Activation of the tissue factor pathway occurs during continuous venovenous hemofiltration

Background. Activation of the tissue factor pathway occurs during continuous venovenous hemofiltration (CVVH). Despite adequate exogenous anticoagulation, the occlusion of CVVH circuits can occur within minutes to a few hours of use and is associated with evidence of thrombin generation. Having found no evidence of activation of the contact factor (intrinsic coagulation) pathway during CVVH, we sought to examine the effect of the first episode of CVVH on the tissue factor (extrinsic) pathway of coagulation and thrombin generation. Methods. Twelve critically ill patients were studied prior to the commencement of hemofiltration and at regular intervals thereafter until the filter clotted. Results. Prior to hemofiltration, most patients had increased levels of plasma tissue factor. thrombin-antithrombin (TAT) complexes, and tissue factor pathway inhibitor (TFPI); during hemofiltration, further generation of TAT complexes occurred. Initially, levels of activated factor VII (FVIIa) fell and TFPI increased, but during the course of hemofiltration, the levels of TFPI fell and FVIIa increased. Levels of tissue factor increased during CVVH in some patients, but this was not related to the generation of FVIIa. Conclusions. These data indicate that activation of FVII occurred during CVVH, which was related to levels of TFPI, but not tissue factor, and was coincidental to thrombin generation.