EP0538327A1

EP0538327A1 - Fluid control apparatus and methods

Info

Publication number: EP0538327A1
Application number: EP91912718A
Authority: EP
Inventors: Edward Hugh Dyson; Edward Goutcher
Original assignee: RENALAID Ltd
Current assignee: RENALAID Ltd
Priority date: 1990-07-06
Filing date: 1991-07-08
Publication date: 1993-04-28
Also published as: WO1992000768A1; GB2246718B; GB2246718A

Abstract

Un appareil de régulation de fluide (50), qui peut être utilisé pour la dialyse rénale, comprend un tube d'alimentation en sang (51) servant à alimenter un côté d'un dialyseur (53) en sang provenant du patient. Du sang est réinjecté au patient par le tube (56). Une pompe péristaltique occlusive (60) est agencée afin d'entraîner du fluide, à partir d'une source de dialysat (80) jusqu'à un autre côté du dialyseur (53) par le tube (61). Les deux côtés du dialyseur sont séparés par une membrane de filtration. Une pompe péristaltique occlusive (65) est installée pour entraîner du fluide à partir du dialyseur (53), le long du tube (62) jusqu'à un récipient pour déchets (66). Un tube pour fluide (70) communique avec le tube (62), une pompe (71) étant installée pour entraîner du fluide le long de ce tube jusqu'à un récipient (73) de collecte de produit filtré. Des pompes occlusives (60, 65) sont mécaniquement reliées pour pomper du fluide avec le même débit. Lors de l'utilisation, du sang est pompé dans les tubes (51, 56), et du fluide est amené à circuler par l'intermédiaire des pompes (60, 65) vers le dialyseur et en provenance de celui-ci. Dans cet agencement, aucun écoulement net de fluide ne passe du côté recevant le sang du dialyseur (53) à l'autre côté. Un écoulement net de fluide à travers la membrane de filtration peut être obtenu lorsque l'on pompe le fluide jusqu'au récipient (73) par l'intermédiaire de la pompe (71). En ce cas, le fluide s'écoule à travers le dialyseur (53) à partir du patient en fonction du volume de fluide enlevé par la pompe (71). Ainsi, la régulation volumétrique du fluide prélevé au patient peut être effectuée. Dans une variante, la régulation volumétrique du fluide prélevé peut être effectuée par le réglage de la différence de vitesse de rotation des pompes (60 et 65) et la collecte du produit ultrafiltré. L'appareil peut être utilisé généralement dans les procédés de filtration ou le traitement par dialyse. L'appareil peut être modifié afin d'effectuer l'hémofiltration.A fluid regulator (50), which can be used for kidney dialysis, includes a blood supply tube (51) for supplying blood from the patient to one side of a dialyzer (53). Blood is reinjected into the patient through the tube (56). An occlusive peristaltic pump (60) is arranged to drive fluid from a source of dialysate (80) to another side of the dialyser (53) through the tube (61). The two sides of the dialyzer are separated by a filtration membrane. An occlusive peristaltic pump (65) is installed to drive fluid from the dialyzer (53), along the tube (62) to a waste container (66). A fluid tube (70) communicates with the tube (62), a pump (71) being installed to drive fluid along the tube to a container (73) for collecting the filtered product. Occlusive pumps (60, 65) are mechanically connected to pump fluid with the same flow. In use, blood is pumped through the tubes (51, 56), and fluid is caused to flow through the pumps (60, 65) to and from the dialyzer. In this arrangement, no net fluid flow passes from the blood receiving side of the dialyzer (53) to the other side. A clear flow of fluid through the filtration membrane can be obtained when the fluid is pumped to the container (73) via the pump (71). In this case, the fluid flows through the dialyzer (53) from the patient depending on the volume of fluid removed by the pump (71). Thus, the volumetric regulation of the fluid withdrawn from the patient can be carried out. In a variant, the volumetric regulation of the fluid withdrawn can be carried out by adjusting the difference in speed of rotation of the pumps (60 and 65) and collecting the ultrafiltered product. The apparatus can be used generally in filtration processes or dialysis treatment. The device can be modified to perform hemofiltration.

Description

FLUID CONTROL APPARATUS AND METHODS

This invention relates to fluid control apparatus and methods and particularly, although not exclusively, provides apparatus for controlling the quantity of fluid and/or solutes removed from or input into a patient and methods relating thereto.

The human kidney is an essential homeostatic organ. It is involved in excretion of unwanted metabolic products and the regulation of the water content of the blood. Kidney failure may arise from trauma, infection or major surgery and this failure is a commonly encountered problem in a hospital's intensive care unit, carrying a high mortality rate.

It is known to provide artificial kidney machines which are linked into, and become a part of, a patient's blood transport system, so as to take over the task of eliminating waste products and water from a patient in the place of the patient's damaged kidney. Figure 1 of the accompanying drawings is a diagrammatic representation of a known continuous arteriovenous haemofiltration apparatus.

One end of a blood input tube 2 is linked to an artery of a patient. The other end of the tube 2 is attached to an upstream side of a filter 3 having a filtration membrane 4. A blood output tube 5 leads from the filter 3 back into a vein of the patient. A filtrate output tube 6 is attached to the filter 3 on the downstream side of the filtration membrane 4.

