CMS SOM App. H, Tag V248

5.6 Dialysate proportioning

[T]he acid and bicarbonate concentrates [must] be matched with respect to the

proportioning ratio and with the model and setup configuration of the dialysis machine.

Several types of three-stream concentrates are available, with different ratios of acid

concentrate to bicarbonate concentrate to water (see Table 3). The different proportioning

types are not compatible with one another.

Interpretive Guidance § 494.40(a)

ANSI/AAMI RD52:2004

5.6 Dialysate proportioning

Essentially, all dialysate is produced with three fluid streams: water, acid concentrate, and

bicarbonate concentrate. This three-stream combination produces a highly buffered dialysate

with a pH between 6.9 and 7.6. Dialysate can also be prepared from a single concentrate that

contains acetate to provide a dialysate in which buffer is provided to the patient in the form of

acetate, which is subsequently metabolized to yield bicarbonate. However, acetate containing

dialysate is now rarely used in clinical practice.

Different manufacturers of dialysis machines use different methods of controlling the

proportions of the concentrates. These can be generally grouped into two categories: “fixed

proportioning” and “servo control.” With both methods, the operator can select a desired

sodium and bicarbonate level, and the machine will make the necessary adjustments to achieve

the selected levels. Both types use a redundant system of controls and monitoring. With fixed

proportioning systems, the pumps are set to established volumes, and the final conductivity is

verified. With servo control machines, the individual concentrates are added until the

conductivity achieves the expected value. A final redundant conductivity monitor verifies the

mixture. Some machines may also monitor the pH of the dialysate as an additional safeguard

against gross errors in dialysate formulation.

Generally, bicarbonate is available in one or two forms for each proportioning type (in liquid,

cartridge, or dry powder, and in various sizes). Each proportioning type has numerous acid

concentrate formulations (“codes”) with different amounts of potassium, calcium, and

magnesium ions, plus dextrose. To help differentiate between concentrates of different

proportioning types, AAMI recommends that the manufacturer include a geometric symbol on

the labels along with acid/base color coding.

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AAMI Rationale for the Development and Provision of This Recommended Practice

A.5.6 Dialysate proportioning

Dialysate is usually prepared by a proportioning system that sequentially adds acid concentrate

and bicarbonate concentrate to purified water. These systems produce a buffered physiologic

dialysate with a pH between 6.9 and 7.6. More recently, systems have been developed that use

three concentrates (bicarbonate, sodium chloride, and an acid concentrate containing the

remaining electrolytes) to allow more sophisticated variation of the dialysate composition during

dialysis.