The role of tidal peritoneal dialysis in modern practice: A European perspective

Tidal peritoneal dialysis (TPD) has been introduced to optimize adequacy of peritoneal dialysis (PD). Early studies reported similar or even better small solute clearances with TPD than those achieved with continuous ambulatory peritoneal dialysis or continuous cyclic peritoneal dialysis. However, in many studies treatment volumes were much higher during TPD compared with other PD modalities. Based on current evidence, TPD provides no advantage of increased small solute clearances, middle molecule clearances, or peritoneal ultrafiltration as compared to non-tidal automated peritoneal dialysis (APD) when dialysate flow is kept constant. However, TPD reduces drainage pain and nightly alarms during cycler treatment. Tidal volume should be kept as high as possible in these patients, especially in those with low average peritoneal transport rates. Based on theoretical considerations and little evidence, TPD could provide better clearances than conventional APD when a very high dialysate flow (≥5 l/h) is used. Such dialysate flow rates are not routinely prescribed in home APD patients. However, they may be interesting for in-center PD patients. One randomized crossover trial reported higher small solute clearances with TPD compared to non-tidal APD in patients with acute renal failure. TPD is also the preferred treatment modality in patients with ascites as it allows a controlled outflow of fluid from the peritoneal cavity. Newer treatment modalities, for example, continuous flow PD, may be interesting alternatives in an effort to increase efficacy of PD in the future. However, because such treatment regimens are expensive and elaborate they have not been established for routine use until now. Tidal peritoneal dialysis (TPD) has been introduced to optimize adequacy of peritoneal dialysis (PD). Early studies reported similar or even better small solute clearances with TPD than those achieved with continuous ambulatory peritoneal dialysis or continuous cyclic peritoneal dialysis. However, in many studies treatment volumes were much higher during TPD compared with other PD modalities. Based on current evidence, TPD provides no advantage of increased small solute clearances, middle molecule clearances, or peritoneal ultrafiltration as compared to non-tidal automated peritoneal dialysis (APD) when dialysate flow is kept constant. However, TPD reduces drainage pain and nightly alarms during cycler treatment. Tidal volume should be kept as high as possible in these patients, especially in those with low average peritoneal transport rates. Based on theoretical considerations and little evidence, TPD could provide better clearances than conventional APD when a very high dialysate flow (≥5 l/h) is used. Such dialysate flow rates are not routinely prescribed in home APD patients. However, they may be interesting for in-center PD patients. One randomized crossover trial reported higher small solute clearances with TPD compared to non-tidal APD in patients with acute renal failure. TPD is also the preferred treatment modality in patients with ascites as it allows a controlled outflow of fluid from the peritoneal cavity. Newer treatment modalities, for example, continuous flow PD, may be interesting alternatives in an effort to increase efficacy of PD in the future. However, because such treatment regimens are expensive and elaborate they have not been established for routine use until now. Dependent on treatment modality, the duration of an automated peritoneal dialysis (APD) session is 8–10 h and includes 3–15 cycles per therapy. Each cycle consists of a dialysate inflow, a dwell time of 30–120 min, and the dialysate outflow. The dialysate outflow can be subdivided into two segments. In the first (fast) segment, up to 80% of dialysate is usually drained within a few minutes. During the second (slow) segment, only the remaining part of the outflow volume is drained. This latter phase does not contribute significantly to dialysis efficacy as only a small amount of dialysate is in contact with the peritoneal membrane, but much more time is needed to drain this last part of the outflow volume. The time point between the first (fast) and second (slow) outflow