In use, blood is pumped by the patient's own arterial blood pressure down input tube 2 to the filter, whereupon - 2 - some blood is filtered. Some blood then flows down output tube 5 back to the patient. Filtrate passes through the filtration membrane 4, out of the filter 3, via ouput tube 6 where it is collected in a container 7. Infusate 8 may be directed into output tube 5 for replacing and/or replenishing the patient's body fluids.

The quantity of fluid removed using this apparatus will depend on a number of factors; for example, the patient's arterial blood pressure; the diameter of tubes 2, 5 and 6; and the permeability of the filtration membrane 4. Additionally, the viscosity of the patient's blood will affect filtrate quantity and, in particular, if the blood starts to clot (as it is prone to do) , the pressure on the upstream side of the filtration membrane 4 will increase, leading to an unpredictable effect on the amount of fluid removed. All of the above mentioned factors are largely unmeasurable and, therefore, the exact control of the quantity of fluid removed by the apparatus is impossible. The inadequacies of the apparatus are furthermore highlighted by noting that attempts to control fluid removal include the use of adjustable clamps, for example, at positions 10, 11 which constrict either one of respective tubes 5, 6 so as to adjust the pressure gradient across the filtration membrane 4 and control the flow of fluid into container 7. Furthermore, flow rate may be decreased by raising the level of tube 6 (as seen in dotted lines in Figure 1) effectively increasing hydrostatic pressure on the downstream side of the filtration membrane 4, or flow rate may be increased by lowering the level of tube 6 to decrease hydrostatic pressure on the downstream side. It will be appreciated from the above that accurate control of the volume of fluid removed or the rate of fluid removal is not possible.

A further known apparatus is shown in Figure 2 of the accompanying drawings which figure is a diagrammatic representation of a continuous arteriovenous hae odialysis apparatus. In the figure, the filter 3 of Figure 1 is replaced by a dialyser 20. Blood flows via tubes 2 and 5 on one side of a dialyser membrane 21. On the other side of the dialyser membrane 21, dialysate fluid flows from a supply 22 via dialysate input tube 23 and dialysate output tube 24 to a container 7.

The control of the amount of fluid removed from the patient is as problematic as stated in relation to the Figure 1 embodiment, and accordingly, accurate control is impossible.

In general terms, patients with multi-organ failure often have a great deal of circulatory instability. Though continuous arteriovenous haemofiltration and continuous haemodialysis are, at present, playing an important role in the management of patients in intensive care units, the following problems may be associated with such techniques:

(i) Even with inotropic support, the patient's blood pressure may be too low to provide an effective ultrafiltration or dialysis rate;

(ii) The removal of volume from the arterial side of the circulation may exacerbate circulatory instability; (iii) As control of the ultrafiltration rate or dialysis rate is often achieved by a gate clip on the filter or dialyser output line, considerable experience and care is required if the desired fluid removal is to be achieved smoothly and with minimum trauma to the patient; and

(iv) Prolonged arterial catheterisa ion may be accompanied by haemorrhage, false aneurysm formation and limb ischaemia.

We aim to improve upon the aforementioned by providing apparatus which may alleviate at least some of the problems associated with known apparatus and techniques.

According to the invention, there is provided fluid control apparatus for use with a treatment member having a first side and a second side separated by a treatment membrane, the apparatus comprising a first occlusive pump means arranged to pump treatment fluid to a first region on one of either the first or second side of a treatment membrane of a treatment member and a second occlusive pump means arranged to pump treatment fluid away from the second side of the treatment membrane, pump control means being provided for controlling the rate of pumping of the first occlusive pump means relative to the second occlusive pump means.

Preferably, the pump control means is arranged to cause the first and second occlusive pump means to ump fluid at the same rate. In this case, therefore, the volume of treatment fluid pumped, over a time "t", by the first occlusive pump means, to the first region, is substantially equal to the volume of fluid pumped away, over time "t", from the second side of the treatment membrane.

Preferably, a first fluid flow path which extends from the first region to the first occlusive pump means is closed to the external atmosphere 3. Preferably, a second fluid flow path which extends from the second side of the treatment membrane to said second occlusive pump means is closed to the external atmosphere. Preferably, a region up-stream of the first occlusive pump means is closed to the external atmosphere 8. Preferably, a treatment fluid supply reservoir is provided up-stream of the said first occlusive pump means, said supply reservoir preferably being closed to the external atmosphere. Said treatment fluid supply reservoir is preferably a collapsible bag.

Preferably, the fluid control apparatus further comprises a third pump means, preferably an occlusive pump means, arranged to pump blood from a patient to the first side of the treatment membrane of the treatment member. Preferably, means is provided for controlling the flow rate of fluid pumped by the third pump means independently of the flow rate of fluid pumped by the first and second occlusive pumps.

Preferably, a region downstream of the second occlusive pump means is open to the external atmosphere. That is, it is open to external atmospheric pressure.

Preferably, a fourth pump means, preferably an occlusive pump means, is provided and arranged to pump fluid away from the second side of the treatment membrane. Preferably, said fourth pump means is arranged to remove fluid from said aforementioned second fluid flow path. Preferably, means is provided for controlling the fourth pump means independently of said first and second and/or third pump means.

