Sodium removal and sodium concentration during peritoneal dialysis: effects of three methods of sodium measurement

Vincenzo La Milia1, Salvatore Di Filippo1, Monica Crepaldi1, Simeone Andrulli1, Lucia Del Vecchio1, Pietro Scaravilli1, Giovambattista Virga2 and Francesco Locatelli1

1 Department of Nephrology and Dialysis, A. Manzoni Hospital, Lecco and 2 Provincial Hospital, Camposampiero, Italy

Correspondence and offprint requests to: Vincenzo La Milia, MD, Department of Nephrology and Dialysis, A. Manzoni Hospital, Via Dell’Eremo 9/11, 23900 Lecco, Italy. Email: v.lamilia{at}ospedale.lecco.it



   Abstract
 Top
 Abstract
 Introduction
 Subjects and methods
 Results
 Discussion
 References
 
Background. Sodium removal (NaR) may have a major impact on the survival of peritoneal dialysis patients. The dialysate/plasma sodium concentration ratio (D/PNa) is an indirect index of transcellular water transport by aquaporin channels, and thus of ultrafiltration. Sodium concentration can be assessed by means of flame photometry (F), and direct (D-ISE) or indirect ion-selective electrodes (I-ISE), but these methods have different properties. I-ISE is being used increasingly in clinical laboratories. The aim of this study was to evaluate NaR and D/PNa using the three different measurement methods.

Methods. We performed peritoneal equilibration tests (PETs) in 44 peritoneal dialysis patients and calculated the NaR. We also calculated D/PNa during the test; plasma and dialysate sodium concentrations were measured by F, D-ISE and I-ISE.

Results. NaR was lower (P<0.001) with D-ISE (69±29 mmol) than with F (81±29 mmol) or I-ISE (79±28 mmol). D/PNa was also lower at baseline (0.92±0.02 vs 0.95±0.02 and 0.95±0.02; P<0.001), after 60 min (0.87±0.03 vs 0.90±0.03 and 0.90±0.03; P<0.001) and at the end of PET (0.88±0.04 vs 0.92±0.04 and 0.92±0.04; P<0.001) when measured by D-ISE in comparison with F and I-ISE, respectively.

Conclusions. NaR and D/PNa were lower when measured by the D-ISE method compared with the F and I-ISE methods. NaR and D/PNa were similar when measured by F or I-ISE. I-ISE can be used reliably in the evaluation of NaR and D/PNa in everyday clinical practice of peritoneal dialysis.

Keywords: flame photometry; ion-selective electrode; peritoneal dialysis; sodium concentration; sodium removal; sodium gradient



   Introduction
 Top
 Abstract
 Introduction
 Subjects and methods
 Results
 Discussion
 References
 
The peritoneal dialysis (PD) population has a high prevalence of hypertension, as illustrated by data obtained from surveys of US [1] and Italian PD populations [2]. The significant negative correlation between blood pressure and sodium removal (NaR) underscores the clinical relevance of NaR in the PD population [3,4].

The dialysate/plasma sodium concentration ratio (D/PNa) is a useful means of studying the hydraulic permeability of the peritoneal membrane, and an indirect index of transcellular water transport by aquaporin channels [57]. As a result of free water transport into the peritoneal cavity, D/PNa decreases markedly during hypertonic dwell (‘sodium sieving’) [57], and nearly 40–50% of ultrafiltration during hypertonic dwell occurs through the aquaporin channels [8]. Dialysate sodium concentration at the end of the peritoneal equilibration test (PET) is also of importance because it can be used to assess transport characteristics across the peritoneal membrane [9].

The sodium concentration of biological fluids is typically measured using flame photometry (F), or ion-selective electrode (ISE) methods. The ISE methods include both direct (D-ISE) and indirect (I-ISE) methodologies [1013]. In normal plasma from healthy subjects, the sodium concentrations are the same on average when measured by F, D-ISE or I-ISE. However, in the plasma of non-healthy subjects, such as uraemic patients, the results obtained by F, D-ISE and I-ISE may diverge [13]. In PD, sodium concentration has been assessed using all three methods [6,7,1416] but, unlike in the setting of haemodialysis [17,18], the method-related differences in measurement have not yet been completely clarified. Furthermore, the peritoneal dialysate has properties distinct from thos of the plasma, and sodium concentrations measured with the three methods can be different in this fluid.