segment is called 'transition point' or 'breakpoint'.1.Brandes J.C. Packard W.J. Watters S.K. et al.Optimization of dialysate flow and mass transfer during automated peritoneal dialysis.Am J Kidney Dis. 1995; 25: 603-610Abstract Full Text PDF PubMed Scopus (60) Google Scholar When increasing the dialysate flow (treatment volume/per time) during cycler therapy, the length of each dwell declines. In this situation, the time spent for inflow and outflow becomes a significant part of the whole treatment. Accordingly, Durand et al.2.Durand P.Y. Freida P. Issad B. et al.How to reach optimal creatinine clearances in automated peritoneal dialysis.Perit Dial Int. 1996; 16: S167-S170PubMed Google Scholar described that with high dialysate flows a maximal treatment volume (maximal effective dialysate flow) is reached where clearances do not increase or even decrease, because dwell times become too short for effective diffusion. The maximal dialysate flow depends on the molecular weight of uremic toxins and is reached earlier for larger than for smaller molecules. The concept of draining only part of the initial fill volume and replacing it by fresh or regenerated dialysate after short dwell times was first described in the late 1970s as 'reciprocating peritoneal dialysis' by Stephen3.Stephen R.L. Reciprocating peritoneal dialysis with a subcutaneuous peritoneal catheter.Dial Transplant. 1978; 7: 834-838Google Scholar and as 'semicontinuous peritoneal dialysis' by Di Paolo.4.Di Paolo N. Semicontinuous peritoneal dialysis.Dial Transplant. 1978; 7: 839-842Google Scholar At the same time, the better efficacy of this technique as compared to other peritoneal dialysis (PD) modalities was also confirmed in an animal study (using 20% exchange volume).5.Finkelstein F.O. Kliger A.S. Enhanced efficiency of peritoneal dialysis using rapid small volume exchanges.ASAIO J. 1979; 2: 103-106Google Scholar In the following years, attention was drawn away from this kind of treatment to other PD modalities, especially to continuous ambulatory peritoneal dialysis (CAPD), which was much easier to handle. In an attempt to increase efficacy of PD in the late 1980s and early 1990s, there was renewed interest in the former mentioned cycler technique, which was now modified by Twardowski and named tidal peritoneal dialysis (TPD).6.Twardowski Z.J. Peritoneal dialysis. Current technology and techniques.Postgrad Med. 1989; 85: 161-164Crossref PubMed Scopus (6) Google Scholar,7.Twardowski Z.J. Prowant B.F. Nolph K.D. et al.Chronic nightly tidal peritoneal dialysis.ASAIO Trans. 1990; 36 (167, 170 passim): M584-M588Crossref PubMed Google Scholar In classical TPD only part of the initial fill volume (tidal volume, usually 50%) is changed during each cycle, leaving the rest of the dialysate (reserve volume) in the peritoneal cavity. At the end of the tidal session, the whole dialysate volume is drained from the peritoneal cavity. It has been expected that TPD would improve clearances mainly because of two reasons. First, the contact time of the peritoneum with larger amounts of dialysate is increased, as only part of the intraperitoneal volume is drained and immediately replaced by fresh dialysis solution. Therefore, the second, less efficient part of the dialysate outflow is excluded. Secondly, during an APD session the number of cycles automatically increases when the exchange volume per cycle is reduced, while holding treatment time and total dialysate volume constant. Therefore, better mixing of the dialysate and reduction of stagnant dialysate fluid layers along the peritoneal membrane by more frequent exchanges may also increase efficacy. This review article gives an overview of the most important clinical studies focusing on TPD during the last 20 years and determines the actual place of this treatment modality within a PD program. Studies in the early 1990s comparing the adequacy of several APD techniques reported favorable results for TPD regarding improvement of dialysis efficacy. For example, Flanigan et al.8.Flanigan M.J. Doyle C. Lim V.S. et al.Tidal peritoneal dialysis: preliminary experience.Perit Dial Int. 1992; 12: 304-308PubMed Google Scholar found similar creatinine and urea nitrogen clearances in 8 h intermittent TPD as compared to continuous