Rotational Thromboelastometry. Rotational Thromboelastometry (ROTEM) is another global coagulation assay which rapidly assesses the dynamics of coagulation and quantitatively measures clot formation. It has a point-of-care application, delivering a representation of the overall platelet function and activity of the coagulation proteases and inhibitors, within 30min. ROTEM consists of four stationary xxxxxxxx with disposable cuvettes in which whole blood is placed and different reagents added. The software gives a graphic representation of clot formation and lysis, via detection of the increasing impedance of a pin rotating in whole blood as a clot forms. (Xxxxxxxxxx, 2005) ROTEM detects changes in all the phases of coagulation and fibrinolysis and measures the firmness of the clot. ROTEM is highly dependent on platelet function, fibrinogen content and integrity, fibrin polymerisation, cross linking and fibrinolysis, as well as thrombin generation and activity. (Xxxxx, 2009) Clotting time (CT) is the time from the start, when blood is mixed with the activator reagent until the waveform (representing the clot formation) reaches 2 mm above baseline. Clot formation time (CFT) is the time from 2 mm above baseline to 20 mm above baseline (clot of firmness of 20 mm). Maximum clot firmness (MCF) is the maximum stabilisation of the clot by polymerised fibrin, thrombocytes and FXIII, as is represented by the maximum amplitude of the waveform. Maximum lysis at specific time points after MCF is the reduction of clot firmness. The alpha angle is the tangent at 2 mm amplitude. (figure 4) Recent reports have discovered inconsistencies in ROTEM results dependent on sample stability, patient age (Sankarankutty et al., 2012) and gender (Xxxxxx et al., 2000). Additionally, assays have not been standardised between centres. FIGURE 5 ROTEM TRACE AND PARAMETERS, FOR A HEALTHY VOLUNTEER SAMPLE, RUNNING FOR 2 HOURS
Rotational Thromboelastometry. Rotational Thromboelastometry (ROTEM®) was performed by the principle researcher within 4 h of venepuncture. The citrated vacutainer containing whole blood together with the ROTEM reagents were placed onto the ROTEM plate and warmed for five minutes to 37˚C. The extrinsic coagulation system was measured using r-ex-TEM reagents, and the intrinsic coagulation system, using r-in-TEM reagents. R-ex-TEM contains an optimised concentration of tissue factor as an activator, phospholipids and heparin inhibitor. In-TEM contains partial thromboplastin phospholipid made of rabbit brain and ellagic acid as activators. Star-TEM is added to re- calcify the reagents and they are mixed with the sample whole blood to commence the coagulation process. A pin is suspended within the cup, which is connected to an optical detector system. The pin is oscillated relative to the cup, which is stationary, and the transmitted impedance of the rotation is detected and a computerised trace is generated. This study used the four xxxxxxxx for two Extem and two Intem reagents, thus, two samples were run on each tray. Extem assess Factors VII, X, V, II, I, platelets and fibrinolysis. Intem measures Factors XII, XI, IX, VII, X, V, II, I, platelets and fibrinolysis. The ROTEM® analyser continuously and automatically monitors the coagulation process, providing a graphical trace (figure 4) and individual values. Controls using ROTROL N, QCexN and QCinN were preformed once a week to calibrate the assay.
