Note: Descriptions are shown in the official language in which they were submitted.
~ 3~ t
Field oE the Invention
The invention relates to a~paratus for preparing and
supplying dialysate from concentrated solutions.
Background of the Invention
In hemodialysis blood flows past one surface of a
semipermeable membrane~ dialysate flows past the other surface,
and transport of chemicals through the membrane occurs. The
dialysate is often prePared continuously from deaerated water
and concentrated dialysate solution. In preparin~ bicarbonate
dialysate from concentrated solution, two concentrates are
required owinq to the insolubility of calcium and maqnesium
salts in concentrated bicarbonate solution. Acetate salts have
been substituted for bicarbonate to permit the ~reparation of
dialysate from a sin~le concentrate, however, in recent ~ears
there has been concern that there may be health problems in
some patients when acetate dialysate is used in ~resent hiqh-
performance dialyzers.
Storey et al. U.S. Patent No. 4,202,760 discloses
dialysate preparation apparatus employing a first recirculation
loop to add concentrated sodium bicarbonate and sodium chloride
to a mixture of water and recirculated diluted bicarbonate
solution at a venturi upstream of a ~ump. The pump also acts
to create a negative pressure or deaeratin~ the water in the
recircuIation loop. The portion of the diluted bicarbonate
which is not recirculated fIows into a second recirculation
loop in which concentrated dialysate solution is added via a
similar venturi and downstream ~ump. In both recirculation
loops the p~ps are controlled by conductivitv sensors within
the recirculation loo~s to maintain at desired levels the
amounts of concentrated solutions entering the venturies by the
pressure in the venturies.
Summary o the Invention
It has been discovered that the ratios of the
concentrations of first and second concentrated solutlon
components le g., bicarbonate and sodium~ to each other or to
total ionic strength can be advantageously varied simply and
directly by employing two independen-tlv controlled pum~s to
directly pump the concentrated solutions to the main dial~vsate
flow line and controlling the pumps with concentration sensors
in the main flow line downstream of the sup~l~ junc-ti.ons of the
pumped concentrate solutions with the flow line.
In preferred embodiments means are provided to vary
the amounts and ratios of concentrates added during a dial~sis
session without changing the makeup of the concentrated
solutions, thereby permittinq tailorinq of the ratios and
changes to the needs of particular patients; the deaeràtion of
the water occurs upstream of the first concentration control
sensor to provide for accurate measurements of even low
concentrationsi an air-bypass chamber is placed downstream of
the first control sensor, and a monitoring cell is placed
downstream of the air-bypass chamber to verify -the correctness
of the amount of added concentrate; the second pump will not
function unless the first concentrated solu-tlon is added to the
flow line in the pro~er concentration; there is a bypass valve
in front oE the dialyzer to cause the mi~ed dialysate solution
to bypass the dialyzer unless both solutions are in the proper
concentrations; the solutions are bicarbonate solution and
acid-sodium solution; a pH sensor is located downstream o:F the
final control cell to independently guarantee that the DH is
within predetermined limits; and an acetate pum~ is added and
connected in parallel with the acid pump, and means are pro
vided for deactivating the bicarbonate ~ump, bicarbonate con-
trol sensor, bicarbonate monitorina cell and acid ~ump in the
event that acetate dialysate is desired.
Description of the Preferred Embodiment
The structure and operation of the presently prefer-
red embodiment will now be described after first briefly des-
cribing the drawings.
Fig. 1 is a diagrammatic representation of dialysate
preparation and supply apparatus according to the invention.
Fig. 2 is a block diagram of the control circuitr~
for the Fig. 1 apparatus.
