Dialysis Delivery Systems and Water Treatment
Systems and water: what must be true before you connect a patient
Picture two circuits that never mix: blood on one side of the membrane, dialysate on the other. Clearance of small solutes rises with blood flow, dialysate flow, and dialyzer surface area; high-flux membranes also remove larger middle molecules. Adequacy is measured by Kt/V (about 1.2 per treatment, single-pool) or urea reduction ratio (at least 65 percent).
Dialysate is proportioned from treated water and concentrate (commonly 1:34 or 1:44 acid concentrate with bicarbonate). Know the usual ranges: sodium 135–145 mEq/L, potassium 0–4 mEq/L, calcium 2.5–3.5 mEq/L, bicarbonate 32–39 mEq/L. Conductivity reflects total solute concentration and should be confirmed with a meter, not just the display.
Water treatment generally runs through a backflow preventer, sediment filter, water softener, carbon tanks, reverse osmosis, deionization, ultraviolet light, and ultrafilters. Carbon is the critical chlorine barrier: chlorine and chloramine cause hemolysis, so testing must occur before the first patient of the day and after any carbon change. AAMI limits include chlorine below 0.1 mg/L, dialysate bacteria below 200 CFU/mL, and endotoxin below 2 EU/mL.
Trap: a conductivity or temperature alarm is never a "watch it" alarm. Divert dialysate to bypass and do not dialyze until the value is back in range and verified.
Rule of thumb: if the water or dialysate is in question, assume it is not safe - hold treatment and escalate.