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Claims  |
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What is claimed is:
1. Apparatus for preparing dialysate for use in hemodialysis which
comprises a main line connected at its inlet end to a water source and at
its exit end to an artificial kidney, a dialysate recirculation line
connected into said main line at an upstream end and at a spaced
downstream end, and including dialysate venturi means connected at its
ends into said recirculation line and at its throat portion with a line to
a dialysate concentrate tank, conductivity measuring means in said
recirculation line adjacent to and downstream of said venturi means, and
pump means in said recirculation line downstream of said conductivity
measuring means.
2. Apparatus in accordance with claim 1 wherein the speed of said pump
means varies in response to variations in the conductivity of said
dialysate from a preselected conductivity value.
3. Apparatus in accordance with claim 1 wherein said conductivity means
includes temperature compensating means.
4. Apparatus in accordance with claim 1 wherein a bicarbonate recirculation
line is interposed between said water source and the upstream end of said
dialysate recirculation line, said bicarbonate line comprising bicarbonate
venturi means connected at its ends into said bicarbonate line and at its
throat portion to a bicarbonate-saline concentrate tank, pump means in
said bicarbonate line downstream of said bicarbonate venturi means, and
conductivity measuring means in said bicarbonate line downstream of said
pump means.
5. Apparatus in accordance with claim 1 wherein a bicarbonate recirculation
line is interposed between said water source and the upstream end of said
dialysate recirculation line, said bicarbonate line comprising bicarbonate
venturi means connected at its ends into said bicarbonate line and at its
throat portion to a bicarbonate-saline concentrate tank, a variable flow
restriction downstream of and adjacent to the exit side of said
bicarbonate venturi, pump means downstream of and adjacent to said
variable flow restriction, conductivity measuring means downstream of and
adjacent to said pump means, and bubble removal means downstream of and
adjacent to said conductivity measuring means.
6. Apparatus for preparing dialysate for use in hemodialysis which
comprises a main line connected at its inlet end to a water source and at
its exit end to an artificial kidney, a dialysate recirculation line
connected into said main line at an upstream end and at a spaced
downstream end, and including dialysate venturi means connected at its
ends into said recirculation line and at its throat portion with a line to
a dialysate concentrate tank, conductivity measuring means in said
recirculation line adjacent to and downstream of said venturi means, pump
means in said recirculation line downstream of said conductivity measuring
means, and a bicarbonate recirculation line interposed between said water
source and the upstream end of said dialysate recirculation line, said
bicarbonate line comprising bicarbonate venturi means connected at its
ends into said bicarbonate line and at its throat portion to a
bicarbonate-saline concentrate tank, pump means in said bicarbonate line
downstream of said bicarbonate venturi means, and conductivity measuring
means in said bicarbonate line downstream of said pump means.
7. Apparatus in accordance with claim 6 wherein the speed of said pump
means in said bicarbonate line varies in response to variations in
conductivity of said bicarbonate solution from a preselected conductivity
value.
8. Apparatus in accordance with claim 6 wherein said conductivity measuring
means includes temperature compensating means.
9. A method for continuously formulating dialysate and supplying same to an
artificial kidney which comprises the steps of:
(1) establishing a main line between a water supply and an artificial
kidney having a recirculation loop therein provided with dialysate venturi
means, recirculation pump means and conductivity measuring means,
(2) establishing a water flow in said main line toward said kidney and
removing dissolved air and bubbles to form a deaerated stream,
(3) establishing sufficient suction in the throat of said venturi means by
recirculation of fluid therethrough to inject dialysate concentrate into
said deaerated stream at said throat,
(4) mixing said concentrate with said recirculating fluid in said venturi
means and in said recirculation loop, and
(5) said recirculating fluid consisting of a mixture of water and a portion
of said dialysate in an amount exceeding the quantity of fresh water fed
into said main line by an amount in the range of about 25% to about 300%.
10. A method in accordance with claim 9 wherein said dialysate has the
composition of normal dialysate for use in hemodialysis.