Preferably, a fourth fluid flow path Which extends between the treatment member and the fourth pump means is closed to the external atmosphere. The fourth fluid flow path may extend from a position in said second fluid flow path to the fourth pump means. Preferably, a region downstream of the fourth pump means is open to the external atmosphere.

Preferably, said pump control means comprises a link means between the first and second occlusive pump means. Said link means is preferably a mechanical link, preferably arranged to cause the first and second occlusive pump means to pump fluid at the same rate.

Preferably, the first occlusive pump means and/or the second occlusive pump means and/or where provided the third pump means and/or the fourth pump means are, independently occlusive pumps, for example, peristaltic pumps.

Preferably, the apparatus includes a treatment membrane location site, wherein a treatment membrane may be located, in use.

The invention extends to a fluid control apparatus as described in any statement herein, in combination with a treatment member as arranged and as described in any statement herein.

Thus, preferably, in accordance with the preceding statements, a fluid control apparatus comprises:- a treatment member having a first side and a second side which sides are separated by a treatment membrane;

a first occlusive pump means arranged to pump fluid to a first region on one of either the first or second side of the treatment member;

a second occlusive pump means arranged to pump fluid away from the second side of the treatment member;

wherein pump control means is provided for controlling the rate of pumping of the first occlusive pump means relative to the second occlusive pump means.

Preferably, the first occlusive pump means and/or the second occlusive pump means are arranged to pump treatment fluid, for example, a dialysate fluid. Preferably, up¬ stream of the first occlusive pump means there is provided a means for connecting the apparatus to a treatment fluid supply reservoir such that fluid from said reservoir may be pumped by said first occlusive pump means to said first region. The apparatus may include a treatment fluid supply reservoir which is arranged to feed treatment fluid into a fluid flow path in which path said first occlusive pump means pumps fluid. Preferably, upstream of the first occlusive pump means is closed to the external atmosphere. The treatment fluid supply reservoir is preferably a collapsible reservoir, for example, a collapsible bag.

Preferably, the apparatus is arranged such that an inter-pump fluid path which extends from the first occlusive pump means to the second occlusive pump means is closed to external atmosphere. The treatment membrane is preferably in said inter-pump fluid flow path. The treatment membrane may define a boundary wall of said path which wall extends in the direction of the inter-pump path. For example, in dialysis, or said treatment membrane may define a boundary wall of said path which wall separates the path into two parts. For example, when the apparatus is arranged for pre-dilutional or post dilutional haemofiltration. Preferably, the first occlusive pump means pumps fluid into the inter-pump fluid path. Preferably, the second occlusive pump means removes fluid from the inter-pump fluid flow path. Disequilibrium means is preferably provided for causing a fluid disequilibrium in said inter-pump fluid path. Said disequilibrium may be produced by causing the rate of flow of fluid to the first region on one of either the first or second side of the treatment membrane to be greater than the rate of flow of fluid away from the treatment membrane, or by causing the rate of flow to the first region to be less than the rate of flow away from the treatment member. Said disequilibrium is preferably produced, for example, in dialysis by causing the rate of flow of fluid to the treatment membrane to be greater than the rate of flow of fluid away from the treatment membrane or by causing the rate of flow of fluid from the treatment membrane to be less than the rate of flow of fluid away from the treatment membrane. In both cases the apparatus is preferably arranged such that fluid may flow from a region outside the inter-pump fluid flow path, but communicating therewith, to re-equilibriate. For example, when the inter-pump fluid flow path extends from the first occlusive pump means to the second side of the treatment member and back to the second occlusive pump means, a fluid disequilibrium caused if, for example, a fourth occlusive means withdraws fluid from a flow path between the second side of the membrane and the second occlusive pump means will be rectified, (that is, re-equilibriation will take place) by means of fluid passing from the first side of the treatment membrane into the second side thereof.

Preferably, the apparatus is arranged such that, in use, the net volume of fluid flowing across the treatment membrane may be controlled, preferaby by a control means, for example, by means of the aforementioned fourth pump means. Preferably, the rate of flow of fluid across the treatment membrane may be controlled. Said treatment membrane may be a dialysis membrane, or a filtration membrane.

The invention extends to a method of filtering fluid, preferably, blood, using a fluid control apparatus as described in any statement herein.

The invention extends to a method of controlling the passage of fluid across a treatment membrane using fluid control apparatus as described in any statement herein.

The invention extends to a method of kidney dialysis or kidney or liver filtration, the method comprising connecting the aforementioned apparatus to a patient so as to dialyse or filter the patient's blood.

The invention extends to a fluid pump comprising a plurality of abutment means rotatably mounted for rotation about an axis, _ and comprising one or a plurality of abutment surface(s) arranged to cooperate with the abutment means so that, in use, a pipe may be squeezed between an abutment means and an abutment surface, the pump being arranged to pump fluid through at least two pipes, the arrangement being such that, at one instance in use, one pipe may be squeezed at a first location and another pipe may be squeezed at a second location, the first and second locations being substantially radially disposed of said axis with an angle θ defined between the radii, wherein θ is greater than 0°.

Preferably, θ is 180°. That is, the first and second locations are substantially diametrically opposed. Two or four abutment means may be provided. The abutment means may be mounted on radial arms pivotable about said axis.

