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Clinical |
Department of Renal Medicine and Transplantation, Barts and The London Hospital NHS Trust, London, United Kingdom
Correspondence to: S. Fan, Department of Renal Medicine and Transplantation, Barts and The London Hospital NHS Trust, Whitechapel, London E1 1BB, United Kingdom.s.fan{at}qmul.ac.uk
Background: Accurate measurement of ultrafiltration (UF)
is important to improve the morbidity and mortality of peritoneal dialysis
(PD) patients. The introduction of "flush-before-fill" PD systems
has led to improved peritonitis rates. Partly to compensate for dialysate lost
during flush-before-fill, extra dialysate was added to each PD bag. A 2-L PD
bag now contains a mean volume of 2.225 L. That overfill volume might be
erroneously measured as UF. We previously studied how this confounding factor
might be affecting the diagnosis of UF failure and found that almost all units
were overestimating daily UF by 900 mL. We now repeat the study to determine
if the accuracy of UF estimation has improved.
Methods: We conducted a telephone survey of PD units in
the UK to determine how drain bags are weighed and how UF is calculated during
formal assessment of adequacy and the peritoneal equilibrium test (PET). We
also retrospectively analyzed our last 100, 24-hour dialysate collections and
PET results to determine the potential clinical impact of overestimating
UF.
Results: There has been an improvement since our last
study, but 70% of PD units in the UK are still overestimating daily UF in
patients on continuous ambulatory PD (CAPD). Half the surveyed units also
inaccurately calculate UF during the PET, and 85% were reporting results of
PET and 24-hour dialysate collections through the software provided by Baxter
Healthcare. By including the overfill volume, 73% of patients with daily UF
<750 mL would not be diagnosed as having inadequate daily UF (assuming that
all were fluid overloaded and anuric). Similarly, 73% with potential UF
failure during the PET (4-hour UF <100 mL) would be missed if overfill
volume was misrepresented as UF.
Conclusion: For patients undergoing CAPD, there requires
standardization on when drain bags are weighed. Awareness that calculation of
UF must exclude overfill volumes has improved but remains poor. The PD
Adequest software (Baxter Healthcare, Compton, UK) is widely adopted in the UK
and perhaps it could draw attention of users to the potential of UF
overestimation in CAPD patients.
KEY WORDS: Ultrafiltration; ultrafiltration failure; flush-before-fill.
Received 20 May 2005; accepted 7 September 2005.
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