Solute clearances during continuous venovenous haemofiltration at various ultrafiltration flow rates using Multiflow-100 and HF1000 filters

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Abstract
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 β2‐microglobulin (β2‐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 β2‐M were lower than those obtained for small solutes. For the M‐100, average β2‐M E/P was 0.62±0.10 and did not significantly change while increasing Quf. For the HF1000, average β2‐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 β2‐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 β2‐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 β2‐M.