An evidence based medicine approach to determining the adequacy of peritoneal dialysis

The most frequently used estimates of adequacy of peritoneal dialysis are Kt/V for urea and creatinine clearance (CCr) expressed as the sum of residual renal and peritoneal clearance. The assumption that renal and peritoneal clearances are equivalent is unproven. Theoretical constructs suggest that a weekly Kt/V of 2.0-2.25 represents adequate dialysis while clinical experience supports a weekly CCr of 40-50L per week. Prospective cohort studies using univariate analysis report better patient survival with weekly Kt/V >1.89. Composite indices show an association of good outcome with weekly Kt/V values of 2.3 and poor outcomes with values of 1.5-1.6. A multicentre prospective cohort study in North America used a multivariate analysis to demonstrate an independent statistically significant association between adequacy of dialysis and patient survival. A 0.1 unit decrease in weekly Kt/V was associated with a 5% increase in the relative risk of death; a 5L/1.73m² per week decrease in CCr was associated with a 7% increase in the relative risk of death. Over the range of 1.5-2.3 in weekly Kt/V and 40-95 L/1.73m2 per week in CCr, there was no plateau effect on patient survival. Optimum dialysis, occurring when the incremental clinical gain from increased dialysis dose is not considered worth the increased patient effort or cost, has not been defined. Strategies to achieve adequate dialysis include an earlier initiation of dialysis, use of optimal dialysate volumes and prescription according to membrane transport characteristics.