Delivery systems

What chemicals are in the bicarbonate concentrates?

"A" indicating acidified concentrate contains most of the sodium, all of the calcium, magnesium and potassium, chloride, and a small amount of acetic acid to maintain pH low enough to keep calcium and magnesium in solution when mixed into dialysate. "B" indicating bicarbonate concentrate contains the sodium bicarbonate. Some systems include part of the sodium chloride as well as the B concentrate; this raises the total conductivity, making it easioer to monitor the concentrate. In the proportioning system, the B concentrate is usually diluted patially with water; the A concentrate is then proportioned into the mixture just before it goes to the dialyzer. In the closed system, CO2 c annot bubble off, the reaction between sodium bicarbonate adn acetic acid cannot proceed to completion, and the hydrogen ion content keeps the calcium in solution.

What is dialysate?

- A solution of purified water and electrolytes in concentration similar to blood. - Consists of the chemicals which we use to clean a patients blood. - Contains essential electrolytes to assure these are not depleted during dialysis

What are the potential problems with bicarbonate dialysate?

- Bicarbonate concentrate is very susceptible to bacterial contamination and proliferation

What does dialysate do?

- Carries away waste products and excess fluid removed from the patient's blood during the dialysis process - Prevents excess removal of essential electrolytes during the dialysis process - averts excess water removal during the procedure

Conductivity is most often checked at what two points?

- dialysate mixing - before dialysate enters the dialyzer

What are the disadvantages of the proportioning systems?

- expensive - many functions are preprogrammed and cannot be readily changed - sensors and monitoring devices must be fail safe and redundant. - troubleshooting is difficult, factory based personnel needed for repairs

What are the disadvantages of the sorbent system?

- expensive sorbent cartridge - limit to the capacity to digest urea and adsorption of ammonia - large patients or those with high serum urea values may require more than one cartridge per dialysis.

What are the system requirements for high-flux dialysis?

- maintain high blood flow rate - high dialysate flow rate - precision control of ultrafiltration volume High flux dialyzers use synthetic membranes of very high permeability, with convective transfer providing a major share of solute transport. These dialyzers have ultrafiltation coefficients of 20 to 70 mL/hr/mm Hg or more

What problems are associated with dialysate flowmeters?

-Solute film tends to build up with time and reduce accuracy. - Calibration of the flow meter or flow controller should be part of the routine servicing of the machine.

What kind of water is used to prepare dialysate?

-The water must meet AAMI standards for chemical content & for bacterial and pyrogen content. - Current AAMI standards for product water used to prepare dialysate states the microbial count has to be lower than 200 CFU/mL and an endotoxin concentration lower than 2 EU/mL

What are advantages of the sorbent system?

-portability - absence of need for a special water supply or drain connections; can be used wherever electricity is available.

What are the two basic types of ultrafiltration controllers?

1. volumetric 2. flowmetric

How does a sorbent system function?

3 actions involved: 1. conversion of urea to ammonium barbonate 2. adsorption of creatinine adn other nonionized solutes 3. ions exchange resins (sodium zirconium phosphate and zirconium oxide)

What are equipment needs for high efficiency dialysis?

4 Requirements - Highly permeable cellulose membrane (ultrathin, cuprophan, hemophan, cellulose acetate esterm ect.) with surface area 1.5 m2 or more - Reliable blood flow of 350 mL/min or more; dialysate flow of 750 mL/min or more - Bicarbonate dialysate delivery system - An ultrafiltration control system The combination of a large area of membrane of high mass transfer capability and high Qb and Qd produces increased small molecule transfer. Intermediate-sized and large solute transfer rates are enhanced by the area and permeability increases.

What kinds of blood pumps are used?

A pump with internal components exposed directly to blood can present major problems in cleaning and sterilization. Peristaltic roller pumps, which work by progressibely compressing special segments of blood tubing against a semicircular houseing, are used almost univeral.

How does a sorbent regenerative supply system work?

A small volume of dialysate is recirculated thorugh a cartridge of adsorbent materials and chemically regenerated. Metabolic waste products transferred from the dialyzer to the dialysate are removed adn the electrolyte content and pH are restored.

How might the problem of reverse filtration be countered?

AAMI standards require not more than 200 CFR of bacteria per milliliter in the water for dialysate, and not more than 200 CFU bacteria or 2 EU by LAL testfor endotoxin in dialysate leaving the delivery system. Addition of molecular filter or ultrafilter to the dialysate path immediatedly ahead of the dialyzer may be neccessary for high flux dialysis.

What is urease?

An enzyme that converts urea to ammonium and carbonate

What is the process of urea conversion?

As dialysate enters the regenerative cartridge, it first passes a carbon layer, which removes heavy metals and oxidant; it then contacts a bed containing urease.

How do blood leak detectors work?

Blood leak detectors are situated in the effluent dialysate line. A beam of light is directed through a comlumn of dialysate onto a photoelectric cell. A change in translucence and light scatter in dialysate reduces the light received by the photocell, stopping the blood pump and activating visual and audible alarms. AAMI standards require detection of less than .45 mL/min of blood at hematocrit 45 over a range of dialysate flows. Check blood leak with HEMOSTIX if it is not visual.

How is bicarbonate bades dialysate prepared?

Calcium and magnesium will not remain in a solution with bicarbonate bc of the low hydrogen ion content. To solve this, two separte concentrates are used. The proportioning delivery system is more complex bc it must mix and monitor three liquids instead of only 2.

How is dialysate concentration controlled and monitored?

Conductivity which much be temperature compensated.

What is the importance of the dialysate pressure monitors?

If ultrafiltration is controlled volumetrically and flowmetrically, the dialysate pressure monitors serve as a check on the ultrafiltration control and the transmembrane pressure.

