Peritoneal dialysis indices: weekly CrCl and weekly Kt/Vurea are linked.

Peritoneal dialysis uses a biological "membrane," the peritoneum, to control solute movement between the patient and the dialysate. Equilibrium thermodynamic models predict that the movement of small molecules across the peritoneum will be restricted in proportion to their permeability indices, the available membrane surface area, and the solute concentration gradient between plasma water and dialysate. During peritoneal dialysis, the membrane surface area, dialysate flow, and solute concentration gradients are quite similar for small solutes such as creatinine and urea. Hence, the clearances of creatinine and urea should be proportional to one another in a ratio equal to that of their membrane permeabilities; if that ratio is known, a peritoneal creatinine clearance could be derived for any known peritoneal urea clearance, and vice versa. Analysis of patient data supports this hypothesis and suggests that if disparate normalization procedures are avoided, peritoneal dialysis patients without residual renal function will have difficulty consistently attaining the weekly normalized creatinine clearance of > or =60 L/1.73 m2 recommended by the National Kidney Foundation-Dialysis Outcomes Quality Indicators (NKF-DOQI) without achieving a weekly Kt/Vurea of > or =2.5.