Structure
Referring to Fig. 1, there is shown dlalysate prepa-
ration and supply a~paratus qenerally desi~nated 10 connectedto dialyzer 12 r source of concentrated bicarbonate solution
14 and source of concentrated acid-sodium solution 16. Appa-
-- 3
ratus 10 has water inlet port 1~ for connection to a sourceo~ water and ports 20, 221 24 for connection to sources oE
bicarbonate concentrated solution, concentrated acetate solu-
tion and concentrated acid-sodium solu-tion, respectively,
and outlet port 26 for connection to a drain for spent dialy-
sate. The water inlet port 18 is connected to flow control
restrictor 28, heater 30, pump 32 and air-bypass chamber 34
to heat and deaerate the incoming water. Bicarbonate intake
port 20 is connected by peristaltic pump 36 to bicarbonate-
water supply and mixing junction 38 and bicarbonate controlcell 40, a conductivity sensor. Supply and mixing junction
38 is constructed to have water enter it at a right angle
to its longitudinal axis causing it to spin along an inner
wall and create a vortex in the center, and to have the con-
centrate be pumped into the vortex so that the centrifugal
force causes the heavier concentrate to pass into the water
layer and mix with water. The outlet of control cell 40 is
connected to air bypass chamber 42, the liquid outlet of which
is connected to bicarbonate monitoring cell 44, including a
conductivity sensor and thermistor. Sampling portal 50 is be-
tween the outlet of monitoring cell 44 and mixing junction
46, which is for adding either acid or acetate solution from
line 48 to diluted bicarbonate or water, respectively. Line
48 is connected ln parallel to acid intaXe port 22 and acetate
intake port 24 by peristaltic pumps 54, 52, respectively. (As
described below, in operation either pump 54 will be operat-
ing or pumps 36, 52 will be operating.) Supply and mixing
D~ --
3L1E~3~ l
junction 46 is similar in construction to junction 3~, and im-
mediately downstream of it is ~inal co.ntrol cell 56 for measur~
ing conductivity of the water stream and the added concentrated
bicarbonate and acid solutions. Control cell 56 is connected
to air-bypass/stabiliza-tion chamber 58 via pH sensor 72. The
liquid outlet of chamber 58-is connected to final monitoring
cell 6Q (a conductivity sensor and thermistor) in turn connected
to two-position four-way valve 62. .Valve 62 is shown in the
dialysate supply mode with line 64 connected to dialyzer supply
line 66, and drain line 68 connected to dialysate return line
70. The flow path for bypass mode of valve 62 is shown in
the lower half of its representation on Fig. 1. In this mode
supply line 64 and drain line 68 are connected, and dialyzer
supply line 66 and return line 70.are blocked. Drain line 68
is connected to drain port 26 by ~ump 74, which has a common
motor and drive shaft with pump 32. Immediately upstream of
pump 74 the drain line 68 joins with air line 76, in which air
removed in chambers 34, 42, and 58 flows.
In the above descrlbed hydraulic circuitry, there
is a main flow line from the water inlet port 18 to dialysate
supply line 66. The liquid flowing in this line is initially
deaerated in chamber 34, concentrated solutions are supplied to
the main flow line at bicarbonate junction 38 and acid/acetate
junction 46, and the increasing conductivity and the pH are
sensed in the control and monitor cells and the pH probe.
The circuitry depicted in the block diagram of Fig.
2 generally includes pH amplifier 81, conductivity setpoint
-- 5 --
control and alarm logie 78, bicarbonate control and monitor
eireui-t S5 r and final eonduetivity control and monitor cir-
cuit 83. This cireuitry can probably best be described as it
relates to the operation of the Fig. 1 apparatus.
Operation
In operation in the biearbonate mode, the solutions,
water souree and dialy~er are connected, and mode select switeh
79 is placed in the biearbonate mode. The desired eonductivity
level at eontrol eell ~0 is entered into conduetivity set point
control alarm logie 78 with `bicarbonate switch ~0 and the de-
sired-eonductivity for final eontrol cell 56 is set by adjust-
ing sodium eoneentration select switeh 82. Control cells 40,
56 have limits of -50~ of the setpoints assoeiated with them,
and monitor eells 44, 60 have primary limits of +5% and redund-
ant limits of +8~ assoeiated with them. As is deseribed below,
when sensed eonduetivity goes beyond these limits, eertain
alarms and safeguards are set into operation.
Container 14 of biearbonate solution contains ap-
proximately 650 gm of sodium bicarbonate in 2 gallons of water.
Souree of eoneentrated aeid-sodium solution 16 eontains the
following eomponents in the following eoneentrations (the eon-
eentrations listed are those that would exist typieally after
dilution with the water from source 18):
Table 1
Chemical Concen-tration
When Diluted 1:~4
Com~onent (mEq/1)
Sodium Chloride 100.0
Calcium Chloride 3.0
Potassium Chloride 2.0
Magnesium Chloride 0.75
Acetic Acid 1.8
Alternately, the solution of concentrated acid can also include
dextrose in sufficient amount to result in a 2.0 gm/l concentra-
tion when diluted.
Water supplied to intake por-t 18 is deaerated prior
to mixing with the concentrated solutions by subjecting it to
low pressure through the actions of positive displacement pump
32 (which is attempting to pump at one flowrate), flow control
restrictor 28 (which permits water flow at a lower flowrate),
and heater 30 (which reduces the solubility of gas by increas-
ing the -temperature of the water~. The air separated from the
water is removed via air line 76 from the top of chamber 34,
and deaerated water passes through the liquid outlet at the
bottom and flows to mixing junction 38. Removal of the air
bubbles prior to mixing with the concentrated solutions and
conductivity sensing permits accurately sensing lower conduc-
tivities and avoids distortion of the conductivity measurements
that would otherwise occur.