How does the flowmetric ultrafiltrate control system work?

In a flowmetric system there are one or two very accurate flowmeters in both the inflow and the outflow dialysate pathways to measure the flow of fluid passing through these pathways. The speed of the dialysate pump in the outflow path is varied by the electronic control module so that the volume through the outflow meter is exactrly equal to the volume through the inflow meter, plus the programmed amount of ultrafiltrate.

What is the delivery system?

It prepares and delivers dialysate to the dialyzer unit. Most systems provide dialysate for a single patient; others have the capacity to supply several dialyzer stations simultaneously.

What is the LAL test?

LAL is the abbreviation for limulus amebocyte lysate. It is an assay for endotoxin that uses a protein extract from the Limulus or horseshoe crab. It is reported in nanograms per milliliter or in endotoxin units. TEST TO TEST MONITOR DIALYSATE FOR ENDOTOXINS

How do proportioning systems correctly mix dialysate?

Liquid concentrate is required. The speed of the pumps and thus the volumes of the concentrates added are precisely controlled by the electronic feedback circuit to ensure that the dialysis fluid is properly mixed.

What secondary tests are used?

Most common test of dialysate is the total conductivity. Alternative secondary check of dialysate is the measurement of total osmolality by either freezing point depression or vapor pressure. These measure total solute in the dialysate.

Why is dialysate verification and monitoryin so important?

Serious patient reactions and deaths have resulted from dialysate preparation errors or equipment malfunction. Dialysate must be verified fro each dialysis. Each delivery system should have a function check daily.

Is dialysate pH monitored?

Should always be pH verification! THE USUAL LIMITS OF PH ARE 6.8-7.6. There should be audible and visual alarms for any out of limits state

What is the solution Delivery System (SDS)?

The SDS is a method of delivering the solutions used to make dialysate to the machine. Bicarbonate from a mixing tank adn acid from a storage tank are transferred to an overhead holding tank. The solutions are then gravity fed to a solution distribution system and then fed out to the patient care area to be delivered through a series of pipes to the machine.

How are creatinine and nitrogenous material removed?

The final layer of the sorbent column contains activated carbon (charcoal) that binds by adsorption of creatinine, uric acid, guanidines, and other organic metabolites

How is dialysate temperature controlled?

The heater or heat exchanger is controlled by one or more sensors and a microcontroller circuit. Fluid temperature should hold within .5 degrees celsius of the set point. There should be a separate sensor, independent of the heat control, for online monitoring with visual and audible alarms for any out of limits state. Many ESRD patients have a body core temp of 36 to 36.5 degrees celsius. Added heat in excess of replacement causes a vasodilatory response, which may be detrimental at a time when the normal vasoconstrictive response to reduce volemia from ultrafiltration is acting to minimize hypotension.

How do volumetric ultrafiltration devices operate?

The most common system employs two diaphragm chambers to balance the inflow and outflow dialysate. While one side of the first chamber is filling with fresh fill dialysate, its diaphragm is forcing out an equal volume of used fluid from the other side. Simultaneously in the second chamber, on e side is fillling with spent fluid from the dialyzer while the opposite side is ejecting an equal volume of fresh dialysate to the dialyzer. When the diaphragms have deflected across the width of the chambers, valves are revered so that the side that was emptying now fills, and vice versa. The volume for ultrafiltrate is removed from the outflow dialysate channel by a metering pump before the outflow volume is matched to inflow, thus removing the desired the desired amount of ultrafiltrate from the patient. Because the volumes in and out of the controller are precisely equalized, whatever pressure (negative or positive) is necessary will be created from the removal of the measured ultrafiltrate volume by the dialyzer.

How are ammonium ions handled?

The next segment of the cartridge contains sodium zirconium phosphate, which act as as exchange resin, taking up the ammonium ions and releasing sodium and hydrogen ions. The carbonate ions equilibrte with hydrogen ions to yield bicarbonate ions and carbon dioxide.

What methods are used to check the dialysate composition?

There are 2 general methods, primary and secondary. A primary method specifically measures the concentration of one solute by a laboratory method of known reliability. Usually 2 solutes are determined, such as sodium by flame photometry and chloride by titration. This is particularly important for bicarbonate dialysis to ensure proper ratio of acid to bicarbnate, as well as the ratio of concentrate to water.

What chemicals are in dialysate?

There are usually five compounds involved: - sodium chloride - sodium bicarbonate or sodium acetate - calcium chloride - potassium chloride - magnesium chloride *Glucose may be included in some formulations

How do ultrafiltration controls work?

These devices exactly match the outflow dialysate volume with the inflow vol., plus a precisely measureed extra effluent vol. representing the desired ultrafiltrate.

Why are deaeration devices necessary?

Water contains considerable dissolved air and microbubbles. When it is warmed, the dissolved air comes out of solution as expanding microbubbles. These have a negative effect on temperature and conductivity sensors, and flowmeters. Bubbles can reduce dialysate/membrane contact in hollow fiber dialyzers. Most deaeration devices use warmers along with negative pressure to bring the dissolved gasses out of solution. An air trap of coalescing filter then captures the gases and vents them to the outside.

Is it necessary to replace calcium, magnesium, or potassium?

Yes. An infusion of calcium and magnesium is made just before the dialysate returns to the dialyzer to keep the desired concentration of these ions. Potassium is added or omitted, according to doctors orders.

Are other ions exchanged in the column?

Yes. Calcium, magnesium, and potassium are exchanged for sodium ions by sodium zirconium phosphate. The third portion of the cartridge contains hydrated zirconium oxide, which removes phosphate ions and fluoride.

A fluid temperater greater than 41 degrees celsius causes what?

hemolysis of RBCs