Said fluid pump may be provided in combination with the invention as described in any statement herein.

By way of example, specific embodiments of the invention will be described, with reference to the accompanying diagrammatic drawings in which:-

Figure 3 is a diagrammatic representation of haemodialysis apparatus.

Figure 4 is a diagrammatic representation of a dialyser.

Figure 5 is a diagrammatic representation of an alternative haemodialysis apparatus;

Figures 6 is a diagrammatic representation of an occlusive peristaltic pump;

Figure 7 is a diagrammatic representation of an alternative occlusive peristaltic pump;

Figures 8 and 9 are diagrammatic representations of pre-dilutional and post-dilutional haemofiltration apparatus respectively; and - 11 -

Figure 10 is a representation of a pump.

In Figure 3, the haemodialysis apparatus 50 comprises a blood delivery line 51 having a first occlusive peristaltic pump 52 arranged to drive fluid through the line 51 towards a dialyser 53.

The line 51 leads into one part 54 of the dialyser 53

(Figure 4) , namely the blood part of the dialyser. The blood part 54 is separated from a dialysate part 58 by a semi-permeable membrane 55. A blood return line 56 is attached to the blood part 54 of the dialyser.

A second occlusive peristaltic pump 60 is arranged to drive fluid through a dialysate delivery line 61 to the dialyser 53. The dialysate delivery line 61 communicates with the dialysate part 58 of the dialyser 53 (Figure 4) . A dialysate return line 62 is attached to the dialyser part -58. A third occlusive peristaltic pump 65 is arranged to drive fluid from the dialysate part 58 along the return line 62 and then along a fluid line 69 towards a waste vessel 66.

A fluid line 70 communicates with the return line 62, between the dialysate part 58 and the third pump 65. A fourth occlusive metering pump 71 is arranged to drive fluid along the fluid line 70. The fluid line 70 leads into a container 73.

As indicated, pumps 60 and 65 are occlusive peristaltic pumps. An occlusive peristaltic pump does not contact the fluid being pumped. It effectively squeezes the tube, for example, dialysate delivery line 61 or return line 62, to push fluid through the tube. A simplified diagrammatic representation of an occlusive peristaltic pump is shown in Figure 6 wherein a length of resilient plastic tube 200 is held in position by suitable means (not shown) against a rigid back member 201. A pump arm 202 is pivotally mounted at pivot point 203, the arm being arranged to rotate about point 203, in the direction shown by arrow 204, by a suitable means, for example, an electric motor. The arm 202 carries, at each end, a rotable rigid abutment member 205.

The arrangement of the apparatus is such that, in use, the abutment member 205 may totally occlude the tube 200, the tube 200 being squeezed between the abutment member 205 and the back member 201. As the arm 202 rotates in an anticlockwise direction, fluid present in tube 200 is pushed in front of the point of contact of the abutment member 205 with the tube 200 and, therefore, driven through the tube 200. Each of the abutment members 205 may squeeze the tube at one time. At another time (seen in Figure 6) during rotation of the arm 202 one of the abutment members 205 will not be suitably disposed to occlude the tube 200. Nevertheless, it should be noted that at all times during rotation of the arm 202, at least one of the respective abutment members 205 totally occludes the tube 200.

The haemodialysis apparatus 50 also includes a dialysate supply 80 communicating via a fluid line 81 with dialysate delivery line 61, the pump 60 being arranged to drive fluid from the supply 80 to the delivery line 61. In the fluid line 81, there is provided a heating device 82 and a supply fluid alarm means 83.

An infusate supply 84 communicates via a fluid line

85 and a valve 86 with blood return line 56. First pressure monitoring means 87 and second pressure monitoring means 88 are arranged to measure pressure in blood return line 56 and dialysate return line 62 respectively. An anticoagulant, for example, heparin or prostacyclin, supply means (not shown) is provided and arranged to feed anticoagulant into line 51.

The apparatus may be used as follows, for example, in venovenous haemodialysis. A dual lumen venous catheter is inserted in a major vein, for example, the internal jugular or subclavian vein of a patient. One lumen of the catheter is arranged to communicate with blood delivery line 51, the other lumen being arranged to communicate with blood return line 56 so as to provide a continuous passage from the vein to the respective lines 51, 56. The first pump 52 may then be operated to pump blood through blood delivery line 51, through the blood part 54 of the dialyser 53, through the blood return line 56 and back to the patient in a closed system, as indicated by arrows 100.

With dialysate fluid in the supply 80, the second pump 60 and the third pump 65 are switched on. Fluid therefore flows from supply 80, through fluid line 81, through dialysate delivery line 61, through the dialysate part 58 of the dialyser 53, through the dialysate return line 62, through fluid line 69 to the waste vessel 66, as indicated by arrows 101.

