A simple and fast method to estimate peritoneal membrane transport characteristics using dialysate sodium concentration.

Abstract

The peritoneal equilibration test (PET) is widely used to classify a patient's peritoneal transport characteristics. However, PET is laborious and the prediction of fluid removal based on PET is generally poor. It is believed that osmosis by glucose occurs partially through transcellular water channels, resulting in sieving of sodium and decrease of dialysate sodium concentration when using hypertonic glucose dialysate.
In this study, we investigated the possibility of using dialysate sodium concentration to classify the patient's peritoneal transport characteristics.
A 6-hour dwell study with frequent dialysate and plasma sampling was performed in 46 patients using 2 L of 3.86% glucose dialysate with 131I-albumin as an intraperitoneal volume (IPV) marker. The peritoneal transport of sodium, creatinine, glucose, and fluid was evaluated.
The dialysate sodium concentration at 240 min (D(Na240)) significantly correlated with D/P creatinine (r = 0.76, p < 0.001) and D/D0 glucose (r = -0.83, p < 0.001) at 240 min of the dwell (better than dialysate sodium concentration at any other time of the dwell). DNa240 also significantly correlated with IPV at 240 min of the dwell (r = -0.61, p < 0.001)(better than D/P creatinine and D/D0 glucose). There were significant correlations between D(Na240) and the sodium-sieving coefficient (r = 0.71, p < 0.001) and the diffusive mass transfer coefficient for sodium (r = 0.50, p < 0.001). When using D(Na240) to divide the patients into four groups, as in the PET method, no significant difference was found between the two methods.
Using 3.86% glucose solution, D(Na240) can be used instead of D/P creatinine to classify patients into different transport groups. D(Na240) provides a better prediction of peritoneal fluid transport and reflects both the diffusive and convective transport properties of the membrane. As only one dialysate sample (and no blood sample) is needed, D(Na240) may offer important clinical advantages compared with PET.

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Proceedings of the ISPD '98 -The VIIIth Congress of the ISPD
August 23 26, 1998, Seoul, Korea
Peritoneal Dialysis International, Vol.19 (1999), Supplement 2
0896-8608/99 $300 + .00
Copyright &#169; 1999 International Society for Peritoneal Dialysis
Printed in Canada All rights reserved
A SIMPLE AND FAST METHOD TO ESTIMATE PERITONEAL MEMBRANE TRANSPORT
CHARACTERISTICS USING DIALYSATE SODIUM CONCENTRATION
Tao Wang, 1 Jacek Waniewski, 1,2 Olof Heimb&#252;rger,1 Jonas Bergstr&#946;m,1 Andrzej Werynski,2 and
Bengt Lindholm1
Divisions of Baxter Novum and Renal Medicine, 1 Department of Clinical Sciences, Karolinska Institute,
Huddinge University Hospital, Stockholm, Sweden; and Institute of Biocybernetics and Biomedical Engineering,2
Warsaw, Poland
.Background:The peritoneal equilibration test (PET) is widely used
to classify a patient's peritoneal transport characteristics. However,
PET is laborious and the prediction of fluid removal based on PET
is generally poor. It is believed that osmosis by glucose occurs
partially through transcellular water channels, resulting in sieving
of sodium and decrease of dialysate sodium concentration when
using hypertonic glucose dialysate.
.Objective: In this study, we investigated the possibility of using
dialysate sodium concentration to classify the patient's peritoneal
transport characteristics.
.Methods: A 6-hour dwell study with frequent dialysate and
plasma sampling was performed in 46 patients using 2 L of 3.86%
glucose dialysate with 1311-albumin as an intraperitoneal volume
(IPV) marker. The peritoneal transport of sodium, creatinine,
glucose, and fluid was evaluated.
