Time dependence of solute removal during a single exchange

The viability of long-term peritoneal dialysis (PD), especially once residual renal function is lost, has been challenged since recently recommended weekly targets of Kt/V of 2.1 and creatine clearance (Ccr) of 70 L/1.73 m2 may be difficult to reach. This study demonstrates the theoretical possibility of achieving these targets in PD patients even without residual renal function. A 6-hour dwell study was performed in 68 PD patients with frequent dialysate and plasma sampling using 2 L of 1.36% (n = 13), 2.27% (n = 9), or 3.86% glucose dialysate (n = 46) with 131I albumin as an intraperitoneal volume marker. Alterations in fluid balance, Kt/V, and Ccr with dwell time (t) as well as the impact of peritoneal fluid absorption on peritoneal fluid and solute removal were evaluated. Kt/V and Ccr did not follow an exponential function with t and, in fact, decreased after 4-5 hours, especially in high transporters. All patients could achieve either weekly Kt/V (especially low transporters) or Ccr target (especially high transporters) if they are treated with automated PD. Calculations showed that eliminating fluid absorption could increase mean fluid removal by 43%-179%, increase mean Kt/V by 17%-32%, and mean Ccr by 16%-30% (depending on the solution used and the patient's peritoneal transport pattern) during a 6-hour dialysis exchange. We reached the following conclusions: (1) Kt/V(urea) and Ccr are markedly time-dependent during a single exchange due to the substantial impact of peritoneal absorption and may, in fact, decline after 4 hours, especially in high transporters. (2) Extrapolating Kt/V and Ccr values from short dwell times [i.e., peritoneal equilibration test (PET) results] to long dwell times will overestimate the peritoneal clearances. (3) Enough fluid removal must be considered as an important target of adequate dialysis along with small solute clearances. (4) If fluid absorption could be eliminated, most continuous ambulatory peritoneal dialysis (CAPD) patients could achieve the recommended Kt/V and/or Ccr targets even without residual renal function.