J. E. Tattersall

Urea kinetics and when to commence dialysis.

Blood urea and serum creatinine levels are important factors in deciding when to start dialysis. Recently, in the assessment of dialysis adequacy, emphasis has shifted from reliance on these parameters to use of kinetic methods. We therefore applied urea kinetic modelling (UKM) to 63 consecutive chronic renal failure (CRF) patients at the time dialysis commenced and compared the results to those obtained after 6 months of dialysis treatment. Mean normalised urea clearance (daily KT/V) at the commencement of dialysis (KTi/V) was 0.15 +/- 0.05, a level indicative of underdialysis in regularly dialysed patients. After 6 months, mean daily KT/V was 0.35 +/- 0.12 in patients subsequently established on CAPD, and 0.49 +/- 0.08 in those subsequently haemodialysed (both p < 0.001 compared to mean KTi/V). Serum creatinine levels on commencing dialysis were similar to those after 6 months treatment by either mode. Mean age (p < 0.01) and co-morbidity index (p < 0.05) were higher, and mean KTi/V lower (p < 0.05) in the 6 patients who died during a mean follow-up period of 10 +/- 4.5 months than in survivors. Hospitalisation rates during follow-up (excluding admissions for access surgery and training) correlated with age (r = 0.332, p < 0.01), co-morbidity index (r = 0.351, p < 0.01) and KTi/V (r = -0.302, p < 0.05). Blood urea and serum creatinine levels on commencing dialysis were the same in those who died and in survivors and did not correlate with hospitalisation rates. Diabetics started dialysis with a similar mean KTi/V to non-diabetics but with a lower mean serum creatinine (p < 0.005).(ABSTRACT TRUNCATED AT 250 WORDS)

Is Continuous Ambulatory Peritoneal Dialysis an Adequate long-Term Therapy for End-Stage Renal Disease?

To date, most work in the area of dialysis adequacy has focused on hemodialysis. While it is now generally accepted that K t N relates to outcome, the optimal value for K t N is still under debate. Most of this debate followed Gotch and Sargent’s analysis of the National Cooperative Dialysis (NCD) Study (1) suggesting that a threshold Kt/V value divided adequate from inadequate treatment. This threshold Kt/V was described as being in the region between 0.8 and 1. While it was considered necessary to ensure that a patient receives adequate Kt/V, there was thought to be little extra benefit to be gained by increasing Kt/V further. The concept of the threshold of adequacy is theoretically plausible for HD. At a Kt/V of 1, 65% of the total urea in the patient has already been removed. There are rapidly diminishing returns from increasing Kt/V, and an infinite increase in Kt/V is required to remove the remaining 35%. However, the concept of this “threshold” has been challenged. Re-analyses of the NCD Study (2) suggest that there may be progressive improvement in outcome as Kt/V increases above 1. A number of dialysis units around the world routinely deliver a K t N of up to 1.6 by thrice weekly hemodialysis (3). These units appear to have significantly better outcome, even when the effect of co-morbidity has been corrected. Retrospective analyses of qualityadjusted survival (4), suggest that there may be a continuous improvement in outcome as Kt/V increases beyond 1.

Hemodialysis Time and Kt/V: Less May Be Better

Current guidelines focus on conventional dialysis defined as 3–5 hours, three times per week, and suggest that longer or more frequent dialysis be considered. This paper presents the case for considering that shorter or less frequent dialysis should also be considered. More frequent and/or longer dialysis facilitates control of fluid overload, blood pressure, and phosphate levels. These benefits will require time to translate into probable hard outcome improvement. Patients are unlikely to participate in productive or pleasurable activities while undergoing dialysis in center or traveling to treatment. So any increase in dialysis time or frequency, during awake hours, will result in an immediate and quantifiable reduction in quality of life. Conventional measures of dialysis adequacy consider only urea clearance. This poorly reflects middle molecule clearance, renal function, and management of fluid and phosphate overload, all of which have a greater impact on outcome than urea clearance. Fluid, phosphate, and uremic toxin overload may be better and less invasively controlled by continuous means such as dietary modification, binders, and preserving renal function. Bioimpedance, blood volume monitoring, and lung ultrasound provide means for improved control of fluid homeostasis. The probability of renal function recovery or preservation is increased by avoiding dehydration. An ideal strategy would be to preserve renal function and employ as little dialysis as possible (if it cannot be avoided altogether). Fluid overload, blood pressure, uremic toxin, and phosphate levels would be monitored and controlled using any means available, preferably by less invasive means than dialysis. Kt/V is useful in controlling the prescribed dose of dialysis, but the achievement of a universal target should not be an end in itself.

Metabolic Alkalosis in CAPD Patients

Over the past year, our PD unit has found metabolic alkalosis to have become a more common problem than metabolic acidosis. I assume its related to the new low calcium dialysate now in use widely. Is this a common experience? Is there a danger from this (soft tissue calcifications, kidney stones, hypoxemia)?