The heated, degassed water is mixed with a concen-
trated bicarbonate solution at junction 38, and the concentrated
bicarbonate solution is mixed in a ratio of approximately 1
part concentrate to 25.2 parts water. The mixed water and
-- 7 ~
concentrated bicarbonate solution passes -through control cell
40 in whieh the conductivity is sensed, and electrical signals
indicating conductivity are supplied to bicarbonate control
and monitor circuit 85. Bicarbonate pump 36 is operated by
circuit 85 in resPonse to signals from setpoint logic 78 and
cell 40 at a speed resultiny in achievin~ the desired conduc~
tivity (and bicarbonate concentration~ in control cell 40. A
thermistor in monitor cell 44 aecounts for the effect of temp-
erature on conductivity. From control cell 40 the water with
biearbonate flows to bypass ehamber 42 in whieh any gas that
has come out of solution exits, and additional mixing of the
solution oeeurs. From there -the solution passes through sample
port 50 from which samples are initially taken to verify the
conduetivity and chemistry independently of the machine. From
sample port 50, the solution passes to junction 46. If the
conduetivity of the bicarbonate solution in control cell 40 or
monitor cell 44 is not within the above-mentioned tolerance
limits, acid pump 52 is prevented from operating, and alarm
indicators are activated with an indication of whether the
conductivity is low or high. The primary alarm limits for
eell 44 are +5%. Cireuit 85 also includes a redundant alarm
limit for cell 44 of +8% in case the circuitry for the primary
alarm limit is malfunctioning. The minus 50~ limit associated
with cell 40 is to indicate that the machine has run out of
coneentrate solution. If the eonductivity at cells 40, 44 is
within the limits, the bicarbonate solution will mix with
eoncentrated acid-sodium solution in mixing junction 46, and
the eonductivity of the overall solution is sensed in Einal
con-trol cell 56, which o~erates acid pump 52. AEter con-trol
eell 56 dialysate solution passes to pH Probe 72 in which acid
concentration is independently tested. From pH probe 72, di-
alysate solution passes to stabilization chamber 58 to separ-
ate any gas that has come out of solution, provide additional
mixing of the dialysate, and dampen flow or pressure surges~
The mixed dialvsate then flows to the final conductivity moni-
tor eell 60 for final eheeking of eonduetivity prior to pas-
sage to valve 62. Final conductivity circuit 83 functions thesame as biearbonate circuit 85 Eor the alarm limits associated
with final cells 56 r 60. If any pH, conductivity or tempera-
ture out-of-tolerance conditions are sensed at cells 40, 44,
56, or 60, valve 62 is moved to the bypass position shown on
the bottom of the valve representation on Fig. 1. Otherwise
dialysate will be supplied to dialyzer 12 and returned to the
system and drained at ort 26 via pump 74.
The concentrations of the sodium and bicarbonate
dialysate eomponents can be adjusted for a particular patient
merely by adjusting the conductivity setpoints with switches
80, 82. Also, the concentrations of the eomponents can be
varied during a dialysis session, and some component concentra-
tions ean be varied while others remain constant. For example
many patients with normally high weight gains between dialysis
sessions experience disequilibrium symptoms during fluid re-
moval with low sodium dialysate owing to rapid ehanges in
6~L !
blood osmolarity. Although higher dlalysa-te sodium concentra-
tions may provide more asymptomatic dialyses, this may result
in weight gains between dialysis sessions that are unacceptably
high owin~ to increased thirst and fluid intake stimulated by
the high levels of sodium retained in the blood a-Eter dialysis.
In these patients, the use of sequential high/low sodium dialy-
sis can provide effective asymptomatic dialyses associated with
high sodium concentrations while reducin~ tendencies -toward in-
creased thirst and fluid intake. With this technique, dialy-
sate sodium concentrations begin high, but are reduced as thedialysis proceeds. Because most fluid is removed when dialysate
sodiums are higher, dialyses tend to be more asymp-tomatic.
However, the subsequent lower dialysate sodium levels also
bring plasma osmolarities down to traditional hy~osmolar levels,
which supresses the thirst stimulus and helps prevent increased
fluid intake between sessions. While the sodium level of the
dialysate is decreased by adjusting sodium concentrate select
switch 82 in this technique, the bicarbonate level can be main-
tained at a constant level tailored to the particuIar patient's
need.
Valve 62 can be independently activated to cause
flow through dialysate lines 66, 70 with out-of-tolerance con-
ductivity or temperature conditions by depressing a rinse
switch 84 on the main control panel, which pressing will pre-
vent the blood pump from opera-ting. Also the rinse switch
-- 10 --
will cause all three concentrate pumps 36, 52, 54 to operate
and permit the pumping of cleaning, dlsinfecting or rinsing
liquids through the hydraulic circuitry.
If the unit is placed in the acetate dialysate mode
by activating switch 79, bicarbonate pump 36 and acid pump 52
are inactivated along with bicarbonate conductivity control and
monitor cells 40, 44, and acetate concentrate is pumped into
mixing junction 46 by pump 54. The control elements downstream
of junction 46 and the water heating and deaerating components
28, 30, 32, 34 operate as described above.
Other embodiments will be within the scope of the
following claims. For example, additional concentrated solu-
tions, pumps, and control cells can be added to permit inde-
pendent adjusting of the level of a third or more components
to tailor the dialysate makeup even further to a particular
patient's need.
What is claimed is:
