Comparative in vitro analysis of topical hemostatic agents

Hemostatic agents are broadly utilized across the surgical specialties. While specific characteristics desirable for individual applications may vary, these agents generally are expected to aid the patient's coagulation system in the rapid development of an occlusive clot. Six commonly utilized hemostatic agents were quantitatively compared in terms of their ability to mediate platelet aggregation, deposition and activation, and initiate gross clot formation in a series of in vitro tests. Three types of collagen sponges (Actifoam, Helistat, Instat), microfibrillar collagen (Avitene), a gelatin sponge (Gelfoam), and oxidized regenerated cellulose (Surgicel) were studied. Platelet aggregation: Citrated platelet rich plasma (PRP) was contacted with hemostatic agents both with and without thrombin in a stirred cuvette and the platelet count was measured over 5 min. Platelet deposition: To approximate arterial wounds, PRP was perfused in a controlled manner through hemostatic agents, and the effluent platelet count was measured over time. Platelet activation: ATP secretion from PRP contacted with hemostatic agents in a stirred cuvette was measured at 1 and 5 min. Clot formation: The clotting time of nonanticoagulated whole blood contacted with the hemostatic agents was measured. Materials which depleted platelets most rapidly and effectively in the perfusion system (Avitene, Helistat, and Actifoam) were also the most effective inducers of platelet aggregation and secretion. Clot formation (likely to be platelet dependent) was also more rapid in this group. An overall activity ranking combined the relative performance of each hemostatic agent on the various tests: Actifoam approximately Avitene > Helistat >> Gelfoam > Instat > Surgicel. The activity ranking generally reflects the materials used in these agents (collagen > gelatin > oxidized regenerated cellulose), as well as their processing (chemical crosslinking in collagen sponges may lower activity). Such in vitro assessment of the relative platelet and coagulation activities of hemostatic agents might serve as a useful screening tool before investigating properties which require more expensive animal or clinical testing.