Residual renal function and volume control in peritoneal dialysis patients

Abstract

Background: Fluid overload is not uncommon in patients on continuous ambulatory peritoneal dialysis (CAPD). Previous studies suggested that residual renal function (RRF) played an important role in maintaining fluid balance. However, good fluid status should be a balance between fluid intake and removal. Therefore, in the present study, we investigated the effect of RRF on patients' fluid status after focusing on the balance between fluid intake and removal in CAPD patients.

Methods: In this cross-sectional study, 195 stable CAPD patients in a single center were included. Patients were divided into three groups according to their urine output: anuric group with urine < or =100 ml/day, oliguric group with urine < or =400 ml/day and UO >400 ml group with urine >400 ml/day. Fluid status was evaluated by bioimpedance analysis and mean arterial pressure (MAP). The sodium removal and plasma sodium concentration were also measured. All the patients were educated to try to achieve good volume control by focusing on salt and fluid intake and their removals.

Results: There were 51, 31 and 113 patients in anuric, oliguric and UO >400 ml group, respectively. Anuric patients were older and had been on CAPD longer than that of the oliguric and UO >400 ml patients (p < 0.05). The urine output in the three groups were 9.28 +/- 22.68, 236.13 +/- 75.43 and 1,013.34 +/- 541.54 ml/day, respectively (p < 0.001). Bioimpedance analysis showed that the differences of extracellular water, intracellular water and total body water were not statistically significant among the three groups. However, there was significant difference in MAP among the three groups (MAP in anuric, oliguric and UO >400 ml groups were 93.27 +/- 13.35, 96.63 +/- 9.94 and 102.36 +/- 13.70 mm Hg, p < 0.01), and UO >400 ml group had higher MAP than anuric and oliguric groups (p < 0.05). The total sodium removal (renal + peritoneal) in anuric, oliguric and UO >400 ml groups were 96.44 +/- 60.18, 98.95 +/- 73.82 and 134.64 +/- 72.44 mmol/day, respectively (p < 0.01). The UO >400 ml group also had higher plasma sodium concentration than anuric and oliguric groups (plasma sodium in the three groups were 137.49 +/- 3.43, 137.82 +/- 2.63 and 139.15 +/- 3.30 mmol/l, respectively; p < 0.01).

Conclusions: This study showed that extracellular water among anuric, oliguric and UO >400 ml groups was not significantly different, which suggested that RRF may be not so important as expected in maintaining good volume status. The higher blood pressure in patients with higher RRF and higher sodium and fluid removal in the present study suggested restricting salt and fluid intake might be more important for better blood pressure control in CAPD patients.