cyclic peritoneal dialysis (CCPD) with 10 h nightly treatment time. The treatment volume, however, was 9.5 l/session in CCPD and 16 l/session in TPD. Therefore, the increase in dialysate flow during TPD had a substantial part in improving clearances. In another study, the same authors found that TPD provided better creatinine clearances and Kt/V values than CCPD when the dialysate flow was increased from 30 to 50 ml/kg/h, which again was much higher than in CCPD.9.Flanigan M.J. Pflederer T.A. Lim V.S. Is 8 hours of nightly peritoneal dialysis enough?.ASAIO J. 1994; 40: 24-26Crossref PubMed Google Scholar Hölttä et al.10.Hölttä T. Rönnholm K. Holmberg C. Adequacy of dialysis with tidal and continuous cycling peritoneal dialysis in children.Nephrol Dial Transplant. 2000; 15: 1438-1442Crossref PubMed Scopus (19) Google Scholar found significantly higher creatinine clearances, comparable Kt/V values, and similar phosphate loss into the dialysate in pediatric patients with high (H)/high average (HA) peritoneal transport rates during TPD (50% tidal volume, 50% TPD) as compared to CCPD. In the study by Fernández Rodríguez et al.,11.Fernández Rodríguez A.M. Vega Diaz N. Palop Cubillo L. et al.Adequacy of dialysis in automated peritoneal dialysis: a clinical experience.Perit Dial Int. 1997; 17: 442-448PubMed Google Scholar 50% TPD with wet daytime provided higher creatinine and urea nitrogen clearances than CCPD. Fischbach et al.12.Fischbach M. Desprez P. Hamel G. et al.Management of fluid overload in infants by tidal peritoneal dialysis: is there a benefit compared with continuous cycling peritoneal dialysis?.Pediatr Nephrol. 1994; 8: 598-600Crossref PubMed Scopus (12) Google Scholar reported higher phosphate and urea clearances in three children with high peritoneal transport rates on 8 h TPD as compared to 8- or 10-h CCPD. In the study by Edefonti et al.,13.Edefonti A. Consalvo G. Picca M. et al.Dialysis delivery in children on nightly intermittent and tidal peritoneal dialysis.Pediatr Nephrol. 1995; 9: 329-332Crossref PubMed Scopus (14) Google Scholar seven pediatric patients were treated with nightly intermittent peritoneal dialysis over 15 months and thereafter with TPD over 13.7 months. The authors reported a significant increase of creatinine and urea clearances during TPD as compared to nightly intermittent peritoneal dialysis. Again, in all four studies,10.Hölttä T. Rönnholm K. Holmberg C. Adequacy of dialysis with tidal and continuous cycling peritoneal dialysis in children.Nephrol Dial Transplant. 2000; 15: 1438-1442Crossref PubMed Scopus (19) Google Scholar, 11.Fernández Rodríguez A.M. Vega Diaz N. Palop Cubillo L. et al.Adequacy of dialysis in automated peritoneal dialysis: a clinical experience.Perit Dial Int. 1997; 17: 442-448PubMed Google Scholar, 12.Fischbach M. Desprez P. Hamel G. et al.Management of fluid overload in infants by tidal peritoneal dialysis: is there a benefit compared with continuous cycling peritoneal dialysis?.Pediatr Nephrol. 1994; 8: 598-600Crossref PubMed Scopus (12) Google Scholar, 13.Edefonti A. Consalvo G. Picca M. et al.Dialysis delivery in children on nightly intermittent and tidal peritoneal dialysis.Pediatr Nephrol. 1995; 9: 329-332Crossref PubMed Scopus (14) Google Scholar dialysate flow during TPD was markedly higher than during non-tidal APD. Studies comparing CAPD with TPD also reported similar or superior clearances with the latter treatment modality.7.Twardowski Z.J. Prowant B.F. Nolph K.D. et al.Chronic nightly tidal peritoneal dialysis.ASAIO Trans. 1990; 36 (167, 170 passim): M584-M588Crossref PubMed Google Scholar, 11.Fernández Rodríguez A.M. Vega Diaz N. Palop Cubillo L. et al.Adequacy of dialysis in automated peritoneal dialysis: a clinical experience.Perit Dial Int. 1997; 17: 442-448PubMed Google Scholar, 14.Flanigan M.J. Lim V.S. Pflederer T.A. Tidal peritoneal dialysis: kinetics and protein balance.Am J Kidney Dis. 1993; 22: 700-707Abstract Full Text PDF PubMed Scopus (16) Google Scholar, 15.Rodríguez A.M.F. Díaz N.V. Cubillo L.P. et al.Automated peritoneal dialysis: a Spanish multicentre study.Nephrol Dial Transplant. 