11. A method in accordance with claim 9 wherein said dialysate contains
sodium acetate in an amount in the range of about 75% to 0% of the sodium
acetate concentration in normal dialysate.
12. A method in accordance with claim 9 wherein the suction in said venturi
means in step (3) varies responsive to conductivity variations from a
preset conductivity range for the desired composition of said dialysate.
13. A method in accordance with claim 9 wherein the quantity of said
recirculating fluid is an amount exceeding the quantity of fresh water fed
into said main line in the range of about 50% to about 150%.
14. A method for continuously formulating a bicarbonate-containing
hemodialysis solution and supplying same to an artificial kidney which
comprises the steps of:
(1) establishing a main line between a water supply and an artificial
kidney having a dialysate recirculation loop therein provided with
dialysate venturi means, recirculation pump means and conductivity
measuring means,
(2) establishing a bicarbonate solution recirculation loop in said main
line interposed between said dialysate recirculation loop and said water
supply, said bicarbonate solution recirculation loop being provided with
bicarbonate venturi means, recirculation pump means, conductivity
measuring means and air removal means,
(3) establishing a water flow in said main line toward said kidney and into
said bicarbonate recirculation loop,
(4) establishing sufficient suction in the throat of said bicarbonate
venturi means by recirculation of fluid therethrough to inject bicarbonate
concentrate into said fluid at said throat and mixing same therewith to
thereby form a deaerated dilute bicarbonate solution,
(5) forwarding said bicarbonate solution to the said dialysate
recirculation loop and recirculating a stream of a mixture of said
bicarbonate solution and an aqueous solution of other dialysate components
through said dialysate venturi means at a velocity to create sufficient
suction to inject dialysate concentrate into said stream at the throat of
said dialysate venturi means and mixing same therewith in said means and
in said dialysate recirculation loop to thereby form
bicarbonate-containing hemodialysis solution having the preselected
composition,
(6) the portion of said bicarbonate solution recirculating in said
bicarbonate recirculation loop exceeding the quantity of fresh water fed
into said main line by an amount in the range of about 25% to about 300%,
and
(7) the portion of said stream of a mixture of said bicarbonate solution
and said bicarbonate-containing hemodialysis solution recirculating in
said dialysate recirculation loop exceeding the quantity of bicarbonate
solution fed to the upstream end of said dialysate recirculation loop by
an amount in the range of about 25% to about 300%.
15. A method in accordance with claim 14 wherein said dialysate contains
sodium acetate in an amount in the range of about 75% to 0% of the sodium
acetate concentration in normal dialysate.
16. A method in accordance with claim 14 wherein the suction in said
venturi means in step (4) varies responsive to conductivity variations
from a preset conductivity range for the desired composition of said
bicarbonate solution.
17. A method in accordance with claim 14 wherein the suction in the venturi
means in step (5) varies responsive to conductivity variations from a
preset conductivity range for the desired composition of said hemodialysis
solution.
18. A method in accordance with claim 14 wherein the quantity of said
recirculating fluids in each of said recirculating loops is an amount in
the range of abut 50% to about 150% of the fresh water fed to said main
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Claims |
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Description |
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BACKGROUND OF THE INVENTION
This invention relates to apparatus and a method of continuously preparing
and supplying an optionally bicarbonate-containing hemodialysis solution
to an artificial kidney.
Premixed batches of dialysate solution supplied from an open tank by
gravity head pressure to a number of artificial kidneys in large clinics
have largely been replaced by systems designed to make up and supply
dialysate only as needed by each individual artificial kidney. U.S. Pat.
Nos. 3,515,275 and 3,920,556 and the several patents identified therein
disclose such background prior art and describe the use of positive
displacement piston pumps in continuous dialysate supply systems for a
single kidney. Other patents which appear to be relevant include U.S. Pat.
