Time and exercise improve phosphate removal in hemodialysis patients

Control of serum phosphate remains a difficult clinical issue in most hemodialysis (HD) patients. This study examines 2 nonpharmacological approaches to improving phosphate control in HD patients.

First, 9 stable HD patients underwent dialysis in random fashion for either 4 hours 3 times weekly or 5 hours 3 times weekly. Adjustments were made to blood flow rates such that Kt/V was the same for all sessions, thus allowing independent assessment of the influence of time. The primary end point was weekly dialysate phosphate removal. In the second study, 12 different patients underwent an exercise program in which they pedaled a bicycle ergometer either immediately before or during dialysis. Again, weekly dialysate phosphate removal was measured.

In the time study, urea reduction ratio (69% +/- 0.02% versus 68% +/- 0.07, 4 versus 5 hours) and weekly urea removal were no different between the 2 groups. However, weekly phosphate removal (3,007 +/- 641 versus 3,400 +/- 647 mg; P < 0.02) significantly improved with longer dialysis duration. Serum phosphate levels improved, but did not reach statistical significance in this short-term study. In the exercise study, weekly phosphate removal improved with exercise, but did not reach significance (2,741 +/- 715 [no exercise] versus 2,917 +/- 833 [exercise predialysis] versus 2,992 +/- 852 mg [exercise during dialysis]; P = 0.055), although comparing only exercise during dialysis with no exercise reached significance (P = 0.02). There was no significant difference in serum phosphate levels.

Both increased dialysis time and exercise result in increased dialytic removal of phosphate and could be expected in the long term to improve phosphate control.