Liquid purification or separation – Processes – Including controlling process in response to a sensed condition
Reexamination Certificate
2001-07-09
2004-11-23
Kim, John (Department: 1723)
Liquid purification or separation
Processes
Including controlling process in response to a sensed condition
C210S085000, C210S087000, C210S090000, C210S097000, C210S102000, C210S103000, C210S134000, C210S143000, C210S321650, C210S645000, C210S646000, C210S650000, C210S740000, C210S741000, C210S746000
Reexamination Certificate
active
06821441
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention refers to a method for blood purification by means of hemodialysis and/or hemofiltration, wherein to the blood in the extra-corporeal circuit of the hemodialysis and/or hemofiltration device a substitution solution is added upstream as well as downstream of the hemodialyser and/or hemofilter.
2. Description of the Related Art
In “Replacement of Renal Function by Dialysis” (Drukker, Parsons and Maher; Kluwer Academic Publishers, 4
th
edition 1996; “Hemodialysis Machines and Monitors” by H.-D. Polaschegg and N. W. Levin)—to the disclosure of which is explicitly referred hereby—a summary of most important hemodialysis procedures and machines is given:
In hemodialysis the blood of a patient is fed through an arterial blood line into the blood chamber of a dialyser. The blood is usually transported by means of a rotary peristalic pump arranged in the arterial blood line. After passing the pump blood is fed through the blood chamber of the dialyser and finally through a venous drip chamber and a venous blood line connected thereto back to the patient. A venous pressure monitor is connected to the venous drip chamber as a protective system for immediate detection of blood loss to the environment. If necessary two needles required for the arterial and venous cannula may be replaced by a single needle in the so-called single-needle-dialysis. In this mode of dialysis, the extra-corporal circuit consists of a single needle cannula with connected Y-piece. From the dialyser the venous line leads back to the Y-piece. The arterial and venous line are occluded alternately by clamps. One or more blood pumps run to manage the alternate flow to and from the Y-piece.
In hemodialysis the solute removal from the blood is driven by diffusion through the dialyser membrane. Though in addition a small transmembrane pressure is applied in order to ultrafiltrate excessive water of a patient, this filtration hardly plays a role for the purification of the blood from specific substances.
Solute removal in hemofiltration is driven by convection rather than by diffusion. At the same time ultrafiltrate is almost entirely replaced by a substitution fluid of a composition similar to dialysate in dialysis. This method emphasizes the similarity to the natural kidney and the more effective removal of larger molecules. On the other hand removal of low molecular substances is reduced as compared to hemodialysis because at best 45% of blood can be ultrafiltrated in the so-called post-dilution hemofiltration. Today, hemofiltration is only used in a small number of patients because of the high cost of commercial replacement fluid and the high blood flow required to perform the treatment in a reasonable time.
Hemofiltration machines for chronic treatment comprise the same extracorporal pumping and monitoring systems as hemodialysis machines. The dialysate circuit is replaced by a fluid balancing and warming system. In the so-called pre-dilution mode substitution fluid is added to blood upstream of the dialyser and the filtrate is produced by the corresponding transmembrane pressure. To be clinically effective a very large amount of substitution fluid is required. Because of the high cost of commercial substitution fluid this method never became widely accepted. More common is the post-dilution mode because less substitution fluid is required. In this mode the substitution fluid is added to the blood downstream of a dialyser. In the post-dilution mode good purification coefficients are obtained. During a 4 hour treatment normally approximately 20 to 24 liters of substitution fluid are added. The efficiency of the method is, however, limited by a critical transmembrane pressure above which blood damage will occur.
Various systems have been proposed for fluid balancing. In the gravimetric balancing method ultrafiltrate may be withdrawn by the ultrafiltrate pump into a bag or container hanging or standing on a balancing platform. Substitution fluid from a bag or container on the same platform is pumped by another pump to the venous drip chamber. Net fluid removal is achieved either by an additional ultrafiltration pump or by a programming unit that controls the substitution pump to deliver less fluid than removed by the filtration pump.
Hemodiafiltration, a combination of hemodialysis and hemofiltration, can be performed by combining the extracorporal circuits of a hemofiltration and a hemodialysis machine. Hemodialysis machines with volumetrically controlled ultrafiltration can be adapted easily for hemodiafiltration which is more cost-effective. This is particularly cost-effective if the substitution fluid is prepared online from the dialysis fluid.
Treatment parameters such as dialysate contents (sodium concentration), ultrafiltration rate, blood and dialysate flow are varied intradialytically in an attempt to increase or maintain efficacy and/or reduce intradialytic symtoms. The variation either follows a kinetic model or, more often, “clinical judgement”. Intradialytic symptoms, especially hypotension, are closely related to ultrafiltration. In dialysis machines having ultrafiltration pumps independent of dialysate pumps, profiling is performed by variation of the ultrafiltration speed.
To summarize in hemodialysis the blood of the patient is purified in that the substances of the blood which have to be removed diffuse through the membrane due to a concentration gradient across the membrane of the dialyser and thereby reach the dialysis fluid. The driving force in hemofiltration is substantially a pressure difference across the membrane which effects a convective transport of substances through the membrane and in doing so cleans the blood above all also from higher-molecular substances. In hemofiltration as well as in the combined method of hemodiafiltration, fluid is removed from the patient blood which has to be substituted except a small difference amount for the control of the fluid balance.
The relatively low efficiency of the pre-dilution mode, especially for low-molecular substances, results from the low concentration gradient across the membrane caused by the dilution and the fact that a purification of the blood as well as of the added substitution liquid is carried out. For the pre-dilution mode, the amounts of substitution fluid added during a 4 hour treatment lie in a range between 40 to 50 liters.
Pre-dilution is used preferably for patients who have a higher risk of coagulation or clotting of the blood. Said risk is reduced by the dilution of the blood prior to blood treatment wherein the cited disadvantages are accepted.
As mentioned above disadvantages occur in post-dilution as it has to be worked with high hemoconcentrations. With respect thereto the hemoconcentrations in predilution are low at least in the entrance section of the hemodialyser and/or hemofilter. Low hematocrit concentrations result in correspondingly large amounts of free water, i.e. unbound water, which renders possible a distinct convective substance transport through the membrane. Correspondingly, the purification effect for middle- and high-molecular substances may be higher in the pre-dilution mode than in the post-dilution mode.
To couple the advantages of the pre- and post-dilution mode it has also been proposed to apply both modes simultaneously with a fixed ratio of pre- and post-dilution substitution fluid flow (L. Pedrini and V. De Cristofaro, Abstract at the EDTA/ERA Congress in Madrid, 1999).
A further disadvantage of the post-dilution mode is that during the blood purification a limiting membrane is built up at the membrane of the hemodialyser and/or hemofilter. The thickness of this membrane increases with increasing duration of treatment, which reduces the permeability of the membrane. Thereby—if the transmembrane pressure remains constant—the purification effect is deteriorated. If a constant purification effect was to be achieved, an increasing trans-membrane pressure would be required which can lead to a damaging of the membrane.
U.S. Pat.
Pedrini Luciano
Wiesen Gerhard
Fresenius Medical Care Deutschland GmbH
Kim John
LandOfFree
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