Dialysis machine

A hemodialysis machine including a main body and a door, the door being capable of opening and closing relative to the main body so as to receive and retain a disposable cartridge therebetween, the machine further including a controller and a pneumatic pump, the cartridge having a chassis with a platen side covered by a first deformable membrane and a door side covered by a second deformable membrane, the chassis and membranes defining a dialysate flow path for delivering a flow of dialysate solution through a dialyzer, the main body having a platen for in use sealing against the platen side of the cartridge and the door having an interface plate for in use sealing against the door side of the cartridge, the pneumatic pump being fluidically connected to an interface plate cavity between the interface plate and the cartridge by a pneumatic supply line, the pump being controlled by the controller to selectively generate a vacuum in the platen cavity so as to affix the cartridge to the door prior to operation of the machine.

The present application is a §371 submission of international application no. PCT/GB2012/000147, which was filed on 14 Feb. 2012 and entitled Dialysis Machine, and which was published in the English language on 22 Aug. 2013 with publication no. WO 2013/121162 A1.

The present invention relates to dialysis machines and in particular, but not exclusively, to a disposable cartridge for use in hemodialysis machine.

Dialysis is a treatment which replaces the renal function of removing excess fluid and waste products, such as potassium and urea, from blood. The treatment is either employed when renal function has deteriorated to an extent that uremic syndrome becomes a threat to the body's physiology (acute renal failure) or, when a longstanding renal condition impairs the performance of the kidneys (chronic renal failure).

There are two major types of dialysis, namely hemodialysis and peritoneal dialysis.

In peritoneal dialysis treatment, a dialysate solution is run through a tube into the peritoneal cavity. The fluid is left in the cavity for a period of time in order to absorb the waste products, and is subsequently removed through the tube for disposal.

It is common for patients in the early stages of treatment for a longstanding renal condition to be treated by peritoneal dialysis before progressing to hemodialysis at a later stage.

In hemodialysis, the patient's blood is removed from the body by an arterial line, is treated by the dialysis machine, and is then returned to the body by a venous line. The machine passes the blood through a dialyser containing tubes formed from a semi permeable membrane. On the exterior of the semi permeable membrane is a dialysate solution. The semi permeable membrane filters the waste products and excess fluid from the blood into the dialysate solution. The membrane allows the waste and a controlled volume of fluid to permeate into the dialysate whilst preventing the loss of larger more desirable molecules, like blood cells and certain proteins and polypeptides.

The action of dialysis across the membrane is achieved primarily by a combination of diffusion (the migration of molecules by random motion from a region of higher concentration to a region of lower concentration), and convection (solute movement that results from bulk movement of solvent, usually in response to differences in hydrostatic pressure).

Fluid removal (otherwise known as ultrafiltration) is achieved by altering the hydrostatic pressure of the dialysate side of the membrane, causing free water to move across the membrane along the pressure gradient.

The correction of uremic acidosis of the blood is achieved by use of a bicarbonate buffer. The bicarbonate buffer also allows the correction of the blood bicarbonate level.

The dialysis solution consists of a sterilized solution of mineral ions. These ions are contained within an acid buffer which is mixed with the sterilised water and bicarbonate base prior to delivery to the dialyser.

Dialysate composition is critical to successful dialysis treatment since the level of dialytic exchange across the membrane, and thus the possibility to restore adequate body electrolytic concentrations and acid-base equilibrium, depends on the composition.

The correct composition is accomplished primarily by formulating a dialysate whose constituent concentrations are set to approximate normal values in the body.

Additionally, the balance of fluids across the dialyser is critical in providing effective treatment. Any instability in the volume of dialysate pumped into and out of the dialyser can cause a flow balance error which can lead to dehydration of over-hydration of the patient over the course of a treatment.

Achieving the correct composition of dialysate and providing accurate flow balance across the dialyser requires the accurate control of low volumes of liquid and at present this is achieved by the provision of complex fluid paths, including multiple pumping and valving components on the dialysis machine.

This adds cost and complexity to the machine and necessitates the sterilisation of the fluid paths, and pumping and valving components between treatments.

The provision of a dialysate cartridge which can be disposed of after a treatment offers a solution to this problem but presents additional technical challenges in terms of achieving an accurate composition of dialysate and the correct balance of fluids across the dialyser.

Thus it is known to provide a dialysate flowpath on a cartridge having membrane on each side of a cartridge chassis. The membranes are actuated by the machine to pump and control the dialysate fluid.

