Single-needle extracorporeal plasmapheresis circuit

Abstract: A single needle extracorporeal plasmapheresis circuit makes use of a membrane filter (1) that separates, under the effect of TMP -transmembrane pressure,- plasma from blood. The filter (1) has two connectors (1a,1b) on the blood side, one of which (1a) is connected to a line ending with a single needle. Blood pump (4) is positioned along this line. The other connector (16) is connected to a second line (11) leading to a blood reservoir. An additional line (17) connects the plasma side of the filter (1) to a plasma collection bag (18) a pump (19) being placed on such line order to maintain the appropriate TMP throughout the whole process. Pump (19) is controlled by an automatic system that senses pressures, bubble levels, and weights of the various bags used in the circuit.

Description: The invention relates to a single-needle extracorporeal plasmapheresis circuit. EP-A-0 128 683 discloses a single-needle extracorporeal plasmapheresis circuit as defined in the preamble of the appended claim 1. It is known that plasmapheresis consists in removing blood from a donor or from a patient to introduce it in an extracorporeal circuit which comprises a filter in which a liquid fraction, called plasma, is separated from the blood mass which contains the cell fraction which is then reintroduced into the donor or patient; the plasma is then kept, in the case of removal from a donor, or eliminated if it is taken from a patient in order to replace it. In proceeding with a single-needle extracorporeal circuit, the process includes a series of cycles, each of which has a blood withdrawal step and a subsequent step for the reintroduction of the fraction which remains after plasma separation, which ends when the plasma collection reaches the required amount. In the extracorporeal circuits more commonly comprised within the known devices and methods, the filter in which the plasma is separated from the blood has a blood circuit connected at one end to a line provided with a pump connected to a single needle and at the other end to a line which leads into a blood collection reservoir, and is furthermore provided with a plasma container connected by a line to a plasma collection bag. The extracorporeal circuit thus configured allows a plasmapheresis process in which the plasma is separated from the blood exclusively during the steps of removal of the blood from the patient or donor, whereas during the subsequent reinfusion steps no plasma separation is performed and the plasma container is simply clamped to prevent pumping plasma or other liquids which are present in the system. Such processes therefore have the disadvantage of one active step out of two for each of the cycles, only one active step out of two, and of consequently entailing long cycle times, which are particularly unpleasant if the plasmapheresis relates a donor. The known devices also include a type of extracorporeal circuit in which there is a line for recirculating part of the blood through a filter during reinfusion, but with this method there is the risk of not operating within the optimum range of pressures of the fluids present in the system, resulting in a decrease in the efficiency of the system. The larger amount of blood not reinfused to the patient or donor leads to a decrease in the amount of fresh blood which can be drawn during a subsequent step. The aim of the present invention is thus to provide a single-needle extracorporeal plasmapheresis circuit which, by operating with the maximum possible efficiency, allows a drastic reduction in the time required for carrying out the plasmapheresis process. This aim is achieved by a single-needle extracorporeal plasmapheresis circuit according to the invention, as defined in the appended claim 1. Further characteristics and advantages will become apparent from the description of a preferred but not exclusive embodiment of the invention, illustrated only by way of non limitative example in the accompanying drawings, wherein: Figure 1 is a schematic view of an extracorporeal circuit. With reference to figure 1, the reference numeral 1 indicates a filter having a membrane through which the plasma is separated from the blood taken from a donor or from a patient. The presence of a transmembrane pressure, between blood and plasma is the difference between the average pressure in the blood circuit and the average pressure in the plasma contained inside the filter. The transmembrane pressure must be maintained at a preset level. The filter 1 has two connections in the blood circuit; the first connection designated by 1a, is connected to the line 2 which ends at a single needle 3. Line 2, can be shut off or closed by means of an electric solenoid clamp 2a. A blood pump 4 is interposed between connection 1a and single needle 3. A level sensor 5 and a bubble sensor 6 are each connected in series with line 2. Another line 7 is connected to the single needle 3 and conveys anticoagulant solution drawn from a bottle 8 by means of a pump 9. A bottle depletion control 10 is interposed between bottle 8 and pump 9 as a safety precaution. A second connection in the blood circuit of the filter 1, designated by 1b, connects line 11 which branches into two lines. Line 12, which can be shut off or closed by means of an electric solenoid clamp 12a, attaches to a blood collection reservoir 13, which is made in the shape of a bag. That bag ensures a pressure value equal to that of the atmospheric pressure therein, thus eliminating a need for detecting the internal bag pressure. Consequently, the system is simplified. Line 14, which can be shut off or closed by means of an electric solenoid clamp 14a attaches to the priming source 15. An automatic system 16 for weighing the reservoir 13 and source 15 is shown schematically in figure 1. An important feature is provided by line 17, which