.Results:The dialysate sodium concentration at 240 min (ONa240)
significantly correlated with O/P creatinine (r = 0.76, p < 0.001)
and O/O0 glucose (r = -0.83, p < 0.001) at 240 min of the dwell
(better than dialysate sodium concentration at any other time of the
dwell). ONa240 also significantly correlated with IPV at 240 min
of the dwell (r = -0.61, p < 0.001) (better than O/P creatinine and
O/O0 glucose). There were significant correlations between
ONa240 and the sodium-sieving coefficient (r= 0.71, p < 0.001)
and the diffusive mass transfer coefficient for sodium (r = 0.50, p
< 0.001 ). When using ONa240 to divide the patients into four
groups, as in the PET method, no significant difference was found
between the two methods.
.Conclusion: Using 3.86% glucose solution, ONa240 can be used
instead of O/P creatinine to classify patients into different
transport groups. ONa240 provides a better prediction of
peritoneal fluid transport and reflects both the diffusive and
convective transport properties of the membrane. As only one
dialysate sample (and no blood sample) is needed, ONa240 may
offer important clinical advantages compared with PET.

sodium; peritoneal transport.
KEY WORDS: Peritoneal equilibration test;
Correspondence to: B. Lindholm, Divisions of Baxter Novum
and Renal Medicine K-56, Huddinge University Hospital,
Karolinska Institute, S-14186 Huddinge, Sweden.
T
port characteristics (1-3). It has been convincingly shown
that PET guides the formulation of an appropriate dialysis
prescription for continuous ambulatory peritoneal dialysis
(CAPD) patients (2,4-7). Also, peritoneal transport
characteristics based on PET have recently been shown to
have a major impact on clinical outcome (8-11). Because
peritoneal transport characteristics change with time on
dialysis, repeated equilibration tests are required to optimize
the peritoneal dialysis prescription for chronic dialysis
patients (12,13).
However, the standard PET has several drawbacks: (1) It
is laborious, requires approximately 5 h to complete, and
consumes nursing time to administer the test (14). (2) Blood
sampling is needed, and the patient has to come to the
hospital to be tested. (3) The method for measurement of
creatinine is affected by dialysate glucose in most clinical
laboratories, and therefore various correction factors must
be set up to correct for the influence of glucose on the
creatinine measurement (1). (4) The prediction ofPET to
peritoneal fluid removal is generally poor (7). Recent studies
suggest that adequacy of peritoneal dialysis is a matter not
only of reaching targets for small-solute clearances, but also
-and maybe even more important -of removing enough fluid
and sodium (10,15). Therefore, it is important to find
parameters that can be used to predict both the peritoneal
membrane diffusive permeability and peritoneal fluid
removal.
It is well known that peritoneal sodium transport is
strongly dependent on peritoneal fluid removal (16,17). In
recent years, the decrease in dialysate sodium concentration
(owing to substantial sieving of sodium) during the initial
part of a peritoneal dialysis dwell using hypertonic 3.86%
glucose solution has been suggested as a measure of trans
cellular water transport (18-21). In addition, DIP sodium at
60 min of the dwell has been proposed to be used as a
marker
he peritoneal equilibration test (PET) is a widely used
method to classify patients' peritoneal trans
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for ultrafiltration failure stems from the abnormalities in
water channels (20). In a previous study, we found that DIP
sodium was significantly higher in high transporters than in
low transporters (17). We also suggested that it might be
possible to use DIP sodium for the classification of patients'
transport characteristics, especially when using DIP values
from the later part of the dwell with 3.86% glucose solution
(during the period between 120 min and 360 min; better
than values at 60 min or 90 min) (17).
Because ultrafiltration (owing to the sodium sieving
associated with convection) has a major impact on the
sodium concentration in dialysate when using 3.86%
glucose solution, and because the sodium concentration in
commercial fresh dialysis solution is generally 132 mmol/L
(close to that in blood), in the present study we further
analyzed the possibility of using dialysate sodium
concentration to classify patients' peritoneal transport
characteristics.
METHODS
In this analysis, we used data from 46 6-hour dwell
studies using 2 L of 3.86% glucose dialysis fluid (Dianeal,
Baxter-Travenol, Deerfield, Illinois, U.S.A.) with an
intraperitoneal volume marker (1311-human albumin,
RISA) and frequent blood and dialysate sampling. The
study protocol has been described in detail previously (22).
