Focus on Dialysis . . . Facilities Take Closer Look at Ultrapure Fluid
More and more dialysis facilities are considering the use of ultrapure dialysate, a purer fluid than what is traditionally used to remove waste and extra fluid from blood.
The use of ultrapure poses certain challenges for dialysis facilities, such as increased regulation, cost, and monitoring, says Conor Curtin, senior vice president of research and development for Fresenius Medical Care and cochair of AAMI’s Renal Disease and Detoxification Committee. “There is a trend toward using higher purity dialysate to minimize the exposure of the patient to toxins, but the jury is still out as to the benefit and the reward for the effort,” he says.
“I think people are becoming more conscious of ultrapure. But in terms of the actual practical implementation, I don’t think it is here yet,” says Nathan Levin, MD, medical director for the Renal Research Institute in New York.
ANSI/AAMI RD52:2004, Dialysate for hemodialysis (Includes Amendments A1:2007, A2:2007, A3:2009, and A4:2009)
AAMI Dialysis Standards Collection
AAMI Standards on CD—Dialysis
AAMI Dialysis Standards Book
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Dialysis is used to provide an artificial replacement for lost kidney function, which usually occurs due to renal disease. “When the kidneys fail, the body does not get rid of a whole range of substances that are the products of normal metabolism,” says Richard Ward, PhD, a professor of medicine at the University of Louisville, and co-chair of AAMI’s Renal Disease and Detoxification Committee. “They range in size from very small, like water, to quite large, like proteins. Most of these substances, at some level, are toxic.”
Conventional dialysis removes those substances through a process called diffusion. Blood and the dialysate or fluid flow on opposite sides of a semi-permeable membrane. The process helps to remove toxins and other substances.
Water is used in all hemodialysis treatments. “A domestic water supply has chlorine in it to suppress bacterial growth. The problem is those chlorine compounds are highly toxic to dialysis patients and have to be removed from the water,” Ward says. “Once the chlorine compounds are gone, there is nothing to stop bacteria growing and releasing products of their metabolism into the water. Many of these substances stimulate an inflammatory response. The idea of ultrapure fluids is that you are really trying to markedly reduce the level of those substances. Evidence continues to mount, mostly indirectly, that using fluids or dialysis that have a far higher purity than what our standards currently allow will reduce microinflammation in patients.”
Current standards set a maximum allowable level of bacteria. Ultrapure dialysate has a maximum of 0.1 colony units (bacteria) per milliliter and 0.03 endotoxin units per milliliter. The present AAMI standard, ANSI/AAMI RD52: 2004, Dialysate for hemodialysis, sets the maximum bacteria level for dialysate at 200 colony units and two endotoxin units. The standard will be revised, and two new amendments have been published (see sidebar).
“Ultrapure is not easy to acquire for a dialysis facility because it needs more frequent attention to detail for the final dialysate, and another filter in the dialysis machine,” says Levin.
Hemodiafiltration
Ultrapure dialysate is also used in a technique called hemodiafiltration, which is used in Europe but hasn’t been approved by the U.S. Food and Drug Administration (FDA) for use in the United States. Hemodiafiltration removes toxins by convection as well as diffusion. “You use very high water flow rates across the membrane so you remove a lot of the small proteins,” Ward says. “You just can’t remove that volume of water from people, so you have to put some water back. Hemodiafiltration makes the water that you are going to put back into the body right there at the machine.”
Ward says there is a fair amount of observational data that shows “these therapies are associated with less mortality and improvements in chronic morbidity. There are clinical trials going on to look at that more formally.”
Curtin says outside the U.S. the applications of ultrapure dialysate for standard dialysis and the use of hemodiafiltration are gaining popularity. The use of ultrapure dialysate is the stated aspiration — not regulation — of caregivers in Europe and Japan. Recent data shows more than 35 million hemodiafilters treatments have been successfully completed worldwide.“We know the native kidney works by convection, not dialysis. We look forward to when technology allows the application of ultrapure dialysate and hemodiafiltration in the U.S.,” Curtin says.
AAMI News: November 2009, Vol. 44, No. 10