It should be noted that the second pump 60 drives dialysate fluid to the dialyser 53 and the third pump 65 drives fluid from the dialyser 53. The second pump 60 and the third pump 65 are mechanically linked by a suitable linking means (not shown) , so that, when in use, their respective pumping actions are synchronised. - 14 -

Given that the diameter of delivery line 61 and the diameter of dialysate return line 62 have substantially exactly the same cross-sectional area, and with the second pump 60 and third pump 65 being synchronised and working at identical rates, the rate of flow of fluid into the dialyser 53 equals the rate of flow of fluid from the dialyser. Thus, a constant flow of dialysate passes through the dialysate input line 61, through the dialysate part 58 of the dialyser, through the dialysate return line 62 and through the fluid line 69 to the waste vessel 66. Thus, there is no net gain or loss of fluid from the blood part 54 of the dialyser 53 to the dialysate part 58. Nevertheless, it should be noted that osmosis will take place across the semi-permeable membrane 55 and, accordingly, the blood will be "cleaned". It is preferable, in certain situations, depending on the type of treatment membrane used, to use sterile dialysate in supply 80 to minimise the risk of patient infection during osmosis.

The rate of osmosis may be controlled, to some extent, by controlling the rate at which pumps 60 and 65 pump dialysate to the membrane 55, as the rate of pumping will affect the concentration gradient across the semi- permeable membrane 55.

The use of the apparatus 50 as described above to "clean" the blood whilst accurately maintaining patient blood volume may substantially reduce patient trauma.

When it is required to remove a measured amount of fluid from the patient, the fourth pump 71 is actuated.

The pump 71 withdraws fluid from line 62 as indicated by arrow 102. This fluid removal causes fluid pressure in line 62 to fall and accordingly, the equilibrium of the system will become unstabilized. However, as pumps 60 and 65 totally occlude respective lines 61, 62 so that fluid can only flow when driven by the respective pumps 60 and 65 and as the pumps 60 and 65 are synchronised so as to pump fluid at the same rate, a new stable fluid equilibrium cannot be achieved by input of additional fluid into the dialysate lines 61, 62 from the supply 80. The only source of fluid available to input into fluid line 62 and restore equilibrium is from the blood part 54 of the dialyser. Thus, equilibrium is restored due to a net volume of fluid flowing from the patient through line 51 and across the membrane 55. (The membrane 55 is selective in that in general only unwanted products pass through in the fluid, such as water and toxins; blood cells, hormones etc. will not in general be removed) .

It should be noted that the quantity of dialysate captured in container 73 is substantially volumetrically exactly the same (within accepted tolerances of the apparatus etc.) as the amount of fluid removed from the patient. This is due to the equality of flow rates into and out of the dialyser due to the synchronicity of pumps 60, 65 and the fact that the only source of fluid to restore the equilibrium is from the patient side of the dialyser 53.

A measured amount of fluid may be inputted into the patient from supply 84, as required. This may be carried out manually, for example, by means of an operator controlling a gate clamp. Preferably, a computer controlled valve is used. It should be appreciated that the amount of fluid infused into the patient may be based upon the amount removed and captured in container 73 and the rate at which, and amount of, fluid removed from the patient may be balanced to the rate at which, and amount of, fluid infused back into the patient, as required. This may serve to substantially reduce patient trauma.

It should now be appreciated, that the rate at which pump 71 drives fluid along line 70 generally equals the rate at which fluid passes from the blood part 54 of the dialyser to dialysate part 58 thereof and, in turn, generally equals the rate at which fluid is removed from the patient. Control means (not shown) is provided to control the speed of pump 71 and, thus, this control means effectively controls the rate of removal of fluid from the patient. Furthermore, it will be appreciated that for a known flow rate, the volume of fluid to be removed from a patient may be predetermined by varying the time for which the pump 71 is actuated, as required.

Suitably, the flow rate of fluid through lines 61, 62 may be selected in the range 30 ml/min (1.8L/hr) to 333 ml/min (20L/hr) . This is less than the 500 ml/min often used in conventional machines. Suitably, the rate of removal of fluid from a patient may be selected in the range 0 to 1000 ml/hour.

Infusate, containing, for example, water, essential salts etc. may be inputted into the line 56 depending on whether valve 86 is open or closed.

Dialysate may be warmed by the heating device 82 as it passes along line 81.

The pressure in lines 51, 56 and 62 may be monitored by means of pressure monitoring means 187, 87 and 88 respectively. Pressure monitoring means in the lines 51,

56 may be arranged to produce a signal if blood starts to clot in the lines or in the dialyser 53. The anticoagulant supply means may be actuated as required to deliver anticoagulant into blood input line 51.

It should be noted that the quantity of fluid removed by apparatus 50 may not, in general, be affected by uncontrollable factors, for example, the patient's arterial blood pressure, the permeability of the filtration membrane and the viscosity of the patient's blood, as in the prior art mentioned previously; that is, the quantity removed may be controlled, irrespective of pressures generated in the blood compartment by the blood flow. The amount of fluid removed depends on conditions appertaining on the dialysate side of the dialyser 53. Even if the blood starts to clot in line 51, the amount of fluid removed from the patient will not b affected, provided, of course, that there is some fluid present in the blood part of the dialyser 53 which can pass through the membrane 55 to replace dialysate removed by pump 71.

