Article published in PDServe Connection Vol 7, No 2, 2003
DOUBLE FEATURE
Higher Clearances - Higher Ultrafiltration
Jose A. Diaz-Buxo, MD, FACP
Fresenius Medical-North America
The PD Plus concept was created to maximize solute clearance and ultrafiltration in the most cost efficient manner1-2. PD Plus incorporates several automated nocturnal exchanges of relatively high volume (2.5 to 3.0 L) and two diurnal exchanges. The first diurnal exchange is the “last automated exchange” and the second is either a manual exchange, or more often, a “pause exchange” provided by the cycler. This schedule totally eliminates long diurnal dwells, known to provide lower net ultrafiltration and clearance of small solutes, than several shorter exchanges. The predicted performance of PD Plus based on theoretical constructs have been corroborated with clinical data including a prospective, randomized study comparing the effectiveness of PD Plus with that of CAPD with increased volume3-5. In addition, PD Plus can provide higher ultrafiltration with conventional solutions.
A recent prospective randomized study shows higher small solute clearance with PD Plus5
The aim of the study was to compare the effectiveness of PD Plus and CAPD with increased volume (Inc Vol) in improving small solute clearance among anuric CAPD patients over a period of 6 months. The target adequate dose was a weekly Kt/V > 1.9 and/or Ccr 60 L/1.73m2. The study randomized anuric patients who had undergone a minimum of 3 months of CAPD and had been identified as under dialyzed (weekly Kt/V < 1.7 and/or Ccr < 50L/1.73m2).
Fourteen patients were identified and randomized to receive either PD Plus or CAPD Inc Vol. Kt/V and Ccr were determined at baseline (T0), 1 month (T1mo) and 6 months (T6mo). Adjustments based on adequacy measurements to PD Plus and CAPD Inc Vol prescription were made at T1mo and T6mo. Patients unable or unwilling to adjust the prescription and those considered under dialyzed, were removed from the study and offered APD.
All patients were studied at baseline and again after 1 month. The CAPD Inc Vol group consisted of 7 patients receiving 4 daily exchanges with 2.5L and 1 patient with 4 daily exchanges of 3L. Patients assigned to PD Plus received 2 diurnal exchanges of 2.5L and 3 nocturnal exchanges of 3L (total 14L). At 1 month, 6 patients in the CAPD Inc Vol group failed (5 for inadequate dialysis and 1 for peritonitis). The other 2 patients were considered to be adequately dialyzed and completed the 6 months study. The PD Plus group suffered 2 losses at 1 month (1 inadequately dialyzed and 1 peritonitis). Of the remainder, 3 completed the study and 1 dropped out due to peritonitis. Two patients in the Inc Vol group and 3 in the PD Plus group remained on their initial therapy at 6 months.
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The between group comparison at 1 month showed a significantly greater change in the PD Plus group parameters compared to the CAPD Inc Vol group, with a mean change in Kt/V of 0.9 versus 0.26 (p=0.0017) [Figure 1]. Similarly, a significantly greater change in Ccr in the PD Plus group compared to the CAPD Inc Vol group was observed, with a mean change of 18.8 versus 2.4 L/wk/1.73m2 (p=0.0031) [Figure 2]. Despite the limited number of patients, these results demonstrate that anuric CAPD patients not achieving adequacy targets can be successfully treated with PD Plus.
PD Plus can improve net ultrafiltration.
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A long dwell time is often associated with poor net ultrafiltration due to glucose absorption and loss of the osmotic gradient, particularly among patients with fast peritoneal transport. This problem can be addressed by: 1. Increasing the glucose concentration of the solution, 2. Utilizing polyglucose, or 3. Avoiding exchanges with long dwells.
Figure 3 is a computer simulation for the net ultrafiltration obtained with 2.5% dextrose solution and with polyglucose 7.5% over a 14-hour period. Based on this information, we can predict better ultrafiltration using two 7-hour dwells with 2.5% dextrose than with the single 14-hour polyglucose dwell for practically all patients, regardless of transport status. The use of 4.25% glucose can further increase net ultrafiltration among the extreme high transporters, but is not necessary in most instances. This simple maneuver can significantly reduce the undesirable effects of hypertonic solutions and the risks associated with polyglucose while providing adequate net ultrafiltration.
In summary, theoretical models and extensive clinical experience including a recent randomized study have shown that PD Plus can effectively increase solute clearance over other PD modalities. The evidence also supports the use of PD Plus to increase ultrafiltration without the added expense and risk associated with polyglucose when CAPD and conventional APD fail to provide adequate fluid removal.
References:
- Diaz-Buxo JA. Enhancement of peritoneal dialysis: The PD Plus concept. Am J Kidney Dis 27:92-98, 1996
- Diaz-Buxo JA. Continuous cycling peritoneal dialysis, PD plus and high-flow automated peritoneal dialysis: A spectrum of therapies. Perit Dial Int 20:S93-S97, 2000
- Diaz-Buxo, J. A., Gotch, F. A., Folden, T. et al. Peritoneal dialysis adequacy: A model to assess feasibility with various modalities. Kidney Int 55:2493-2501, 1999
- Diaz-Buxo JA, Youngblood BP, Torres AM. Delivered dialysis dose with PD Plus therapy: A multicenter study. Am J Nephrol 18:520-524, 1998
5- Iles-Smith H, Curwell J, Gokal R. PD plus concept leads to significant increases in solute clearances in anuric CAPD patients. Perit Dial Int 22:719-721, 2002