Rationale for Guideline Kt/V urea Targets for Peritoneal Dialysis

Peritoneal Dialysis Adequacy Targets

Contribution from the KDOQI 2006 Peritoneal Dialysis Update workgroup

Source: KDOQI PD Adequacy guidelines for 2006 (National Kidney Foundation. KDOQI Clinical Practice Guidelines and Clinical Practice Recommendations for 2006 Updates: Hemodialysis Adequacy, Peritoneal Dialysis Adequacy and Vascular Access. Am J Kidney Dis 48:S1-S322, 2006 (suppl 1).

Guidelines: 2.1. For patients with RKF (considered to be significant when urine volume is > 100 mL/d): 2.1.1. The minimal “delivered” dose of total small-solute clearance should be a total (peritoneal and kidney) Kt/Vurea of at least 1.7 per week.

2.1.2. Total solute clearance (residual kidney and peritoneal, in terms of Kt/Vurea) should be measured within the first month after initiating dialysis therapy and at least once every 4 months thereafter.

2.1.3. If the patient has greater than 100 mL/d of residual kidney volume and residual kidney clearance is being considered as part of the patient’s total weekly solute clearance goal, a 24-hour urine collection for urine volume and solute clearance determinations should be obtained at a minimum of every 2 months.

2.2. For patients without RKF (considered insignificant when urine volume is <100 mL/d):

2.2.1. The minimal “delivered” dose of total small-solute clearance should be a peritoneal Kt/Vurea of at least 1.7 per week measured within the first month after starting dialysis therapy and at least once every 4 months thereafter.

Clinical Practice Recommendations: 2.7. The determination of peritoneal CCr is of little added value for predicting risk for death; therefore, for simplicity, adequacy targets are based on urea kinetics only. Peritoneal creatinine excretion rate may be used to monitor estimates of muscle mass over time.

Rationale: Previous studies suggested that improved survival on PD therapy was associated with higher total small-molecule clearances.[1] Extrapolations from the Canada-United States (CANUSA) Study led to the prior guidelines of a total weekly Kt/Vurea of 2.0 and creatinine clearance (CCr) of 60 L/wk/1.73 m2 for CAPD patients. Higher targets were chosen for continuous cycling PD (CCPD) and patients on APD with no daytime dwell (dry day), and, in the absence of data, based on theoretical considerations. Reanalysis of the CANUSA Study showed that RKF, rather than peritoneal clearance, was associated with improved survival.[2] Greater urine volume was a significant and important predictor of better survival, as well. Results of this reanalysis subsequently were supported by the Adequacy of PD in Mexico (ADEMEX) Study randomized trial of CAPD patients comparing 2 levels of PD prescription.[3] The 2 groups of patients had identical survival, indicating no benefit on survival for greater small-molecule peritoneal clearance and confirming the benefit of RKF on survival. Further support was supplied by another randomized trial of CAPD patients from Hong Kong [4] comparing 3 levels of total Kt/ Vurea in patients with small degrees of RKF, with the lowest group randomized to a total Kt/Vurea of 1.5 to 1.7, with no difference in survival. Thus, 2 randomized trials examining different levels of small-molecule clearance have been done in CAPD patients, showing no benefit of the higher small-molecule clearances on patient survival, nutritional status or hospitalization. Emerging data suggest that the focus to improve survival in PD patients should be on preserving RKF, controlling volume overload (and thus blood pressure), treating metabolic acidosis, and perhaps use of protein supplements. Therefore, the minimal target is changed from a target Kt/V of 2.0 to a minimum Kt/Vurea of 1.7 per week; however, careful attention must be paid to adherence to the prescription. The Work Group wishes to emphasize that this minimal target should not be interpreted as an average value for a program, but that each patient should have a total Kt/Vurea at 1.7 or higher.

Total CCr in patients with RKF is much a reflection of RKF. In the absence of RKF, CCr seems to add little to the use of urea clearance. A study examined 912 PD patients by using the USRDS data set, as well as by questionnaires completed by centers, and found that kidney urea clearance but not dialysate urea clearance) was predictive of 12-month mortality. Neither kidney nor dialysate CCr were predictive.[5] However, peritoneal and kidney creatinine excretion is a good measure of muscle mass and may be used to measure this sequentially if it seems appropriate.[6,7]

References:

1. Churchill DN, Thorpe KE, Nolph KD, Keshaviah PR,Oreopoulos DG, Page D: Increased peritoneal membrane transport is associated with decreased patient and technique survival for continuous peritoneal dialysis patients. The Canada-USA (CANUSA) Peritoneal Dialysis Study Group. JAm Soc Nephrol 9:1285-1292, 1998
2. Bargman JM, Thorpe KE, Churchill DN: Relative contribution of residual renal function and peritoneal clearance to adequacy of dialysis: A reanalysis of the CANUSA Study. JAm Soc Nephrol 12:2158-2162, 2001
3. Paniagua R, Amato D, Vonesh E, et al: Effects of increased peritoneal clearances on mortality rates in peritoneal dialysis: ADEMEX, a prospective, randomized, controlled trial. JAm Soc Nephrol 13:1307-1320, 2002
4. Lo WK, Ho YW, Li CS, et al: Effect of Kt/V on survival and clinical outcome in CAPD patients in a randomized prospective study. Kidney Int 64:649-656, 2003
5. Rocco MV, Frankenfield DL, Prowant B, Frederick P, Flanigan MJ: Risk factors for early mortality in U.S. peritoneal dialysis patients: Impact of residual renal function. Perit Dial Int 22:371-379, 2002
6. Keshaviah PR, Nolph KD, Moore HL, et al: Lean body mass estimation by creatinine kinetics. J Am Soc Nephrol 4:1475-1485, 1994
7. Lo WK, Prowant BF, Moore HL, et al: Comparison of different measurements of lean body mass in normal individuals and in chronic peritoneal dialysis patients. Am J Kidney Dis 23:74-85, 1994

Prepared on behalf of the National Kidney Foundation KDOQI Peritoneal Dialysis guideline workgroup by Michael Rocco (KDOQI Vice-Chair).