1998; 13: 2335-2340Crossref PubMed Scopus (47) Google Scholar The difference in dialysate treatment volumes between CAPD and TPD patients was even larger than in the previous mentioned studies, making interpretation of these results difficult. Therefore, all above mentioned studies reported that TPD with a rather high dialysate flow is more or at least as efficient than other PD treatment modalities, but they could not answer the question if the tidal mode, independent of other factors (e.g. dialysate flow), increases efficacy of PD. This latter question can be only answered when TPD and non-tidal APD are compared under similar conditions. In a crossover study, Balaskas et al.16.Balaskas E.V. Izatt S. Chu M. et al.Tidal volume peritoneal dialysis versus intermittent peritoneal dialysis.Adv Perit Dial. 1993; 9: 105-109PubMed Google Scholar treated 12 patients with high-volume TPD and intermittent peritoneal dialysis (IPD) for 3 months each. Treatment volume and treatment time were similar for both treatments (dialysate flow approximately 4 l/h). There were no differences in biochemical parameters (serum urea, creatinine, sodium, potassium, calcium, phosphate, total protein, and albumin) or hematological parameters (hemoglobin, hematocrit) between the two treatments. Clearances were not measured. In a study of six patients, Steinhauer et al.17.Steinhauer H.B. Keck I. Lubrich-Birkner I. et al.Increased dialysis efficiency in tidal peritoneal dialysis compared to intermittent peritoneal dialysis.Nephron. 1991; 58: 500-501Crossref PubMed Google Scholar compared IPD and 50% TPD with similar mean dialysate volumes (23 l), treatment time (7.5 h), dialysate glucose concentration, and total fill volume per cycle (1.5 or 2 l). These authors found a significantly increased phosphate clearance during TPD, whereas clearances of creatinine, urea, and potassium were not significantly different between the two treatment modalities. Piraino et al.18.Piraino B. Bender F. Bernardini J. A comparison of clearances on tidal peritoneal dialysis and intermittent peritoneal dialysis.Perit Dial Int. 1994; 14: 145-148PubMed Google Scholar found, in six patients, no significant differences in clearances of urea nitrogen, creatinine, phosphate, and potassium between 50% TPD and IPD, when the same dialysate flow rate (3.7 l/h for IPD, 3.8 l/h for TPD), initial fill volume (2 l), and dialysate glucose concentration (1.9 g/dl on average) was used. Quellhorst et al.19.Quellhorst E. Solf A. Hildebrand U. Tidal peritoneal dialysis (TPD) is superior to intermittent peritoneal dialysis (IPD) in long term treatment of patients with chronic renal insufficiency (CRI).Perit Dial Int. 1991; 11 (abstract): 217PubMed Google Scholar treated 12 patients with TPD and IPD (10 months each) using a treatment volume of 60 l/cycler therapy and a constant composition of dialysate in both sessions. Despite an approximately 25% reduced treatment time, TPD provided significantly better creatinine and urea clearances than IPD as well as decreased serum phosphate levels. Serum parathyroid hormone levels tended to normalize during TPD but remained unchanged in IPD patients. Although these latter studies compared TPD and non-tidal APD under similar conditions, almost all of them used dialysate flow rates of 3.5–5 l/h, which are rarely prescribed in home APD patients. There are only few papers investigating adequacy of TPD with lower dialysate flow rates. In the Spanish multicenter study, patients were treated with either CAPD, CCPD, or TPD for 2 months each.15.Rodríguez A.M.F. Díaz N.V. Cubillo L.P. et al.Automated peritoneal dialysis: a Spanish multicentre study.Nephrol Dial Transplant. 1998; 13: 2335-2340Crossref PubMed Scopus (47) Google Scholar The treatment volume (14–15 l/night, 1.8–2.0 l/daytime) between CCPD and TPD was comparable. Creatinine and urea nitrogen clearances were significantly lower on CAPD than on all APD techniques. Within APD modalities, urea clearances were highest on CCPD, whereas creatinine clearances were comparable between CCPD and 50% TPD. In a study of six patients (all H/HA transporters), Aasarød et al.20.Aasarød K. Widerøe T.E. Flakne S.C. A comparison of solute clearance and ultrafiltration volume in peritoneal dialysis with total or fractional (50%) intraperitoneal volume exchange with the same dialysate flow rate.Nephrol Dial Transplant. 