Water is an essential component of renal replacement therapy by dialysis. Water serves as a solvent to electrolytic concentrates for the preparation of dialysis fluids. The proportioning haemodialysis machine ensures a continuous and precise mixing of electrolytes and water to achieve the prescribed electrolytes composition. Dialysis fluid is the exchange media with patient blood that ensures solutes transport from the ´internal milieu´ (patient) to the ´external milieu´(waste) through a thin semipermeable dialyzer membrane. In that sense, dialysis fluid may be considered as an extension of the extracellular compartment of a dialysis patient exposing the patient to biohazards.
Acknowledging the fact that 120 to 150 litres of dialysis fluid circulate against blood three times a week, indicates that the blood is exposed to 30 to 40 times more water than the general population. In addition, anuric dialysis patients are exposed for long periods of time and have by the way considerable cumulative time exposure that needs to be considered in the risk assessment.
Based on these risk considerations, one must recognize that dialysis water purity must comply with higher standards than deionized water. Contemporary dialysis treatments have contributed significantly to an increase in risks associated to dialysis water. Highly permeable membranes, used to remove middle and large uremic retention solutes, favour transmembrane passage of dialysis fluid contaminants. Ultrafiltration modules and capillary filters induce a backtransport phenomenon of dialysis fluid contaminants. Highly efficient dialysis modalities, imposing high solute mass transfer, also enhance the transport of dialysis fluid contaminants to the blood stream of the patients. Online convective dialysis modalities (e.g. haemodiafiltration) further enhance convective transport (20-30 litres/session), while replacing ultrafiltrate by direct IV infusion of online prepared substitution fluid. This increases the hazards related to dialysis fluid contamination.
"The textbook represents the ´state of the art´ in terms of dialysis water and dialysis fluid purity that should become the desk reference book for all hemodialysis centres and staff involved in the field of renal replacement therapy," Prof. Bernard Canaud comments.