Prakash Keshaviah

On-line monitoring of the delivery of the hemodialysis prescription

The BioStat 1000 is a new device which employs dialysate-based urea kinetics to calculate the dose of dialysis (Kt/V) based on a two-pool model and protein catabolic rate (PCR). Previous methods relying on blood sampling techniques were subject to error and difficult to implement. This paper describes the features of the Biostat and the results of the first clinical validation study with an early prototype. The BioStat was found to compare favorably with the reference method of direct dialysate quantification (mDDQ) which had been modified to obtain a “two-pool” Kt/V. In 31 patients no significant difference was found between mean Kt/V from the mDDQ and the mean Kt/V from the BioStat (1.35±0.33 versus 1.38±0.36, respectively). The PCR was also not significantly different (53.4±18.5 g/day versus 51.8±16 g/day, respectively). The BioStat was demonstrated to be a convenient method producing reliable results.

Pitfalls of In Vivo Dialyzer Clearance Measurement

Dialyzer small-molecule clearance measurements are commonly made to help identify the cause of inadequate dialysis prescriptions, to determine the efficacy of reuse procedures, or to choose between different types of dialyzers. Clearance measurements can be blood-side- or dialysate-side-based. While blood-side clearance measurement is the classical technique, it suffers from several serious flaws that decrease its accuracy. Chief among these are the inability to accurately measure the blood flow rate and the difficulty in accounting for the presence of nonaqueous components in the blood. Using a dialysate-based clearance measurement technique overcomes these problems for most solutes, provided appropriate guidelines are followed. This article reviews the theory behind both blood- and dialysate-side techniques as well as discussing the practical application of that theory to clearance measurement.

Can Peritoneal Dialysis Be Equivalent to (or Better Than) Optimal Hemodialysis

than are currently delivered are necessary to achieve acceptable mortality rates. A study by Keshaviah et al. (10) also supports the notion that the difference in mortality observed between PD and HD may be related to dose of dialysis. This study used the “peak concentration hypothesis” in order to directly compare dose of dialysis among PD and HD treated patients (e.g., KtiV of 2.0 weekly for PD is “equivalent” to Kt/V of 1.3 per treatment for thrice weekly HD). This study, published in abstract form, found comparable survival rates for PD and HD treated patients treated with “equivalent” doses of dialysis. Assuming that it is appropriate to compare dose in this way, these results would suggest that by increasing dose of PD, yes, “Peritoneal Dialysis (may) Be Equivalent to Optimal Hemodialysis”. The practical concern, of course, is whether the dose of PD can be increased to be “equivalent” to the dose of HD. The dose of HD can be relatively easily increased with a change to a dialyzer with better clearance, an increase in blood flow or an increase in dialysis time. For patients using standard CAPD, increasing the number or volume of exchanges may be less acceptable. Furthermore, in patients with decreasing or absent residual renal function, large body mass, or low membrane permeability characteristics, it may be impossible to deliver adequate clearance using standard CAPD. However, the use of automated techniques hold the promise to meet these needs. There is hope that future technological advances in PD delivery techniques will allow the provision of optimal therapy at a cost that is not prohibitive, either from an economic perspective or in terms of the patient’s lifestyle.

Comparing the Adequacy of Continuous Ambulatory Peritoneal Dialysis (CAPD) and Hemodialysis

The KT/V urea index (K, clearance; T, treatment time; V, volume of urea distribution) has become an established index of hemodialysis (HD) adequacy, values of KT/V less than 0.8 being associated with overt uremic toxicity. For the typical continuous ambulatory peritoneal dialysis (CAPD) regimen of 4 X 2 L exchanges/day, the equivalent KT/V approximately 0.6. Paradoxically, overt uremic toxicity is not commonly observed in CAPD patients with this typical therapy prescription. Application of the urea kinetic model demonstrates that HD and CAPD have the same time-averaged urea concentration at the same KT/V. However, as HD is an intermittent therapy, the urea concentration in HD exceeds the time-averaged concentration for about half the hours in the week. If uremic toxicity is related to the peak rather than the time-averaged urea concentration, a higher KT/V would be required in HD to achieve a peak concentration at or below the steady-state CAPD concentration. This peak concentration hypothesis predicts, based on the results of the National Cooperative Dialysis Study, that underdialysis with CAPD would occur at KT/V less than 0.4 for a protein intake of 1.1 gm/kg/day.