A functional clotting assay to monitor the hirudin dosage.

Hirudin, a direct thrombin inhibitor, has potential advantages over indirect thrombin inhibitors and is increasingly used in clinical settings. There are, however, large variations in individual responses to this drug and no recognized clinical laboratory tests used to monitor its anticoagulant effects. We evaluated the use of the thromboelastograph, a common clinical coagulation instrument, to monitor the effects of hirudin in vitro. We developed a novel, whole blood clotting assay that utilizes the tissue factor stimulating properties of mercuric ion to measure the anticoagulant potential of therapeutic doses of hirudin. At doses equivalent to those found in the therapeutic range, the thromboelastograph was capable of showing significant changes when compared with control and different concentrations of hirudin (P < 0.05). A linear relationship was observed between increasing concentrations of recombinant hirudin and clotting times. In conclusion, the use of this test system warrants further investigation for monitoring hirudin.

Pravastatin potentiates the anticoagulant effects of low molecular weight heparin.

INTRODUCTION: Statins have been shown in randomized trials to reduce coronary events independent of baseline LDL-C level. In the case of pravastatin sodium (PS), there is conflicting evidence as to what is the actual mechanism of its non-lipid lowering beneficial effects. Because pravastatin has been found to prolong the clotting time in vitro, we conducted a study to determine if pravastatin plus low molecular weight heparin (LMWH) would result in a synergistic effect on the in vitro clotting time, thus supporting the hypothesis that pravastatin exerts antithrombotic effects through reduction of fibrin formation. MATERIALS AND METHODS: Aliquots of PS were combined with dalteparin, a LMWH, in 500 microl of human whole blood. The clotting time in seconds was analyzed on a Sonoclot Coagulation Analyzer, a miniviscometer that is sensitive to early fibrin generation. RESULTS: PS and LMWH, each resulted in a significant prolongation of the clotting time compared with control. The combination of PS and LMWH resulted in a significantly prolonged clotting time compared with either given alone. All values were significantly different from each other (p<0.05). Our results showed that the combination of PS and a LMWH prolongs the clotting time to a significantly greater degree when compared to either administered alone. CONCLUSIONS: The synergistic effect of PS and LMWH on prolongation of the clotting time suggests that PS exerts its effect by inhibition of the coagulation cascade and fibrin formation.

Influence of storage on red blood cell rheological properties.

BACKGROUND: It is known that the age of transfused blood is a risk factor for the development of multiple organ failure in surgical patients. However, the character of hemorrheological changes in stored blood as well as the time when they appear remains disputable. We assumed that blood storage was accompanied by a progressive decrease of RBC deformability and rheological disorders. The degree of rheological disturbances should be directly proportional to the number of RBC with altered geometry. MATERIALS AND METHODS: Nine packages of RBC kept in adenine saline solution were examined from the 5th to the 42nd day of storage. RBC deformability index (DI) was determined by micropore filtration technique. RBC shape was estimated by means of scanning electron microscopy. Blood clotting time was measured by Sonoclot coagulation analyzer. RESULTS: Significant alterations of RBC shape started at the second week of storage and progressed during the rest of the storage period. RBC shape changes were accompanied by progressive decrease in DI and increase in hemolysis and acidosis. The correlation index between the percentage of abnormally shaped RBC and DI was -0.81 (P = 0.0258). Blood clotting progressively decreased after 2 weeks of storage, probably due to the exhaustion of some procoagulant plasma factors. CONCLUSIONS: Serious hemorrheological disorders, including the decrease in RBC deformability secondary to shape abnormalities, acidosis, and the decrease of blood clotting, start already at the second week of storage and progress up to the end of the storage period. Transfusion of packed RBC older than 7 days may contribute to hemorrheological disorders in critically ill patients.