaltic pump, an additional function of the pump is to assure that there is no retrograde flow of the patient's blood back into the sterile fluid reservoir. Due to pressure pulsations caused by the peristaltic pump, some retrograde flow of blood into the sterile tubing set occurs. Because of this, the sterile tubing set is disposed at the end of the treatment. Typically, in this arrangement, the sterile tubing set contains a special pump segment sized for the peristaltic pump. This results in a greater cost when compared to using a standard intravenous (IV) administration set.

A second strategy employed when larger volumes of fluid are required is to proportion water and salts to produce a solution that is similar in ionic content to plasma water as done by a dialysis machine to make dialysate. In this configuration, the dialysate solution or a portion of the solution must be treated (such as by filtration) to ensure it is of injectable quality prior to being used as a replacement or infusion fluid. Typically, a pump, such as a gear pump, peristaltic pump or piston pump is used to create the pressures required to move the required volume of fluid through the sterilizing filter(s) and to the point of use. Various articles describe many configurations of the substitution pump relative to the sterilizing filters in online hemodiafiltration systems. For example, in U.S. Pat. No. 4,702,829 ('829), to Polaschegg et al., which is incorporated herein by reference, the substitution pump is placed between two (redundant) sterilizing filters. The object of the '829 apparatus is to minimize the amount of negative pressure that would potentially occur if the pump were placed on the downstream side of the two sterilizing filters. In addition, this configuration allows the first filter to be operated in a cross-flow mode. The '829 patent does not address any means of preventing the final sterilizing filter (located between the venous drip chamber and the substitution pump) from being contaminated by blood products (red cells, proteins, etc.). For example, it is very common for blood to back-up in the drip chambers when pressures build up, such as when a blood line becomes kinked downstream of the drip chamber.

Though the infusion tubing segment between the final filter and the venous chamber may include a microfilter (e.g., 0.22 micron nominal pore size), it is understood by those skilled in the art that this microfilter does not prevent the final sterility filter from being contaminated by blood proteins when blood backs up into the infusion tubing set that is attached to the final sterility filter. Thus, it is implied that one would need to disinfect or sterilize the apparatus, including the final sterilization filter, before a new treatment is performed on the next patient.

In an article by Canaud, B. et al., “Hemodiafiltration Using Dialysate as Substitution Fluid”, Artificial Organs, Vol. 11(2), pp. 188-190, which is incorporated herein by reference, two different configurations are shown. In one configuration, the substitution pump is located before the two redundant sterilizing filters, while in the other configuration, the substitution pump is located between the two filters similar to that described in the '829 patent. The article fails to elaborate or teach the function of a stop valve which is shown in one of the figures. In addition, the article states that the machine and the infusate circuit is disinfected twice a day with perchloric acid and sterilized at the end of each day with 2.5 formalin. This implies that it is necessary to perform a disinfection process that includes the machine and the sterility filters between treatments in order to assure no cross contamination occurs between patients treated serially with the same system.

In U.S. Pat. No. 5,846,419 ('419) to Nederlof, which is incorporated herein by reference, two configurations are described. One configuration has the substitution pump between two sterilizing filters, while a second configuration has the substitution pump between the final sterilizing filter and the bloodline drip chamber. The '419 patent is directed to a method for preventing accumulation of germs and pyrogens on the upstream side of the sterility filters by enabling them to be operated in a cross-flow mode during treatment with these systems. The patent does not consider contamination of the downstream side of the final sterility filter such that can occur when blood backs up in the drip chamber shown in the figures of the patent.

In addition, there are several dialysis/diafiltration machines on the market that generate substitution fluid online using dialysate. In one system, the substitution pump is located between a second and third ultrafiltration or sterility filter. The third (final) sterility filter is part of the infusion set, thus the infusion set and final sterility filter is used only once to prevent any cross contamination. This type of system is embodied in a product commercially distributed under the trade name Gambro AK 200 Ultra™, from Gambro AB of Lund Sweden.

