Abstract: Objective To evaluate the ability changes of the CRRT filter in removing inflammatory mediators at different time points in order to determine whether the filter should be changed. Methods The patients on CRRT therapy for the treatment of multiple organ dysfunction syndrome (MODS) were prospectively studied. Each filter was used for 1h, 24h, 48h, or longer, and the instrument was converted to the after-filter continuous veno-venous hemofiltration (CVVH) mode using the same parameters. Blood flow rate was set at 100 ml/min, and post-replacement volume plus dehydration volume was set at 1,000 ml/h. After the dialysis for 10-30 minutes, blood samples before the filter and after the filter and the ultrafiltration fluid were collected for TNFα concentration measurement. The instrument was then adjusted to the original treatment mode. The TNFα concentrations at each time-point of a filter were recruited, from which the filtration coefficient and adsorption rate of a filter were derived. Results Five MODS patients were involved in this study. Each patient used one filter for the examination. The CRRT filter was used for <24 hours in cases 1～3, for >24 hours in case 4, and for >48 hours in case 5. Serum TNFα concentration before the filters was 20.9～86.3 ng/L, higher than the normal value (Normal TNFα concentration was 14.6～19.5 ng/L in this laboratory). TNFα could be detected in ultrafiltration fluids in the 5 cases with the average concentration of 12.2～26.4 ng/L. The filtration coefficient at early stage (after one hour) was 44.3～73.6% in the 5 patients. The filtration coefficient of the filter was 71.2% and 48.1% in case 4 after one hour and 4 hours respectively, and was 44.3%, 44.8%, 66.2% in case 5 after one hour, 24 hours and 48 hours respectively, reflecting the dynamic changes of the filters’ability. Adsorption was present in filters based on the calculation of TNFα concentrations in the blood samples before and after the filter as well as in ultrafiltration fluids, and the adsorption rate was 306.7-5448.3 pg/min at the 8 time-points of the 5 filters. The clearance rates in case 5 after 48 hours (filtration coefficient 66.2% and adsorption rate 616.7 pg/min) and in case 1 after one hour (filtration coefficient 68.5% and adsorption rate 638.3 pg/min) were similar, but were higher than the clearance rate in case 4 after 24 hours (filtration coefficient 48.1% and adsorption rate 595.0 pg/min). Conclusions TNFα can be filtered and adsorbed by the filters used in CRRT, but the clearance rate among filters was uncomparable. The filtration coefficient and adsorption rate at different time-points of a filter can be used to evaluate the dynamic change of the filter in removing
inflammatory mediators. To determine how long the filter can be used during CRRT when removal of inflammatory mediators is clinically critical and the parameters such as the pipeline clotting function and the pressure across the filter are maintained in reasonable ranges, the concentrations of inflammatory mediators in ultrafiltration fluid, the filtration coefficient and the adsorption rate can be recognized as the objective indices, rather than simply based on the elapsed time the filter being used.

Key words: Continuous renal replacement therapy, Inflammatory mediators, TNF, Filter coefficients, Life span