CASE DISCUSSION RELATED TO CONDUCTIVITY ISSUES DURING DIALYSIS THERAPY BY DR JIGAR SHRIMALI

32-year-old male, who is k/c/o HTN, DM, CVA, CKD Stage 5D on thrice a week MHD with left BC AVF. He was posted for right carotid endarterectomy. For that, pre-op heparin free dialysis was planned. After dialysis, the next morning the patient’s blood pressure was 70/52 mm of Hg. On evaluation found to have severe hyperkalaemia with serum potassium 7.2 mEq/L and ABGA s/o severe metabolic acidosis with pH 6.9 and bicarb 7 mEq/L. So, on further evaluation we found that in that particular hospital there was non-availability of bicarb part. So, it was brought from a nearby hospital by a technician in powder form. After the start of dialysis there were repeated alarms related to conductivity but it was bypassed and then the conductivity set limit was changed. This issue was followed by repeated blood leak detection alarms but they were also bypassed. But still with these alarms dialysis was done. Surgery was postponed and urgent haemodialysis was done and after that electrolytes and acid base status was stable.

The conductivity monitor of the dialysis machine indicated improper conductivity, but the dialysis technician was able to readjust alarm limits of the conductivity monitor (a poor practice) to bypass the alarm and proceeded to dialyze the patient. Blood leak alarms were due to haemolysis related to change in conductivity.

Discussion

 Dialysis circuitry requires monitoring to assure patient safety. Every nephrologist and technician should “know their machine” in order to safely troubleshoot problems.

The dialysate is prepared by mixing three liquids inside the machine – the Acid solution (Part A), the Bicarbonate solution (Part B) and RO water in a certain proportion.

Until the early 1980s, acetate concentrates were used almost exclusively. Since all concentrates had similar compositions and were diluted with treated water at a ratio of 34:1 (35x). Even if the chosen concentrate had an incorrect ionic content, the resulting dialysate was still acceptably buffered.

Almost all dialysis solutions used today are bicarbonate based, and this engenders a solubility issue. When making a bicarbonate solution of about 30 mM, the pH will be close to 8.0. At this pH, calcium and magnesium will precipitate out from solution, reducing their diffusible concentration and also contributing to scaling on dialysis machine lines and passages. To circumvent the problem of calcium and magnesium precipitation, a bicarbonate-based dialysis solution–generating system utilizes two concentrates: a “bicarbonate” concentrate and an “acid” concentrate. The “acid” concentrate contains a small amount of acetic or citric acid plus sodium, potassium (as needed), calcium, magnesium, chloride, and dextrose (optional). The low pH of the acid concentrate keeps the calcium and magnesium in solution, even in concentrated form.

Specially designed double proportioning systems mix the two concentrates sequentially with purified water to make the final dialysis solution. During mixing, the small amount of acetic acid in the “acid” concentrate (about 2–4 mM) reacts with an equimolar amount of bicarbonate in the “bicarbonate” concentrate to generate carbon dioxide. The carbon dioxide generated forms carbonic acid, which lowers the pH of the final bicarbonate- containing solution to approximately 7.0–7.4. At this pH range, the calcium and magnesium in the product dialysis solution remain dissolved.

Acid + Bicarbonate →Carbonic acid

↓

C0₂

The ratio of “acid” concentrate to “base” concentrate to water in the various proportioning systems available depends on the machine manufacturer. Liquid “acid” concentrates are available between 35 times and 45 times concentrated, and the corresponding liquid “bicarbonate” concentrates are also concentrated differently. In units using more than one brand of dialysis machine, it is important to use concentrate designed for the proportioning ratio of a given machine.

Say for for Fresenius machine

1)Hemodialysis solution liquid concentrate

Part A     :                 Part B     :                 Purified Water

(V/V)

1               :                 1.83        :                 34

2)Hemodialysis solution cartridge containing dry sodium bicarbonate concentrate

Part A     :                 Part B     :                 Purified Water

(V/V)

1               :                 1.225     :                 32.775

Concentrates in use

1) “ACID” component (PART-A)

It contains Acetic acid + Citric acid + Sodium Chloride + Potassium (if needed) + Dextrose (optional) All calcium + All magnesium. While acetic acid is a liquid, dry “acid” concentrates can be made using either citric acid or sodium diacetate. The low concentration of citrate generated in citric acid–based dialysis solution may chelate plasma calcium that is adjacent to the dialysis membrane, impeding coagulation, improving dialyzer clearance slightly, and increasing the dialyzer reuse number.

2) Bicarbonate (PART-B)

It comes in two forms, liquid “bicarbonate” concentrate, a cartridge containing dry sodium bicarbonate. Use of dry bicarbonate cartridges obviates the problem of bacterial growth in “bicarbonate” concentrate and the concern of subsequent contamination of the final dialysis solutions.

Sodium chloride + Sodium bicarbonate

Final dialysis solution composition

The composition range of typically used dialysis solutions is given in Table 1. The concentrations of sodium, potassium, and calcium can be varied by choosing different “acid” concentrates or by adding salts of these cations to the appropriate “acid” concentrates prior to use.

In addition, some dialysis machines allow the concentration of sodium in the dialysis solution to be varied during the course of an individual treatment—a practice known as sodium profiling. Sodium profiling may help reduce the tendency to intradialytic hypotension and the post dialysis washed-out feeling in some patients, but whenever the average dialysis solution sodium level is increased, this may predispose to increased thirst, excessive fluid intake, and hypertension.

Most dialysis machines allow the bicarbonate level to be varied without changing to a different concentrate by altering the proportioning pump ratio. This allows use of dialysis solution bicarbonate levels from 20 to 40 mM, and such a feature is particularly useful when more frequent dialysis is employed, when dialyzing nonuremic patients (e.g., to treat poisoning) or to treat alkalotic patients. Minor changes in calcium, magnesium, and potassium (if present) will take place whenever dialysate bicarbonate level is altered.

Figure 1   Typical composition of bicarbonate-containing final dialysis solution

Either acetate or bicarbonate dialysis, both concentrate systems may be stored and used within one dialysis clinic or unit. The availability of acid/bicarbonate concentrates with varying ionic contents and proportioning ratios increases the probability of an inappropriate dialysate. The problem is further compounded by the availability of two types of hemodialysis machines with different proportioning systems: fixed-ratio and servo-controlled (variable-rate).

1. In the fixed-ratio proportioning systems, cylinders of known volumes are used to proportion dialysate concentrate and treated water in exact amounts, and a series of valves control the cyclic filling and emptying of each cylinder. All available fixed-ratio systems incorporate an electrical conductivity sensor to monitor the mixture and to initiate action (e.g., bypass, alarms) if the conductivity of the dialysate is not within preset limits.
2. Servo-controlled systems use a control sensor to monitor the conductivity of the dialysate and regulate the flow of the dialysate concentrate within the specified conductivity limits. Flow can be regulated using variable-speed pumps, variable-orifice valves, or other mechanisms. Like fixed-ratio systems, servo systems also employ a second conductivity sensor to monitor the mixture and to initiate action (e.g., bypass, alarms) if conductivity is not within specified limits.

Thus, while fixed-ratio proportioners will mix specific volumes of concentrate and treated water, servo-controlled proportioning systems will attempt to deliver as much or as little concentrate as required to satisfy the conductivity sensor.

The conductivity setting of the dialysis machine directly corresponds to the level of sodium in the dialysate. A higher conductivity means a higher sodium level in the dialysate and vice versa. By altering the conductivity desired, we can tell the machine what sodium level we would like the blood to be exposed to. The machine does this by altering the proportion in which it mixes these three liquids.

There is no one single number for conductivity that is suited to all. Generally, a high conductivity causes excess sodium to be present in the dialysate and as a direct consequence, in our blood while a lower conductivity causes lower amounts of sodium to be present in the dialysate and in our blood. Excess sodium causes excess thirst and causes us to drink more water while low sodium causes low blood pressure and cramps as well.

So, if you come back with excess fluid weight gain, it is quite likely that your conductivity setting was higher than you need it to be. If a patient is getting cramps or low blood pressure, go up a point or two (0.1 or 0.2) at a time. If, on the other hand, a patient is feeling too thirsty, try going down a notch at a time (0.1 or 0.2).

The dialysate proportioning system tests the conductivity of the dialysate. A pair of electrodes or a sensor cell is placed in the dialysate. The machine applies a charge and measures the current. This tells us the total ion concentration level—mainly sodium—of the dialysate.