In a second system, the substitution pump is located after the final sterility filter. Because this system uses an occluding type (peristaltic) pump, it assures that no blood products will back up into the sterilizing filters. Therefore, disinfecting between treatments may not be required. The disadvantage of this system is that the system requires a special infusion tubing set that includes a dedicated pump segment for its operation. This infusion tubing set is accordingly more complex and costly than a standard IV administration set (that is typically used to prime the circuit with saline or for infusing sterile fluid into the blood circuit during dialysis treatment). Again, to prevent cross contamination, this special infusion tubing set is used once and is then discarded. An example of this type of system is a product system commercially available under the trade name Fresenius OnLine Plus™ System, available from Fresenius Medical Care of Bad Homburg, Germany.

SUMMARY OF INVENTION

The present invention provides a method and an apparatus that prevents retrograde flow of fluid, e.g., blood products (i.e., blood proteins), into a source of sterile substitution fluid. The apparatus of the present invention includes a controllable valve mechanism having a valve member that is placed on a section of a conduit which carries sterile substitution fluid to an extracorporeal circuit. In one embodiment, the controllable valve member is in the form of a pinch valve which is placed along a section of flexible tubing. Control over the pinch valve is based on a control unit, e.g., a feedback control loop, using fluid pressures that are sensed upstream and downstream of the pinch valve. The pinch valve is preferably opened only when the upstream pressure is greater than the downstream pressure. This assures that the substitution fluid flows only in a single direction (i.e. from the higher pressure substitution fluid source to the lower pressure extracorporeal circuit) when the pinch valve is in the open position.

Because the pinch valve completely occludes the conduit (flexible tubing) when in the closed position, blood (and its associated blood proteins) will not contaminate the sterile fluid delivery system upstream of the pinch valve by being drawn into the flexible tubing due to pressure differences. As a result, this enables the sterile fluid delivery system (excluding the flexible tubing contained in the pinch valve) to be used multiple times on multiple patients without disinfection of the fluid delivery system between treatments. The valve mechanism of the present invention thus overcomes the disadvantages of the conventional devices because it greatly reduces costs associated with disinfecting the sterile fluid delivery system, not to mention the lost time associated with having to disinfect the system between each treatment.

For those systems using an occlusive type substitution fluid pump requiring a special single use infusion set (which may contain a single use final sterilizing filter), the present invention has the advantage in that a low cost IV administration set or a drip chamber level adjust line on an existing bloodline set can be used instead.

According to the present invention, the valve mechanism may be incorporated into a system in which sterile substitution fluid is introduced into the blood stream either in a pre-dilution mode or in a post-dilution mode relative to a dialyzer cartridge. In addition, the valve mechanism may also be incorporated into a hemodiafiltration scheme using first and second dialyzer cartridges. In this embodiment, the substitution fluid is introduced into a partially diafiltered blood stream at a location between the first and second dialyzer cartridges.

Other features and advantages of the present invention will be apparent from the following detailed description when read in conjunction with the accompanying drawings.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Reference is made toFIG. 1which schematically illustrates a first embodiment. In this first embodiment, the present scheme is shown as being part of a substitution fluid delivery system typical of a hemodiafiltration system with online substitution fluid. The embodiment ofFIG. 1illustrates a hemodiafiltration scheme in which the substitution fluid is introduced into the blood stream in a post-dilution mode. Blood from a patient enters an extracorporeal circuit. The extracorporeal circuit generally includes an arterial bloodline10, a dialyzer cartridge20having a dialysate compartment22and a blood compartment24, and a venous bloodline30. The dialyzer cartridge20includes a semipermeable membrane26which divides the cartridge20into the compartments22,24. Pressures in the extracorporeal circuit are typically monitored, as represented by arterial pressure at a first monitoring device13and venous pressure at a second monitoring device122. The first and second monitoring devices13,122may be in the form of any number of devices and in one exemplary embodiment, the devices13,122are pressure sensors which detect fluid pressure at these locations.

According to this embodiment, the dialyzer cartridge20preferably is a medium or high flux dialyzer, for example, Fresenius hemodialyzers F40, F50, F60, F70, F80, F60M, F80M, available from Fresenius Medical Care of Bad Homburg, Germany; Baxter hemodialyzers CT 110G, CT 190G and Atraflux 140, 170, 200, available from Baxter of Deerfield, Ill.; and Hospal AN69 hemodialyzers Filtral 12, 16, 20, available from Hospal of Meyzieu, France. Any suitable bloodline material known in the art may be used to carry the fluids in the system of the present invention. Examples include but are not limited to MediSystems Ready Set bloodlines, available from MediSystems of Seattle, Wash., and Fresenius Medical Care bloodlines, available from Fresenius Medical Care of Bad Homburg, Germany.