connects the plasma side of filter 1 to a plasma collection bag 18. Line 17 has a plasma pump 19, which is controlled by automatic control means connected to a microprocessor 20 thereby maintaining in the filter 1 the transmembrane pressure at the preset level, i.e. a substantially constant value within an optimum operating range for filter 1 during the entire duration of a plasmapheresis process. Therefore, the transmembrane pressure remains the same during the removal steps and during the reinfusion steps. An automatic system for weighing 18a is shown for bag 18 in figure 1. The signals detected by the sensors 5 and 6, by the bottle depletion control 10 and by the weighing systems 16 and 18a, together with those of the system pressure transducers 21, 22 and 23, reach a microprocessor 20, which is programmed to analyze information from the sensors and control the pumps 9, 4 and 19 and the electric clamps 2a, 12a and 14a thereby automatically operating the entire system. In figure 1, the broken lines represent the various electrical connections between the sensors and the microprocessor 20 of the control system. The operation of the invention is as follows: After the initial priming step and with washing liquid in the bag 15, a plasmapheresis process may begin with a removal step during which the blood, drawn by the pump 4, is supplied to the filter 1, by line 2. A certain amount of plasma is separated while the transmembrane pressure is maintained substantially constant. Operation of pump 19 ensures the constant transmembrane pressure by removing plasma and sending it to the collection bag 18. Residual blood leaves the filter 1, enters the lines 11 and 12 and collects in the bag 13. The substantially constant value of the transmembrane pressure is maintained within the optimum operating range of the system in the filter 1 by the action of the pump 19. The transmembrane pressure does not drop below the minimum values for the good efficiency of filter 1 and does not exceed the maximum values above which blood hemolysis risks arise. The removal step ends when a preset amount of blood in the bag 13 is reached, and the step of reinfusion of the blood contained in the bag 13 to the patient or donor begins with the reversal of the direction of rotation of the pump 4, to send the blood along the reversed path through the filter 1. The pump 19 operates during this reinfusion step as well, so as to maintain the transmembrane pressure in the filter 1 at an optimum value which may be preset by the operator, and therefore plasma separation continues during this reinfusion step as well as when the pump 19 conveys plasma to the bag 18. When the bag 13 is completely empty, the reinfusion step ends and a new cycle starts in a manner identical to the one described; the removal and the reinfusion steps thus follow one another and are adjusted by the circuit control of the system according to the microprocessor 20 until the required amount of plasma has been collected in the bag 18; at this point the process stops. The described operating condition is quite favorable, since the dual separations of plasma from blood during the removal steps and during the reinfusion steps allow an increase in the efficiency of the filter and consequently a drastic reduction in the time required for the process with respect to what occurs in the known devices and methods. The following numerical example is provided to show the importance of the invention. Assume one wishes to remove from a donor or patient an amount equal to 600 ml (milliliters) of plasma, removing 300 ml of blood during each of two cycles. Assuming a 20% efficiency of the filter, by working according to the most common known devices and procedures with plasma separation only during the removal step, a plasma volume equal to 300 ml x 0.20 = 60 ml is obtained for each cycle. Therefore, 600 ml + 60 ml = 10 cycles which are necessary in order to collect the required 600 ml of plasma. Things proceed quite differently with the extracorporeal circuit according to the invention, as is apparent by examining the amount of plasma collected for each cycle for an equal volume of removed blood, i.e. 300 ml, and for an equal efficiency of the filter, i.e. 20%. During the removal step, the plasma collection is again 300 ml x 0.20 = 60 ml, as with the known devices and methods, but plasma is now processed and obtained also during the step of reinfusion of the 300 ml - 60 ml = 240 ml of blood which remains. An amount of plasma equal to 240 ml x 0.20 = 48 ml is separated during reinfusion. During each cycle, therefore, one obtains 60 ml + 48 ml = 108 ml of plasma, and therefore, the required 600 ml of plasma are collected with a process which comprises only 600 ml + 108 ml = approximately 6 cycles, as opposed to the 10 cycles required when one operates with the previously described process. As mentioned, the achieved time saving is almost half which is truly considerable. The described invention is susceptible to numerous modifications and variations, all of which are within the scope of the inventive concept: thus, for example, the control system can allow, during operation, a certain variability in the transmembrane pressure in the filter 1, while maintaining the value within the optimum operating range. In the practical execution of the invention, the materials employed, as well as the shapes and the dimensions, may be any according to the requirements of a skilled practitioner; all the details may furthermore be replaced with other technically equivalent elements. Where technical features mentioned in any claim are followed by reference signs, those reference signs have been included for the sole purpose of increasing the intelligibility of the claims and accordingly, such reference signs do not have any limiting effect on the scope of each element identified by way of example by such reference signs.

