THE PROPORTIONING SYSTEM/MIXING SYSTEM.

THE PROPORTIONING SYSTEM/MIXING SYSTEM.

 INTRODUCTION.

In the proportioning system, the treated water, acid concentrate and Bicarbonate concentrate mix together to formulate a solution known as dialysate. The constituents are mixed at a certain proportion 1 part of A 1.83 of B and 34 part of RO water. The dialysate is thus mixed and delivered through a conduit of tubing’s, valves and pushed across by inbuilt pumps within the hydraulic circuit. The pumps built into the delivery system controls the mixing and delivery of the dialysate to the dialyzer and back again to the machine for volumetric uf control.

The water passes through the water treatment system through a series of components in order to make it ultra-pure free from any contaminants, bacteria’s, viruses and endotoxins.

The two concentrates A and B can reach the machine in three different ways;

      a. Prepared liquid concentrate in single carboy jugs connected to concentrate input lines on the machine. A color-coded red and blue lines.

      b. Central concentrate delivery system CDS with delivery points near each station. We connect the concentrate input lines to concentrate at the station.

      c. Dry bicarbonate Bibag option. A container of dialysate powder is mounted on the machine. A hydraulic path adds water into the container to make a liquid.

NB... The biggest advantage of using a bibag Option over the others is that there will be 100% carbon dioxide utilization and it also avoids minimal contamination with bacteria as the concentrate is freshly and readily prepared, the liquid should be utilized and consumed within 6hrs otherwise after the 6hrs, the concentrate is subject to bacteria contamination. WATER from the water treatment system The RO plant reaches the machine through a Distribution piping PEX system.

Simple Block Diagram showing Dialysate pathway.

1.      Solenoid valves

      2.      Tubing’s

      3.      Pumps- Degassing, A&B Concentrate pumps, Dearator pump, Flow pump, UF pump.

      4.      Blocks with vital and complex functions-Heater block, Heat exchanger, Multifunction block,        Mixing chamber, balancing chamber.

      5.      Bypass valve

      6.      Filters

      7.      Pressure measuring points

      8.      Conductivity cell

      9.      Temperature sensors

     10.  PH meter

     11.  Shunt Door interlock switches

     12.  Drainage

PARTS OF THE HYDRAULIC CIRCUIT.

      

    1)   SOLENOID VALVES.

The solenoid valves control the movement of fluids by opening and closing on a command depending on the program set. They receive orders from the electronic circuit. These valves are supposed to be on a signal control.

MAIN VALVES IN THE HYDRAULIC CIRCUIT;

   o   Valve #41- Water inlet valve

   o   Valve #61- Water inflow pressure regulator valve

   o   Valve #26-Bypass valve.

   o   Valve #24a and #24b-Dialyzer valves

   o   Valve #31- #38; balancing chamber valves 8 in total.

   o   Valve #84-Disinfection valve

   o   Valve #87- Drain valve

   o   Valve #86-Recirculation valve.

Diagram showing solenoid valves in Fresenius 2008s machine. 

    1)   TUBINGS.

A conduit/pathway for fluid in this case water+ dialysate. The tubings are made of silicon to withstand high temperatures and pressures in the circuit. The tubings should be Non-corrosive, Non-reactive, Non-expansive, heat resistant and Durable.

Diagram showing Tubing in Fresenius 4008s machine.

     1)   PUMPS.

The pumps built-in the hydraulic machine form an integral part and role by ensuring a sufficient flow of dialysate at certain pressures. They draw fluid, in this case, our water and dialysate.

MAJOR PUMPS IN THE HYDRAULIC CIRCUIT OF A DIALYSIS MACHINE.

      1.      Degassing pump #29

      2.      Acid concentrate pump #23

      3.      Bicarbonate pump #25

      4.      Deaerator pump #97

      5.      UF Pump #22

1. DEGASSING PUMP #29

Water heated to physiological temperature is subjected to a negative pressure of -0.8 bars 0.81 to 0.85 Bar to remove any air/dissolved gases. The air in the circuit could interfere with the flow of dialysate. The machine could indicate flow alarms, balancing errors cyclic error in the display monitor.

The purpose of the degassing pump, therefore, is to remove any traces of air from the INCOMING HEATED WATER by applying negative pressure and then pushing the water to the multifunction block in the primary air separator using positive pressure. The primary air separator in the multifunction block removes the air that has been degassed by the degassing pump and the water loop. Heating treated water helps in degassing it. The degassing pump is responsible for carrying air-free dialysate to a dialyzer.

