Hazard [Health Devices Oct 1983;12(12):315-8]
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
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
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:
- 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).
- 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
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.
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.
- 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.
- 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
- 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.
- 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
- Double-check and record concentrate formulas on the
patient's record. Consider a procedure for countersigning patient and
- Do not dispense concentrates from large containers
into smaller ones without a "keyed" dispensing system. Whenever
possible, purchase concentrates in single-treatment (2½-gallon)
- 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.
- Whenever possible, standardize equipment so that only one
bicarbonate concentrate system is used.
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
- 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
Dialysate, Hemodialysis [16-641]
Cause of Device-Related Incident
User errors: Incorrect clinical use; Incorrect control settings
Mechanism of Injury or Death