However, the positioning of the cartridge in the machine is critical to achieving accurate mixing and flow balance since any variation in position of the cartridge can lead to irregular actuation of the membrane and consequently variation in pumped fluid volume.

Furthermore any unwanted compliancy in the membrane can lead to inconsistent dialysate composition and flow balance accuracy due to volumetric variation in the fluid system.

It is an object of the present invention to provide a hemodialysis machine which at least mitigates some of the problems described above.

According to the invention there is provided a hemodialysis machine includinga main body and a door, the door being capable of opening and closing relative to the main body so as to receive and retain a disposable cartridge therebetween,the machine further including a controller and a pneumatic pump,the cartridge having a chassis with a platen side covered by a first deformable membrane and a door side covered by a second deformable membrane, the chassis and membranes defining a dialysate flow path for delivering a flow of dialysate solution through a dialyser,the main body having a platen for in use sealing against the platen side of the cartridge and the door having an interface plate for in use sealing against the door side of the cartridge,the pneumatic pump being fluidically connected to an interface plate cavity between the interface plate and the cartridge by a pneumatic supply line, the pump being controlled by the controller to selectively generate a vacuum in the platen cavity so as to affix the cartridge to the door prior to operation of the machine.

Advantageously, the generation of a vacuum in the interface cavity causes the second deformable membrane to be drawn into contact with the interface plate. The prevents deflection of the second membrane as a result of the pressure variations observed on the inner surface of the membrane resulting from the actuation of the first membrane to pump fluid through the cartridge. This in turn ensures that the cross section of the fluid pathways, defined at least in part by the second membrane, does not vary through the course of a treatment. This ensures the accuracy of the pumping of fluid on the cartridge by reducing volumetric errors which can accumulate over the course of a treatment to adversely affect flow balance or mixing accuracy.

Preferably, the pneumatic supply line is defined at least in part by a port through the cartridge which permits the gas in the interface cavity to be exhausted from the cavity by the pump to generate a vacuum in the cavity.

Preferably, the platen defines an aperture in fluid communication with the port in the cartridge, the aperture permitting the gas in the interface cavity to be exhausted from the cavity by the pump to generate a vacuum in the cavity.

Preferably, the platen includes at least one o-ring seal situated circumferentially around the aperture in order to form a seal between the platen and the cartridge.

Preferably, the interface plate carries an interface plate gasket for holding the vacuum in the interface cavity between the interface plate and at least part of the second deformable membrane.

Preferably, the door includes an actuator operable to apply a closure load to the cartridge.

Preferably, the closure load is sufficient to cause the cartridge to engage substantially the entire interface plate gasket sealing surface.

Preferably, the actuator is a pneumatically operable airbag.

Preferably, the interface plate has a recess in its surface to allow the exhaustion of gas from the interface plate cavity.

Preferably, the recess includes a depression aligned with the port in the cartridge.

Referring toFIG. 1, a dialysis machine10is shown having a main body12and a hinged door14. The door14is hinged so as to allow a dialysis cartridge16(seeFIG. 6) to be received between the main body12and the door. The machine10has a blood pumping portion indicated generally at9for pumping patient blood to and from a dialyser (not shown for clarity) in a known manner.

Referring toFIG. 2, the main body12has a platen21behind which is an engine portion (not shown for clarity). The platen21is configured to receive the cartridge16within a recessed portion25. The engine portion includes a pneumatic pump for providing pressure and vacuum to operate the machine and a controller to control retention of the cartridge16within the machine10and fluid flow on the cartridge16as will be discussed in further detail below.

The door14is shown in further detail inFIGS. 3 and 4. The door14has an outer side including a user interface2, an edge defining a handle3for opening and closing the door and an inner side including an interface plate8for engaging the cartridge16when the door is closed. The interface plate8has a flat profile which defines a series of recesses7which, in this example, form a grid. The grid is surrounded by an interface plate gasket in the form of continuous seal11. The recesses are recessed by approximately 0.7 mm from the surface of the interface plate8. The recesses7include an access depression5, the purpose of which will be described in further detail shortly.

Referring now toFIG. 5, the door14includes an actuator in the form of an airbag31situated between the interface plate8and a door chassis33. The airbag31is operable by the engine portion to urge the interface plate21away from the door chassis33towards the main body12via a pneumatic line which runs through the hinge between the door14and the main body12. In this way the airbag31provides a closure load to close the cartridge onto the platen and to ensure that the continuous seal11fully engages the cartridge16. Upon deactivation of the airbag31, the interface plate8returns to its original position under the action of springs35.

