Joachim F. Schenk

No Coagulation Disorders under High-Dose Volume Therapy with Low-Molecular-Weight Hydroxyethyl Starch

Hydroxyethyl starch (HES) is often used for volume therapy. Since bleeding complications have been reported repeatedly, a strict dose limitation of a maximum of 1,500 ml 6% solution per day is recommended. However, many indications require higher dosages. Bleeding complications are known to be caused by an acquired von Willebrand syndrome. It has been shown that the accumulation of large molecules and their impairment in the coagulation system can be avoided by using HES preparations with a low in vivo molecular weight. However, the effects of a high-dose therapy have not been studied yet. We have investigated, how a 4-day high-dose therapy, using 3,000 ml 6% HES 70/0.5 on the 1st day and 1,500 ml on days 2-4, affects the coagulation system and hemorheological parameters of acute stroke patients. Thromboplastin time, activated partial thromboplastin time and thrombin time showed no significant changes, except for a slight, clinically irrelevant change due to dilution. The subunits of von Willebrand factor VIII showed no significant change. Hematocrit decreased from 42.3 +/- 4.6 to 37.4 +/- 3.9% (p < 0.05) after day 1, reaching 35.3 +/- 4.2% (p < 0.01) at the end of the therapy, demonstrating a substantial volume effect. Plasma viscosity and erythrocyte aggregation decreased slightly, however not significantly. Our study shows that even a high-dose therapy with 6% HES 70/0.5 has no influence on the coagulation system.

Platelet activation and its role in thrombin generation in platelet-induced thrombin generation time

Platelet-induced thrombin generation time (PITT) is a newly developed global coagulation assay in which a small amount of partially anticoagulated platelet-rich plasma (PRP) is rotated in a disc-shaped cuvette within the light beam of a photometer. The time intervals from onset of rotation until aggregation and coagulation of the sample are registered. The aim of our study was to compare platelet activation with generation of thrombin during rotation of PRP in PITT system. Aliquots of PRP were taken before, 1, 3, and 8 min after the onset of rotation as well as at the beginning of aggregation and shortly before coagulation. Thrombin activity was measured with chromogenic substrate S-2238. We have also measured the level of generated prothrombin activation fragment 1+2 (F1+2), which reflects the concentration of liberated thrombin. Platelet activation was assayed by means of platelet factor 4 (PF4) and beta-thromboglobulin (beta-TG) concentration and registration of the aggregation. The concentrations of the F1+2, PF4, beta-TG increased very slowly from the beginning of the test until aggregation occurred. From the start of aggregation, the levels of F1+2 rose rapidly. In contrast to the F1+2 measurements, thrombin activity has not been detected from onset of rotation until the end of the test. Only trace thrombin activity was detectable just after the plasma sample had been clotted in the cuvette. Our results demonstrate that there exists a close relationship between platelet activation and thrombin generation. Viable platelets, which adhered to the cuvette walls, form an active template on which thrombin can be generated from prothrombin.

On the prophylactic and therapeutic use of danaparoid sodium (Orgaran®) in patients with heparin-induced thrombocytopenia

Heparin-induced thrombocytopenia (HIT) is a rare but dangerous complication of heparin prophylaxis or treatment. The present laboratory tests to measure heparin-associated antibodies are not specific. The diagnosis of HIT mainly depends on the decrease in platelet count and on clinical symptoms. To evaluate clinical outcome, bleeding complications and platelet counts were evaluated in 45 patients with HIT type II (HIT II) treated prophylactically (subcutaneous injections) or therapeutically (intravenous infusion) with danaparoid. Group I included 24 patients with HIT II without thromboembolic complications who received danaparoid twice daily subcutaneously (10 IU/kg) for a mean of 16 days. Group II included 21 patients with thromboembolic complications. They were treated with intravenous danaparoid (2.6 IU/kg/h ± 1.1) for a mean of 17 days. During subcutaneous prophylaxis, mean anti-Xa levels of 0.2 U/mL and during intravenous treatment, mean anti-Xa levels of 0.4 U/mL were reached. No deaths, amputations, or serious bleeding complications occurred, and no new thromboses were observed in both patient groups.Treatment with danaparoid led to a fast normalization of the platelet counts. This normalization occurred earlier and the concentration of platelets was higher in patients treated with intravenous doses. Danaparoid with subsequent vitamin K-antagonist treatment effectively prevents thromboembolic complications in patients with HIT.

