Perit Dial Int
29(Supplement_2):
233-235
2009
© 2009 International Society for Peritoneal Dialysis
Part 9: PD and Residual Renal Function |
PERITONEAL DIALYSIS IN ANURIC PATIENTS: OLD PROBLEMS AND NEW PERSPECTIVES
Anabela S. Rodrigues
Nephrology Department, Hospital Geral Santo Antonio, Porto,
Portugal
Correspondence to: A.S. Rodrigues, Nephrology Department, Hospital Geral Santo
Antonio, Largo Abel Salazar 4100 Porto, Portugal.
ar.cbs{at}mail.telepac.pt
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ABSTRACT
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Anuric patients are often excluded from peritoneal dialysis (PD) because
of the fear that PD is inadequate to treat this higher-risk group of patients.
However, advances in PD knowledge and technique allow better and adjusted
treatments. There is now clinical evidence that anuric patients can be
successfully treated with PD, while new solutions promise to mitigate some
limitations of automated PD, such as sodium and fluid removal and preservation
of membrane function.
KEY WORDS: Anuric patient.
Despite the skepticism, there is evidence that anuric patients can be
successfully maintained on peritoneal dialysis (PD), specifically, on
automated PD (APD) (1). These
patients challenge clinicians but can profit from the modality as part of an
integrated plan of renal replacement therapy.
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WHAT DOES PD OFFER?
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Peritoneal dialysis allows better preservation of residual renal function.
In addition, while accomplishing solute and fluid removal, and ionic and
acid–base equilibrium, PD is also a vehicle of intraperitoneal caloric
and, optionally, amino acid absorption. This support can mitigate the risk of
malnutrition in uremic PD patients. These benefits are routinely
quantifiable.
However, PD also offers well known, less easily quantifiable, and often
underestimated advantages associated with auto-dialysis: flexibility,
autonomy, and quality of life.
Also relevant and mandatory is leveling the risk and morbidity associated
with a central catheter before excluding an anuric patient with vascular
access problems from PD. This approach means an integrated plan of renal
replacement therapy with the intention of longer patient survival.
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WHAT ARE THE PROBLEMS FACED IN DEALING WITH ANURIC PATIENTS?
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Anuria adversely impacts survival and anuric patients are often older and
have a longer duration of previous renal replacement therapy. Additional
comorbidity, such as atherosclerotic disease and elevated C-reactive protein,
predict higher mortality in anuric patients
(2).
The concern is PD (in)adequacy; specifically, the possibility of
insufficient small solute, medium molecule, and fluid removal, leading to
systemic inflammation, technical failure, and mortality.
Previous focus on Kt/V as a measure of small solute clearance proved to be
misleading. Considered almost a "magic" number, that focus on Kt/V
often lead to neglect of the limitations of the V calculation in PD patients,
the particularities of a continuous versus an intermittent dialysis procedure,
and the relevance of middle molecule removal. In the ADEMEX study, increments
of weekly Kt/V over 1.7 did not significantly improve 2-year patient survival,
which averaged 70% (3). Anuric
patients from EAPOS (1)
achieved similar or better survival despite additional patient comorbidity.
Interestingly, in the HEMO study, a similar 2-year patient survival rate was
achieved irrespective of higher Kt/V increments
(4), while, in another study,
the length of the session and the ultrafiltration (UF) rate were associated
with survival (5).
Improvements in PD technique and knowledge now allow a better and adjusted
prescription, taking into account that intermittent PD should be exceptional
and that the wet day and the PD Plus concept can improve adequacy beyond Kt/V
in anuric patients. However, increasing the dialysis cycles and total
nocturnal volume only minimally increases some higher molecule removal, such
as B2-microglobulin
(6) and phosphorus
(7).
It has been pointed that, as the body size of the subject increases, such
as has been occurring in USA and Canadian populations, the actual recommended
minimal PD target dose would be insufficient
(8); however, no evidence
exists that this is true, although it is recognized that larger body sized
patients with slow membrane transport will be difficult or impossible to
manage under APD.