In plasma, F measures total sodium concentration (i.e. the ionic concentration plus the amount complexed with anions) after the aspiration of a known plasma volume. However, nearly 6% of plasma consists of colloidal proteins and lipids, whose physical structure occupies space that is not penetrated by water, and so the sodium concentration measured by F is in 0.94 l of plasma water. For example, a plasma sodium concentration of 140 mmol/l measured by F (NaFp) corresponds to a total sodium concentration in plasma water of 149 mmol/l (NaFpw), a value that is obtained by correcting the observed concentration for the volume of plasma water (i.e. 0.94). Indeed, any time we add protein or lipid to a saline solution, the sodium concentration measured by F decreases in proportion to the amount of protein or lipid added [12]. A certain amount of NaFpw (nearly 7 mmol/l) is complexed with anions (in particular, proteins and bicarbonate) [17]. The ionic sodium concentration in plasma water (Na+pw) can be directly measured by D-ISE, which detects the chemical activity of sodium ions in a solution, but not the volume in which they are dissolved. The sodium activity is then converted into sodium concentration using the activity coefficient of the solution [18,19]. It follows that an Na+pw of 142 mmol/l detected by D-ISE corresponds to an NaFp of 140 mmol/l and an NaFpw of 149 mmol/l.

Given that peritoneal dialysate is almost free of proteins and lipids, it can be assumed that F measures its total sodium concentration (NaFD), whereas D-ISE only measures its sodium activity, i.e. its ionized sodium concentration (Na+D) [16,17]. However, the pH and the concentration of other ions (carbonate, bicarbonate, etc.) of the peritoneal dialysate can change the activity coefficient of the solution [18,19].

I-ISE, a method of sodium measurement that is used increasingly in clinical laboratories, is an auto-analyser that aspirates a known plasma volume, dilutes it with a buffered solution (to bring the activity coefficient near to 1.0) and presents the diluted sample to a sodium electrode for activity measurement. These indirect readings are calibrated against reference values determined by F [18].

The aim of this study was to evaluate the differences in the three methods of measurement on NaR and D/PNa in PD patients.



   Subjects and methods
 Top
 Abstract
 Introduction
 Subjects and methods
 Results
 Discussion
 References
 
After having given their informed consent, all of the 44 PD patients (18 males and 26 females with a mean age 60.7±14.0 years) attending the Manzoni Hospital Lecco between January 2001 and January 2003 underwent a PET. They had all been on regular PD for at least 3 months; their medical condition was stable and they had been free of peritonitis for at least 3 months. The median time on PD was 61.5 months (interquartile range: 52.0–72.5 months).

We used a modified PET, which differed from the classical method [20] insofar as the PD solution contained a 3.86% instead of 2.27% concentration of anhydrous glucose. Lactate (35 mEq/l) was used as the buffer, with a nominal pH of 5.0–6.5 and a nominal sodium concentration of 132–134 mmol/l.

The overnight dwell before PET was performed using a PD solution containing a glucose concentration of 1.36%, with lactate as the buffer; the overnight dialysate was instilled in the evening before the test (11.00 p.m.) and drained at 7 a.m.

Blood samples were taken at the start of the test (P0), after 60 min (P60) and at the end of the test (P240). The overnight dialysate (DNight) samples were taken from the bag; the fresh PD fluid (D0) samples were taken from the bag at the end of the infusion. After the complete infusion of the PD solution, and after having flushed back 30 ml of dialysate, 20 ml dialysate samples were taken after 1, 60, 120, 180 and 240 min (D1, D60, D120, D180 and D240).

The patients were instructed to sit up or move about in bed before the collection of each dialysate sample; otherwise, they remained recumbent throughout the 4-h investigation.

After 240 min, the dialysate was gravity collected for at least 20 min. The volumes of the infused fresh peritoneal dialysis solution and the drained dialysate were measured by weighing the bag and then subtracting the weight of the empty bag; no corrections were made for the differences in the specific weight of the solutions.

Sodium measurements
Plasma and dialysate sodium concentrations were analysed using an IL 943 flame photometer (Instrumentation Laboratory, Milan, Italy), a Stat Profile M direct ion-selective electrode (Nova Biomedical Corp., Waltham, MA) and a Hitachi 717 indirect ion-selective electrode (Hitachi Ltd, Tokyo, Japan). Each method was calibrated and performed according to the manufacturer's specifications via internal (ISO 9001) and external (Regional Interlaboratory) quality controls. The coefficient of variation was 1% for IL 943, 0.5% for Stat Profile M and 1% for Hitachi 717. The accuracy, i.e. the difference of agreement with the target values of an internal quality control, was 0.15% for IL 943, 0.06% for Stat Profile M and 0.48% for Hitachi 717.

