CMS SOM App. H, Tag V202

5.2.8 Deionization: (continuous monitor resistivity)

6.2.8 Deionization (monitoring)

Deionization: Deionization systems, when used to prepare water for hemodialysis

applications, shall be monitored continuously to produce water of one megohm/cm or

greater specific resistivity (or conductivity of one microsiemen/cm or less) at 25°C.

[Guidance for deionization systems monitoring in ANSI/AAMI RD52:2004 directs users to

ANSI/AAMI RD62:2001; Section 4.3.6]

5.2.8 Deionization

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Deionization may be used to polish product water from a reverse osmosis system or may be

used as a standby if the reverse osmosis system fails.

6.2.8 Deionization

Deionizers shall be monitored continuously using resistivity monitors that compensate for

temperature and are equipped with audible and visual alarms. Resistivity monitors shall

have a minimum sensitivity of 1.0 megohm-cm. Patients shall not be dialyzed on deionized

water with resistivity less than 1.0 megohm-cm measured at the output of the deionizer

Resistivity monitor readings should be recorded on a log sheet twice each treatment day.

Interpretive Guidance § 494.40(a)

ANSI/AAMI RD52:2004

5.2.8 Deionization

Deionization (DI) is an ion exchange process that removes both anions (negatively charged ions)

and cations (positively charged ions) from water. During the exchange process, hydroxyl ions

replace other feed water anions, and hydrogen ions replace other feed water cations; the

hydroxyl and hydrogen ions then combine to form pure water.

Water treated by DI may be very high quality with regard to the absence of ionized

contaminants, but the process does not remove nonionized substances, including bacteria and

bacterial endotoxins. DI systems may contain anion and cation resin in separate vessels, known

as “dual-bed systems,” or may have both resin types mixed together in a single vessel, known as

“mixed-bed” or “unibed systems.”

AAMI Rationale for the Development and Provision of this Recommended Practice

A.5.2.8 Deionization

Deionizers are an effective means of removing ionic contaminants from water. However, they do

not remove nonionic species (such as bacteria), and they may contribute bacterial contaminants

to the water rather than remove them. The inability of deionizers to remove nonionic

contaminants may limit the removal of aluminum by deionization. Deionizers have a finite

capacity for contaminant removal. Once the deionizer is depleted of hydrogen and hydroxyl ions,

the next least avidly bound ions will be displaced by more avidly bound ions. For example, once

the hydroxyl ions are depleted, anionic contaminants in the water will displace fluoride ions

from the anion exchange resin.

This phenomenon has led to high levels of fluoride in the product water, with subsequent patient

injury and/or death. For the above reasons, the use of deionization as the primary means of

purification is strongly discouraged. Deionization may be used to polish product water from a

reverse osmosis system or may be used as a standby if the reverse osmosis system fails.

Deionizers offer a large surface area for bacterial proliferation and deionizers generally

contribute to the bioburden in the water. The tendency for deionizers to contribute bacterial

contaminants to the water is greater when deionizers are kept as a backup for a reverse osmosis

system, particularly if there is no flow through the deionizers. Some facilities counter this

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tendency by connecting the deionizers in parallel to the main water line and by maintaining a

low flow through them. An alternative approach is to contract with a local vendor to provide

backup deionizers on demand.

Suggested deionizer monitoring guidelines from ANSI/AAMI RD52, Table 4 include:

Product water resistivity must be continuously monitored, with a result of resistivity >1

megohm-cm.

Additional Guidance:

If DI tanks are available for back-up use, the facility should take action to counter the tendency

of DI to contribute bacterial contaminants to the water. This may be accomplished by either

storing the tanks dry, placing the tanks on line post-RO so that there is a low flow of water

through them, or flushing the DI tanks daily. DI tanks should not be stored “wet,” i.e., filled with

stagnant water.

Exhausted DI tanks (<1.0 megohm-cm) present a serious risk to patients, and use of exhausted

DI tanks have resulted in deaths. If the water system uses DI as primary purification or as a

polish, the system must be closely monitored by knowledgeable staff. Pure water has a resistivity

of 18.3 megohms. Documentation of a reading greater than 18.3 megohms would indicate some

error. Exhausted DI tanks should be returned to the vendor for recharging. The date of exchange

should be posted on the tank(s) and recorded in a log.

Deionization is not required in every facility; the source water should determine the water

treatment components needed. If deionization is in use, the facility must follow these

requirements.