The different water purification systems used in hemodialysis are reviewed here. Discussions concerning the water-borne contaminants to which hemodialysis patients are exposed and the methods of monitoring the various water delivery systems are presented separately. (See "Contaminants in water used for hemodialysis" and "Maintaining water quality for hemodialysis".)
RATIONALE FOR WATER PURIFICATION SYSTEMS
Hemodialysis patients are particularly vulnerable to contaminants in the water used to prepare concentrate and dialysate, or in water used for reprocessing dialyzers. Compared to healthy individuals, hemodialysis patients are exposed to extremely large volumes of water, have inadequate barriers to such toxins, and cannot easily eliminate contaminants:
- The estimated water intake of a healthy individual is 2 L per day or 14 L per week. By comparison, a hemodialysis patient may be exposed to 350 to 500 L of water per week, depending upon their treatment time and dialysate flow rate.
- With normal individuals, the gastrointestinal tract separates blood from contaminants in the water. By comparison, the barrier between blood and water in hemodialysis patients is a thin membrane, through which transfer of contaminants is limited only by the size of the contaminant.
- When dialyzers are reused, water is introduced into the blood compartment of the dialyzer during reprocessing. Contaminants in this water may be trapped in the blood compartment and the patient directly exposed to them during the next dialysis treatment.
- Hemodialysis patients are unable to renally excrete any contaminants taken up from the dialysate.
Accumulated experience, combined with the observation that some of the most toxic contaminants arise from municipal water treatment practices, suggests that no municipal water can be considered safe for direct use in hemodialysis applications. All dialysis facilities therefore require a properly designed and maintained water treatment system to safeguard patients .
CHOOSING A WATER TREATMENT SYSTEM
Most dialysis facilities obtain their water treatment system from a vendor specializing in such equipment. However, the medical staff of a facility should understand enough about water treatment to critically appraise the system they purchase. This is necessary for the following reasons: