Surgery – Blood drawn and replaced or treated and returned to body – Constituent removed from blood and remainder returned to body
Reexamination Certificate
1998-01-07
2003-11-18
Sykes, Angela D. (Department: 3762)
Surgery
Blood drawn and replaced or treated and returned to body
Constituent removed from blood and remainder returned to body
C604S004010, C600S505000, C210S646000
Reexamination Certificate
active
06648845
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a method and apparatus for determining hemodialysis parameters in a dialysis system, especially blood access flow rates and recirculation. More particularly, the invention relates to the calculation of hemodialysis parameters from multiple dialysance measurements. According to one method, a first dialysance measurement is made when the arterial and venous lines running from the patient to the dialyzer are in a first orientation and a second dialysance measurement is made when the arterial and venous lines are switched or reconfigured so they are in a second orientation. The invention includes a method for determining hemodialysis parameters in a non-invasive manner. The invention also provides a dialysis apparatus which includes a fluid conduit set for reconfiguring the arterial and venous lines between the first and second orientations, thereby providing an automated apparatus for determining hemodialysis parameters.
BACKGROUND OF THE INVENTION
Hemodialysis (or simply dialysis) is a process which employs an artificial kidney to aid patients whose renal function has deteriorated to the point where their body cannot adequately rid itself of toxins. In hemodialysis a dialyzer is used which contains a semi-permeable membrane, the membrane serving to divide the dialyzer into two chambers. Blood is pumped through one chamber and a dialysis solution through the second. As the blood flows by the dialysis fluid, impurities, such as urea and creatinine, diffuse through the semi-permeable membrane into the dialysis solution. The electrolyte concentration of the dialysis fluid is set so as to maintain electrolytic balance within the patient.
Further purification in an artificial kidney is possible through ultrafiltration. Ultrafiltration results from the normal situation wherein there is a positive pressure differential between the blood and the dialysis fluid chambers. This pressure differential causes water in the blood to pass through the membrane into the dialysis solution. This provides the benefit of reducing a dialysis patient's excess water load which normally would be eliminated through proper kidney functioning.
Typically, an arterio-venous shunt, frequently termed a “fistula,” is surgically inserted between a patient's artery and vein to facilitate transfer of blood from the patient to the dialyzer. During a normal dialysis treatment, one end of an arterial line or tube is inserted into the upstream end of the fistula (i.e., at a point near the patient's artery) and transports blood withdrawn from the upstream portion of the fistula to the inlet of the dialyzer; a venous line or tube connected to the output of the blood side of the dialyzer returns treated blood to the fistula at an insertion point downstream of the arterial line (i.e., at a point nearer the patient's vein).
Successful dialysis treatment requires knowledge of several hemodialysis parameters in order to optimize the overall efficacy of the dialysis procedure, to assess the condition of the fistula and to determine the actual purification achieved. One key measure of dialysis efficiency is described by the ratio Kt/V, where K is the clearance or dialysance (both terms representing the purification efficiency of the dialyzer), t is treatment time and V is the patient's total water volume. Studies have demonstrated that patient survival increases when the Kt/V ratio has a value of 0.8 or greater (Gotch, F. A. & Sargent, S. A. “A Mechanistic Analysis of the National Cooperative Dialysis Study.” Kidney International., Vol. 28, pp. 526-34 (1985)). The water volume of the patient, V, can be estimated from a patient's weight, age, sex and percentage of body fat. Hence, with knowledge of clearance, K, it is possible to determine the time, t, for optimal dialysis treatment according to the above relationship.
Dialysance or clearance, as noted above, is a measure of the purification efficiency of the dialyzer. More specifically, dialysance is a measure of the volume of blood cleared of urea or some other solute within a certain time period. Hence, one way to determine dialysance is to make in-vivo urea concentration measurements. This is a time-consuming approach, since it requires that samples be withdrawn and analyzed in a laboratory. Alternatively, sodium chloride dialysance or clearance can be measured, since it is known that the clearance of sodium chloride is equivalent to urea clearance. Because sodium and chloride ions comprise essentially all the electrolytes giving rise to the conductivity of both blood and the dialysis solution, dialysance or clearance can simply be determined by making conductivity measurements.
As shown by Sargent, J. A. and Gotch, F. A. (“Principles and Biophysics of Dialysis,” in: Replacement of Renal Function by Dialysis, (W. Drukker, et al., Eds.), Nijoff, The Hague (1983) incorporated herein by reference), it is possible to define dialysance in terms of concentrations at the inlet and outlet to the blood side of the dialyzer, the inlet to the dialysis solution side of the dialyzer and the blood flow rate according to the following equation:
D
=
Qb
·
Cbi
-
Cbo
Cbi
-
Cdi
(
1
)
where:
Cbi=blood inlet concentration
Cbo=blood outlet concentration
Qb=blood flow rate
D=dialysance
Cdi=dialysis fluid inlet concentration
Cdo=dialysis fluid outlet concentration
As demonstrated in U.S. Pat. No. 5,100,554 to Polaschegg, this equation can be rewritten strictly in terms of dialysis solution concentrations. In particular, from mass balance based upon flow across the dialysis membrane, the following relationship can be established:
Qb
(
Cbi−Cbo
)=−
Qd
(
Cdi−Cdo
) (2)
Thus, it is possible from equations (1) and (2) to rewrite equation (1) without a Cbo term as follows:
D
=
-
Qd
·
Cdi
-
Cdo
Cbi
-
Cdi
(
3
)
where:
Qd=dialysis flow rate; the rest of the terms are as defined for equation (1).
In equation (3), the terms Qd and Cdi are known and a value for Cdo can be easily determined by placing a detector at the dialysis solution outlet of the dialyzer. This leaves D and Cbi as the only unknown values. Using two dialysis solutions having different initial concentrations of a substance, it is possible to write two equations with two unknowns and solve for dialysance, as shown in the following equation:
D
=
Qd
·
(
Cdi1
-
Cdo1
)
-
(
Cdi2
-
Cdo2
)
Cdi1
-
Cdi2
(
4
)
where:
D=dialysance
Qd=dialysis flow rate
Cdi
1
=concentration of substance upstream of dialyzer, first dialysis solution
Cdo
1
=concentration of substance downstream of dialyzer, first dialysis solution
Cdi
2
=concentration of substance upstream of dialyzer, second dialysis solution
Cdo
2
=concentration of substance downstream of dialyzer, second dialysis solution
Other methods and apparatus for determining dialysance are described in U.S. Pat. No. 5,024,756 to Sternby, U.S. Pat. No. 5,567,320 to Goux, and U.S. Pat. No. 4,668,400 to Veech, as well as European Patents EP 330,892 B1 and EP 547,025 B1 to Sternby and European Patent Application 547,025 A1 by Sternby.
Blood access flow rate is another hemodialysis parameter which is of critical importance in optimizing dialysis procedures and in monitoring the general condition of the fistula. Blood access flow rate is defined as the blood flow rate at the entrance to the fistula as the blood flows in from a patient's artery. Blood access flow rate is important for at least two reasons. First, with time it is possible for the fistula to become clotted or stenose. Hence, flow rate can serve as an indicator of changes in the integrity of the fistula. Secondly, the rate of access flow relative to dialyzer flow rate affects recirculation, the phenomenon whereby treated blood from the venous line commingles with untreated blood in the fistula and is drawn into the arterial line and then carried back to the dialyzer. It can readily be appreciated that as recirculation inc
Folden Thomas I.
Gotch Frank A.
Bianco Patricia
Fresenius Medical Care North America
Gibson Dunn & Crutcher, LLP
Sykes Angela D.
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