Follow up study in the assessment of rVlla as a universal haemostatic agent in a model of haemodilution

Introduction

Large volume fluid replacement to treat haemorrhagic shock can result in haemostatic failure due both to a dilution effect [1] and an intrinsic effect [2,3]. Recombinant factor Vlla (rVlla) is seen increasingly as a possible universal haemostatic agent that could act to reverse or even prevent the dilution and intrinsic effects of fluids used within the 'golden' hour of haemorrhagic shock. Our preliminary findings demonstrated that rVlla appeared to improve markers of global haemostasis in a model of large volume fluid replacement. This follow up study assessed what effects rVlla had on global haemostasis and the electron microscopic appearances of clot formation when haemaccel or sodium chloride were used as diluents to create a model of large volume fluid replacement.

Methods

One hundred whole blood samples from normal donors were tested undiluted, or diluted to 50% and 80% using haemaccel or sodium chloride (NaCl). Each sample was tested with and without addition of 90 µg/kg of rVlla. Global haemostasis was assessed using thrombelastography (TEG). Parameters measured were: Time to initial fibrin formation (R), Time to 20 mm clot amplitude (K), Rapidity of fibrin build up and cross-linking (a), Maximum clot amplitude (MA), Time to MA (TMA), and Clot firmness (G). Haemostatic testing was terminated when maximum clot amplitude was reached and samples were then examined by electron microscopy.

Results

One hundred samples analysed. Twenty samples for each of five fluid groups. Each sample tested ± rVlla. Without addition of rVlla, an intrinsic effect with worsening of TEG parameters was noted with increasing dilution in the fluid groups. Addition of rVlla produced significant improvement in TEG parameters: P < 0.05 R, K, a, TMA for all fluid groups; P < 0.05 MA and G for 80% Haem, 50% and 80% NaCl. Moreover with increasing dilution there was a greater relative improvement in TEG parameters in rVlla added groups. When fluid groups were compared to each other to see if the beneficial effects of rVlla produced a difference, no significant difference was found between groups except for 50% haemaccel compared with 50% NaCl where K, MA and G were significantly better (P < 0.05) in the haemaccel group. Electron microscopy demonstrated a reversal of both the dilution and intrinsic inhibitory effects, with increased fibrin deposition and meshwork with greater cross-linking following addition of rVlla.

Conclusion

In this in vitro model of large volume fluid replacement with associated haemodilution, the addition of rVlla appeared to improve markers of global haemostasis and caused increased fibrin deposition with a tighter resultant meshwork on electron microscopy. Further work is required to assess the potential value of rVlla as a universal haemostatic agent in trauma settings involving large volume fluid resuscitation.