Calcium mass balances during standard bicarbonate hemodialysis and long-hour slow-flow bicarbonate hemodialysis.

BACKGROUND: Dialysate calcium (Ca) concentration should be viewed as part of the integrated therapeutic regimen to control renal osteodystrophy and maintain normal mineral metabolism. Thus, a correct ionized calcium mass balance (Ca++MB) during hemodialysis (HD) is crucial in the treatment of renal osteodystrophy. The GENIUS single-pass batch dialysis system (Fresenius Medical Care, Germany) consists of a closed dialysate tank of 90 L; it offers the opportunity of effecting mass balances of any solute in a very precise way. METHODS: The present study has a crossover design: 11 stable anuric HD patients underwent 2 bicarbonate HD sessions, 1 of 4 hours (4h) and the other of 8 hours (8h) in a random sequence, always at the same interdialytic interval, at least 1 week apart. The GENIUS system and high-flux FX80 dialyzers (Fresenius Medical Care, Germany) were used. The volume of blood and dialysate processed, volume of ultrafiltration and dialysate Ca concentrations (1.50 mmol/L) were prescribed to be the same. Trends of plasma Ca++, blood pH and bicarbonates during dialysis, as well as Ca++MBs were determined. Plasma parathyroid hormone (PTH) levels at the start and end of the 2 treatments were measured. RESULTS: Ca++MBs (mean ± SD) were +284.6 ± 137.4 mg and +297.7 ± 131.6 mg (p=0.307) in the 4h and 8h treatments, respectively. No single session out of the 22 had a negative Ca++MB for the patient. Mean plasma Ca++, blood pH and bicarbonate levels were not statistically significantly different when comparing the start and end of the sessions of the 2 treatments. Mean plasma Ca++, blood pH and bicarbonate levels increased significantly along the time points in both 4h and 8h HD sessions (repeated measures ANOVA: p<0.0001). Mean plasma PTH levels were not statistically significantly different when comparing the start and end of the sessions of the 2 treatments. The differences between predialysis and postdialysis plasma PTH levels were not statistically significantly different either in 4h or 8h sessions (Wilcoxon's test: p=NS), even though a trend toward lower postdialysis plasma PTH levels was observed in both 4h and 8h treatments. CONCLUSIONS: Our data show incontrovertibly that, when dialyzing with a dialysate Ca concentration of 1.50 mmol/L, 4h standard bicarbonate HD and 8h slow-flow bicarbonate HD always achieve a quite similar positive Ca++MB for the patients.

Removal of uraemic retention solutes in standard bicarbonate haemodialysis and long-hour slow-flow bicarbonate haemodialysis.

BACKGROUND: Several studies already stressed the importance of haemodialysis (HD) time in the removal of uraemic toxins. In those studies, however, also the amount of dialysate and/or processed blood was altered. The present study aimed to investigate the isolated effect of the factor time t (by processing the same total blood and dialysate volume in two different time schedules) on the removal and kinetic behaviour of some small, middle and protein-bound molecules. METHODS: The present study had a crossover design: 11 stable anuric HD patients underwent two bicarbonate HD sessions (~ 4 and ~ 8 h) in a random sequence, at least 1 week apart. The GENIUS single-pass batch dialysis system and the high-flux FX80 dialysers (Fresenius Medical Care, Bad Homburg, Germany) were used. The volume of blood and dialysate processed, volume of ultrafiltration, and dialysate composition were prescribed to be the same. For each patient, blood was sampled from the arterial line at 0, 60, 120, 180 and 240 min (all sessions), and at 360 and 480 min (8-h sessions). Dialysate was sampled at the end of HD from the dialysate tank. The following solutes were investigated: (i) small molecules: urea, creatinine, phosphorus and uric acid; (ii) middle molecule: ß(2)M; and (iii) protein-bound molecules: homocysteine, hippuric acid, indole-3-acetic acid and indoxyl sulphate. Total solute removals (solute concentration in the spent dialysate of each analyte × 90 L - the volume of dialysate) (TSR), clearances (TSR of a solute/area under the plasma water concentration time curve of the solute) (K), total cleared volumes (K × dialysis time) (TCV), and dialyser extraction ratios (K/blood flow rate) (ER) were determined. The percent differences of TSR, K, TCV and ER between 4- and 8-h dialyses were calculated. Single-pool Kt/Vurea, and post-dialysis percent rebounds of urea, creatinine and ß(2)M were computed. RESULTS: TSR, TCV and ER were statistically significantly larger during prolonged HD for all small and middle molecules (at least, P < 0.01). Specifically, the percent increases of TSR (8 h vs 4 h) were: for urea 22.6.0% (P < 0.003), for creatinine 24.8% (P < 0.002), for phosphorus 26.6% (P < 0.001), and for ß(2)M 39.2% (P < 0.005). No statistically significant difference was observed for protein-bound solutes in any of the parameters being studied. Single-pool Kt/Vurea was 1.41 ± 0.19 for the 4-h dialysis sessions and 1.80 ± 0.29 for the 8-h ones. The difference was statistically significant (P < 0.0001). Post-dialysis percent rebounds of urea, creatinine and ß(2)M were statistically significantly greater in the 4-h dialysis sessions (at least, P < 0.0002). CONCLUSIONS: The present controlled study using a crossover design indicates that small and middle molecules are removed more adequately from the deeper compartments when performing a prolonged HD, even if blood and dialysate volumes are kept constant. Hence, factor time t is very important for these retention solutes. The kinetic behaviour of protein-bound solutes is completely different from that of small and middle molecules, mainly because of the strength of their protein binding.

