Sonoclot Signature Analysis in Patients with Liver Disease and Its Correlation with Conventional Coagulation Studies

Perioperative monitoring of blood coagulation is critical to better understand causes of hemorrhage, to guide hemostatic therapies, and to predict the risk of bleeding during the consecutive anesthetic or surgical procedures. Point-of-care (POC) coagulation monitoring devices assessing the viscoelastic properties of whole blood, i.e., thrombelastography, rotation thrombelastometry, and Sonoclot analysis, may overcome several limitations of routine coagulation tests in the perioperative setting. The advantage of these techniques is that they have the potential to measure the clotting process, starting with fibrin formation and continue through to clot retraction and fibrinolysis at the bedside, with minimal delays. Furthermore, the coagulation status of patients is assessed in whole blood, allowing the plasmatic coagulation system to interact with platelets and red cells, and thereby providing useful additional information on platelet function. Viscoelastic POC coagulation devices are increasingly being used in clinical practice, especially in the management of patients undergoing cardiac and liver surgery. Furthermore, they provide useful information in a large variety of clinical scenarios, e.g., massive hemorrhage, assessment of hypo- and hypercoagulable states, guiding pro- and anticoagulant therapies, and in diagnosing of a surgical bleeding. A surgical etiology of bleeding has to be considered when viscoelastic test results are normal. In summary, viscoelastic POC coagulation devices may help identify the cause of bleeding and guide pro- and anticoagulant therapies. To ensure optimal accuracy and performance, standardized procedures for blood sampling and handling, strict quality controls and trained personnel are required.

The literature was systematically reviewed to determine whether a prolonged prothrombin time or elevated international normalized ratio predicts bleeding during invasive diagnostic procedures. MEDLINE and CENTRAL were searched through August 2004, with no language restriction, and reference lists were reviewed. For inclusion, articles must have reported on bleeding in more than five patients with abnormal test results undergoing diagnostic procedures. One trial and 24 observational studies were included. In 2 studies of bronchoscopy, the bleeding rates were similar among those with normal and abnormal tests, with wide confidence intervals (CIs) around the risk differences. During central vein cannulation (3 studies), bleeding rates among those with abnormal tests was unlikely to exceed 2.3 percent. The largest of 3 studies of arteriography found equivalent bleeding rates in patients with and without abnormal tests (risk difference, 0%; 95% CI, -3% to 2%). In the 3 studies of liver biopsy with plugging, bleeding rates were 0, 4, and 5 percent with the upper bounds of the CI as high as 17 percent. In the largest study of transjugular biopsy, the bleeding rate was 1.5 percent (95% CI, 0.3%-4%) in patients with abnormal tests. The highest bleeding rate in the 3 studies of percutaneous liver biopsy was 5.3 percent (95% CI, 1%-13%), similar to the rate in patients with normal test results. There is insufficient evidence to conclude that abnormal test results predict bleeding. Randomized controlled trials should be performed to provide stronger evidence for clinical decision making regarding preprocedure transfusion.

By the use of a fluorogenic thrombin substrate and continuous calibration of each individual sample, it is now possible to obtain a thrombin generation (TG) curve (or thrombogram) in plasma, with or without platelets, in an easy routine procedure at high throughput and with an acceptable experimental error (<5%). Evidence is growing that the parameters of the thrombogram, and notably the area under the curve (endogenous thrombin potential, ETP), are useful in assessing bleeding- or thrombotic risk and its modification by antithrombotic- or haemostatic treatment. Available data strongly suggest that conditions (congenital, acquired, drug-induced) that increase TG all cause a thrombotic tendency and that conditions that decrease TG prevent thrombosis but, beyond a limit, cause bleeding. Diminution of TG is a common denominator of all antithrombotic treatment, including anti-platelet drugs. The thrombogram can also be used as a tool in the search for new antithrombotics and reflects the haemorrhagic or thrombotic side effects of other drugs (e.g. oral contraceptives). The thrombogram thus is a promising new approach to clinical management of bleeding and thrombotic disease as well as a tool in drug research and epidemiology. Our experience at this moment is insufficient, however, to already clearly define its limits.