The pH of the peritoneal dialysis fluid and dialysate was measured by means of the Stat Profile M.

NaR was calculated as follows:

where V is the volume of the peritoneal dialysis solution expressed in litres, and DNa the dialysate sodium concentration expressed in mmol/l.

D/PNa was calculated at the start (D1/PNa0), after 60 min (D60/PNa60) and at the end of the test (D240/PNa240).

Statistical analysis
The data were expressed as mean values±1 SD, together with their 95% confidence intervals (95% CIs). Analysis of variance (ANOVA) was used to compare the three approaches with the estimation of NaR according to the method of sodium measurement, with the NaR calculated according to the F method being considered the reference. If the total F-test was statistically significant, two specific contrasts were tested: NaR measured by F vs NaR measured by D-ISE, and NaR measured by F vs NaR measured by I-ISE. Repeated measures ANOVA was used to evaluate the differences between the three measurements of sodium in the plasma and dialysate samples, their ratio, the effect of the time course of PET on the same variables, and the effect of their interactions. The F method of sodium measurement was considered the reference for both the plasma and the dialysate samples. Bonferroni's adjustment was used for multiple comparisons at the different times of PET, which were expressed as mean differences and 95% CIs. Correlations between the different methods of sodium measurement were estimated using Pearson correlation coefficients. Bland–Altman plots were used to assess agreement between the different methods of sodium measurement visually. This statistical method compares two measurement techniques by plotting the absolute differences against the averages of the two techniques.

A P-value of ≤0.05 was considered significant. All of the statistical analyses were made using SPSS for Windows statistical software (release 11.0).



   Results
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 Abstract
 Introduction
 Subjects and methods
 Results
 Discussion
 References
 
The mean ultrafiltration during the PETs was 720±245 ml (95% CI 646–795 ml).

Figure 1 shows the mean plasma sodium concentrations measured by F, D-ISE and I-ISE. The mean plasma sodium concentrations measured by D-ISE were significantly higher than those measured by F and I-ISE (P<0.001), which were similar.



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Fig. 1. Mean plasma sodium concentrations during PET, as measured by a flame photometer (F), a direct ion-selective electrode (D-ISE) and an indirect ion-selective electrode (I-ISE). *P<0.001 vs F and I-ISE.

 
The dialysate sodium concentrations during PET are shown in Figure 2. The sodium concentrations measured by D-ISE were lower than those measured by F and I-ISE at all of the time points, and similar results were obtained in the overnight dialysate (DNight) (P<0.001). The dialysate sodium concentrations measured by F and I-ISE were not statistically different (P = 0.405).



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Fig. 2. Dialysate sodium concentrations during PET as measured by F, D-ISE and I-ISE. *P<0.001 vs F and I-ISE.

 
The NaR measured by D-ISE [69±28 mmol (95% CI 60–77 mmol)] was lower (P<0.001) than that measured by F [81±29 mmol (95% CI 72–90 mmol)] or I-ISE [79±28 mmol (95% CI 71–88 mmol)]. The NaR measured by I-ISE was not different from that measured by F (P = 0.09). The mean difference in NaR measured by F and D-ISE was 12±5 mmol (95% CI 11–14 mmol); the mean difference in NaR measured by F and I-ISE was 2±6 mmol (95% CI 0.2–4 mmol). The correlation coefficient between NaR measured by F and D-ISE was 0.987, and between NaR measured by F and I-ISE it was 0.982. The Bland–Altman plots and the limits of agreement for NaR measured by F, D-ISE and I-ISE are shown in Figure 3. The visual inspection of the plot (top) underlines the bias when the NaR was measured by D-ISE: NaR is clearly underestimated when measured with D-ISE (on the y-axis; the solid line representing the absolute difference between F and D-ISE is far from zero).



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Fig. 3. Bland–Altman plots of the limits of agreement between the sodium removal (NaR) during PET measured by F and D-ISE (top) and by F and an indirect ion-selective electrode (I-ISE) (bottom). The x-axis shows the mean of the results of the two methods, whereas the y-axis represents the absolute difference between the two methods. The solid line indicates the mean difference; broken lines indicate –2 SD and +2 SD.

 
Table 1 summarizes D/PNa at the start (D1/PNa0), after 60 min (D60/PNa60) and at the end of the test (D240/PNa240).