Claims: A single-needle extracorporeal plasmapheresis circuit, comprising: a filter (1) for plasma separation from blood, the filter includes a membrane with a transmembrane pressure thereacross, the transmembrane pressure being the force to separate plasma from blood, the filter (1) having two connections (1a,1b) into the blood circuit, one connection (1a) on the blood side of the membrane includes a line (2) ending at a single needle (3), the line (2) with therein an interposed pump (4) for moving the blood therethrough, another connection (1b) in fluid communication with the blood side of the membrane of the filter (1) includes another line (11) connecting to a blood reservoir (13); the circuit being characterized in that said pump (4) interposed in the line (2) is a reversible pump (4) which is used during a removal step to draw blood and send it in a first direction in the line (2) to the filter (1) and which is used during a reinfusion step with the reversal of the direction of rotation of the pump (4) to send the blood along the reversed path through the filter (1), the reversed path being in a second direction opposite said first direction in the line (2), the circuit further comprising: a further line (17) between the plasma side of the membrane of the filter (1) and a plasma collecting bag (18), the further line (17) having another pump (19) therein, the other pump (19) operated by an automatic control means (20) for maintaining the transmembrane pressure across the membrane of the filter (1) at a value within an optimum range during the entire duration of the plasmapheresis process. The circuit according to claim 1, characterized in that the other pump (19) in the further line (17) between the plasma side of the membrane of the filter (1) and the plasma collection bag (18) is controlled by the automatic control means (20) to maintain the transmembrane pressure across the membrane of the filter (1) at a preset and substantially constant value within an optimum range during the entire duration of the plasmapheresis process. The circuit according to claim 1, characterized in that the blood reservoir (13) is a flexible bag and the pressure therein equals atmospheric pressure. The circuit of claim 3 characterized in that a pressure sensor (22) connected to the line (2) monitors pressure on the blood side of the membrane of the filter (1) and pressure sensor (23) monitors pressure on the plasma side of the membrane of the filter (1) so that the transmembrane pressure differential is transmitted to the automatic control means (20), the automatic control means (20) has a microprocessor arranged to analyze the signals and operate the other pump (19) for maintaining the transmembrane pressure at the preset and substantially constant value. The circuit of claim 1 characterized in that the blood reservoir (13) includes an automatic weighing system (16) to indicate to the automatic control means (20) the amount of blood in the blood reservoir (13) so the amount of blood in the blood reservoir and the automatic control means (20) end blood removal and start reinfusion; or, conversely, end blood reinfusion and start removal. The circuit of claim 1 characterized in that the plasma collection bag (18) includes an automatic weighing system (18a) to indicate to the automatic control means (20) the amount of plasma in the plasma collection bag (18) and to end the procedure when a preset amount of plasma in the plasma collection bag is reached.

Inventors: PANZANI IVO, PANZANI, IVO
Applicants: DIDECO SPA, DIDECO S.P.A.
Application year: 1991
Main classification: A61M1
IPC codes: A61M1, B01D61