The dwell studies were performed as part of a long-term
follow-up of CAPD patients or as part of studies on
alternative osmotic agents, and some of the dwell studies
reported here have been partly analyzed before (17,22,23).
Blood and dialysate samples were analyzed for RISA
activity on an Intertechnique CG Gamma Counter
(lntertechnique, Plaisir, France). Glucose and creatinine
concentrations were measured with an IL 919 system
(lnstrumentation Laboratory, Milan, Italy), and sodium
concentration, with an IL
(lnstrumentation Laboratory, Milan, Italy).
Intraperitoneal dialysate volumes (V J were estimated
from the dilution of RISA with corrections applied for the
elimination rate of RISA from peritoneal cavity (KE,
mL/min) and sample volumes. KE was used for estimating
the peritoneal fluid absorption rate (24). The dialysate
concentration (CD) over plasma concentration (CE) ratio,
DIP, during the dwell study was calculated by dividing the
dialysate concentration of a solute with the plasma water
concentration of the investigated solute (25). The diffusive
mass transport coefficient, KED (mL/min), and the sieving
coefficient, S, were calculated using the modified Babb-
Randerson-Farrell model as described previously (26) using
the computer program PERTRAN (Baxter Novum,
Karolinska Institute, Stockholm, Sweden).
743 flame photometer
We classified the patients into four groups in a way
similar to that used in PET (1): high, high-average, low-
average, and low transport. However, in the present study,
we classified the patients using two different solutes: one
using DIP creatinine at 240 min of the dwell, and the other
using dialysate sodium concentration at 240 min of the
dwell (DNa24O).
Spearman non parametric measures of association and
the chi-square test were used in the statistical analysis. Data
are expressed as mean &#177; standard deviation, unless
otherwise noted. Statistical significance was accepted ifp <
0.05.
RESULTS
The distribution of the dialysate sodium concentration at
various dwell times and ofDIP sodium, DIP creatinine, and
D/Do glucose at 240 min of the dwell are shown in Table 1.
As shown in Table 2, dialysate sodium concentrations at
various dwell times significantly correlated with DIP
creatinine and DIDo glucose at 240 min of the dwell. The
correlation coefficients were higher with DNa24O as
compared with the dialysate sodium concentrations at other
dwell times. DNa24O also significantly correlated with
intraperitoneal volume at 240 min. The correlations between
dialysate sodium concentration and intraperitoneal volume
at 240 min of the dwell were better and more significant
than the correlation between D/Do glucose or DIP
creatinine (at 240 min) and the intraperitoneal volume at
240 min of the dwell. DNa24O also significantly correlated
with the sodium-sieving coefficient (S) and with the sodium
diffusive transport coefficient (KED). At the earlier dwell
times, dialysate sodium
correlations with S, but weaker correlations with KED.
Although DIP creatinine significantly
concentrations had better

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correlated with KED creatinine, there was no significant
correlation between DIP creatinine and S for creatinine. The
plasma concentration of sodium was 140 &#177; 3.6
mmol/L (range: 133 -149.5 mmol/L). Unlike the strong
correlation between dialysate creatinine concentration at
240 min and plasma creatinine concentration (r = 0.86), a
weak though significant correlation existed between
DNa24O and plasma sodium concentration (r = 0.41).
The classifications using DIP creatinine and DNa24O
are shown in Table 3. There were 6 high transporters, 17
high-average transporters, 14low-average transporters, and
9 low transporters with both methods. Although no
significant difference was found between the two
classification methods, some patients were partitioned into
different groups by the two methods (especially the high-
average and lowaverage groups according to the PET
method).
DISCUSSION
The present study shows that, as with DIP creatinine
used in the standard PET test, dialysate sodium
concentration at 240 min of a dwell using 3.86% glucose
dialysis fluid could be used to classify patients' peritoneal
transport characteristics.