The cartridge16will now be described in further detail with reference initially toFIG. 6. The cartridge16has a chassis defining a door side20(shown in further detail inFIG. 7) and a platen side18(shown in further detail inFIG. 8). In use the platen side18of the cartridge16engages the platen21on the main body12of the machine10, and the door side20engages the interface plate8on the door14of the machine10. The cartridge has a vacuum passage port23which is open on both sides of the cartridge16, the purpose of which will be described in further detail below.

The cartridge16is formed from an acrylic such as SG-10 which is moulded in two parts (a platen side and a patient side) before being bonded together to form the chassis. Both the platen side18and door side20are covered in a clear flexible membrane13formed from, for example, DEHP-free PVC which is operable by pneumatic pressure applied to the membrane by the pneumatic compressor in the main body via the platen21. In this way a series of flow paths are formed in the cartridge for carrying dialysate and its constituent parts of water, bicarbonate solution and acid solution.

In use the engine portion of the machine10applies either a positive or negative pressure to the membrane via the platen21in order to selectively open and close valves and pumps to pump fluid through the cartridge. The fluid flow through the cartridge will now be described in detail.

The cartridge16has a dialysate mixing portion indicated generally at17inFIG. 6and a flow balancer indicated generally at19inFIG. 6. The purpose of the mixing portion is to deliver accurately mixed homogeneous dialysate solution to the flow balancer which is provided to ensure that the flow of fluid supplied to the dialyser matches (to within clinical tolerances) the volume of fluid drawn from the dialyser.

Dialysate Mixing

Dialysate is mixed on the cartridge by combining water with two dialysate base solutions, namely a bicarbonate solution and an acid solution. This process will now be described in further detail.

Referring now toFIGS. 7 and 8, dialysate solution is mixed in the mixing portion17of the cartridge16as follows. Reverse osmosis (RO) water is admitted onto the cartridge via RO water inlet port30. Water passes up channel32and exits the cartridge16at RO water outlet port34. From here the water is carried via a tube (not shown for clarity) and passes through a bicarbonate cartridge in a known manner to generate a bicarbonate solution. The bicarbonate solution is admitted onto the cartridge16via bicarbonate inlet port36. The temperature of the bicarbonate solution is measured at sensing port38and the bicarbonate solution pressure is measured at sensing port40(FIG. 8only). The bicarbonate solution passes a bicarbonate control valve42before entering a bicarbonate solution reservoir44. A first dialysate base solution pump chamber in the form of a bicarbonate dosing pump chamber46has an associated inlet valve48and outlet valve50. From the outlet valve50the bicarbonate solution passes to a first mixing pump chamber in the form of a bicarbonate pump chamber52via bicarbonate pump inlet valve54. The bicarbonate pump inlet valve54also admits RO water into the bicarbonate pump chamber52from the RO water inlet port30. In this way RO water and bicarbonate solution can be admitted into the bicarbonate pump chamber52for subsequent pumping out of the bicarbonate pump chamber52of a mixed bicarbonate and water solution (called bicarbonate mixture from hereon in for ease of reference) via a bicarbonate pump outlet valve56. From the bicarbonate pump outlet valve56the bicarbonate mixture enters a bicarbonate mixture sensor channel58in which the machine12measures the conductivity of the mixture in a known manner. The mixture then enters a bicarbonate mixture temperature sensor60before entering a second mixing pump chamber in the form of an acid pump chamber62via acid pump inlet valve64. Also admitted into the acid pump chamber62is an acid solution which enters the cartridge from a known bagged supply (not shown for clarity) at an acid solution inlet port66. From the acid inlet port66the acid solution passes through a second dialysate base solution pump chamber in the form of an acid dosing pump chamber68via acid dosing pump chamber inlet valve70and an outlet valve72. In this way bicarbonate mixture and acid solution are admitted into the acid pump chamber62for subsequent pumping out of the pump chamber62of a fully mixed dialysate solution via an acid pump outlet valve74. From here the fully mixed dialysate solution passes through a first dialysate temperature sensor76and first dialysate conductivity sensor78. A second dialysate temperature sensor80and second dialysate conductivity sensor82are provided to corroborate the data provided by the first sensors76,78.

Fully mixed dialysate solution then passes through aperture84(shown inFIG. 7only) to be received by the flow balance portion19of the cartridge16.

Flow Balance

The flow balancer19is mirrored about centreline A-A as shown inFIG. 7. The flow balancer19will be described with reference toFIGS. 7 and 8.