1997; 12: 2128-2132Crossref PubMed Scopus (17) Google Scholar showed that with a treatment volume of 10 l (fill volume 2 l, treatment time 9 h), clearances of creatinine, urea, and uric acid were significantly higher with IPD than with 50% TPD. When increasing the treatment volume to 14 or 24 l, no significant difference was found between the two treatment modalities. Perez et al.21.Perez R.A. Blake P.G. McMurray S. et al.What is the optimal frequency of cycling in automated peritoneal dialysis?.Perit Dial Int. 2000; 20: 548-556PubMed Google Scholar reported that there were no differences in creatinine clearances, urea clearances, and potassium removal between non-tidal APD (7 × 2 l per night) and 50% TPD (14 l/night, fill volume 2 l, tidal volume 1 l). We22.Vychytil A. Lilaj T. Schneider B. et al.Tidal peritoneal dialysis for home-treated patients: should it be preferred?.Am J Kidney Dis. 1999; 33: 334-343Abstract Full Text Full Text PDF PubMed Scopus (35) Google Scholar found similar creatinine and phosphate clearances and significantly better urea nitrogen clearances with non-tidal APD (IPD) as compared to 50% TPD when using a dialysate flow of 1.7 l/h (15 l/9 h). The initial fill volume (2500 ml) and dialysate glucose concentration (1.36%) was identical in both treatments. After increasing the dialysate flow to 3 l/h (30 l/10 h), there were no significant differences in small solute clearances between both treatment modalities.22.Vychytil A. Lilaj T. Schneider B. et al.Tidal peritoneal dialysis for home-treated patients: should it be preferred?.Am J Kidney Dis. 1999; 33: 334-343Abstract Full Text Full Text PDF PubMed Scopus (35) Google Scholar In a clinical study of eight anuric patients, Amici23.Amici G. Solute kinetics in automated peritoneal dialysis.Perit Dial Int. 2000; 20: S77-S82PubMed Google Scholar showed that clearances of creatinine, urea, phosphate, and urate increased with higher nightly cycler treatment volumes (20 vs 15 l). However, there was no difference between 70% TPD (2500 ml fill volume, 1750 ml tidal volume) and non-tidal APD (fill volume 2500 ml) when the dialysate treatment volume was kept constant. Using dialysate volumes of 15 or 24 l, Juergensen et al.24.Juergensen P.H. Murphy A.L. Pherson K.A. et al.Tidal peritoneal dialysis: comparison of different tidal regimens and automated peritoneal dialysis.Kidney Int. 2000; 57: 2603-2607Abstract Full Text Full Text PDF PubMed Scopus (28) Google Scholar found similar creatinine clearances and Kt/V values between 50% TPD and non-tidal APD (fill volume 25–35 ml/kg, treatment time 9.5 h for both modalities). In a recent study of 10 patients, the same group25.Juergensen P. Eras J. McClure B. et al.The impact of various cycling regimens on phosphorus removal in chronic peritoneal dialysis patients.Int J Artif Organs. 2005; 28: 1219-1223PubMed Google Scholar showed that during non-tidal APD, creatinine clearances improved by 27% and phosphate clearances by 19% when the nightly dialysate volume was increased from 14 to 24 l. With TPD an increase of treatment volume to 24 l provided also higher creatinine and phosphate clearances. However, these values were less than those achieved with the 24 l non-tidal APD regimen. In summary, based on the majority of studies there is no clear evidence that in home APD patients TPD has any advantage over other PD modalities in improving small solute clearances, provided that fill volume, glucose concentration, and dialysate flow are kept constant. Moreover, at least with low dialysate flow, some studies suggest that non-tidal APD becomes the more efficient therapy. To the best of our knowledge, only one study has compared clearances of larger molecules between TPD and conventional APD (IPD).22.Vychytil A. Lilaj T. Schneider B. et al.Tidal peritoneal dialysis for home-treated patients: should it be preferred?.Am J Kidney Dis. 1999; 33: 334-343Abstract Full Text Full Text PDF PubMed Scopus (35) Google Scholar Neither with low (1.7 l/h) nor with high dialysate flow (3 l/h) was there a difference in β2-microglobulin clearances between both APD modalities when treatment duration, dialysate volume, glucose concentration, and fill volume were kept constant. Most of the studies comparing TPD with other PD treatment modalities have focused on small solute clearances. Recent trials show that other factors such as sodium removal and volume control have an important influence on patient morbidity and mortality.26.Ates K. Nergizoglu G. Keven K. et al.Effect of fluid and sodium removal on mortality in peritoneal dialysis patients.Kidney Int. 2001; 60: 767-776Abstract Full Text Full Text PDF PubMed Scopus (332) Google Scholar,27.Brown E.A. Davies S.J. Rutherford P. et al.Survival of functionally anuric patients on automated peritoneal dialysis: the European APD Outcome Study.J Am Soc Nephrol. 