Modeling of bicarbonate within the dialysate fluid, specifically a lower than standard concentration has been suggested in facilitating the removal of phosphate and potassium. To test this hypothesis, the study will use a cross-over study design to evaluate phosphate and potassium removal during dialysis by altering bicarbonate concentration in dialysis fluid (i.e. high bicarbonate, standard bicarbonate washout, low bicarbonate), and compare the effects of the different dialysate bicarbonate concentrations on the removal of phosphate and potassium during hemodialysis

Elevation of blood phosphate levels in chronic dialysis patients is associated with increased mortality due to cardiovascular events, and if sustained leads to hyperactivity of parathyroid glands and renal bone disease. Similarly, increased calcium-phosphate product as a result of elevated levels of phosphate in the blood is an additional risk factor for vascular calcification. Elevated blood potassium levels is another major electrolyte disorder in patients with advanced renal disease which is potentially life threatening. Therefore control of blood phosphate and potassium levels is a fundamental component of treatment for end stage renal disease. Management of hyperelectrolyte levels in renal failure patients requires restriction of phosphate and potassium intake through dietary measures, promotion of excretion via GI tract through medication delivery (i.e. supplementary binders), and removal through dialysis. All these strategies come with limitations however, specifically adherence to dietary restrictions and medication compliance is poor due to lack of immediate repercussions, as well as the complex kinetics involved with removal via dialysis given the dependence on duration and frequency of dialysis whose manipulation is limited by time considerations for the patient and scheduling issues in the dialysis unit.

Inclusion Criteria:

• Patients 0-18 years old
• Patients receiving maintenance hemodialysis* for a total of 9-15 hours per week
• Pre-dialysis serum potassium value between 4.0 and 6.5 mmol/L on the first day of the treatment protocol
• Pre-dialysis serum phosphate value greater than low normal for age on the first day of the treatment protocol
• Pre-dialysis serum bicarbonate (total CO2) value between 18 and 30 mmol/L on the first day of the treatment protocol
• Pre-dialysis corrected calcium value between 1.80-2.85 mmol/L on the first day of the treatment protocol

Exclusion Criteria:

• Hemodynamically unstable patients (requiring inotropes or midodrine for support).
• Pre-dialysis potassium value < 4.0 or > 6.5 mmol/L on the first day of the treatment protocol
• Pre-dialysis serum phosphate value less than low normal for age on the first day of the treatment protocol (i.e. hypophosphatemia)
• Pre-dialysis serum bicarbonate (total CO2) value <18 or > 30 mmol/L on the first day of the treatment protocol
• Pre-dialysis corrected calcium <1.8 and >2.85 mmol/L on the first day of the treatment protocol
• Patients mechanically ventilated
• Drugs that could modify internal phosphate and potassium balance such as insulin, bicarbonate injection, hypertonic dextrose solution or mannitol infusion during HD