Background: In continuous venovenous haemofiltration (CVVH), high ultrafiltration rates provide survival benefits in acute renal failure. This study measured clearances obtained at ultrafiltration rates of up to 4.5 l/h.
Methods: Clearances of small solutes (urea, creatinine, phosphate and urate) and of beta(2)-microglobulin (beta(2)-M) were measured during CVVH. Five preset Multiflow-100 (M-100) and five HF1000 hollow-fibre filters were compared. For the M-100, clearances obtained by haemofiltration were compared with those obtained by haemodiafiltration at similar total effluent rates from a previous study.
Results: For small solutes, the effluent to plasma ratio (E/P) remained close to 1.0 at all ultrafiltration rates; filter clearances were thus equal to Quf for both filters. Increasing Quf from 1.0 to 4.5 l/h did not significantly modify E/P. Convective clearances of beta(2)-M were lower than those obtained for small solutes. For the M-100, average beta(2)-M E/P was 0.62+/-0.10 and did not significantly change while increasing Quf. For the HF1000, average beta(2)-M E/P were significantly lower compared with the M-100 (0.42+/-0.09 at 1.0 l/h) and decreased progressively to 0.26+/-0.06 while increasing Quf to 4.5 l/h. With pre-dilution, progressive decreases in clearances delivered to patients were observed reaching 40% at a Quf rate of 4.5 l/h. There was no clinically significant adsorption of beta(2)-M. For the M-100, at similar total effluent flow rates, clearances delivered to patients using haemodiafiltration were significantly higher for small solutes but lower for beta(2)-M in comparison to haemofiltration only.
Conclusions: Filter clearance for small solutes equalled Quf at evaluated rates. At high ultrafiltration rates there was significant loss of clearances with pre-dilution. At similar total effluent rates with the use of pre-dilution, haemodiafiltration is superior to haemofiltration for small solute clearance but inferior for beta(2)-M.