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Table 1. Dialysate/plasma sodium concentration ratio (D/PNa) during PET, as measured by F, D-ISE and I-ISE

 
The D/PNa measured by D-ISE was significantly lower than that measured by F and I-ISE at all of the time points (P<0.001); there was no difference between the F and I-ISE measurements (P = 0.99).

The correlation coefficient between D1/PNa0 measured by F and D-ISE was 0.767 and the mean difference was 0.023±0.015 (95% CI 0.018–0.028). The correlation coefficient between D1/PNa0 measured by F and I-ISE was 0.743 and the mean difference was –0.002±0.015 (95% CI –0.007 to 0.003). The correlation coefficient between D60/PNa60 measured by F and D-ISE was 0.905 and the mean difference was 0.033±0.013 (95% CI 0.029–0.037). The correlation coefficient between D60/PNa60 measured by F and I-ISE was 0.861 and the mean difference was 0.001±0.016 (95% CI –0.004 to 0.006). The correlation coefficient between D240/PNa240 measured by F and D-ISE was 0.954 and the mean difference was 0.045±0.011 (95% CI 0.041–0.048). The correlation coefficient between D240/PNa240 measured by F and I-ISE was 0.883 and the mean difference was –0.003±0.019 (95% CI –0.009 to 0.002). Figure 4 shows the Bland–Altman plots for D/PNa measured by F, D-ISE and I-ISE. Similarly to Figure 3, the visual inspection of the plots underlines the bias when the D/PNa was measured by D-ISE: D/PNa is clearly underestimated when measured with D-ISE (on the y-axis; the solid line representing the absolute difference between F and D-ISE is far from zero).



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Fig. 4. Bland–Altman plots of the limits of agreement between dialysate/plasma sodium ratio (D/PNa) measured by F and D-ISE and by F and I-ISE at the start of PET (A and B), after 60 min of PET (C and D) and at the end of PET (E and F). The x-axis shows the mean of the results of the two methods, whereas the y-axis represents the absolute difference between the two methods. The solid line indicates the mean difference; broken lines indicate –2 SD and +2 SD.

 


   Discussion
 Top
 Abstract
 Introduction
 Subjects and methods
 Results
 Discussion
 References
 
NaR may have an important impact on the survival of patients on PD. In a study of 125 incident PD patients, it was more predictive of survival than Kt/V [3]. These data indicate that more attention needs to be paid to the overall management of PD patients, particularly in relation to volume control, and total fluid and sodium removal.

Given the importance of the degree of sodium removal on patient outcome, and the relevance of the sodium gradient across the peritoneal membrane, sodium concentrations must be assessed rigorously. In contrast to normal healthy subjects, the plasma of patients with end-stage renal disease who receive PD contains a number of abnormal substances (known and unknown uraemic toxins). As already demonstrated in the setting of haemodialysis [1719], this can give different values of sodium concentrations compared with normal healthy subjects when different methods of sodium measurement are used. Besides, the dialysate displays properties different from those of the plasma (lower pH, higher glucose concentration, very low protein concentration) and these properties change throughout the dwell. These characteristics of the dialysate are to be kept in mind when evaluating the data of PET according to the method of sodium measurement used.

In PD, the sodium concentrations have been measured traditionally using F, D-ISE and I-ISE; the differences in the values obtained have not yet been clearly defined [3,4,6,7,1416]. We previously demonstrated that NaR and D/PNa were different when measured by F and an old D-ISE method [21], but most laboratories now use I-ISE to analyse sodium concentrations because it is easy and simple to use. We therefore compared I-ISE with F and D-ISE, in order to verify the impact of the differences in sodium concentration measurement on NaR and D/PNa.

The results of this study confirm that, in PD patients, NaR and D/PNa vary significantly depending on the method used to measure sodium concentrations. The plasma sodium concentrations measured by D-ISE were higher than those measured by F or I-ISE, which is in accord with the results of previous studies [17,18]. As D-ISE directly measures sodium activity (i.e. the amount of ionized sodium), the obtained concentration is the amount of diffusible sodium. F measures the total amount of sodium (i.e. ionized sodium plus the sodium complexed with anions), but does not take into account the fact that nearly 6% of plasma is occupied by proteins. I-ISE measures sodium activity but, because it aspirates a known plasma volume and dilutes it with a buffered solution (to bring the activity coefficient near to 1.0), the sodium concentration values obtained were similar to those obtained by means of F (we found similar plasma sodium concentrations as measured by F and I-ISE at all of the time points).