The apparatus 50 may be modified and augmented in many ways. For example, blood monitoring means may be provided to monitor concentrations of solutes (eg. sodium ions, potassium ions, lactate, urea, creatinine, alcohol, poisons etc.), the patient's blood pressure, blood viscosity and, in particular, whether the blood is in danger of clotting, in one or both of blood lines 51 and 56. The information may be continuously fed into a computer to control any action necessary to alleviate low blood sodium levels, high pH or high water levels etc. The action necessary may include inputting a predetermined amount of sodium into the patient's blood, inputting a predetermined amount of an acetate buffer into the blood or removing water from the blood by actuating the fourth pump 71 for a predetermined time so as to remove fluid from the patient's blood. Alarm means may be provided, for example alarm 83, so as to alert when either the apparatus or the patient require human intervention, for example, when dialysate 80 needs replenishing. Further alarm means may be provided to detect, for example, if the patient's blood pressure falls to a dangerously low level.

A patient may be connected to apparatus 50 for a long period of time without the need for constant human intervention and supervision. Reduction in human intervention and supervision may provide substantial cost savings. Furthermore, dialysate may be caused to flow relatively slowly, compared to prior known apparatus, through apparatus 50 and fluid may suitably be removed from the patient much more slowly than in the prior art machines - to some extent the apparatus 53 may behave more like a human kidney. For example, in an intensive care situation, the apparatus 50 may be used to remove a desired quantity of fluid over a 44 hour period whereas in prior known machines the same quantity of fluid may be removed in only 4 hours. Alternatively, the apparatus may be used in an intensive care situation simply to "clean" the patient's blood with no net loss or gain of fluid from or to the patient. Furthermore, slow dialysis may increase the efficiency of removal of unwanted molecules. Using the apparatus 50, therefore, may reduce the amount of dialysate needed in a particular situation and thereby provide substantial cost savings. As mentioned previously, sterile dialysate may be used in supply 80 of apparatus 50. Such sterile dialysate may be circulated through the dialyser 53 a plurality of times. As this sterile dialysate will only become "contaminated" by the patient's blood during passage through the apparatus 50, there are unlikely to be any detrimental effects on the patient should some such contaminated dialysate pass to - 19 - the blood part of the dialyser. The use of recirculated dialysate may further reduce the costs involved in a treatment. Thus, the apparatus may be used as a substantially autonomous means of monitoring and controlling fluid and solute levels in a patient's bloodstream.

Any pump that may be arranged to function in an occlusive manner may be of utility instead of the occlusive peristaltic pumps described above.

As previously mentioned, the second pump 60 and third pump 65 are mechanically linked. Such a linkage may take a number of alternative forms; for example the arm 202 of each pump may be mounted on a single driven shaft so that rotation of the shaft causes rotation of the respective arms of each of pumps 60 and 65. Alternatively, each arm of pumps 60, 65 may be mounted on separate shafts, each respective shaft being driven, via intermediate gearing, by a single driven shaft. In a further alternative arrangement, each shaft of a respective pump 60, 65 may be driven by a respective motor, the rate of the respective motors being computer controlled thereby to synchronise the pumps as desired.

A means of linking two pump means is shown in Figure 7. In the Figure, a pump 300 includes a cross-shaped pump head 301, having four abutment members 302 which are arranged so that each of fluid pipes 303, 304 are totally occluded at any one time. Rotation of the pump head 301 about an axis 305 causes fluid to be pumped along pipes 303, 304 in the direction of arrows 306, 307 respectively. This pump 300 may be a particularly advantageous way of providing linked pump means and may be of general use in any of the embodiments described herein. The pump 300 may, furthermore, be relatively durable and reliable, as it should be noted that, an equal and opposite force is applied to opposite abutment members 302 by respective pipes 303,304, and, accordingly, there is no resultant stress on axis 305, as may be the case in relation to the Figure 6 embodiment.

An additional means of linking two pump means is shown in Figure 10. In the Figure, a pump 600 includes an arm 601, pivotally mounted at pivot point 602, the arm 601 being arranged to rotate about point 602 in the direction of arrow 603 by suitable means. The arm 601 carries, at each end, a rotatable rigid abutment member 604, the abutment members being disposed at an angle θ which is 180° in the embodiment. A stepped abutment member 605 is provided. The member 605 is arranged to receive pipes 606 and 607. In the region of respective arcs 608, 609 of the pipes 606, 607, the member 605 provides abutment surface regions 610, 611, against which respective pipes 606, 607 may be urged by abutment members 604, in use.

In use, the arm 601 rotates and the abutment members 604 co-operate with the abutment surface regions 610, 611 so as to occlude the pipes 606, 607. It should be noted that at any one time, each of pipes 606, 607, is totally occluded. It may be noted that pipes 606, 607 leave the pump 600 from the same side from which they entered the pump 60. The pipes are, therefore, led through an angle of 180° in the pump.

A number of variations and extensions of the apparatus 50 may be provided, as follows:-

The apparatus 50 may be used in reverse so as to cause fluid and/or solute to pass from the dialysate part 58 of the dialyser to the blood part 54. To do this, the fourth pump 71 may be reversed so as to pump, for example, sterile plasma from container 73 into return line 62. This will tend to increase the fluid pressure in return line 62. As discussed previously, the supply lines between pumps 60, 65 and 70 provide an occluded system so that when fluid pressure within one or more of the lines 61, 62 or 70 is increased or reduced, a new equilibrium is established due to fluid leaving or entering respectively the supply lines via the dialyser. Thus, an increase in fluid pressure in return line 62 is reduced and a new equilibrium established due to fluid flowing from the dialysate part to the blood part of the dialyser. Additionally, it will be appreciated that fluid may be inputted into line 61, subsequently causing fluid to pass to the blood part of the dialyser.

