Cause of Device-Related Incident
Device factors; External factors

Clinical Specialty or Hospital Department
Clinical/Biomedical Engineering; Dialysis; Nephrology

Device Factors
Device interaction

Document Type
User Experience Network (UEN) reports

External Factors
Water supply

Mechanism of Injury or Death
Failure to deliver therapy; Hemolysis; Infection

Support System Failures
*Not stated

Tampering and/or Sabotage
*Not stated

User Errors
*Not stated

UMDNS
Water Purification Systems [15-612]; Water Purification Systems, Reverse Osmosis [14-437]

Importance of Pretreating Municipal Water Used for Dialysis



User Experience Network™ [Health Devices Feb-Mar 1996;25(2-3):110-11]

This report is reprinted, in part, from our Evaluation "Hemodialysis Machines," published in Health Devices 20(6), Jun 1991.

Hospital

We purchased a portable reverse osmosis water purification system for use in our hemodialysis clinic. Shortly after the first use of this system, a physician noted a 5% drop in the patient's hematocrit levels. (The drop in hematocrit required no medical intervention.) It was determined that the patient was receiving excess amounts of chlorine from the product water. We have since learned that the carbon pretreatment filter supplied with our reverse osmosis unit could not effectively treat our source water, whose chlorine level exceeds the maximum specified by the manufacturer. When is pretreatment (or additional pretreatment) needed? Why is it necessary?

ECRI

During dialysis, water in large amounts (almost 50 times the normal exposure experienced by healthy people) bypasses the normal protective mechanisms of the gastrointestinal tract and is in nearly direct contact with the patient's blood (separated by only the thin semipermeable membrane of the dialyzer). It is therefore critical that the quality of the water used to prepare dialysate be carefully monitored and accurately controlled.

In the early years of hemodialysis, tap water was used for dialysate preparation. However, tap water varies in quality throughout the country and, untreated, is rarely pure enough for preparing dialysate. Patients dialyzed with tap water were exposed to substances such as aluminum, iron, chlorine, and organic compounds, producing symptoms such as anemia, metabolic acidosis, nausea and vomiting, hemolysis, and encephalopathy.

After these complications were recognized, the Association for the Advancement of Medical Instrumentation (AAMI) developed standards (subsequently approved by the American National Standards Institute [ANSI] for the quality of water used for hemodialysis. Those standards specify water purity far exceeding that required for drinking water in the United States as regulated by the Safe Drinking Water Act (SDWA) of 1974 (amended in 1986); see the table below. (The SDWA directed the U.S. Environmental Protection Agency [EPA] to issue National Primary Drinking Water Regulations establishing enforceable maximum contaminant levels [MCLs] for all public drinking water systems. Note that the AAMI/ANSI standards include several contaminants not covered by EPA's MCLs.)

In the past, compliance with the AAMI/ANSI maximum levels was voluntary. But today, the Health Care Financing Administration (HCFA) requires that facilities performing hemodialysis comply with these water-purity guidelines before it will approve reimbursement for dialysis treatment. Therefore, tap water must be treated before it can be used for dialysis.

Water treatment systems that supply hemodialysis machines remove contaminants through various treatment stages, which for any given system can include filtration, adsorption, deionization, and/or reverse osmosis. Each of these stages is limited in the amount of contaminant that it can remove. In some instances, a stage must be repeated one or more times to be effective; this can require added equipment. In the case mentioned by the hospital, for example, the chlorine contaminant exceeded the amount that the water purification system and the supplied prefilter could remove, and the excess chlorine entered the dialysate and was taken up by the patient. Some additional form of pretreatment, such as a carbon filter, should have been used.

As the experience of the hospital shows, selecting a water purification system requires care. Institutions may find an analysis of the local water supply helpful in establishing a baseline for specific contaminants that must be removed. Facilities should contact their respective water departments to acquire quality data (i.e., ranges in contaminant levels) for their supply water. This information must be interpreted with caution, however, because municipal water may come from a variety of supplies with different levels of contaminants that are likely to vary over time. Additionally, facilities should periodically monitor the quality of their water before and after treatment through a comprehensive preventive maintenance program (including testing—performed in-house and/or by an outside laboratory—and correcting for conductivity, flow, water temperature, and chlorine levels).

Manufacturers should supply, with their systems, specifications listing the maximum allowable concentration that can be efficiently removed by their water purification systems. If a facility's intake water supply might or does exceed these limits, one or more additional pretreatment devices should be considered when purchasing the dialysis system. The water filtration company's sales representative should be able to design a system based on the hospital's flow rates, intake water quality, and demand level requirements.

 

Comparison of Drinking Water and Dialysis Water Standards*

Contaminant

Drinking Water: Maximum Contaminant Level (MCL) under National Primary Drinking Water Regulations, mg/L**

Dialysis Water: AAMI/ANSI Maximum Allowable Chemical Contaminant Levels, mg/L***

Aluminum

0.01

Arsenic

0.05

0.005

Barium

1.0

0.1

Cadmium

0.005

0.001

Calcium

2.0

Chloramine

0.1

Chlorine (free)

0.5

Chromium

0.05

0.014

Copper

No MCL

0.1

Fluoride

4.0

0.2

Lead

No MCL††

0.005

Magnesium

4.0

Mercury

0.002

0.0002

Nitrate (N)

10.0

2.0

Potassium

8.0

Selenium

0.09

Silver

0.005

Sodium

70.0

Sulfate

100.0

Zinc

0.1

* Not applicable or nonregulated parameters are indicated by a dash.

** Source: Philadelphia Water Department (PWD). Water quality data for Philadelphia. Philadelphia: PWD, 1994.

*** Source: AAMI/ANSI. American national standard for hemodialysis systems. RD5-1992.

† Action Level = 1.3 mg/L of copper at consumer's tap.

†† Action Level = 0.015 mg/L of lead at consumer's tap.

 

UMDNS Terms

  • Water Purification Systems [15-612]
  • Water Purification Systems, Reverse Osmosis [14-437]

Cause of Device-Related Incident

Device factor: Device interaction

External factor: Water supply

Mechanism of Injury or Death

Failure to deliver therapy; Hemolysis; Infection

 

 


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