Chronic renal replacement therapy in children: which index is best for adequacy?

BACKGROUND

The dialysis dose, Kt/V, and Solute Removal Index (SRI) have been proposed as tools to measure and compare adequacy of different renal replacement therapies in adults. The aim of our study was to elucidate whether the Kt/V and SRI could be appropriate parameters to compare different treatments and define adequacy targets in children.

METHODS

Twenty-two pediatric chronic dialysis patients (2 to 17 years) were prospectively studied. Six patients were on continuous ambulatory peritoneal dialysis (CAPD), 7 patients were on automatic nightly peritoneal dialysis (ANPD), and 9 were on hemodialysis (HD). Patients had no peritonitis and were not hospitalized during the previous two months and, as proved by growth and subjective well being, were in steady state condition at the initiation of the protocol. As a consequence, the treatment delivered was assumed to be adequate and the prospective analysis was carried out within one month. Urea levels in dialysate, plasma and urine were measured to determine urea kinetics and measure adequacy parameters.

RESULTS

Instantaneous urea clearance was much higher when hemodialysis was used (124.67 +/- 32.04 ml/min) compared to CAPD (2.79 +/- 0.29 ml/min) and ANPD (6.60 +/- 1.42 ml/min), as expected. The Urea dialytic clearance per week was greater in HD (67320 +/- 17299 ml) than in CAPD(28144 +/- 2895 ml) and ANPD (29910 +/- 4234 ml). Residual renal function contributed to the overall weekly clearance by 47% in CAPD, while it was only by 19% in HD and 26% in ANPD. The overall weekly clearance was therefore 79,842 ml/week in HD, 53,340 ml/week in CAPD and 41,012 ml/week in ANPD. Weekly dialytic Kt/V results were much higher in HD (3.75) than in CAPD (1.78) and ANPD (2.37). To these values, the renal Kt/V was added, reaching the values of overall (dialytic + renal) weekly Kt/V of 4.53 in HD, 3.41 in CAPD and 3.41 in ANPD. Although higher Kt/V values were observed in HD, when the SRI % was considered, HD appeared to be less efficient compared with the other two techniques. Since postdialytic rebound in HD patients averaged 22.5%, we may speculate that hemodialysis in children is less efficient than continuous or daily peritoneal dialysis because of a remarkable cardipulmonary recirculation and solute sequestration.

CONCLUSION

In the global evaluation, dialysis SRI% appears to be more reliable as an index of adequacy compared to Kt/V in children. At least an integration between the two indices is strongly recommended.