Nos. 3,406,826, 3,598,727 and 3,878,095; they disclose double acting
piston and cylinder units, or variable output positive displacement pumps,
which are mechanically adjustable for controllable responsive to
measurement of conductivity or dialysate component concentrations to
adjust the product solution to preset limits. U.S. Pat. No. 3,847,809
continuously recirculates a dialysate concentrate and at the intersection
with the water supply line adds the desired amount of concentrate. In U.S.
Pat. No. 2,304,661 a regenerating solution for ion-exchange resins is
prepared by mixing acid and water from a measuring tank for the acid
previously filled by using the suction created by water flowing through a
venturi in the preceding water rinse step. Dialysis concentrate and water
are mixed in a venturi device in the direct supply line to a dialysis
storage tank in U.S. Pat. No. 3,528,550; additional patents which should
be considered to put the present invention in proper perspective with
respect to recirculation and venturi use include U.S. Pat. Nos. 3,352,779,
3,690,340, 3,722,680, 3,753,493, 3,843,099 and 3,882,020.
SUMMARY OF THE INVENTION
This invention provides a hemodialysis system which enables continuous
formulation and supply to an artificial kidney of a hemodialysis solution,
or dialysate, which contains the normally present sodium acetate
component, or optionally may contain bicarbonate as a partial or total
replacement therefor.
The apparatus comprises a main supply line between a water supply and the
kidney and includes a primary recirculation loop including venturi means
for mixing the dialysate concentrate with deaerated water and, optionally,
a secondary recirculation loop for preliminarily forming a dilute
bicarbonate-containing solution which is then fed to the primary
recirculation loop for mixing with the other dialysate components and
supply to the kidney.
The method requires recirculation of a quantity of the mixed fluid through
the mixing venturi in either recirculation loop in an amount which exceeds
the fresh water input rate, by an amount of, preferably, 50% to 150% of
the fresh water. The preferred operating method includes the bicarbonate
addition step as a partial or complete replacement for acetate in the
product hemodialysis solution.
GENERAL DESCRIPTION OF THE DRAWINGS
FIG. 1 illustrates the apparatus of this invention in the best known form
and arrangement of elements to enable practice of the method disclosed and
claimed herein.
FIG. 2 shows a mixing venturi in cross section.
Generally stated, the apparatus consists of a water source, generally
designated 10, and a hemodialysis device or artificial kidney generally
designated 20 which are interconnected by a main line 30. A dialysate
recirculation loop generally designated 40 is located adjacent to the
kidney; a bicarbonate recirculation loop generally designated 50 is
located adjacent to the water source and both loops are directly connected
into main line 30. Dialysate recirculation loop 40 functions to provide
normal hemodialysis solution containing acetate whereas the bicarbonate
recirculation loop 50 provides a dilute bicarbonate solution which is then
fed to downstream loop 40 to be blended, or mixed, with the other
dialysate chemical components of normal dialysate concentrate to thereby
form the bicarbonate-containing hemodialysis solution of this invention.
Loop 50 also contains means for removing dissolved air and bubbles from
the incoming water. Each of the recirculation loops 40 and 50, and the
method of their use will now be described.
DETAILED DESCRIPTION OF THE INVENTION
As seen in FIG. 1, water enters main line 30 through pressure regulator
valve 12, of conventional construction, at a controlled, preselected
pressure usually in the range of about 1-10 psi and moves from left to
right, toward kidney 20.
The bicarbonate recirculation loop 50 includes a section of main line 30
and a recirculation line 13 which extends from junction 14 at its upstream
end to junction 15 at its downstream end. Loop 50 and the elements
attached in line 13 provide the dual function of supplying the desired
dilute bicarbonate solution and deaeration of the fluid circulating
therein. Mixing venturi 16 is located adjacent to junction 14. The throat
portion 17 of venturi 16 is connected by line 18 and valve 11 to the pool
of aqueous bicarbonate-containing concentrate in tank 19.
