Anesthesia & Analgesia:
Thromboelastography: The Next Step
Samama, Charles Marc MD, PhD
Department of Anesthesia and Intensive Care, Hôpital Avicenne, Bobigny, France
December 5, 2000.
Address correspondence and reprint requests to Charles Marc Samama, MD, PhD, Département d’Anesthésie-Réanimation, Hôpital Avicenne, 125 route de Stalingrad, 93009 Bobigny Cedex, France. Address e-mail to email@example.com.
Thromboelastography is now widely used as a near-site hemostasis monitor (1–6). Because it is computerized, thromboelastography is easy to use and the results can be recorded and stored. It is considered a very helpful coagulation tool by a growing number of physicians, among whom anesthesiologists play a leading role. Thromboelastographs can be found in many operating theaters, helping physicians monitor intraoperative bleeding and choose the most adequate blood transfusion products to achieve an optimal biological hemostasis. The development of nomograms by using thromboelastography variables has led to a substantial decrease in blood product transfusion in cardiac surgery, as compared with conventional tests (5–7). It is amazing to note how thromboelastography studies cover the entire field of hemostasis in the perioperative setting, from “platelet function” to fibrinolysis (3,8). Furthermore, thromboelastography is the leading point-of-care monitor for hypercoagulability (9,10). It has become so popular that many groups consider thromboelastography a self-sufficient coagulation test.
However, thromboelastography is not a conventional hemostasis test. First, as it uses whole blood samples, it can be defined as a global nonspecific test, as compared with analytical coagulation tests (activated partial thromboplastin time, prothrombin time (PT), fibrinogen) which are performed with platelet-poor plasma. Second, it has never been included by hemostasis laboratories in quality-assurance procedures. Third, it has never met the demands of large, randomized, highly powered comparative biological studies. Thus, it remains a second-level test and therefore does not reach the standards acceptable of most academic hemostasis societies. These major drawbacks have to be taken into account when thromboelastography or modified-thromboelastography is proposed as the only available hemostasis tests in a study. Thromboelastography is not validated, as far as international standards are concerned, and it has never been standardized. Most of the studies evidencing the benefit of thromboelastography measurements as compared with conventional hemostasis tests have mainly been performed by anesthesiologists or surgeons (11–14). Formerly used in hematology laboratories during the 1950s and 1960s when no analytical coagulation tests were available (15), thromboelastography has been progressively replaced by coagulation tests (activated partial thromboplastin time, prothrombin time, fibrinogen), platelet count, and more sophisticated assays. Yet, very few hematologists would accept reconsidering this analytical way of thinking and admit the potential advantages of thromboelastography in the operating room, even if, for instance, they know they cannot provide an assessment of the coagulation status within 30 minutes.
In this issue of Anesthesia & Analgesia, two articles emphasize the benefit of two different modified-thromboelastography monitoring in assessing intra- and postoperative hemostasis. The study by Haisch et al. (13) offers the opportunity to compare moderate doses of a new hydroxyethylstarch (HES) solution (mean molecular weight of 130,000 Daltons; degree of substitution of 0.4 (HES 130/0.4)) with a gelatin in patients undergoing major abdominal surgery. This reassuring study does not show any difference in allogeneic blood/blood products transfusion and coagulation variables including thromboelastography. In the study by Mahla et al. (14), modified-thromboelastography provides valuable information on the respective role of platelets and procoagulatory proteins on clot strength and postoperative hypercoagulability. This study gives an interesting assessment of the discrepancy between standard coagulation monitoring and thromboelastography. Both of these two studies are well performed, provide useful data for the daily clinical practice, and could have an impact on patient care. Unfortunately, from an hematologic point of view, adequate hemostasis tests are lacking in both articles. HESs are responsible for a decrease in factor VIII and von Willebrand factor levels (von Willebrand antigen, vWF ristocetin cofactor activity) (11,16–20). These variables are not considered in the study by Haisch et al. (13), who state that vWF measurement has little importance. They would have been more convincing had the mea-surements been available.
Postoperative hypercoagulability exploration requires the use of specific hemostasis tools as platelet aggregation variables, platelet activation measurements (flow cytometry variables), thrombin-antithrombin complexes, prothrombin fragment 1 + 2, type 1 plasminogen activator inhibitor, or plasmin-antiplasmin complexes (21). None of these measurements is performed in the Mahla et al. (14) study. Even a modified-thromboelastography, mainly described in anesthetic journals (22,23), should not be used alone to express a hypercoagulable state.
Indeed, the recent and important investment of anesthesiologists in the field of hemostasis is very exciting. Therefore, if thromboelastography is now to be considered a promising hemostasis tool, its global management must be improved (24). Thromboelastography deserves a new evaluation leading to a final validation or it will remain an expensive, nonvalidated point-of-care monitor. The next step is to develop an extended collaboration with hemostasis research teams and to increase the number of collaborative studies (5,8,9). Until now, very few hematology journals have been considered by anesthetic authors for publishing thromboelastography trials. Most of these studies are published in anesthetic journals. We need to build new collaborative studies to allow this popular technique to gain international scientific agreement and final worldwide recognition.
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