An alternative means of controlling the rate at which fluid is removed from a patient and ultimately have volumetric control of fluid removal, is shown in Figure 5. In that Figure, the apparatus is generally as shown in Figure 3, except that line 70 and pump 71 are eliminated. A second pump 160 and a third pump 161 are provided to control fluid removal from the patient. A control means (not shown) is provided for controlling the relative speed of pumps 160 and 162.

Presuming that the cross-sections of lines 61 and 62 are identical, with pumps 160 and 162 working at the same rate, the rate of flow of fluid into the dialyser 53 will equal the rate of flow of fluid from the dialyser, as discussed in relation to the Figure 3 embodiment. If for example, however, pump 160 is set to run at 50 revolutions per minute (r.p.m.) and pump 162 is set to run at 51 r.p.m., there will be a fluid disequilibrium and so fluid will be drawn from the patient side of the dialyser through the dialysis membrane into the dialysate side of the dialyser to restore the equilibrium. Thus, fluid will be removed from the patient in dependence upon the relative speeds of pumps 160 and 162. Provided the rates of pumps 160 and 162 are precisely controlled and these rates are accurately known, the rate of removal of fluid and fluid volume removed can be predetermined.

The aforementioned embodiments may be modified so as to effect filtration instead of dialysis, so as to provide a means of volumetric haemofiltration.

A pre-dilutional haemofiltration apparatus is shown in Figure 8. The apparatus includes a blood delivery line 300 which is connected to the blood part of a filter unit 301. A blood return line 302 leaves the blood part of the filter unit 301 so as to return filtered blood to the patient. An occlusive peristaltic pump 303 is provided in the line 300 in order to deliver blood to the unit 301. An occlusive peristaltic pump 304, in the form shown in Figure 7, is provided and arranged to pump fluid through fluid lines 305, 306 in the direction of respective arrows 307, 308. The line 305 is arranged to deliver fluid from a replacement fluid supply 309 into the blood delivery line 300 so as to dilute the blood in the line 300 prior to it entering the filter unit 301. Fluid line 306 is connected to the filtrate side of the filter unit 301 in order to remove filtrate to a waste vessel 310.

The pump 304, which may simply be thought of as two linked pump means (similar to pumps 60, 65, shown in Figure 3) , is arranged to pump fluid along fluid lines 305 and 306 at identical rates. As the apparatus provides an occluded system, the volume of fluid removed from the patient by pump 304 along line 306 will be, for substantially all intents and purposes, volumetrically identical to the amount of replacement fluid pumped from supply 309, via line 305, into line 300. Thus, the patient may not suffer a net gain or loss of fluid during haemofiltration. Furthermore, as the rate of pump 304 is controllable, the rate of haemofiltration may be accurately controlled.

A post-dilutional haemofiltration apparatus is shown in Figure 9. The apparatus is similar to that shown in Figure 8. However, in Figure 9, the occlusive pump 304 is arranged to pump fluid in the direction of arrow 307 through a fluid line 320 which delivers replacement fluid into line 302 after the filter unit 301, so as to provide post-dilution. Again, as in Figure 8, the apparatus provides an occlusive system and, accordingly, the volume of fluid removed from the patient by pump 304 along line 306 will be, for all intents and purposes, volumetrically identical to the amount of replacement fluid pumped from supply 309, via line 305, into line 302, the patient thereby suffers no net fluid loss or gain.

It will be appreciated that it may be desired to produce a net loss or gain of patient fluid during haemofiltration. This may be achieved by providing means for affecting the relative rate of fluid flow in line 305, 306 or using an additional pump means, as discussed in relation to the Figure 3 embodiment.

Each of the embodiments described herein may include a means for causing a positive pressure on the upstream side of the occlusive pump which pumps dialysate from the dialysate supply. For example, referring to Figure 3, a variable speed occlusive pump means (or other variable pump means) may be provided between occlusive pump 60 and the supply 80. Alternatively, or additionally, each embodiment described herein may include a means for causing a negative pressure on the downstream side of the occlusive pump which pumps fluid to waste. For example, referring to Figure 3, a variable speed occlusive pump means (or other variable pump means) may be provided on the downstream side of pump 65. The rates of the aforementioned pumps may be adjusted to compensate for pressure variations within the apparatus due to tolerances in pipes, pumps etc.

As a predetermined and/or predictable volume of fluid may be removed from or infused into a patient, apparatus may be provided and steps may be taken to control relatively precisely the blood temperature. For example, a known quantity of fluid at a known temperature may be infused into a patient using the apparatus disclosed herein to either warm up (eg. in the case of a drowning patient) or cool down (eg. in the case of a hyperpyrexial patient) a patient. Thus, the apparatus may include heater means and/or refrigerator means to carry out this task.

The use of slow dialysis (or haemofiltration) made possible by the aforementioned apparatus, may greatly simplify fluid balance management in oliguric patients and may be used to aid temperature control. The apparatus may be of use in treating Adult Respiratory Distress Syndrome by aggressive fluid removal with inotropic support. The arrangement of the apparatus may be such as to allow a means of accurate volumetric control over a prolonged period. The apparatus disclosed herein may be of utility in any form of dialysis or filtration, for example, in arteriovenous or venovenous filtration or dialysis.

