Care of filters used in dialysis

FDA Consumer, Oct, 1989

Care of Filters Used in Dialysis

FDA has alerted hemodialysis personnel and water service contractors about the necessity of adequately rinsing dialysis water treatment filters before use to avoid contamination with sodium azide and other preservatives.

In a letter sent in March, FDA recommended that new sodium azide-preserved filters be rinsed with a minimum of 500 gallons of water, which should then be discarded before beginning production of dialysis-quality water.

FDA sent out the alert after nine patients in a dialysis facility in New York developed life-threatening hypotension (low blood pressure) shortly after treatment started. Some of these patients also had blurred vision, severe abdominal pain, headache, and loss of consciousness.

A hemodialysis machine does the job of the kidneys--removing liquid and toxins from the blood--in patients whose kidneys are impaired or have been removed. The problem in New York has been attributed to contamination of the water treatment system with sodium azide, a potent hypotensive agent. The incident occurred after four new ultrafilters, which had been packed in a preservative solution of 0.25 percent sodium azide and 25 percent glycerine, were installed without pre-rinsing.

Because ultrafilters preserved with sodium azide typically are intended for industrial use, they are not labeled for medical use by their manufacturers. However, these filters are used in some dialysis facilities, particularly in areas where water contains a high-silt concentration.

In its safety alert letter, FDA said that dialysis facilities that use sodium azide-preserved filters should be certain to install them according to the manufacturer's recommendations. In addition, the agency warned that thorough rinsing of these filters was essential because no readily available test can detect traces of sodium azide in dialysis water.

FDA also warned that all newly installed filters--not just those preserved with sodium azide--require thorough rinsing. Other preservatives used in manufacturing water treatment filters, such as formaldehyde and sodium bisulfite, are also toxic. The filter manufacturer should be consulted regarding any questions about preservatives in filters.