Cause of Device-Related Incident
User errors

Clinical Specialty or Hospital Department
Dialysis; Nephrology

Device Factors
*Not stated

Document Type
Hazard Reports

External Factors
*Not stated

Mechanism of Injury or Death
Wrong drug

Support System Failures
*Not stated

Tampering and/or Sabotage
*Not stated

User Errors
Incorrect clinical use; Incorrect control settings

UMDNS
Dialysate, Hemodialysis [16-641]

Improper Dialysate



Hazard [Health Devices Oct 1983;12(12):315-8]

Problem

ECRI received a report of a patient death due to the inadvertent use of acid concentrate (the acid part of a two-part bicarbonate concentrate system) in a hemodialysis machine designed to proportion acetate concentrate. The conductivity monitor of the dialysis machine indicated improper (low) 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. The patient died of metabolic acidosis during dialysis.

Discussion

Until the early 1980s, acetate concentrates were used almost exclusively. The consequences of using a concentrate that was not designed for a given machine were not serious, 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.

The recent resurgence of bicarbonate dialysis has resulted in several potential problems. Although acetate concentrates can be used interchangeably on all acetate proportioning dialysis machines, concentrates for bicarbonate proportioning systems are not as flexible. Bicarbonate dialysis requires mixing two concentrates acid and bicarbonate with treated water. (See Health Devices 9:126-29, February-March 1980 for a discussion of water treatment.) Bicarbonate concentrate is typically supplied in powder form, to be mixed with treated water immediately preceding dialysis. Acid concentrate, containing an electrolyte composition similar to that of acetate concentrates but at a lower pH, is supplied in liquid form.

Either acetate or bicarbonate dialysis may be prescribed for a patient and, therefore, 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).

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.

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. (For more information regarding dialysis units, see Health Devices 9:87-122, February-March 1980.)

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.

It is beyond the scope of this report to describe all the possible combinations of problems that could exist, given the variety of concentrates of different formulations and the variety of dialysis delivery systems in use. However, the 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.

Proportioning of mismatched (i.e., improper ionic composition or concentration) acid and bicarbonate concentrates, or the substitution of acetate concentrate for either acid or bicarbonate concentrate, can result in ionic imbalances that, while probably not immediately life-threatening, can create clinically significant electrolyte imbalances. Depending on the mismatched combination used, an inappropriate dialysate may not fall within acceptable conductivity and pH ranges and may have long-term effects which compromise patient welfare.

Recommendations

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.

  1. Check the pH and conductivity of the dialysate, as well as 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. (Only by determination of pH, conductivity, and acetate and bicarbonate levels would it be possible to determine safe and acceptable dialysate composition.) 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. Whenever possible, develop (or use if available) a system of labeling (see recommendations for manufacturers) connectors and containers that prevents or minimizes crossed connections and use of mismatched concentrates. When ordering solutions, request that such systems be incorporated (e.g., color coding, different connectors) in delivered products, not shipped separately.
  4. Store and dispense dialysate concentrates as though they were drugs. Develop a policy, management, and storage 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 (2½-gallon) containers.
  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.

Manufacturers' Responsibilities

We believe that control of the risks associated with hemodialysis is also a responsibility of the manufacturers of dialysis equipment and consumables. Therefore, we urge the dialysis industry, with input from the healthcare community, to consider some or all of the following as minimum controls:

  • Develop industry-wide standardized coding systems to clearly identify dialysate concentrates and machine connectors.
  • Attempt to standardize proportioning ratios of all concentrates.
  • Label all acid solutions with warnings indicating a) the hazard of using them with acetate-proportioning dialysis machines and b) that these acid solutions should not be used alone.
  • 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.
  • Develop monitoring and control systems in dialysis equipment to prevent lethal cross-connections.

UMDNS Term

Dialysate, Hemodialysis [16-641]

Cause of Device-Related Incident

User errors: Incorrect clinical use; Incorrect control settings

Mechanism of Injury or Death

Wrong drug


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