What We Have Learned about Uremia from Peritoneal Dialysis

Weekly clearances of small solutes such as urea are relatively low on continuous ambulatory peritoneal dialysis (CAPD) compared to those of thrice weekly hemodialysis (HD); large solute clearances are more comparable. Some believe that good clinical outcomes with chronic peritoneal dialysis support the importance of larger molecular weight toxins. However, CAPD patients of large size or approaching an anephric state occasionally develop uremic symptoms that can be reversed with an increased exchange volume or an increased number of exchanges. Increasing exchange volume or the number of exchanges increases small solute clearances by an amount near the increase in drain volume, but clearances of larger molecular weight substances are minimally affected. Thus, peritoneal dialysis experiences initially focused attention on large molecules and now appear to confirm the importance of small solutes in uremic toxicity but at lower clearance requirements than needed in HD.