A New Method to Increase Ultrafiltration in Peritoneal Dialysis: Steady Concentration Peritoneal Dialysis

Abstract

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Background: Peritoneal dialysis (PD) has limited power for liquid extraction (ultrafiltration), so fluid overload remains a major cause of treatment failure. ♦

Methods: We present steady concentration peritonal dialysis (SCPD), which increases ultrafiltration of PD exchanges by maintaining a constant peritoneal glucose concentration. This is achieved by infusing 50% glucose solution at a constant rate (typically 40 mL/h) during the 4-hour dwell of a 2-L 1.36% glucose exchange. We treated 21 fluid overload episodes on 6 PD patients with high or average-high peritoneal transport characteristics who refused hemodialysis as an alternative. Each treatment consisted of a single session with 1 to 4 SCPD exchanges (as needed). ♦

Results: Ultrafiltration averaged 653 ± 363 mL/4 h - twice the ultrafiltration of the peritoneal equilibration test (PET) (300 ± 251 mL/4 h, p < 0.001) and 6-fold the daily ultrafiltration (100 ± 123 mL/4 h, p < 0.001). Serum and peritoneal glucose stability and dialysis efficacy were excellent (glycemia 126 ± 25 mg/dL, peritoneal glucose 1,830 ± 365 mg/dL, D/P creatinine 0.77 ± 0.08). The treatment reversed all episodes of fluid overload, avoiding transfer to hemodialysis. Ultrafiltration was proportional to fluid overload (p < 0.01) and inversely proportional to final peritoneal glucose concentration (p < 0.05). ♦

Conclusion: This preliminary clinical experience confirms the potential of SCPD to safely and effectively increase ultrafiltration of PD exchanges. It also shows peritoneal transport in a new dynamic context, enhancing the influence of factors unrelated to the osmotic gradient.

Keywords: Ultrafiltration; fluid overload; fluid transport kinetics; glucose concentration; hydrostatic pressure; intraperitoneal pressure; osmotic gradient; technique failure.

Figure 1 —

Steady concentration PD increases ultrafiltration for all patients. Black: Estimated ultrafiltration of a 4-hour exchange in the daily PD scheme for each patient, calculated with slight excess as daily ultrafiltration divided by 5 (to account for the infusion and drain times). Gray: Ultrafiltration in the last PET; PET was done with 2.27% glucose for patients 1, 2, and 4 and with 3.86% glucose for patients 3, 5, and 6. White: Ultrafiltration per exchange of SCPD (average across all exchanges; error bars limit the full range of measurements; 4 measurements for patient 1 were excluded because ultrafiltration could not be measured accurately, see Materials & Methods). The group of bars on the right-hand side shows the average values across all patients. PD = peritoneal dialysis; PET = peritoneal equilibration test; SCPD = steady concentration PD.

Figure 2 —

Negative correlation between ultrafiltration volume and glucose concentration in the effluent of steady concentration PD exchanges. Symbols: Experimental data for the 31 exchanges where infusion rate was 40 mL/h and ultrafiltration was measured accurately. Line: Linear fit. r=-0.4, p=0.02. PD = peritoneal dialysis; UF = ultrafiltration.

Figure 3 —

Ultrafiltration correlates with fluid overload. Successive ultrafiltration volumes in treatments with more than one consecutive SCPD exchange. The patients did not eat or drink during treatment, so each exchange reduces fluid overload by the amount of ultrafiltered volume. b) Circles: Ultrafiltration per SCPD exchange vs estimated overweight over the patient's dry weight for patient 6. Overweight was estimated from clinical data (complemented in 2 cases by vectorial bioimpedance) with an estimated accuracy of about ±0.25 kg, as indicated by the error bars. In treatments with a second SCPD exchange, overweight for the second exchange was calculated as overweight at the beginning of the treatment minus ultrafiltration of the first exchange. Line: linear fit (r = 0.98, p<0.0001). SCPD = steady concentration peritoneal dialysis.