Blood is propelled through the extracorporeal circuit using a blood pump40. Preferably, the blood is propelled in a counter-current configuration relative to the flow of a dialysate solution in the dialysate compartment22. A dialysate fluid circuit is provided for preparing a source of fresh dialysate, generally indicated at50. For example, the fresh dialysate50may be prepared by volumetric proportioning, e.g., mixing volumes of fresh water with dialysate concentrate at predetermined proportions, resulting in dialysate fluid50that is compatible with human blood but may not be sterile and may not be non-pyrogenic at this point. The dialysate fluid circuit also includes a flow balance system62(e.g., balance chambers) which may be used to prepare the dialysate fluid50having the predetermined desired properties. Fresh dialysate flows from the fresh source50through a first conduit51to the flow balance system62.

A dialysate pump64is used to propel the dialysate fluid50through the dialysate fluid circuit which also includes a fresh dialysate conduit68for carrying fresh dialysate fluid50from the flow balance system62to the cartridge20and a spent dialysate conduit70for carrying spent dialysate fluid from a dialysate outlet port65of the cartridge20. The dialysate conduit70is connected between the cartridge20and the flow balance system62. A UF pump72is generally used to shunt a portion of spent dialysate fluid from the flow balance system62as a means to remove a controlled amount of fluid from the patient.

According to this embodiment, to make substitution fluid online, a portion of the fresh dialysate fluid50is drawn into a substitution fluid conduit80. This can be accomplished using several different techniques including using a substitution pump82for pumping a portion of fluid50into the substitution fluid conduit80from the fresh dialysate conduit68. In order to make fresh dialysate fluid50of an injectable quality, the fluid50may be filtered through a substitution filter unit84. The substitution filter unit84may include one or more substitution fluid filters used to filter the fresh dialysate fluid50according to the present invention. The substitution filter unit84may include any filtration membrane known in the art and may be similar in composition to the membrane26used in hemodialyzers, such as dialyzer cartridge20. However, preferably, the molecular weight cut-off of the filtration membrane is smaller than that of typical high flux dialyzers, whereby a better retention of endotoxin fragments, etc. is achieved. A desirable range of the molecular weight cut-off for the filtration membrane may be from about 5,000 to about 30,000 Daltons.

Although it is possible to use a substitution filter unit84having a single filtration stage (i.e. without redundant filtration) as the final filtration, preferably, the substitution filter unit84has redundant filtration characteristics. Accordingly, it is preferred that the substitution filter unit84has redundant filtration sections to assure the sterility of the filtered fluid in the event that one of the filters fails during the filtration process, as is known in the art. For example, the substitution filter unit84may consist of two single filter cartridges, or it may be designed as a single cartridge unit having multiple filtration sections. Thus while it is possible to use a single filtration phase (i.e. without redundant filtration) as a final filtration unit, it is generally undesirable due to patient safety issues that may arise should the filter fail during operation. Redundant filtration is thus generally required by industry standards.

The dialysate path in the embodiment ofFIG. 1may be arranged as follows. The fresh dialysate conduit68extends from the flow balance system62to a dialysate inlet port63of dialyzer cartridge20so that a portion of the fresh dialysate fluid50is delivered to the dialyzer cartridge20. As previously-mentioned, a portion of the fresh dialysate fluid50is used to make substitution fluid online and flows from the fresh dialysate conduit68to the substitution filter unit84through the conduit80. After the dialysate fluid passes through the substitution filter unit84, the sterile substitution fluid is delivered to a suitable connector86which mates with another connector88that is part of a conduit90that leads to the extracorporeal circuit. In one embodiment, the conduit90is flexible tubing extending between the connector88and the extracorporeal circuit. The flexible tubing90may be considered the single use or disposable section of the infusion line pathway. For example, it may be part of a portion of a bloodline, such as a drip chamber level adjust line (as shown inFIG. 1), or an IV administration set connected to a suitable port in the extracorporeal circuit (e.g., drip chamber level adjust line, saline line tee, or special infusion port made as part of the hemodialyzer, hemodiafilter, or hemofiltration cartridge).