For safety, most HD machines have two or more conductivity alarms. Each has its own sensors and circuits to monitor the dialysate as it is made. This redundant monitoring is used so two sensors would have to fail before a patient could be harmed. Conductivity is most often checked at two points:

1. Dialysate mixing
2. Before dialysate enters the dialyzer

The Mho is an American unit of measure. The Siemen is an international unit. The two units have the same value. So, a dialysate with 14.1 mMho/cm conductivity is equal to 14.1 mS/cm. One Siemen (S) is equal to the reciprocal of one ohm (an alternative term for a Siemen is “mho”). The normal conductivity range for dialysis solution is 12–16 mS/cm.

Most dialysate delivery systems have pre-set conductivity limits.

Dialysate that is outside the limits triggers a conductivity monitoring circuit. The circuit stops the flow of dialysate to the dialyzer and shunts it to the drain. This is called bypass. Bypass keeps the wrong dialysate from reaching the patient. The circuit also sets off noise and light alarms to alert the staff:

Low conductivity alarms

• Most common
• Can result in rapid hemolysis and severe hyponatremia and hyperkalemia
• Acid or bicarb jug runs out of solution
• Low flow pressure.

High conductivity alarm

• Can lead to hypernatremia and other electrolyte disturbances
• Poor water flow to the proportioning system
• Untreated incoming water
• Use of the wrong concentrate(s)

Incorrect dialysate related problems fall into two major categories:

1. Crossed or improper connections the delivery of the wrong type of concentrate to a particular proportioning system or inlet port (e.g., acid concentrate used alone in an acetate proportioning system; acetate concentrate used in the bicarbonate inlet port).
2. Incompatibility: The use of mismatched concentrates in a particular bicarbonate delivery system.

Crossed or improper connections can result in problems ranging from dialysate compositions that differ from the prescribed formulation to dialysates that prove fatal. Delivery of acid concentrate alone can be fatal, depending on the proportioning system used and the conductivity and other alarm limits of the dialysis machine.

Some servo-controlled proportioners can proportion acid concentrate to the proper conductivity, although the resulting pH of the solution (2 to 3) will be lethal. Some fixed-rate proportioners may also deliver dialysate of the proper conductivity but wrong pH, depending on alarm limits and the proportioning ratio of the concentrate used. This is due to the inherent limitations of conductivity measurement. Conductivity is a measure relating only to the total ionic content, not pH or composition.

The composition of available bicarbonate and acid concentrates is not similar. There are currently at least two different bicarbonate concentrates on the market: one with sodium bicarbonate as the only ingredient and one with sodium chloride added to the sodium bicarbonate to increase the ionic concentration and, therefore, the conductivity. Acid concentrates are available with specifically tailored ionic compositions for use with one of the above bicarbonate concentrates. In addition to varying ionic compositions, dilutions are made at different ratios, depending on the manufacturer of the concentrates and the design of the dialysis machine.

Recommendations to prevent Incorrect dialysate related problems

The range of clinical requirements for individual patients and the various designs of dialysis equipment in use at individual dialysis units makes it impractical to standardize on one dialysis machine or dialysate concentrate for acetate and bicarbonate dialysis. In addition, new therapies may require additional dialysis solutions or equipment. Therefore, we recommend the following steps.

Before each treatment, check the conductivity alarm to verify that it is working. Check the machine readings against a separate meter as well. You must always have enough of both concentrates in the system for a whole treatment.

If any conductivity related alarm check for

1. What type of machine is being used?  With different manufacturers different machines will have change in proportion ratios. In Fresenius dialysis machine proportion ratio for bibag is 1:1.225:32.775 and for bicarbonate powder is 1:1.83:34.
2. What is the set proportioning of the dialysis machines in your unit? Is it set for bibag or bicarbonate powder?
3. Also find out if the machine had any service recently? During that time the engineer may have changed any proportion ratios.
4. Check what is the proportioning of concentrates, when the technician makes the bicarbonate concentrate or are they factory mixed packs of bicarbonate concentrate.
5. Check for correct acid and bicarbonate concentrate are connected.
6. Also check to see if this is the same machine (most facilities have a machine number on the front).
7. How high is the conductivity going to cause the alarm? Also for repeated alarms whether any changes were made in the range of conductivity by the technician?
8. Does the conductivity vary or does it go high and stay high? If it fluctuates frequently ask the engineer to check the gearhead of both the flow pump and deaeration. Maybe it is time to get the carbon brush or the motor change.
9. Did you notice if your temperature display was stable? Temperature display accuracy is supposed to be checked regularly.
10. What is the specific gravity of your acid and bicarb solution? We need a hydrometer to measure the specific gravity. Specific gravity parameters are 1.062-1.065.

