Citrate Anticoagulant Artificially Masks the Hemostatic Effect of Recombinant Factor VIIA in Dilutional Coagulopathy.

Introduction: Dilutional coagulopathy may develop in massively bleeding patients who are substituted with synthetic colloid plasma expanders. A series of recent studies have demonstrated that synthetic colloids may induce abnormal function of fibrinogen by compromising fibrin polymerization and substitution with a fibrinogen concentrate appeared to reverse this coagulopathy and arrest traumatic bleeds. Clinical experiences, several case reports as well as a randomised trial point toward a beneficial effect of rFVIIa in control of massive bleeding associated with hemodilution caused by excessive volume substitution. Our haemostasis center recently put forward that rFVIIa, in vitro, was unsuccessful in correction of dilutional coagulopathy induced by HES 130/04. In addition, other investigations utilising a rabbit model have indicated that colloid hemodilution may attenuate the haemostatic potential of rFVIIa. For half a Century laboratory coagulation tests have been carried out using re-calcified citrated blood. However, recent experimental work has revealed that citrate dependent calcium chelation significantly changes the dynamic course of thrombin generation, suspectedly due to interference with the enzymatic properties of coagulation factors. In addition it has been documented that citrate and calcium chelation interferes with the metabolism in platelets. In the present study we aimed at investigating the haemostatic effect of rFVIIa in a laboratory whole blood model of colloid hemodilution using citrate as well as iso-citrate stabilized blood comparing to native whole blood and whole blood stabilized with corn trypsin inhibitor (CTI) that specifically blocks factor XIIa.

Materials and Methods: Following informed consent 11 healthy male volunteers with a mean age of 30 years (range 26–38 years) delivered blood for study. Dynamic whole blood coagulation profiles were recorded using thrombelastography activated with minute amounts of tissue factor in a model of ex vivo hemodilution with HES 130/0.4 in a prospective approach. Analyses were evaluated at 30% dilution level, and following ex vivo addition of rFVIIa to whole blood collected into tubes containing citrate, iso-citrate, CTI, or no stabilizer.

Results: Hemodilution with HES 130/0.4 induces a coagulopathy characterized by a reduced maximum rate of clot formation and a pronounced reduction in the final clot firmness. With all test mediums investigated, rFVIIa significantly shortened the clot initiation phase. In cases of native whole blood and CTI stabilized whole blood rFVIIa shortens the clotting time but also demonstrated an acceleration of the maximum velocity of clot formation.

Conclusion: When citrate or iso-citrate is used as anticoagulants in thromboelastographic clotting assays, these anticoagulants may artificially mask the haemostatic effect of rFVIIa in colloid hemodilution blood. The effect in vitro of rFVIIa in citrated blood samples may significantly underestimate the haemostatic potential of rFVIIa. In cases where the hemostatic potential of rFVIIa is tested in vitro a potentially efficacious rescue treatment may be delayed or excluded.