According to the present invention, a valve mechanism is provided and generally indicated at100. The valve mechanism100is designed to prevent retrograde flow of blood products (e.g., blood proteins) into the source of sterile substitution fluid (substitution fluid that has passed through the substitution filter unit84). In one embodiment, the valve mechanism100includes a main control valve110(e.g., a tubing pinch valve) and a control unit120that commands the main control valve110to open or close. The pinch valve110may be located in several different locations including on the flexible tubing90that is either an integral part of the bloodline tubing set (such as the drip chamber level adjust line) or is connected to the extracorporeal circuit (such as an IV administration set). The pinch valve110may be any number of suitable pinch valve mechanisms and in one embodiment the pinch valve110is a Sari pinch valve available from Farmington Engineering Inc., Madison, Conn. The pinch valve110fully occludes the flexible tubing90in the “closed” position and allows flow through the flexible tubing90in the “open” position. It will also be understood that it is within the scope of the present invention that the main control valve110is not limited to a pinch valve and may comprise other types of valve assemblies which serve to selectively occlude the flexible tubing90in the “closed” position and allow flow through the flexible tubing90in the “open” position. Other type of valves that can be used are those valves that are configured to occlude and conversely open the flexible tubing90when a signal or the like is sent to the valve from a programmable control unit, such as control unit120, a microprocessor device, etc.

In accordance with one embodiment of the present invention (FIG. 1), control of the pinch valve110is based on fluid pressures (directly or indirectly) sensed before and after the pinch valve110. In other words, the fluid pressure is measured at a location upstream of the pinch valve110and at a location downstream of the pinch valve110. The sensing of the fluid pressures upstream and downstream of the pinch valve110may be accomplished by a third monitoring device121(i.e. an upstream sensor) and the second monitoring device122(i.e. a downstream sensor), respectively. For example and according to one embodiment, the upstream sensor121is an upstream pressure transducer121and the downstream sensor122is a downstream pressure transducer122. Preferably, the venous pressure is also monitored at location122, as previously indicated. The upstream side of the pinch valve110includes the substitution equipment which extends from the substitution pump82to the pinch valve110. The downstream side of the pinch valve110includes both the extracorporeal circuit and the portion of the flexible tubing90which extends from the pinch valve110to the extracorporeal circuit. It will be appreciated that other types of sensing devices may be used to sense the fluid pressure in both the upstream and downstream locations. The fluid pressure is continuously monitored by the upstream sensor121and the downstream sensor122. Control of the pinch valve110is thus based on a feedback control loop (control unit120) which is designed to position the pinch valve110in either the open or closed position based upon the sensed information received from the sensors121,122. Control unit120is preferably a programmable unit that permits the operator/user to program selected pressure differentials that will trigger the control unit120to vary the position of the valve110.

According to the present invention, control of the pinch valve110is as follows. When the pinch valve110is in a “closed” position (and assuming the substitution pump82is stopped), the pressure on the upstream side of the pinch valve110could be less than the pressure on the downstream side of the pinch valve110. The opening of the pinch valve110under these conditions could result in blood flowing from the extracorporeal circuit toward the sterile source of substitution fluid. This is referred to as retrograde blood flow and the occurrence of which is undesirable as outlined in the discussion of the disadvantages of conventional systems. To initiate the flow of substitution fluid, the substitution fluid pump82is started with the pinch valve110remaining in the “closed” position. In this configuration, pressure on the upstream side of the pinch valve110will increase. When the sensed upstream pressure at sensor121exceeds the sensed downstream pressure at sensor122by some predetermined value, the pinch valve110is opened. The control unit120opens the pinch valve110by known techniques, such as sending a command signal to the pinch valve110(that is in communication with the control unit120).