The Degassing pump is the only pump in a Fresenius 4008 series machine that runs continuously when the machine has been powered up.

Diagram Showing Degassing Pump in Fresenius 4008s machine.

2. ACID CONCENTRATE PUMP #23

 Draws the acid concentrate from the A containers to the mixing chamber for mixing/proportioning to be mixed with water and Bicarbonate. The acid concentrate has all electrolytes + calcium and magnesium. It has also some acetic/lactic acid in it.

Also housed near the pump#23 is primary air separator#201 and level sensor#202 to remove any presence of air in the Acid concentrate before flowing to the mixing chamber. The level sensor is responsible to sense any presence of air and activate the acid pump to raise the level of fluid in order to eliminate any air.

Diagram showing Acid Concentrate pump to the right in  Fresenius 4008s machine.

3. BICARBONATE PUMP #25

Draws Bicarbonate concentrate to the mixing chamber to be mixed with A and treated water to formulate a dialysate. Acid and Bicarb reacts to form Carbonic acid and carbon dioxide to be used to clear metabolic acidosis from the patient.

Also housed near the pump#25 is primary air separator#203 and level sensor#204 to remove any presence of air in the bicarbonate before flowing to the mixing chamber. The level sensor is responsible to sense any presence of air and activate the bicarb pump to raise the level of fluid in order to eliminate any air.

In the early 1960s, acetate became the standard dialysate buffer for correcting uremic acidosis over the next several years, reports began to accumulate that linked routine use of acetate with cardiovascular instability and hypotension during dialysis. As a result, dialysate containing bicarbonate began to re-emerge as the principle dialysate buffer, the only disadvantage with bicarbonate is the high incidence of bacterial contamination and formation of white precipitate due to ca and mg deposits but zero disadvantage to the patient so it’s the preferred type of use up to date.

Diagram showing a Bicarbonate Pump To the left in Fresenius 4008s machine.

4. DEARATOR PUMP #97

The deaerator pump just like degassing pump removes air/dissolved gasses only that this time its removing air from the spent/used dialysate in the secondary air separator of the multifunction block before flowing to the balancing chamber. Any presence of air could disturb the flow of the dialysate and cause flow alarms, balancing errors, cyclic pht errors in the display monitor of the machine. These provisions ensure no air flows to the balancing chamber in order not to cause errors in the machine.

The level sensor #6 will activate the deaerator pump to eliminate any air and to raise the level of fluid.

Diagram showing deaerator pump Fresenius 4008s machine.

5. FLOW PUMP #21

The flow pump is responsible to press used/spent dialysate from the secondary air separator in Multifunction block into the balancing chamber #68 for volumetric control.

A flow pump controls the rate that dialysate flows to the dialyzer 300,500 and 800ml/min in order to achieve proper rationing between the blood and dialysate flow of 1:2. This is a very important, crucial, vital necessitated point that in order to achieve dialysate flows you need the flow pump whereas in order to achieve blood flow, you require the blood pump. The higher the dialysate flows, the more the clearance of solutes or the more the diffusion but this again under the advice of the Nephrologist who describes the particular blood flow of a patient according to KDOQI guidelines in dialysis adequacy.

Also present in the flow pump is a pressure relief valve #78 which is used to limit the pressure of the flow pump to approx. 2bar.

Diagram showing flow pump Fresenius 4008s machine.

5. ULTRAFILTRATION PUMP THE UF PUMP #22

The uf pump is particularly of importance in any hemodialysis machine as it helps us to achieve ultrafiltration during treatment (the removal of excess water from the patient). The uf pump draws any excess fluid from the patient by applying a negative pressure from the Multifunction block in the secondary air separator and pushing the same fluid using positive pressure.

It also helps to achieve volumetric uf controlling in order to balance the dialysate in the balancing chamber. The uf pump will only suck the Uf goal target set of a particular patient…the rest of the used dialysate is sent to the balancing chamber to achieve volumetric control. The pressure is applied to the blood side compartment to push excess water/fluid to the dialysate, this phenomenon is also of importance while calculating TMP (The Trans-membrane pressure)

TMP= VENOUS PRESSURE (+VE), Vp – DIALYSATE PRESSURE (BLOOD SIDE PRESSURE +VE, db + NEGATIVE UF PUMP PRESSURE –VE, dp)

If the uf is not functioning and takes less volume of fluid, then an error message will appear on the screen detailing UF Function Failure. A Haemodialysis delivery system using balancing chambers must have an Accurate UF pump to measure the UF since the uf pump helps in Volumetric control.      

Diagram showing UF pump Fresenius 2008k machine.