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Fast Transport Status in Peritoneal Dialysis Patients
area, known as the mass transfer area coefficient (MTAC). This measures Facing these doubts, a recent review
45
suggested that either the use of
the theoretical maximal diffusive transport rate at time zero, at the maximum dip of D/P sodium or the exact amount of free water
beginning of the dwell before diffusion and ultrafiltration has begun. transported through the water channels, calculated by the La Milia
Simplified models for MTAC calculation, such as the Garred and Krediet method, are accurate in following our patients, while the use of the mini-
formulae, have been developed to be accessible in clinical practice.
30,31
PET as a tool for small-solute characterisation should still be explored.
Values of MTAC for low-molecular-weight solutes can be more easily
calculated. The introduction of the peritoneal equilibration test (PET),
2
Although D/P creatinine at one hour might overestimate peritoneal
followed by the standard permeability analysis (SPA)
32
and recently the transport rate in continuously applied peritoneal dialysis (CAPD), this
personal dialysis capacity (PDC) test,
33
have offered the clinician simplified value may be useful to guide automated peritoneal dialysis (APD)
methods of monitoring membrane function. prescription when short cycles with individualised dwell times must
be prescribed.
The PET is the most widely used standardised form of peritoneal transport
assessment, and is also useful for longitudinal evaluation of patients.
34,35
To correlate functional and morphological peritoneal membrane changes
D/P creatinine at the end of four hours of standardised dwell closely in our patients, repeated biopsies are not feasible. The Peritoneal Biopsy
correlates with MTAC creatinine. The small differences related to the use Registry
46
carried out important investigations of vascular and fibrotic
of a more complex method are less significant than the differences changes, but only cross-sectional results of PD patient membrane could
induced by clinical collection and laboratory measurement errors. In be obtained without dynamic functional–structural correlation.
addition, inter- and intra-individual changes also occur when more
rigorous calculation methods are used. One limitation of PET assessment To evaluate the relationship between membrane function and status,
is that it does not allow the diagnosis of ultrafiltration failure (UFF) due to effluent cancer antigen-125 (CA125), interleukin-6 (IL-6) and VEGF can
lymphatic absorption. Although increased lymphatic absorption is one of be monitored longitudinally in vivo.
17,25,47–50
Tissue TGF-β concentration is,
the causes of ultrafiltration capacity failure, lymphatic absorption does however, more informative than effluent levels.
not seem to change with the duration of peritoneal dialysis.
36
Another
method for more accurate peritoneal transport assessment is the SPA,
37
CA125 seems to be most useful. Exposition to more biocompatible
which includes the evaluation of an intraperitoneal marker – dextran – solutions was associated with mesothelial repair and increase of CA125.
51
using the disappearance rate as an index of peritoneal membrane
absorption. This, however, remains a research domain test, with
sophisticated calculations.
Peritoneal transport evaluation is a key
The International Society for Peritoneal Dialysis (ISPD) recommended
issue in the management of peritoneal
protocol with PET 3.86%
38
should be elected to evaluate small-solute
transport rate and water transport. It provides similar information about dialysis patients, in whom it is
small-solute transport compared with the standard 2.27% PET, but is
important to ensure adequate small-
more sensitive for the definition and investigation of ultrafiltration
capacity failure. Because of the importance of fluid removal in the
solute transport and fluid removal.
management of PD patients, added evaluation steps were recently
proposed. Sodium sieving at 60min can be calculated as an estimate of
free water transport. It avoids complex formulae, and a method
applicable to the PET can also be used to estimate free water transport Although some authors suggested limitations of CA125 as an index of
with correction for sodium diffusion: this might be useful since a fast peritoneal mesothelial cell mass,
52
they demonstrated a reduction of
transport rate with rapid sodium diffusion may mask the initial decrease CA125 secretion and expression with chronic exposition to glucose
of intraperitoneal sodium due to ultrafiltration.
39
solutions. A consistent decrease of CA125 appearance rate after a certain
time on dialysis has been shown to parallel functional estimates such as
Measurement of D/P sodium at 60min dwell also allows the detection of increased D/P creatinine.
25
Its prognostic significance is also supported by
cases of UFF associated with impaired free water transport. Functionally, the fact that lower levels are found in patients with peritoneal sclerosis.
UFF is characterised in most cases by an enhanced peritoneal MTAC for It has been concluded that CA125 was very low in patients who
glucose combined with a largely unchanged peritoneal glucose-osmotic developed peritoneal sclerosis, and a lack of response to a peritoneal rest
conductance.
40
However, this may be decreased in cases of more severe also predicted peritoneal encapsulating sclerosis after PD discontinuation.
53
acquired UFF in long-term PD patients.
41
Aquaporin-1 dysfunction and/or
interstitial fibrosis might be the causes of such late changes. The Time-course of Peritoneal Membrane Characteristics
The changeover time of D/P creatinine on PD has been a matter of debate.
Recently, La Milia and co-workers
42
proposed the fast-fast PET with only Some authors reported a sustained increase of D/P creatinine after the
60min dwell determinations, which allows quantification of actual free first year of PD,
22,54
while others found no clinically significant changes
water removal while also categorising small-solute transport based on after up to three or four years under treatment,
55,56
particularly in those
D/P creatinine at 60min. However, an overestimation of MTAC at 60min patients without serious peritonitis. Also, not all long-term PD patients
may occur due to the contribution of convective transport and the fact develop a fast transport status. These variable and inconsistent results
that permeability surface area (PS) during the first hour of dwell is underline the extreme inter-patient variability of peritoneal transport and
significantly higher than during subsequent hours.
43,44
its determinants.
EUROPEAN RENAL DISEASE 2007 45
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