The opening of the pinch valve110permits flow of substitution fluid to the extracorporeal circuit. While the pinch valve110is in the “open” position, upstream and downstream pressures are continuously monitored at sensors121,122to assure that the upstream pressure is greater than the downstream pressure. This information is thus continuously relayed from the sensors121,122to the control unit120. In the event that there is a sudden drop in the upstream pressure or a sudden increase in the downstream pressure, the pinch valve110is immediately closed to prevent blood and blood proteins from backing up and contaminating the substitution fluid delivery system. After the pinch valve110is closed, the substitution pump82is stopped to prevent over pressurizing the fluid path between the outlet of the substitution pump82and the pinch valve110. This can be accomplished by sending a signal from the control unit120to the substitution pump82.

An alternative to the feedback control scheme described above which is based on inputs of both upstream and downstream pressures is a feedback control scheme based only on the upstream pressure (i.e., as detected at an upstream location, such as at sensor121). In this control scheme, the downstream pressure would be assigned a constant value that represents a maximum pressure condition based upon a predetermined set of treatment parameters (e.g., flows, filters, dialyzer cartridge, etc.). Operation of the valve mechanism100then becomes similar to that described above except that the control unit120only receives input from the sensed upstream pressure at sensor121and the control unit120includes a comparator or the like to compare the upstream pressure and the constant value. In this case, to initiate flow of substitution fluid after the substitution pump82is started, the pinch valve110will not open until the sensed upstream pressure at sensor121exceeds the downstream constant pressure value by some predetermined value. After the pinch valve110is opened, the control unit120can begin to monitor the upstream pressure for sudden changes. For example, a sudden drop in the upstream pressure results in the closing of the pinch valve110to prevent blood and blood proteins from backing up and contaminating the substitution delivery system followed by a stopping of the substitution pump82. Again, the observed change in pressure at the upstream location that causes the opening or closing of the pinch valve110can be defined in a number of different ways. For example, the pressure change can be defined as the upstream pressure value exceeding the constant pressure value by a predetermined percentage or by the upstream pressure value being less than the constant pressure value by a predetermined percentage.

Yet another alternative arrangement is one in which the sensor122is still a downstream pressure sensor, or the like; however, the sensor122in this embodiment is positioned along the length of a downstream portion of conduit90downstream of the valve110. Thus, the downstream pressure sensor122monitors the flow pressure of the substitution fluid as it flows within the conduit90after flowing through the valve110and before the substitution fluid is delivered to its point of use, i.e., mixing chamber140in the embodiment ofFIG. 1. Thus in this embodiment, both the first and second sensors121,122monitor the flow pressure of the substitution fluid with the sensor121monitoring an upstream flow pressure and the sensor122monitoring a downstream flow pressure. The control unit120in this embodiment operates in essentially the same manner as the valve110is opened and closed based on information received from the sensors121,122.

Because the present invention prevents retrograde blood flow, the substitution delivery system does not need to be disinfected before a next treatment is initiated. This greatly reduces the costs associated with the treatment and also saves valuable time as th system may be reused without having to undergo a time consuming cleaning process.

According to the present invention, a pressure based valve mechanism100is provided to eliminate the risk of system contamination due to retrograde blood flow into the sterile substitution fluid source. The principal reason retrograde blood flow occurs is that a pressure imbalance occurs and the downstream fluid pressure (i.e., near122) is greater than the upstream fluid pressure (i.e., near121). This results in the blood flowing from a location where the blood is mixed with sterile dialysate fluid, such as in a drip chamber or a mixing chamber140, toward the source of the substitution fluid. The mixing chamber140is fluidly connected to the flexible tubing90which carries the sterilized substitution fluid to the mixing chamber140and is also fluidly connected to the dialyzer cartridge20by venous bloodline30for receiving filtered blood from the dialyzer cartridge20. A conduit142delivers the blood/substitution fluid mixture from the mixing chamber140to the patient. Conduit142may therefore be referred to as a bloodline.

For those systems using an occlusive type substitution fluid pump requiring a special single use infusion set (possibly containing a single use sterilization filter), the present invention has the advantage in that a low cost IV administration set or a drip chamber level adjust line can be used instead.

Reference is made toFIG. 2which schematically illustrates a second embodiment. In this second embodiment, the present scheme is shown as being part of a substitution fluid delivery system typical of a hemodiafiltration system in which the sterile substitution fluid is introduced into the blood stream in a predilution mode relative to the dialyzer cartridge20.