The elements for deaerating the circulating fluid consist of variable flow
restriction 21, pump 22 and bubble removal means, or air trap 23 which are
located downstream of venturi 16, as shown. Conductivity measuring means
27, including probes 24, 25 and a temperature compensation probe 26, all
of conventional construction, is located immediately downstream of pump
22; these probes continuously monitor the conductivity of the
recirculating fluid which is a mixture of the incoming water and the
bicarbonate concentrate from tank 19.
The bicarbonate concentrate may be a simple aqueous bicarbonate solution
formulated from sodium bicarbonate and water; other alkali metal
carbonates, particularly potassium, are preferably avoided. The preferred
concentrate is one which contains a mixture of sodium chloride and sodium
bicarbonate with sufficient sodium chloride content to be conductive to a
degree that permits accurate determination of small variations from a
preset conductivity representing the desired bicarbonate concentration. A
concentrate for this purpose may satisfactorily contains 40 g/l to 80 g/l
sodium bicarbonate, and 20 g/l to 50 g/l NaCl.
Loop 50 functions to form a dilute aqueous bicarbonate solution and to
recirculate same by the pumping action of pump 22, preferably of the gear
type. The speed of pump 22 is controlled by, and varies responsive to,
control signals from bicarbonate servo-controller 28 functioning in
conjunction with temperaure compensator 29; such controls are known and
familiar to those skilled in the hemodialysis art and a number of
satisfactory units are available commercially in the United States. In
accordance with the method of this invention, bicarbonate may replace a
portion, or all, of the acetate which is in normal dialysate that is in
widespread use in hemodialysis as practiced throughout the world. Loop 50
provides an arrangement whereby any desired strength of aqueous
bicarbonate solution may be continuously formulated by first mixing water
and concentrate in venturi 16 and then more thoroughly mixing and
rendering more uniform the composition of the dilute solution during
recirculation in loop 50; the speed of pump 22 has a minimum which
produces a velocity of fluid circulation in line 13 that exceeds the rate
of flow of incoming water to line 30, we well as the rate of final
dialysate flow to kidney 20. Such minimum speed of pump 22 insures
recirculation of some quantity of mixed, dilute bicarbonate solution in
main line 30 between junctions 15 and 14. It has been found to be
desirable to insure that the quantity of mixed fluid recirculating exceeds
the quantity of incoming water and is in the range of about 25% to about
300% of that water volume, preferably in the range of about 50% to about
150% of the input water volume.
The momentary speed of pump 22 varies as required to accomplish its
multi-functions. The quantity of bicarbonate concentrate which enters the
system is dependent on the degree of suction created in the throat 17 of
venturi 16 and this suction is directly dependent on the rate of flow of
recirculating fluid in line 13; moreover pump 22, venturi 16, and variable
restriction valve 21 function to reduce the pressure from the normal input
water pressure at 14 of about 1-10 psi downwardly to within the range of
450 to 650 millimeters of mercury negative relative to atmospheric between
restriction 21 and pump 22 for the purpose of forming bubbles from the
dissolved air in the incoming water so that they may be removed in bubble
removing means, or air trap 23. Air trap 23 is satisfactorily of
conventional design, and as illustrated includes floating ball 31 carrying
stem 32, the vertical movement of which opens or closes air vent 33 as
closure 34 seats thereagainst. As above indicated, the speed of pump 22 is
increased, or decreased, to create sufficient suction to pull the quantity
of bicarbonate concentrate into venturi 16 that after dilution with the
incoming water produces the preset conductivity value that is being
continuously measured by conductivity unit 27. Typically a small range of
conductivity is preset in control 28 and measured variations therefrom
cause pump 22 to increase or decrease as needed to maintain the
preselected bicarbonate concentration in the dilute solution. Control unit
28 also provides control signals to variable flow restriction 21 to insure
sufficient pressure drop in the recirculating fluid to insure bubble
formation as the speed of pump 22 varies to maintain the desired
bicarbonate concentration. This arrangement of the combination of
deaeration and bicarbonate solution formation through the use of a common
pump 22, controlled as stated, and their location in a recirculation loop
off of main line 30 provides the further advantage that the pressure
established by inlet pressure regulator valve 12 extends through junction
14 beyond, and downstream to junction 15, and this constancy of inlet and
outlet pressure to loop 50 tends to offset any tendency of pump 22 to
undesirably affect the balance of the system due to fluctuations in speed
in response to control signals or bubbles of air passing therethrough.