Unlike plasma, dialysate is almost free of proteins, and so F measures the total sodium concentration, whereas D-ISE only measures its sodium activity, i.e. its ionized sodium concentration. This explains why D-ISE showed lower dialysate sodium concentrations than F at all of the PET time points, whereas those measured by F and I-ISE were similar. I-ISE only measures ionized sodium but, because it dilutes the aspirate with a buffered solution, to bring the activity coefficient near to 1.0, the sodium concentrations in the peritoneal dialysate were similar to those obtained by means of F.

The difference in the sodium concentrations in peritoneal dialysate measured by F and D-ISE is minimal in a fresh dialysis solution that contains lactate as a buffer and has an acidic pH, but progressively increases during the dwell in the peritoneal cavity and is maximal at the end of the night dwell, which lasts nearly 8 h. At the end of this dwell, the difference is similar to that observed in the dialysate used for haemodialysis [17,18] (Figure 2). This is explained by the fact that the pH of the dialysate progressively increases during the dwell (Figure 5), thus favouring the binding of sodium with other anions (mainly bicarbonate). The variation of the pH of peritoneal dialysate during the PET did not influence the measurement of the sodium concentration by means of I-ISE.



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Fig. 5. Dialysate pH during PET.

 
We found that the NaR measured by D-ISE was lower than that measured by F and I-ISE because the peritoneal dialysate sodium concentrations at the end of PET were lower when measured by D-ISE; this did not occur at the beginning of PET, because the high acidic pH of a fresh peritoneal dialysis solution increases the ionized sodium concentration. D-ISE underestimates NaR. This could be of particular clinical relevance when NaR is calculated on large dialysate volumes, as in the case of automated peritoneal dialysis (APD). For this reason, F and I-ISE are to be preferred when estimating NaR.

We found that the D/PNa measured by F and I-ISE was not statistically different, whereas that measured by D-ISE was lower. This can be explained by the differences in the sodium concentration measurements provided by the three methods. The sodium concentrations measured by D-ISE are higher in plasma and lower in dialysate (after a few minutes of PET) than those measured by F and I-ISE, and the difference in dialysate sodium concentrations progressively increases with longer times of dialysate permanence in the peritoneal cavity.

In comparison with F, I-ISE is being used increasingly in clinical laboratories because it allows the immediate measurement of various electrolytes (sodium, potassium, calcium, etc.), does not require a gas supply and because of its ease of handling and simple daily maintenance. Most of the studies of PD have assessed NaR and D/PNa using I-ISE [7,14,15], but no previous study compared the results either with I-ISE or with F. We did not find any differences in NaR and D/PNa when sodium concentrations were measured by F or I-ISE. This finding has important practical implications: for clinical purposes, I-ISE can replace F (which is unwieldy and available in only a few laboratories) in evaluating sodium concentrations, D/PNa and NaR.

In conclusion, the method of sodium measurement significantly influences the obtained values of NaR and D/PNa, with D-ISE differing significantly from F and I-ISE. A clear understanding of the differences in sodium concentrations in uraemic plasma of PD patients and in the dialysate according to the method of measurement is very important when comparing results of different studies. Furthermore, these differences are not only to be kept in mind when building complex mathematical models of the hydraulic permeability of the peritoneal membrane in the experimental setting, but they should also be considered in everyday clinical practice, in order to assess and understand NaR and D/PNa correctly. These two indexes give us important information on transport characteristics through the peritoneal membrane. This has become of particular interest since it has been supposed that a high transport status allows less removal of sodium and water and this can be an independent risk factor for mortality, and causes decreased technique survival [22].

Conflict of interest statement. None declared.



   References
 Top
 Abstract
 Introduction
 Subjects and methods
 Results
 Discussion
 References
 