In this embodiment, the flexible tubing90extends between the connector88and a mixing chamber150which receives blood through the arterial bloodline10. Thus, the sterile substitution fluid is delivered to and mixed with blood in the chamber150to form a blood/substitution fluid mixture. Preferably, the blood and substitution fluid enter the mixing chamber150at one end and a conduit11extends from an opposite end of the mixing chamber150. The conduit11is preferably similar to the arterial bloodline10and differs in that the conduit11carries the blood/substitution fluid mixture from the mixing chamber150to the first cartridge20(blood compartment24thereof).

In this embodiment, the first monitoring device13acts as a downstream sensor for monitoring the fluid pressure at downstream locations relative to the pinch valve110. Preferably, the arterial pressure is also measured at the location of the first monitoring device13. As with th first embodiment, the fluid pressure of the substitution fluid is continuously monitored at the upstream sensor121.

In this embodiment, the second monitoring device122(i.e. the second sensor) does not serve as a downstream sensor for monitoring the flow pressure of the substitution fluid after the fluid passes through the pinch valve110but rather acts as a venous pressure sensor. Sensor122thus measures the pressure of the fluid as it enters the chamber140. Chamber140is therefore not a mixing chamber but rather is a chamber which receives the fluid from the dialyzer cartridge20and is coupled to conduit142which delivers the filtered blood back to the patient. Alternatively, chamber140can be eliminated and the filtered blood can simply flow through conduit142back to the patient.

In the second embodiment, control of the pinch valve110is the same as or similar to the control thereof in the first embodiment in that the pinch valve110is designed to prevent retrograde blood flow. More specifically, the pinch valve110is opened when the sensed upstream pressure at sensor121exceeds the sensed downstream pressure at sensor13by a predetermined valve. In the open position, the substitution fluid flows through the pinch valve110within the flexible tubing90to the mixing chamber150. In the event that there is a sudden drop in the upstream pressure or a sudden increase in the downstream pressure, the pinch valve110is immediately closed to prevent blood and blood proteins from backing up and contaminating the substitution delivery system. After the pinch valve110is closed, the substitution pump82is stopped to prevent over pressurizing the fluid path between the outlet of the substitution pump82and the pinch valve110. This may be accomplished by sending a signal from the control unit120to the substitution pump82.

Advantageously, the second embodiment prevents retrograde blood flow from the chamber150into the flexible tubing90which is connected thereto in a pre-dilution scheme. In each embodiment of the present invention, the valve mechanism100is easily incorporated into a variety of existing hemodiafiltration apparatus or the like.

Reference is made toFIG. 3which schematically illustrates a third embodiment of the present invention. In this third embodiment, the present invention is shown as being part of a substitution fluid delivery system typical of a hemodiafiltration system having first and second dialyzer cartridges20,200in which the sterile substitution fluid is introduced at a location between the first and second dialyzer cartridges20,200. The substitution fluid can be introduced (i.e., through a connector) into a conduit that extends between and links the first and second dialyzer cartridges20,200or the substitution fluid can be introduced into a chamber that is disposed between the first and second dialyzer cartridges20,200and is connected thereto by one or more conduits.

In this third embodiment, blood is propelled through the extracorporeal circuit using the blood pump40. The blood flows through the bloodline10to the chamber160. The arterial pressure is measured at the first monitoring device13and the measured information is continuously transmitted to the control unit120. A conduit (bloodline)162fluidly connects the chamber160to the first dialyzer cartridge20. The second dialyzer cartridge200is similar to the first dialyzer cartridge20and may be of any type suitable for hemodialysis, hemodiafiltration, hemofiltration, or heomoconcentration as is the case with the first dialyzer cartridge20. More specifically, the second dialyzer cartridge200has a dialysate compartment210and a blood compartment220defined by a semipermeable membrane221. The second dialysate cartridge200also includes a dialysate inlet port222for receiving a flow of dialysate fluid and a dialysate outlet port224which carries spent dialysate fluid from the second dialysate cartridge200.