The existing evidence favors UF as the more relevant target once a minimum
small solute removal rate is guaranteed
(9). Ultrafiltration can be
optimized in APD and in hybrid schedules with daytime exchanges. The link
between poor UF and increased mortality has not yet been explained and is
possibly more complex than we think. Even the largest multicenter study with
anuric APD patients was unable to discover the link between higher mortality
and UF lower than 750 mL/day
(10); blood pressure, baseline
comorbidity, and nutritional status were not associated with UF. Presumably,
UF is related to the relevance of euvolemia and sodium removal in the
preservation of cardiovascular status. Higher UF also allows convective
removal of more uremic toxins, which is not usually measured but is certainly
important.
To add complexity to this issue, volume expansion in PD patients might also
be related to malnutrition and inflammation, irrespective of peritoneal
removal of sodium and fluid
(11), indicating the relevance
of fluid corporal distribution and extracellular body water more than total
body water.
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ADVANCES IN PD FOR ANURIC PATIENTS
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Automated and individualized continuous cyclic PD, with profiling of
drainage and dwell times and optimized with an extra daytime exchange, proved
to overcome some limitations of PD in terms of solute, fluid, and sodium
removal
(12,13).
As a critical example, fast transporters had been associated with worse
patient survival but prescription of APD abolished that negative impact
(14). Automated PD with
icodextrin in the long dwell is able to improve UF and sodium removal,
resulting in better patient outcomes. There is also hope that alternative low
glucose degradation product (GDP) solutions and glucose-sparing regimens will
be beneficial in minimizing the membrane lesions associated with cumulative
exposure to PD. Automated PD has been associated with a faster decline in
membrane UF but icodextrin use spares the peritoneal membrane from such
deterioration (15). Combining
crystalloid and colloid osmotic agents enhanced peritoneal fluid and solute
transport in a recent investigation
(16). Neutral pH and low-GDP
solution showed higher UF and better membrane preservation in anuric patients
(17).
Although it might be difficult to achieve euvolemia in some anuric patients
without the cost (literally and functionally) of increasing exposure to solute
glucose, the results from real-life clinical PD studies are reassuring:
adjusted and adequately prescribed PD can overcome the handicap of anuria,
while allowing the patient to experience the benefits of auto-dialysis.
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CONCLUSIONS
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There are certainly arguments against PD for anuric patients: (1)
fear of inadequate removal of small solutes, phosphorus, and fluid; (2) lower
removal of sodium in APD than in continuous ambulatory PD; (3) fear of
membrane changes under higher cumulative exposure to glucose; (4) awareness
that APD is not the answer for all problems with PD; and (5) short PD
technique survival.
But for arguments can be highlighted as well: (1) the patient has
the right to choose the therapy that better fits his lifestyle; (2) individual
quality of life matters; (3) adequacy in anuric PD patients is beyond Kt/V,
and the benefits of a continuous dialytic procedure should not be forgotten;
(4) PD is often a planned therapy to avoid vascular capital exhaustion and a
central vascular catheter, which is associated with morbidity and mortality;
and (5) from an integrated care perspective, patient survival is the target
and a planned transfer to hemodialysis should not be considered PD technique
failure but, instead, adequate treatment.
Finally, I would like to underline that PD is on the move: there have been
great advances in PD that are applicable to riskier patients, including anuric
patients: (1) clinicians' awareness of the importance of restricting dietary
sodium intake; (2) user-friendly cycles; (3) optimized cycler performance
(tidal, drainage breakpoint, individualized profiles); (4) APD with
icodextrin; (5) low-GDP and neutral solutions, promising better membrane
preservation; and (6) glucose-sparing regimens with the possibility of using
amino acid solutions and alternative osmotic/colloid-osmotic solutions.
An integrated care approach to renal replacement therapy requires
open-minded informed clinicians and strict respect for the informed anuric
patient's options.
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ABSTRACT
WHAT DOES PD OFFER?