The apparatus disclosed herein may be of particular, although not exclusive, use in the treatment of kidney disorders. Additionally, however, the apparatus may be of use in treating liver disorders. For example, a treatment membrane, preferably a filtration membrane, may be arranged to cooperate with liver fluids and the apparatus may then be used to volumetrically control the fluid and toxins removed from the liver. The ability to provide volumetric control of filtration in relation to liver support may be particularly critical as incorrect fluid balance may lead to swelling in a patient's brain.

Furthermore, the apparatus may have more general use for filtering fluids, for example, in the purification of chemicals or other products.

The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification and which are open to public inspection with this specification, and the contents oi all sucn papers and documents are incorporated herein by reference.

All of the features disclosed in this specification (including any accompanying claims, abstract and drawings) , and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

Each feature disclosed in this specification (including any accompanying claims, abstract and - 26 - drawings) , may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

The invention is not restricted to the details of the foregoing embodiment(s) . The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings) , or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Claims

CLAIMS .

1. A fluid control apparatus for use with a treatment member having a first side and a second side separated by a treatment membrane, the apparatus comprising a first occlusive pump means arranged to pump treatment fluid to a first region on one of either the first or second side of a treatment membrane of a treatment member and a second occlusive pump means arranged to pump treatment fluid away from the second side of the treatment membrane, pump control means being provided for controlling the rate of pumping of the first occlusive pump means relative to the second occlusive pump means.

2. Apparatus according to claim 1, wherein the pump control means is arranged to cause the first aπd second occlusive pump means to pump fluid at the same rate.

3. Apparatus according to claim 1 or claim 2, wherein a first fluid flow path which extends from the first region to the first occlusive pump means is closed to the external atmosphere.

4. Apparatus according to any of the preceding claims, wherein a second fluid flow path which extends from the second side of the treatment membrane to said second occlusive pump means is closed to the external atmosphere.

5. Apparatus according to any of the preceding claims, wherein a region up-stream of the first occlusive pump means is closed to the external atmosphere.

6. Apparatus according to any of the preceding claims, wherein the fluid control apparatus further comprises a third pump means arranged to pump blood from a patient to the first side of the treatment membrane of the treatment member.

7. Apparatus according to any of the preceding claims, wherein a region downstream of the second occlusive pump means is open to the external atmosphere.

8. Apparatus according to any of the preceding claims, wherein a fourth pump means is provided and arranged to pump fluid away from the second side of the treatment membrane.

9. Apparatus according to claim 8, wherein a region downstream of the fourth pump means is open to the external atmosphere.

10. Apparatus according to any of the preceding claims, wherein said pump control means comprises a link means between the first and second occlusive pump means.

11. A fluid control apparatus according to any of the preceding claims in combination with a treatment member as arranged and as described in any of the preceding claims.

12. A fluid control apparatus comprising:-

a treatment member having a first side and a second side which sides are separated by a treatment membrane;

a first occlusive pump means arranged to pump fluid to a first region on one of either the first or second side of the treatment member; a second occlusive pump means arranged to pump fluid away from the second side of the treatment member;

13. Apparatus according to any of the preceding claims, wherein up-stream of the first occlusive pump means there is provided a means for connecting the apparatus to a treatment fluid supply reservoir such that fluid from said reservoir may be pumped by said first occlusive pump means to said first region.

14. Apparatus according to any of the preceding claims, wherein the apparatus includes a treatment fluid supply reservoir which is arranged to feed treatment fluid into a fluid flow path in which path said first occlusive pump means pumps fluid.

15. Apparatus according to any of the preceding claims, wherein the apparatus is arranged such that an inter-pump fluid path which extends from the first occlusive pump means to the second occlusive pump means is closed to external atmosphere.

16. Apparatus according to any of the preceding claims, wherein the treatment membrane is in said inter-pump fluid path.

17. Apparatus according to any of the preceding claims, wherein the apparatus is arranged such that, in use, the net volume of fluid flowing across the treatment membrane is controllable.

18. Apparatus according to any of the preceding claims, wherein the rate of flow of fluid across the treatment membrane is controllable.

19. A method of filtering a fluid, using a fluid control apparatus according to any of the preceding claims.

20. A method of controlling the passage of fluid across a treatment membrane using a fluid control apparatus according to any of the preceding claims.

21. A method of kidney dialysis or kidney or liver filtration, the method comprising connecting an apparatus according to any of the preceding claims to a patient so as to dialyse or filter the patient's blood.

22. A fluid pump comprising a plurality of abutment means rotatably mounted for rotation about an axis, and comprising one or a plurality of abutment surface(s) arranged to cooperate with the abutment means so that, in use, a pipe may be squeezed between an abutment means and an abutment surface, the pump being arranged to pump fluid through at least two pipes, the arrangement being such that, at one instance in use, one pipe may be squeezed at a first location and another pipe may be squeezed at a second location, the first and second locations being substantially radially disposed of said axis with an angle θ defined between the radii, wherein θ is greater than 0°.

23. A fluid pump according to claim 22 in combination with apparatus described in any of claims 1 to 21.