The first and second dialysate cartridges20,200are conventionally arranged with the fresh dialysate conduit68being connected to the dialysate inlet port222so that a portion of the fresh dialysate fluid50is delivered to the second dialyzer cartridge200. After the dialysate fluid flows through the dialysate compartment210, the dialysate fluid exits the second dialyzer cartridge200through the dialysate outlet port224and is introduced into the inlet dialysate port63of the first dialyzer cartridge20. Preferably, th dialysate fluid is delivered from the second dialyzer cartridge200to the first dialyzer cartridge20using a device, such as an interstage pump230. The dialysate outlet port65of the first dialyzer cartridge20is connected to the spent dialysate conduit70which carries the spent dialysate fluid away as in the other embodiments. The first and second dialyzer cartridges20,200are also arranged so that blood flows from the blood compartment24of the first dialyzer cartridge20to the blood compartment220of the second dialyzer cartridge200where it is further filtered.

Similar to the first embodiment, the second dialyzer cartridge200is connected to a chamber140by the venous bloodline30. Conduit142transports the filtered blood from the chamber140back to the patient. The second monitoring device122, i.e. second sensor, is preferably positioned at the chamber140or thereabouts along the venous bloodline30so as to monitor the venous pressure of the fluid as it flows through the bloodline30. The second sensor122continuously provides venous pressure data to the control unit120.

In this embodiment, the substitution fluid is mixed with partially diafiltered blood, denoted231, between first and second stages of filtering the blood. As used herein, the expression “partially diafiltered blood” refers to blood that has had an amount of toxins removed therefrom using a hemodiafiltration process. The sterile substitution fluid is mixed with the partially diafiltered blood231after the blood231has been filtered in the first dialyzer cartridge20but before the blood231is introduced into the second dialyzer cartridge200. The mixing of the partially diafiltered blood231and the substitution fluid forms a blood/substitution fluid mixture, denoted233. This fluid mixture233is then introduced into the blood compartment220of the second dialyzer cartridge200. Preferably, in both the first and second dialyzer cartridges20,200, the blood is propelled in a counter-current configuration relative to the flow of the dialysate solution in the dialysate compartments22,210. Blood being discharged from the second dialyzer cartridge200can be referred to as being diafiltered blood. As used herein, the expression “diafiltered blood” refers to partially diafiltered blood that has been further subjected to a hemodiafiltration process in order to further remove more toxins from the blood.

In the third embodiment, control of the pinch valve110is the same as or similar to control thereof in the other embodiment in that the pinch valve110is designed to prevent retrograde blood flow. More specifically, the pinch valve110is opened when the sensed upstream pressure at sensor121exceeds the sensed downstream pressure at a sensor by the predetermined valve. In this embodiment, the downstream pressure may be represented by an average of the arterial pressure measured at the first monitoring device13and the venous pressure measured at the second monitoring device122. In this embodiment, the control unit120receives the signals from the respective monitoring devices13,122and generates an average pressure value. Alternatively, the downstream pressure value that is delivered to the control unit120can be based on a downstream pressure value at one of the devices13,122. In the open position, the substitution fluid flows through the pinch valve110within the flexible tubing90to the location where it is mixed with the partially diafiltered blood231between the first and second filtering stages. In the event that there is a sudden drop in the upstream pressure or a sudden increase in the downstream pressure, the pinch valve110is immediately closed to prevent blood and blood proteins from backing up and contaminating the substitution delivery system. After the pinch valve110is closed, the substitution pump82is stopped to prevent over pressurizing the fluid path between the outlet of the substitution pump82and the pinch valve110. This can be accomplished by sending a signal from the control unit120to the substitution pump82.

The present invention prevents the possibility of retrograde flow from the point of use to the fresh fluid supply path and the fluid supply source and therefore can effectively eliminate the risk of cross contamination that may result when a single fluid source is repeatedly used to treat several patients serially. The present invention is easily incorporated into existing apparatuses. For example, the present invention may be used in conjunction with other system components such as pressure or flow sensors which periodically check system conduit and connection integrity.

It will be appreciated by persons skilled in the art that the present invention is not limited to the embodiments described thus far with reference to the accompanying drawing. Rather the present invention is limited only by the following claims.