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The weekly Ccr and KT/V targets may not be achieved simultaneously in the individual patient for two reasons. Firstly, creatinine is secreted into the glomerular filtrate by the kidney, while urea is reabsorbed. Clearly, the residual renal creatinine clearance, even when it is estimated by the average of renal urea and creatinine clearance, is higher than the residual renal urea clearance. The relative contribution of renal creatinine clearance to total (renal + peritoneal) clearance tends to be higher than that of renal urea clearance to total KT/V.

Secondly, because the transport of creatinine across the peritoneal membrane is slower than for urea, it is harder to achieve high peritoneal creatinine clearance than it is to achieve peritoneal KT/V. This is especially so in automated peritoneal dialysis (APD), when dwell times are shorter. There is no definitive proof regarding selection of the measure of clearance. Until there are data that support the use of either Ccr or KT/V exclusively as a clinical measure of PD adequacy, both should be used to assess therapy efficacy. If a discrepancy exists between these two measures, that is, one achieves KT/V but not Ccr, the patient should not be considered a failure. Instead, the targets should be considered in the total context of the patient's management through careful review and ongoing monitoring of clinical symptoms.

CLINICAL ASSESSMENT AND QUALITY-OF-LIFE CONSIDERATIONS

It is important to evaluate the patient frequently, taking into account clinical assessment, biochemical parameters, and life-style, because achieving adequate clearance does not guarantee decreased mortality. Clinical assessment should include evaluating the patient's uremic symptoms, nutritional state, and comorbid disease. If a patient does not meet total solute clearance targets, but clinical assessment shows the patient is thriving, consideration of life-style is important in the decision of whether or not to modify the prescription or transfer the patient to hemodialysis. Frequent ongoing assessment is required in this situation. Conversely, if a patient appears uremic despite meeting clearance targets, alterations in prescription should be considered.

RECOMMENDED CLINICAL PRACTICES TO ACHIEVE CLEARANCE GUIDELINES

The recommended clinical practice is to provide the most dialysis that can be delivered to the individual patient, within the constraints of social and clinical circumstances, quality of life, life-style, and cost.

The recommended numeric clearance guidelines for continuous PD (treatment given 24 hours/day) are shown in Table 4. These guidelines are for total clearance, peritoneal + renal.

Only when special clinical or social circumstances dictate should the first two levels of prescription ("use caution," "borderline") be acceptable. Exceptions to these guidelines should be considered when individual patient needs and quality-of-life considerations exceed the gains achieved from increasing creatinine clearance. For example, a 94-year-old patient with other systemic disease and Ccr = 50 mL/wk who is asymptomatic may choose not to be involved with a more aggressive therapy.

In recommending these guidelines, it must also be noted that an increase in peritoneal clearance will be required to compensate for the decline in residual function. In situations where KT/V guidelines but not Ccr targets are met, attempts to increase Ccr should be made, but failure to do so should not be considered an indication for transfer to hemodialysis.

In discussions of dialysis adequacy, it is important to point out that renal and peritoneal clearances have been considered equivalent. One milliliter/minute of corrected Ccr, or 1 U of KT/V due to residual renal function, is assumed to equal that from peritoneal clearance. These guidelines assume that an increase in peritoneal clearance will compensate for the decline in residual function, although this has not been formally proven. Most opinion leaders would agree that renal clearance is more valuable than peritoneal clearance, but this issue needs to be resolved by further research.

Peritoneal Dialysis International, Vol. 16, pp. 448­456 Printed in Canada. All rights reserved. Copyright © 1996 International Society for Peritoneal Dialysis 0896-8608/96 $3.00 + .00