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Comparison of high-efficiency and standard haemodialysis providing equal urea clearances by partial and total
R A Mactier1, A M Madi, B F Allam
1Renal Unit, Stobhill Hospital, Glasgow, UK.
Background:
Short-duration high-efficiency haemodialysis has been utilized increasingly in recent years to deliver adequate blood urea clearances per dialysis session. However, high-efficiency and standard-duration haemodialysis schedules, which achieve equal patient urea clearances, may not represent equivalent dialytic therapy due to solute differences in intercompartmental dysequilibrium during dialysis and differences in dialysis mechanics.
Methods:
To circumvent the effects of intercompartmental dysequilibrium and postdialysis rebound solute clearances were measured by direct dialysis quantification (total and partial dialysate collections) rather than blood clearances. High-efficiency haemodialysis (dialyser blood flow rate = 400 ml/min; dialysis time = 170.67 min) was compared with standard haemodialysis (dialyser blood flow rate = 200 ml/min; dialysis time = 240 min) performed in random order in six anuric patients using Fresenius F8 dialysers and the same haemodialysis machine. Such haemodialysis schedules were prescribed to provide equivalent urea clearances.
Results:
Patient plasma water urea clearances measured by direct dialysis quantification were equivalent, whereas high efficiency haemodialysis achieved significantly lower phosphate clearances (P = 0.01), less net bicarbonate absorption (P = 0.01), and lower beta 2 microglobulin removal (P < 0.001) than standard haemodialysis. Estimated total dialysate effluent volumes with partial dialysate collection and total dialysate collection correlated closely (r = 0.95) and there were no differences between patient urea, creatinine and phosphate clearances measured by partial and total dialysate quantification.
Conclusions:
The data indicate that even if high-efficiency and standard haemodialysis provide equal whole-body urea clearances, delivered dialysis therapy is not equivalent. The partial dialysate collection method is as accurate as the cumbersome total dialysate collection approach and may be applied to assess delivered dialysis dose by minor modification of current haemodialysis machines.