CA1183461A

CA1183461A - Dialysate preparation apparatus

Info

Publication number: CA1183461A
Application number: CA000396260A
Authority: CA
Inventors: Russell L. Jeffery
Original assignee: Cobe Laboratories Inc
Current assignee: Terumo BCT Inc
Priority date: 1981-05-01
Filing date: 1982-02-15
Publication date: 1985-03-05
Also published as: DE3215824A1; FR2504817A1

Abstract

Abstract of the Disclosure Dialysate preparation and supply apparatus including a flow line-having an inlet for a water source at one end, a dialysate outlet for a dialyzer at another end, a first pump connected to supply first concentrated solution to the line at a first supply junction, a first control cell on the line downstream of the first supply junction to control the first pump, a second pump connected to supply second concentrated solution to the flow line at a second supply junction down-stream of the first control cell, and a final control cell on the line downstream of the second supply junction to control the second pump.

Description

~ 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-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 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 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:

Claims

1. Apparatus for continuously preparing dialysate from two concentrated solutions, said apparatus comprising a flow line having an inlet for a water source at one end and an outlet for a dialyzer at another end and a first supply junction, a first control cell to sense the concentra-tion of a first concentrated solution in said line downstream of said first supply junction, a second supply junction, and a final control cell to sense the concentration of a second concentrated solution in said line downstream of said second supply junction, all along said flow line between said inlet and outlet, a first pump connected between a first concentrated solution intake port and said first supply junction and re-sponsive to said first control cell to pump the proper amount of first concentrated solution to maintain the concentration of said first concentrated solution in dialysate supplied to said outlet within first predetermined limits, and a second pump connected between a second concen-trated solution intake port and said second supply junction and responsive to said second control cell to pump the proper amount of second concentrated solution to maintain the con-centration of said second concentrated solution in dialysate supplied to said outlet within second predetermined limits.

2. The apparatus of claim 1 further comprising means to adjust said predetermined limits during a dialysis session.

3. The apparatus of claim 2 wherein means are sup-plied on said flowline upstream of said first control cell to deaerate water from said source.

4. The apparatus of claim 3 wherein said flow line also includes downstream of said first control cell an air-bypass chamber to remove any gas that has come out of the solu-tion, and wherein a monitoring cell is downstream of said by-pass stabilization chamber to verify the concentration of said first concentrated solution.

5. The apparatus of claim 1 further comprising means to prevent said second pump from operating unless the first solution concentration sensed in said first control cell is within predetermined limits.

6. The apparatus of claim 5 further comprising a bypass valve downstream of said final control cell, which bypass valve causes said outlet to be connected to said dialyzer when concentrations measured by said control and monitor cells are within predetermined limits and causes said dialyzer to be isolated from the flow line when said concen-trations are not within predetermined limits.

7. The apparatus of claim 1 in which said first concentrated solution is bicarbonate solution and said second concentrated solution is acid solution including sodium.

8. The apparatus of claim 7 further comprising a pH sensor downstream of said final control cell to independently measure the concentration of acid in said flow line prior to entering said dialyzer.

9. The apparatus of claim 8 further comprising an acetate pump connected to said acid supply junction and means for inactivating said bicarbonate pump, bicarbonate control cell, said bicarbonate monitoring cell, and said acid pump.

10. A method of continuously preparing dialysate during a dialysis session, said method comprising supplying water to a flow line, pumping a first concentrated solution to a first junction on said flow line with a first pump controlled by a first sensor located downstream of said first junction to maintain the level of said first concentrated solution added within first predetermined limits, pumping a second concentrated solution to a second junction on said flow line with a second pump controlled by a second sensor located downstream of said first junction to maintain the level of said second concentrated solution added within second predetermined limits, and changing one said predetermined limits to vary the level of one said concentrated solution during said dialysis session.

11. The method of claim 10 further comprising deaerating said water upstream of said first junction.

12. The method of claim 11 further comprising removing air from said water and added first concentrated solution downstream of said first junction in an air-bypass chamber and sensing the level of said first concentrated solution downstream of said air-bypass chamber.

13. The method of claim 12 wherein said pumping a second concentrate does not occur unless the level of said first concentrated solution is within said first predetermined limits.

14. The method of claim 10 wherein a bypass valve is provided on said line downstream of said second sensor, and said valve blocks flow to a dialyzer when the level of said first or second concentrated solution is not within its respective predetermined limits.

15. The method of claim 10 in which said first concentrated solution is bicarbonate solution, and said second concentrated solution is acid solution including sodium.

16. The method of claim 15 wherein the pH of the water and first and second concentrated solution is monitored downstream of said second sensor.