State-of-the-Art Review : Heparin-Induced Thrombocytopenia: A Critical Risk/Benefit Analysis of Patients in Intensive Care Treated With R-Hirudin

Patients in intensive care may be at high risk of in vivo platelet activation because comorbid conditions, such as infections, septicemia, shock, disseminated intravascular co agulation, and cancer represent procoagulant states. Hyperre activity of platelets with or without a decline of cell count may result in thromboembolic complications potentially associated with the phenomenon of heparin-induced thrombocytopenia. We analyzed the data of 10 patients highly suspected of having heparin-induced thrombocytopenia during their intensive care treatment of 29 plus or minus 22 days. In seven patients, throm bocytopenia coincided with thromboembolic complications. Six patients had additionally undergone fibrinolytic therapy before starting activated partial thromboplastin time-adapted alternative anticoagulation with r-hirudin. In three patients, the platelet count decreased without a clinical manifestation. of heparin-induced thrombocytopenia. R-Hirudin treatment moni tored by activated partial thromboplastin time and prothrombin time (PT) was effective and safe. The target value for activated partial thromboplastin time was a twofold prolongation. In four of five patients with deep venous thrombosis, a partial recana lization of the lower extremity could be achieved. Three pa tients with pulmonary embolism associated with deep venous thrombosis in two cases and in one additional case with an acute myocardial infarction did clinically profit from fibrino lysis with recombinant tissue plasminogen activator (rtPA) and r-hirudin treatment. Two lethal events probably caused by the underlying multimorbidity could not be prevented. No recur rence of thrombosis occurred, and there were no severe bleed ing complications attributed to r-hirudin treatment. Platelet counts were significantly reduced on day 9.4 plus or minus 6.4 of heparin administration in all cases (>50% decrease related to the initial values) from 224,000 plus or minus 126,000/μL to 96,000 plus or minus 61,000/μL, and increased during r- hirudin treatment to mean values of 224,000 plus or minus 126,000/μL. The heparin-induced platelet activation assay (HIPAA) assay was positive in 8/10 cases, whereas the PF4 enzyme-linked immunosorbent assay showed a positive result in four of eight analyzed cases. In four cases, the assays were concordantly positive. The PF4 enzyme-linked immunosorbent assay was not performed in two cases.

TFPI Release by GAGs and Its Role in Their Mechanism of Action

Tissue factor pathway inhibitor (TFPI) formerly named Extrinsic Pathway Inhibitor (EPI) or Lipoprotein Associated Coagulation Inhibitor (LACI) is a Kunitz-type protein with three inhibitory domains1. The first domain binds to the tissue factor/factor VII a — complex, while the second one has been identified as the factor Xa binding site. The third domain is probably involved in the association of TFPI with plasma lipoproteins and heparins1,2. TFPI inhibitory activity as well as antigen level in plasma can be measured but there are large discrepances between TFPI results from the functional and immunologic assays. It has been recently postulated that only the free form of TFPI is biologically active3. TFPI is synthesized in endothelial cells and megakariocytes4,5. In normal individuals there is a quite broad range of TFPI activities and antigen levels ranging from 50 to 170 ng/ml6,7,8. The biggest TFPI-pool is bound to the main site of its synthesis -endothelium. About 90% of blood TFPI is associated with lipoproteins9,10. The major part with LDL, less with HDL. About 5% plasma TFPI remains in a free form. TFPI has also been found in platelets — about 8% of the whole blood TFPI5 (Fig.1). Tissue factor pathway inhibitor has a double, two step inhibitory effect. It inhibits the active factor X and in a complex with this factor TFPI binds to the tissue factor/factor VIIa complex inhibiting its enzymatic activity11,12 (Fig.2).