Dialysate solution passes from the aperture84into the first flow balance pump chamber104through inlet valve106upon the actuation of the membrane by the machine10to draw the dialysate into the pump chamber of pump104. The dialysate solution is then pumped out of the pump chamber104via outlet valve108upon the closure of the inlet valve106. The dialysate solution then passes down a channel110before passing into a dialyser outlet channel112. From there the dialysate solution exits the cartridge via dialyser outlet114and is carried to a dialyser (not shown for clarity).

The dialysate solution returns to the cartridge from the dialyser via a tubing set (also not shown for clarity). A second flow balance pump chamber126is actuated to draw the dialysate solution through the inlet122, down dialyser inlet channel124, passed the second flow balance pump inlet valve128and into the pump chamber126. The dialysate solution is then pumped out of the pump chamber126via an outlet valve130upon the closure of the inlet valve128. The dialysate solution then passes down a drain outlet channel132. From there the dialysate solution exits the cartridge via drain outlet134and is carried to a drain (not shown for clarity).

The operation of the first and second flow balance pumps can be switched by virtue of the mirroring of the valves and pump chambers. In this way the first flow balance pump104is also used to draw dialysate solution form the dialyser118and the second flow balance pump126is used to pump dialysate solution into the dialyser118. This allows the pumps to switch over the course of a treatment ensuring that any geometric variance between the first and second pump chambers is balanced out.

Control of Dialysate Mixing

In use the volume of bicarbonate and acid solution mixed with the RO water must be closely monitored and controlled in order to achieve effective treatment. The monitoring is achieved in a known manner using conductivity sensors78,82(seeFIG. 7). In the present invention the conductivity signal generated by these sensors (which is indicative of the strength of the admixture) is used to control the volume of bicarbonate solution pumped through the bicarbonate dosing pump chamber46into the bicarbonate pump chamber52and the volume of acid solution pumped through the acid dosing pump chamber68into the acid pump chamber62as follows.

Referring toFIG. 9the platen21has features which correspond to the features on the cartridge16. The platen21has the following features:a first dialysate base solution pump cavity in the form of bicarbonate dosing pump cavity210which corresponds to the bicarbonate dosing pump chamber46on the cartridge16and which together form a first dialysate base solution pump;a second dialysate base solution pump cavity in the form of an acid dosing pump cavity212which corresponds to the acid dosing pump chamber68on the cartridge16which together form a first dialysate base solution pump;a first mixing pump cavity in the form of a bicarbonate pump cavity214which corresponds to the bicarbonate pump chamber52on the cartridge16which together form a first mixing pump;a second mixing pump cavity in the form of an acid pump cavity216which corresponds to the acid pump chamber62on the cartridge16which together form a second mixing pump;a first flow balance pump cavity218which corresponds to the first flow balance pump chamber104on the cartridge16which together form a first flow balance pump; anda second flow balance pump cavity220which corresponds to the second flow balance pump chamber126on the cartridge16which together form a second flow balance pump.
Vacuum Attachment

The platen21has an aperture in the form of vacuum attachment port230surrounded by an o-ring seal231. In use the vacuum passage port23on the cartridge16aligns with the vacuum attachment port230. Similarly the access depression5on the interface plate8aligns with the vacuum passage port23on the door side of the cartridge16to form a pneumatic supply line between the engine portion and the interface plate8.

In use the door14is opened by the user and the cartridge16inserted into the recess25in the platen21. The door14is then closed. A load is then applied to the rear of the interface plate8by the airbag31in the door14in order for the cartridge to engage the gasket seal11on the interface place. This forms an interface cavity between the interface plate and the cartridge16. The engine portion then applies a vacuum to the interface cavity via the pneumatic supply line (the recess7, the access depression5, the vacuum passage port23through the cartridge16, and the vacuum attachment port230). Under the action of the vacuum air is drawn from the recess7via the depression5which acts to ease the removal of air from the recess7. This evacuation of air has the effect of pulling the membrane13on the door side of the cartridge16against the interface plate8. This in turn reduces the compliancy in the membrane13by overcoming any pressure fluctuation observed by the membrane13on the door side of the cartridge16caused by operation of the membrane on the body side of the cartridge to pump fluid through the cartridge. This reduction in compliancy is achieved by reducing the tendency of the membrane to move under operation of the cartridge to mix and pump dialysate. This increases the volumetric accuracy of the mixing and pumping which leads to improved accuracy of dialysate composition and flow balance.

It will be appreciated that the pattern of the recesses7formed in the interface plate8is given by way of example only and that the configuration of the recesses could be changed without departure from the invention.