Review: The Perioperative Use of Thromboelastography for Liver Transplant Patients.

Thromboelastography (TEG) is a viscoelastic test that allows rapid evaluation of clot formation and fibrinolysis from a sample of whole blood. TEG is increasingly utilized to guide blood product resuscitation in surgical patients and transfusions for liver transplant patients. Patients with severe liver failure have significant derangement of their clotting function due to impaired production of procoagulant and anticoagulant factors. Traditional coagulation studies are limited by the short time needed for the result and provide little information about the dynamics and strength of clot formation. In addition, traditional coagulation studies do not correlate well with bleeding episodes and may lead to over-transfusion of various blood products. Evidence is less robust regarding the use of TEG for transfusion management decisions in severe liver failure patients awaiting, undergoing, or immediately after liver transplant surgery. However, the available evidence suggests that systematic implementation of TEG rather than traditional coagulation studies results in the administration of fewer blood products without increased mortality or complications. The purpose of this study is to review the literature regarding the use of TEG in liver failure patients prior to liver transplant, intraoperatively, and postoperatively. Additional high-quality randomized controlled studies should be performed to evaluate the use of TEG to guide transfusion decisions, particularly in the postoperative period following liver transplantation.

Epidemiologic features of von Willebrand's disease in Doberman pinschers, Scottish terriers, and Shetland sheepdogs: 260 cases (1984-1988)

During a study period from 1985 through 1988, plasma von Willebrand's factor antigen (vWF:Ag) concentration was measured as a marker for prevalence of the von Willebrand's disease (vWD) trait in Doberman Pinschers (doberman, n = 5,554), Scottish Terriers (scottie, n = 1,363), and Shetland Sheepdogs (sheltie, n = 4,279). Significant increase in prevalence of the trait was seen in scotties and shelties during this period. In 1988, 73% of dobermans, 30% of scotties, and 28% of shelties tested had abnormal vWF:Ag concentration (less than 50% vWF:Ag). We found significant differences between breeds with respect to age and vWF:Ag concentration of clinically affected dogs at time of diagnosis. The affected dobermans were older (doberman mean age, 4.6 years; scottie mean age, 1.7 years; sheltie mean age, 1.9 years) and had higher concentration of plasma vWF:Ag (doberman mean vWF:Ag, 15%; scottie mean vWF:Ag, 0%; sheltie mean vWF:Ag, 8%). Bleeding in affected dogs of all 3 breeds was observed predominantly from mucosal surfaces and from cutaneous sites of surgery or trauma. The most common site of mucosal bleeding in scotties and shelties was oral or nasal cavity, and in dobermans was the urogenital tract. Differences in clinical manifestations of vWD in purebred dogs may reflect heterogeneous defects within the vWF gene, causing a variety of abnormalities in production, structure, and function of vWF protein. Analogous to vWD in human beings, acquired deficiencies of vWF may also contribute to the clinical variability of vWD in dogs.

Defective platelet-fibrinogen interaction in hereditary canine thrombopathia.

A unique, intrinsic, hereditary canine platelet disorder attributable to abnormal fibrinogen receptor availability is described. Thrombopathic platelets from 13 severely affected basset hounds failed to aggregate in response to all agonists tested except thrombin. Normal platelet interaction with the various stimuli was inferred on the basis of their ability to elicit unimpaired shape change in thrombopathic platelets. No quantitative differences in major platelet membrane glycoproteins, intraplatelet fibrinogen, adenine nucleotides, or serotonin uptake were detected. Dense granule secretion was impaired. The ultrastructural appearance of thrombopathic platelets was normal. Fibrinogen-platelet interaction was evaluated by reacting platelet-rich plasma (PRP) with fibrinogen coupled to polymeric acrylonitrile beads and scoring the extent of stimulus-induced agglutination. The aggregatory responses of normal and thrombopathic platelets were closely correlated with fibrinogen receptor availability. In contrast to human platelets, epinephrine-stimulated canine platelets did not interact with immobilized fibrinogen, and arachidonate generally induced only weak agglutination. Thrombopathic platelets agglutinated fibrinogen beads at reduced rates when stimulated with physiologic doses of thrombin and high-dose calcium ionophore, A23187. Our data suggest that thrombin-mediated induction of canine platelet fibrinogen receptors may proceed by pathway(s) alternate to those shared by other platelet agonists, and/or that secreted granule constituents may act synergistically with thrombin to overcome inhibition of signal-response-coupled reactions mediating the interaction of fibrinogen with its receptor. This congenital platelet defect provides further evidence, in a species other than human, for the pivotal role of fibrinogen receptor induction in platelet aggregation.

Characterization of the fawn-hooded rat as a model for hemostatic studies.

A large colony of fawn-hooded (FH) rats, comprising five original families and six generations of their progeny, was developed for genetic and comparative studies of their bleeding tendency. The characteristics of the bleeding diathesis in these rats are similar to those originally reported in related rats by Tschopp and Zucker. FH rats have normal clot retraction, ADP-induced platelet aggregation and platelet ADP; variable aggregation with collagen; minimal aggregation with adrenaline and cobra venom factor; and reduced platelet ATP, ATP/ADP ratio, serotonin content and -14C-serotonin release. In comparison to age- and sex-matched Wistar rats, FH rats have significantly prolonged partial thromboplastin time, shortened Russell's viper venom time and increased factor X and XI levels. Other coagulation screening tests and specific assays for fibrinogen, plasminogen and factors VII, VIII and IX were normal. Some age- and sex-related differences in coagulation and other parameters were observed within each rat strain. Plasma proteins, glycoproteins and ceruloplasmin (copper oxidase activity) showed no abnormalities, nor did initial studies of immunoglobulins and complement. However, FH rats have significantly lower glucose and higher cholesterol levels than comparable Wistar rats.