Haemodynamic stability in standard bicarbonate haemodialysis and long-hour slow-flow bicarbonate haemodialysis.

BACKGROUND: The interplay of correct solute mass balances, such as that of sodium (Na+) and potassium (K+) (respectively, Na+MB and K+MB) with adequate ultrafiltration volumes (V(UF)), is crucial in order to achieve haemodynamic stability during haemodialysis (HD). The GENIUS single-pass batch dialysis system (Fresenius Medical Care, Germany) consists of a closed dialysate tank of 90 L; it offers the unique opportunity of effecting mass balances of any solute in a very precise way. METHODS: The present study has a crossover design: 11 stable anuric HD patients underwent two bicarbonate HD sessions, one of 4 h and the other of 8 h in a random sequence, always at the same interdialytic interval, at least 1 week apart. The GENIUS system and high-flux FX80 dialysers (Fresenius Medical Care, Germany) were used. The volume of blood and dialysate processed, V(UF) and dialysate Na+ and K+ concentrations were prescribed to be the same. Plasma water Na+ and K+ trends during dialysis as well as Na+MBs and K+MBs were determined. At the same time, systolic blood pressure (SBP) and diastolic blood pressure (DBP), mean arterial pressure (MAP) and heart rate trends during dialysis were analysed. Plasma volume (PV) changes were computed from plasma total protein concentrations and their trends analysed. RESULTS: Plasma water Na+ and K+ levels were not significantly different when comparing the start and the end of the sessions of the two treatments. Both the increase of plasma water Na+ levels and the decrease of plasma water K+ levels in the first 4 h were significantly slower during the 8-h sessions when compared with the 4-h ones (P < 0.048 and P < 0.006, respectively). Dialysis sessions were uneventful. SBP decreased significantly during the 4-h sessions, whereas it remained stable during the 8-h ones (P < 0.0001 and P = NS, respectively). Statistically significantly lower intradialysis decreases of SBP (-4.5 ± 16.2 vs -20.0 ± 15.0 mmHg, P < 0.02) and MAP (-1.4 ± 11.7 vs -8.6 ± 11.0 mmHg, P < 0.04) were achieved in the 8-h sessions with respect to the 4-h sessions, in spite of no significant difference for mean V(UF) (2.9 ± 0.9 vs 2.9 ± 0.8 L; P = NS) and mean Na+MBs (-298.1 ± 142.2 vs -286.2 ± 150.7 mmol; P = NS). The decrease of PV levels in the first 4 h was significantly slower during the 8-h sessions when compared with the 4-h ones (P < 0.0001). PV decrease was significantly higher at the end of the 4-h HD sessions than at the end of the 8-h HD sessions (P < 0.043). CONCLUSIONS: The present highly controlled experiments using a crossover design and precise Na+MB and K+MB controls showed that better haemodynamic stability was achieved in the 8-h sessions with respect to the 4-h sessions, in spite of no difference for mean V(UF) and Na+MBs. Thus, other pathophysiological mechanisms, namely, a better PV preservation, must be advocated in order to explain the better haemodynamic stability peculiar to long-hour slow-flow nocturnal HD treatments.