  1. Frankenfield DL, Prowant BF, Flanigan MJ et al. Trends in clinical indicators of care for adult peritoneal dialysis patients in the United States from 1995 to 1997. ESRD Core Indicators Work-group. Kidney Int 55: 1999; 1998–2010[CrossRef][ISI][Medline]
  2. Cocchi R, Degli Esposti E, Fabbri A et al. Prevalence of hypertension in patients on peritoneal dialysis: results of an Italian multicentre study. Nephrol Dial Transplant 14: 1999; 1536–1540[Abstract]
  3. Ates K, Nergizoglu G, Keven K et al. Effect of fluid and sodium removal on mortality in peritoneal dialysis patients. Kidney Int 2001; 60: 767–776[CrossRef][ISI][Medline]
  4. Ortega O, Gallar P, Carreno A et al. Peritoneal sodium mass removal in continuous ambulatory peritoneal dialysis and automated peritoneal dialysis: influence on blood pressure control. Am J Nephrol 2001; 21: 189–193[CrossRef][ISI][Medline]
  5. Rippe B, Stelin G, Haraldsson B. Computer simulation of peritoneal fluid transport in CAPD. Kidney Int 1991; 40: 315–325[ISI][Medline]
  6. Wang T, Waniewski J, Heimburger O, Werynsky A, Lindholm BV. A quantitative analysis of sodium transport and removal during peritoneal dialysis. Kidney Int 1997; 52: 1609–1616[ISI][Medline]
  7. Ho-Dac-Pannekeet MM, Atasever B, Struijk DG, Krediet RT. Analysis of ultrafiltration failure in peritoneal dialysis by means of standard peritoneal permeability analysis. Perit Dial Int 1997; 17: 144–150[ISI][Medline]
  8. Mujais S, Nolph K, Gokal R et al. Evaluation and management of ultrafiltration problems in peritoneal dialysis. International Society for Peritoneal Dialysis. Ad Hoc Committee on Ultrafiltration Management in Peritoneal Dialysis. Perit Dial Int 2000; 20: S5–S21
  9. Wang T, Waniewski J, Heimburger O, Bergstrom J, Werynski A, Lindholm B. A simple and fast method to estimate peritoneal membrane transport characteristics using dialysate sodium concentration. Perit Dial Int 1999; 19 [Suppl]: S212–S216
  10. Stiller S, Mann H. Ionometry versus flame photometry in dialysis therapy. ESAO Proc 1985; 12: 63–69
  11. Maas AHJ, Siggaard-Andersen O, Weisbergn HF, Zijistra W. Ion-selective electrodes for sodium and potassium: a new problem of what is measured and what should be reported. Clin Chem 1985; 31: 482–485[Abstract/Free Full Text]
  12. Worth HGJ. A comparison of the measurement of sodium and potassium by flame photometry and ion-selective electrode. Ann Clin Biochem 1985; 22: 343–350[ISI][Medline]
  13. Burnett RW, Covington AK, Fogh-Andersen N et al. Recommendations for measurement of and conventions for reporting sodium and potassium by ion-selective electrodes in undiluted serum, plasma or whole blood. The IFCC Working Group on Selective Electrodes. Clin Chem Lab Med 2000; 38: 1065–1071[ISI][Medline]
  14. Leypoldt JK, Charney DI, Cheung AK, Naprestek CL, Akin BH, Shockley TR. Ultrafiltration and solute kinetics using low sodium peritoneal dialysate. Kidney Int 1995; 48: 1959–1966[ISI][Medline]
  15. Imholz ALT, Koomen GCM, Struijk DG, Arisz L, Krediet RT. Fluid and solute transport in CAPD patients using ultralow sodium dialysate. Kidney Int 1994; 46: 333–340[ISI][Medline]
  16. Nakayama M, Yokoyama K, Kubo H et al. The effect of ultra-low sodium dialysate in CAPD. A kinetic and clinical analysis. Clin Nephrol 1996; 45: 188–193[ISI][Medline]
  17. Locatelli F, Ponti R, Pedrini L, Di Filippo S. Sodium and dialysis: a deeper insight. Int Artif Organs 1989; 12: 71–74[ISI]
  18. Flanigan MJ. Sodium flux and dialysate sodium in hemodialysis. Semin Dial 1988; 11: 298–304
  19. Flanigan MJ. Role of sodium in hemodialysis. Kidney Int 2000; 58 [Suppl 76]: S72–S78[CrossRef]
  20. Twardowski ZJ, Nolph KD, Khanna R et al. Peritoneal equilibration test. Perit Dial Bull 1987; 3: 138–147
  21. La Milia V, Di Filippo S, Crepaldi M et al. Spurious estimations of sodium removal during CAPD when [Na]+ is measured by Na electrode methodology. Kidney Int 2000; 58: 2194–2199[ISI][Medline]
  22. Churchill DN, Thorpe KE, Nolph KD, Keshaviah PR, Oreopoulos DG, Page D. Increased peritoneal membrane transport is associated with decreased patient and technique survival for continuous peritoneal dialysis patients. The Canada–USA (CANUSA) Peritoneal Dialysis Study Group. J Am Soc Nephrol 1998; 9: 1285–1292[Abstract]
Received for publication: 23.10.03
Accepted in revised form: 18. 2.04





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