2003; 14: 2948-2957Crossref PubMed Scopus (338) Google Scholar In one study17.Steinhauer H.B. Keck I. Lubrich-Birkner I. et al.Increased dialysis efficiency in tidal peritoneal dialysis compared to intermittent peritoneal dialysis.Nephron. 1991; 58: 500-501Crossref PubMed Google Scholar of six patients, TPD provided significantly better ultrafiltration than IPD, when dialysate volume, treatment time, and dialysate glucose concentration were similar (mean dialysate flow was 3.1 l/h). Piraino et al.18.Piraino B. Bender F. Bernardini J. A comparison of clearances on tidal peritoneal dialysis and intermittent peritoneal dialysis.Perit Dial Int. 1994; 14: 145-148PubMed Google Scholar also found higher peritoneal ultrafiltration in TPD as compared to IPD (2.9±0.9 l/session vs 3.3±1.6 l/session). This difference, however, was not significant, most likely because of the small patient number (six patients). In contrast, in the clinical study by Aasarød et al. of six patients with H/HA peritoneal transport rates, peritoneal ultrafiltration was higher with IPD than with TPD when a treatment volume of 10 or 14 l was used (treatment time 9 h), whereas there was no significant difference between the two modalities when dialysate volume was increased to 24 l.20.Aasarød K. Widerøe T.E. Flakne S.C. A comparison of solute clearance and ultrafiltration volume in peritoneal dialysis with total or fractional (50%) intraperitoneal volume exchange with the same dialysate flow rate.Nephrol Dial Transplant. 1997; 12: 2128-2132Crossref PubMed Scopus (17) Google Scholar Peritoneal ultrafiltration in the Spanish multicenter study15.Rodríguez A.M.F. Díaz N.V. Cubillo L.P. et al.Automated peritoneal dialysis: a Spanish multicentre study.Nephrol Dial Transplant. 1998; 13: 2335-2340Crossref PubMed Scopus (47) Google Scholar was comparable between CAPD, CCPD, 25% TPD, and 50% TPD. None of the four above-mentioned studies has provided results on sodium removal, which may behave differently from ultrafiltration, especially when a high dialysate flow is used. Sodium elimination is impaired in APD as compared to CAPD patients because of the phenomenon of sodium sieving, which occurs early in the dwell. During this first phase of the dwell time, transcellular water transport through aquaporins is high, resulting in peritoneal removal of relatively more water than sodium. Thereafter, diffusive and convective sodium transport into the peritoneal cavity increases continuously. Accordingly sodium sieving is more marked during short dwell times.28.Struijk D.G. Krediet R.T. Sodium balance in automated peritoneal dialysis.Perit Dial Int. 2000; 20: S101-S105PubMed Google Scholar, 29.Rodríguez-Carmona A. Fontán M.P. Sodium removal in patients undergoing CAPD and automated peritoneal dialysis.Perit Dial Int. 2002; 22: 705-713PubMed Google Scholar, 30.Rodríguez-Carmona A. Pérez-Fontán M. García-Naveiro R. et al.Compared time profiles of ultrafiltration, sodium removal, and renal function in incident CAPD and automated peritoneal dialysis patients.Am J Kidney Dis. 2004; 44: 132-145Abstract Full Text Full Text PDF PubMed Scopus (115) Google Scholar Therefore, it has to be considered that treatment regimens with high dialysate flow and rather short dwell times may be associated with impaired sodium removal even if they can improve small solute clearances. Only a few studies looked at sodium removal in TPD patients. Amici23.Amici G. Solute kinetics in automated peritoneal dialysis.Perit Dial Int. 2000; 20: S77-S82PubMed Google Scholar showed, in eight anuric patients, that the mass transfer of sodium was comparable between 70% TPD and CCPD (the daytime dwell was excluded from analysis). Quellhorst et al.19.Quellhorst E. Solf A. Hildebrand U. Tidal peritoneal