To prevent issues related to the dialysate composition there are some responsibilities towards dialysis units and manufacturers

A) Dialysis Unit’s Responsibilities

1. Check the pH and conductivity of the dialysate, and the conductivity, pH, and temperature alarm systems, before each dialysis treatment. If the pH is below 6.5 or above 7.5, do not begin dialysis even if the conductivity is within acceptable limits. The pH may be checked with a dedicated pH meter or pH paper. Checks of proper concentrate, conductivity, and pH should be included in the pretreatment check of all components and alarm systems of the dialysis machine.
2. Make sure that all personnel in your unit are aware of the types of dialysate concentrates available, even if you currently use only one type. Be sure that this information is included in the orientation program for new employees. (Previous experience with one type of dialysis could lead to confusion and mistakes.) Institute an ongoing educational program to keep employees informed of developments in all areas of dialysis treatment.
3. Develop a system of labelling connectors and containers that prevents or minimizes crossed connections and use of mismatched concentrates.
4. Store and dispense dialysate concentrates as though they are drugs. Develop a system that will effectively control the mixing and dispensing of all concentrates. Storing concentrates according to type, composition, and proportioning ratios should reduce the risk of mismatching concentrates. Prohibit access to storage areas and allow only authorized, specially trained personnel to mix and dispense concentrates.
5. Double-check and record concentrate formulas on the patient’s record. Consider a procedure for countersigning patient and storage records.
6. Do not dispense concentrates from large containers into smaller ones without a “keyed” dispensing system. Whenever possible, purchase concentrates in single-treatment containers. Locally 
concentrates are available with different packing size from 3.78 liter, 5 liter, 10 liter and 30 liter.
7. Always dispose of concentrates remaining from the previous treatment. Do not pour remaining concentrate into another container or use in the next treatment. Replace empty or partially full containers with full ones.
8. Whenever possible, standardize equipment so that only one bicarbonate concentrate system is used.
9. Whenever there is change from cartridge containing dry sodium bicarbonate concentrate to bicarbonate liquid concentrate then we need to change proportion ratios from the service menu of the dialysis machine. Proportion ratio for bibag is 1:1.225:32.775 (for A part:B part: RO water) and for bicarbonate powder is 1:1.83:34 (for A part:B part: RO water).

B) Manufacturers’ Responsibilities

1. Develop industry-wide standardized coding systems to clearly identify dialysate concentrates and machine connectors.
2. 
Attempt to standardize proportioning ratios of all concentrates among different manufacturers.
3. 
Label all acid solutions with warnings indicating that these acid solutions should not be used alone.
4. 
Label concentrates with information and warnings regarding known incompatibilities, proper mixing instructions, the specific solutions they must be used with, the specific machines they are to be used with, and the dilution ratio.
5. 
Develop monitoring and control systems in dialysis equipment to prevent lethal cross-connections.

C)Checklist for Preventing Use of incorrect Dialyzer or Dialysate

1. Two staff members independently check and initial the dialyzer and dialysate.
2. The patient checks and initials dialyzer and dialysate. Patients, educated on the dialysis procedure, dialysate and labs (connection between their potassium level and dialysate), will be able to identify if the wrong potassium bath is being used. (Staff should provide dialysis prescription updates to patients.)
3. Staff and patients are educated on the dialysis treatment/procedure, explaining each step in the process, including what each identified area on the panel means, e.g., UFR, BFR, etc.
4. Develop system for reporting errors/adverse events
5. All staff—clinical, clerical, housekeeping, and maintenance—as well as patients, need specific, written directions on how to report errors or adverse events.
6. There should be discussions to ensure that all team members clearly know what staff is responsible for responding to errors and near misses immediately.
7. A reporting form should be created for documentation.
8. Conduct root cause analyses
9. Every wrong dialysate or dialyzer event should lead to a “huddle” to discuss what went wrong and how to prevent future episodes
10. For more serious events the facility should conduct a root cause analysis.

Article Courtesy – Dr. Jigar Shrimali

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