RESUMO
BACKGROUND: The removal of small and middle molecules has a relevant impact on haemodialysis (HD) patient survival. Mid-dilution (MD) is a technique combining ease of use with high diffusive-convective clearances. However, MD may increase the intrafilter blood pressure due to the high filtration fraction. We devised a new filter configuration, reverse MD, with an inverted blood inlet and outlet. We compared biochemical and technical performances of reverse MD vs standard MD. METHODS: Eight HD patients underwent one standard MD treatment and one reverse MD. Samples for instantaneous clearance and total mass removed from dialysate spilling (urea, phosphate, beta2-microglobulin, angiogenin) were obtained. Dialysate and blood pressures in the circuit were monitored every 15 min. The reinfusion rate was set at 6 l/h for both treatments. RESULTS: Absolute removals were very high and statistically comparable in both the configurations. Pressures were significantly lower with the reverse compared with the standard MD: inlet blood pressure was 731+/-222 and 595+/-119 mmHg in the standard and in the reverse MD, respectively. The transmembrane pressures were lower in the reverse compared with the standard MD (422+/-90 and 611+/-136 mmHg for 1st stage; 188+/-54 and 307+/-56 mmHg for 2nd stage). CONCLUSIONS: Reverse MD could be an ideal technique for high ultrafiltration routine treatments without any external fluid reinfusion. It allows a very high removal of small and middle molecules, with relatively lower intrafilter pressures.