dialysis (TPD) is superior to intermittent peritoneal dialysis (IPD) in long term treatment of patients with chronic renal insufficiency (CRI).Perit Dial Int. 1991; 11 (abstract): 217PubMed Google Scholar compared TPD and IPD using a very high dialysate flow (60 l/session, observation period 10 months/treatment modality). Sodium removal was higher with TPD, but the authors did not include results of peritoneal ultrafiltration in their abstract. In another study (Freida P, Potier J, Postec JM. Perit Dial Int 1993; 13(Suppl 1): S13, abstract), hypertonic TPD provided better sodium removal than hypertonic CCPD or nightly intermittent peritoneal dialysis. No data on treatment volumes are included in this abstract. In the study by Perez et al.,21.Perez R.A. Blake P.G. McMurray S. et al.What is the optimal frequency of cycling in automated peritoneal dialysis?.Perit Dial Int. 2000; 20: 548-556PubMed Google Scholar there was no significant difference in peritoneal ultrafiltration and glucose absorption between 50% TPD (14 l) and 7 × 2 l non-tidal APD. Sodium removal with 50% TPD was 181.6± 79.8 mmol/treatment vs 138.2±74.9 mmol/treatment with 7 × 2 l non-tidal APD. This difference was not significant. However, compared to 5 × 2 l non-tidal APD (sodium removal 114.9±45.6 mmol/treatment), only 50% TPD (14 l) but not 7 × 2 l non-tidal APD achieved a significantly higher sodium loss. We reanalyzed sodium removal of patients included in our previous study.22.Vychytil A. Lilaj T. Schneider B. et al.Tidal peritoneal dialysis for home-treated patients: should it be preferred?.Am J Kidney Dis. 1999; 33: 334-343Abstract Full Text Full Text PDF PubMed Scopus (35) Google Scholar Results on sodium elimination during TPD and IPD were available in 27 of the 30 included patients for the low-flow regimen (1.7 l/h), and in 16 of the 17 patients for the high flow regimen (3 l/h). In 15 patients, data on sodium loss of all sessions were available (Tables 1 and 2). Treatment volume (15 and 30 l), dialysate volume (2.5 l), treatment duration (9 h for the 15 l regimen, 10 h for the 30 l regimen), and glucose concentration (exclusively 1.36% glucose) were the same for both APD modalities. During TPD, a tidal volume of 50% (1250 ml) was prescribed. The results of peritoneal ultrafiltration and sodium removal are shown in Table 1. Peritoneal ultrafiltration tended to be lower during TPD than IPD in low (L)/low average (LA) transporters (not significant). Neither with the low dialysate flow nor with the high dialysate flow was there a significant difference in sodium removal between the two treatment regimens (Table 1). In order to study the effect of dialysate flow on sodium removal and ultrafiltration, only patients who performed all four treatments were analyzed (Table 2). Whereas ultrafiltration tended to increase with higher dialysate flow, sodium loss decreased. These changes seemed to be more marked in L/LA transporters and during IPD (P=0.082, Table 2). Mean ultrafiltrate volume with 1.36% glucose solution was rather low (<1 l/for all treatments) and, especially with a dialysate flow of 3l/h, there was a huge interindividual variability in sodium transport, ranging from sodium loss of up to 160 mmol/treatment to a net gain of 90 mmol sodium/treatment (data not shown). Although differences in sodium removal between treatments with low and high dialysate flow did not reach the level of significance, they are in agreement with other studies showing more marked sodium sieving when shorter dwell times are used.28.Struijk D.G. Krediet R.T. Sodium balance in automated peritoneal dialysis.Perit Dial Int. 2000; 20: S101-S105PubMed Google Scholar, 29.Rodríguez-Carmona A. Fontán M.P. Sodium removal in patients undergoing CAPD and automated peritoneal dialysis.Perit Dial Int. 2002; 22: 705-713PubMed Google Scholar, 30.Rodríguez-Carmona A. Pérez-Fontán M. García-Naveiro R. et al.Compared time profiles of ultrafiltration, sodium removal, and renal function in incident CAPD and automated peritoneal dialysis patients.Am J Kidney Dis. 2004; 44: 132-145Abstract Full Text Full Text PDF PubMed Scopus (115) Google Scholar The above mentioned studies suggest a possible benefit of TPD compared to non-tidal APD when the dialysate flow has to be increased (at lea