The deaerated dilute bicarbonate-containing solution exits at junction 15
from loop 50 into main line 30 and enters loop 40 at junction 37.
Recirculation loop 40 includes, in downstream toward the kidney order,
dialysate venturi 39, conductivity measuring unit 41 and pump 43. Venturi
39 is connected at each end into recirculation line 42. The throat 44 of
venturi 39 is connected by line 46 to dialysate concentrate tank 48.
Conductivity unit 41 is similar to the corresponding unit 27 in loop 50
and includes probes 51, 52 connected to dialysate servo control unit 54,
and temperature compensation probe 56, which is connected to temperature
compensator control 58 that is, in turn, interconnected with dialysate
control 54. Control signals are fed from dialysate servo control 54 to
pump 43, which is satisfactorily of the gear or positive displacement
type, as in loop 50.
The elements in loop 50 are in operation at all times that a product
dialysate is being supplied to kidney 20 except that bicarbonate
concentrate tank 19 is inoperative to supply bicarbonate to the throat of
venturi 16 when no bicarbonate is desired in the product dialysate. During
such time, valve 11 is closed and incoming water passes through line 13,
venturi 16, variable flow restriction 21, pump 22 and air trap 23 to
thereby remove dissolved air and bubbles therefrom and thus provide a
deaerated stream of water to 37 for circulation in dialysate loop 40. It
is only necessary to slightly adjust the setting of variable restriction
21 and pump 22 for zero bicarbonate input by appropriate adjustment of
bicarbonate servo control 28.
Dialysate venturi 39 and bicarbonate venturi 16 are similar in construction
and may best be seen in FIG. 2. The venturi illustrated in FIG. 2 is of
the type having a short lead in section 60, an elongated throat portion 62
into the downstream end portion of which concentrate supply line 64 is
attached. The downstream or exit end portion 66 is angled much less
severely than section 60. The lead in angle, exit angle, throat diameter
and overall length of venturis 16 and 39 were selected to maximize suction
in throat portion 62 at minimum pressure drop across the venturi for any
selected fluid velocity therethrough. Venturis of this general type are
commercially available and satisfactory performance has been obtained with
a standard Herschel-type venturi.
Dialysate recirculation loop 40 functions on a continuous basis to
formulate dialysate solution having the preselected composition and to
supply same from pump 43 to main line 30 through line 45, and thence to
kidney 20. Pump 43 is controlled similarly to the control of pump 22 in
loop 50, as above explained. The amount of recirculation of the mixture of
the stream from loop 50 and the fluid formulated in loop 50 which joins
that stream at junction 37 should be a quantity which exceeds the incoming
stream by an amount in the range of about 25% to about 300% and preferably
between about 50% and 150%.
The desired final formulation of dialysate is obtained, and maintained
substantially constant by preselecting the small range of conductivity
values which correspond to the desired, preselected concentration of
bicarbonate and acetate in the otherwise normal dialysate solution.
