Post-Filter Hematocrit

Filter clotting is a major complication of continuous renal replacement therapy (CRRT), resulting in blood loss, reduced treatment efficacy, and increased cost. One modifiable factor associated with filter clotting is filtration fraction (FF), or the proportion of plasma water being removed from the blood over the course of the filter. In convention, a cutoff of FF\<20-30% has been used to prevent hemofilter clotting, but no evidence correlating FF with hemofilter clotting has been documented. Some experts have proposed that post-filter hematocrit (Hct) could be a more direct marker for determining hemofilter clotting risk, but evidence supporting clinical utility of this marker is lacking. HCTpost=HCTpre/(FF(HCTpre-1)+1) In our proposed validation study, we hope to determine whether our formula for post-filter Hct provides accurate results when compared to measured values. The information obtained from this study will potentially justify the use of utilizing the formula in future studies. The procedure of this study is collecting blood samples from the post-filter lines of patients on CRRT at different time points and different flow rates. This will be considered the "measured post-filter hematocrit" which will then be compared to the calculated formula above, using the other values obtained from daily labs (for pre-filter hematocrit) and CRRT machine settings.