The strong association found in the present study
between DNa24O and the intraperitoneal volume at 240 min
of the dwell is not unexpected. In a previous study, we
demonstrated that peritoneal sodium transport is strongly
related to peritoneal fluid removal (17). It has recently been
suggested that the transport of water devoid of solute across
aquaporins is apparently the main reason for the sieving of
sodium during peritoneal dialysis (21,27-29). Monquil et al
reported on a selective decrease in ultrafiltration with
normal glucose transport in a few CAPD patients (with loss
of ultrafiltration capacity) who had minor declines of
dialysate sodium concentra
tion when using hypertonic glucose solution; it was
suggested that these alterations were perhaps due to a
reduced number ofultrasmall pores (19). Therefore, the
magnitude of the initial decrease in DIP values for sodium,
using 3.86% glucose solution, has recently been suggested
as an indicator of transcellular water transport through the
ultrasmall pores (18,30). The significant correlation
between DNa24O and the sodium-sieving coefficients (and
creatinine as well) suggest that using DNa24O' we can also
estimate the convective transport properties (and perhaps
water-channel status) of the membrane, which could not be
done by standard PET. Owing to the close link to the
ultrafiltration process, it is not surprising that the correlation
between DNa24O and intraperitoneal volume was better and
more significant than the correlations between DIDo
glucose (and DIP creatinine) and the intraperitoneal
volume.
Even though diffusive transport of sodium with current
dialysis fluid composition is not the major transport
component in peritoneal sodium transport (17), the present
study shows that significant correlations exist between
DNa24O and DIP creatinine or DIDo glucose, and, more
importantly, that significant


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correlations exist between DNa240 and diffusive mass
transport coefficients for sodium and creatinine. These
results suggest that DNa240 reflects in part the diffusive
permeability of the peritoneal membrane and could thus be
used as a marker to classify a patient's peritoneal diffusive
transport characteristics.
Although DIP sodium at 240 min of the dwell had better
correlation with the fluid and other solute transport
parameters, the differences were quite small. Note that
dialysate sodium concentrations had weak correlations with
the plasma sodium concentration, whereas a strong
correlation existed between dialysate creatinine and plasma
creatinine concentrations. This result suggests that although
DIP for sodium is better than DNa240 in the correlation to
solute transport and fluid transport, we can still use
dialysate sodium concentration as a sufficiently accurate
marker, whose use has the advantage of eliminating the
need for blood sampling. Although the influence of plasma
sodium concentration on the dialysate sodium concentration
is less in the initial part of the dwell, our results indicate
that the dialysate sodium concentration in the early dwell
does not reflect the peritoneal membrane diffusive transport
characteristics as well (compared to DNa240).
We found no significant difference in the classification
of patients' peritoneal transport using DIP creatinine or
DNa240. However, we noted that some patients may be
allocated to different groups with these two methods; the
different allocation mainly happened to high-average and
low-average transporters. The clinical significance of the
allocations needs further study to elucidate. Because
inadequate fluid (and sodium) removal and inadequate
blood pressure control are common problems in CAPD
patients (31,32), the better prediction of peritoneal fluid
removal and peritoneal sodium transport using DNa240
warrants us to speculate that the new classification method
may have an important impact on measurements of
adequacy of peritoneal dialysis.
In summary, the present study suggests that dialysate
sodium concentration at 240 min of a dwell using 3.86%
glucose dialysis solution could be used to classify patients'
peritoneal transport characteristics. The benefits (compared
to standard PET) ofusing DNa240 to classify patients'
peritoneal transport characteristics may include: (1) The
better prediction, by DNa240' of peritoneal fluid transport
than by D/D0 glucose and DIP creatinine. (2) The
reflection, by DNa240' ofboth diffusive and convective
transport. (3) A perhaps better understanding, enabled by
DNa240 measurement, of the possible role of water
channels in peritoneal fluid transport.
Furthermore, DNa240 measurement does not suffer from
interference with dialysate glucose and needs only one
dialysate sample. On the other hand, owing
to the small number of patients in the present study and the
possible variation of dialysate sodium concentration in the fresh
dialysate, further studies are needed to evaluate the clinical
importance of this simplified classification method.
ACKNOWLEDGMENT
This study was supported by a grant from Baxter
Healthcare Corporation, McGaw Park, Illinois, U.S.A.
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