As used in this specification and in the claims the expression "normal
dialysate" refers to the dilute solution which circulates in the
artificial kidney on one side of the dialysis membrane and has the
following range of composition:
Sodium: 120-150 milliequivalents/liter
Chloride: 90-110 milliequivalents/liter
Calcium: 1-4 milliequivalents/liter
Magnesium: 0-2 milliequivalents/liter
Potassium: 0-3 milliequivalents/liter
Acetate: 30-50 milliequivalents/liter
Dextrose (D-glucose): 0-4 grams/liter
Using a selected bicarbonate-saline concentrate within the ranges stated
above, conductivity measurements are experimentally determined as a
function of bicarbonate concentration in dilute solutions thereof and used
for controlling limits for bicarbonate servo control 28. In order to
arrive at the appropriate sodium concentration in the final dialysate it
is necessary to provide a dialysate concentrate for tank 48 which contains
less than the normal amount of sodium and chloride to accommodate the
quantities of those ions which are added in the bicarbonate-saline
solution product from loop 50 which becomes the input fluid to loop 40 at
junction 37. A suitable dialysate concentrate for use in tank 48 may have
the following composition:
Sodium Chloride: 100-200 grams per liter
Potassium Chloride: 0.5-7.0 grams per liter
Calcium Chloride: 3-10 grams per liter
Magnesium Chloride: 0.5-8.0 grams per liter
Hydrochloric Acid: 0-8.4 grams per liter
Sodium Acetate: 0-140 grams per liter
Dextrose (D-glucose): 0-135 grams per liter
The method of this invention, and the apparatus in loops 50 and 40, provide
a spectrum of bicarbonate-acetate containing hemodialysis solutions
ranging from no bicarbonate to no acetate. It is to be understood however
that all of the dialysate components in the improved hemodialysis
solutions of this invention that are present in normal dialysate as above
defined, other than acetate, must be present. Moreover where bicarbonate
replaces acetate, improvement in patient acceptance occurs in those
patients who exhibit some degree of inability to metabolize acetate; where
acetate is reduced by as must as about one-fourth of concentration of
acetate in normal dialysate, and substituted by bicarbonate, substantial
relief from effects approaching morbidity can be realized. Further
substitution of bicarbonate for acetate, to and including total
substitution is available for election and use by the physician in
appropriate cases. Where the concentration of acetate is only reduced,
formulations of dialysate concentrates containing lower concentrations of
acetate should be substituted in tank 48 to thereby obtain the desired
blend of acetate and bicarbonate.
Blends of acetate and bicarbonate offer in combination of advantageous
characteristics which include avoidance of undesirable precipitation
problems with magnesium or calcium in bicarbonate concentrates and the
concurrent ability to avoid undesirable effects with certain patients. The
final product hemodialysis solution of this invention is one having a
composition as follows:
Sodium ion: 120-150 milliequivalents/liter
Potassium ion: 0-3 milliequivalents/liter
Calcium ion: 1-4 milliequivalents/liter
Magnesium ion: 0-2 milliequivalents/liter
Bicarbonate ion: 0-40 milliequivalents/liter
Chloride ion: 90-110 milliequivalents/liter
Acetate ion: 45-0 milliequivalents/liter
Dextrose (D-glucose): 0-4 grams/liter
The following example is set forth to illustrate the best form of the
invention presently contemplated for use in hemodialysis where all of the
acetate in normal dialysate is replaced by bicarbonate. The hemodialysis
solution contains in milli equivalents per liter: Na.sup.+ -137; K.sup.+
-2; Ca.sup.+ -3; Mg.sup.+2 -1.5; HCO.sub.3.sup.- -36; Cl.sup.- -107.5.
This solution was obtained by using as the bicarbonate-saline concentrate
a mixture of 31.4 g/l of NaCl and 60.6 gm/l of NaHCO.sub.3 and a modified
dialysate concentrate containing 160 gm/l NaCl, 5.5 gm/l KCl, 8.2 g/l
CaCl.sub.2, 5.6 gm/l MgCl.sub.2 and 5.1 gm/l HCl.
As will be readily apparent to those of ordinary skill in this art,
hemodialysis solutions having a selected blend of acetate and bicarbonate
may be formulated by the routine steps of initial selection of the desired
proportions of bicarbonate and acetate, and employed the applicable
conductivity values in controllers 28 and 54, together with modifications
of the concentrates for tanks 19 and 48; these steps required only routine
application of engineering procedures after a few experimental
conductivity tests are completed on selected modified concentrates.
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