Metabolic and volume status evaluation of hemodialysis patients with and without residual renal function in the long interdialytic interval

INTRODUCTION: It is unclear whether residual renal function (RRF) in dialysis patients can attenuate the metabolic impact of the long 68-hour interdialytic interval, in which water, acid, and electrolyte accumulation occurs. OBJECTIVE: to evaluate serum electrolyte levels, water balance, and acid-base status in dialytic patients with and without RRF over the long interdialytic interval (LII). METHODOLOGY: this was a single-center, cross-sectional, and analytical study that compared patients with and without RRF, defined by diuresis above 200 mL in 24 hours. Patients were weighed and serum samples were collected for biochemical and gasometric analysis at the beginning and at the end of the LII. RESULTS: 27 and 24 patients with and without RRF were evaluated, respectively. Patients without RRF had a higher increase in serum potassium during the LII (2.67 x 1.14 mEq/L, p < 0.001), reaching higher values at the end of the study (6.8 x 5.72 mEq/L, p < 0.001) and lower pH value at the beginning of the interval (7.40 x 7.43, p = 0.018). More patients with serum bicarbonate < 18 mEq/L (50 x 14.8%, p = 0.007) and mixed acid-base disorder (57.7 x 29.2%, p = 0.042), as well as greater interdialytic weight gain (14.67 x 8.87 mL/kg/h, p < 0.001) and lower natremia (137 x 139 mEq/L, p = 0.02) at the end of the interval. Calcemia and phosphatemia were not different between the groups. CONCLUSION: Patients with RRF had better control of serum potassium, sodium, acid-base status, and volemia throughout the LII.