The ROTEM system is a point‑of‑care device used to help detect, manage and monitor haemostasis associated with high blood loss. The device uses thromboelastometry, a viscoelastometric method, to test for haemostasis in whole blood including the initiation of clotting, platelet count, fibrinogen and fibrinolysis.
During and after surgery, ROTEM is intended to be used to help identify the probable cause of bleeding and to help the clinician determine whether bleeding is a result of a coagulopathy or a surgical bleed.
ROTEM uses a combination of 5 assays (INTEM, EXTEM, FIBTEM, APTEM and HEPTEM) to characterise the coagulation profile of a sample of whole blood. Initial testing using the INTEM and EXTEM assays can indicate whether there is a clotting factor deficiency. If the initial test results appear normal, this indicates that surgical bleeding rather than coagulopathy is present. Additional assays include FIBTEM, which can indicate a fibrinogen deficiency; APTEM, which can indicate hyperfibrinolysis; and HEPTEM, which can indicate whether coagulopathy is due to the presence of residual heparin. Platelet function analysers may be used in conjunction with ROTEM to test platelet function when patients are taking antiplatelet drugs such as aspirin or clopidogrel.
The ROTEM analysis is generally done with citrated whole blood near the patient during the surgery, although the device may be positioned in the laboratory. A blood sample is taken from the patient and placed in a cuvette. A cylindrical pin is then immersed and oscillated by a spring to the right and the left. The movement of the pin is unrestricted as long as the blood is liquid but encounters resistance as the blood begins to clot. As the clot becomes firmer, it increasingly restricts the rotation of the pin.
The manufacturer claims that a complete set of results from ROTEM will determine the presence and type of coagulopathy, indicate a need for fibrinogen or platelet administration, and facilitate the monitoring of heparin and protamine. ROTEM also provides information on the qualitative aspect of clot formation by looking at the elasticity of a clot to determine how well certain parameters of the sample are forming.
Initial results are available within 5 to 10 minutes and full qualitative results are available in 20 minutes. Some results, such as for the diagnosis of fibrinolysis, may take more than 20 minutes.
The thromboelastography (TEG) system is a device that is designed to detect, monitor and analyse clot formation in a blood sample. Like ROTEM, the TEG system is based on the viscoelastometric method but its mechanical system is slightly different. Whole blood is pipetted into a warmed disposable cup. A disposable pin is then lowered into the fluid blood. The cup is rotated every 10 seconds and the pin is initially stationary. As the first fibrin strands are formed, the pin becomes tethered to the cup and starts to follow its motion. When maximum clot firmness is achieved, the cup and pin move in unison. The motion of the pin is detected by a torsion wire linked to a transducer; and a mechanical‑electrical signal is relayed through a computer interface where real‑time analysis is displayed.
The TEG assays include:
a kaolin‑activated test, which assesses clot formation, fibrin polymerisation and fibrinolysis
a kaolin with heparinase test, which assesses clot formation in people who have been given heparin
a functional fibrinogen assay, which measures the fibrinogen impact on the clot strength (made possible by the suppression of the platelet contribution factor)
platelet mapping that assesses platelet function and monitors antiplatelet therapy
a rapid TEG, which provides a more rapid measurement of the clot strength than a standard kaolin assay and is used mainly in emergency situations such as trauma.
Like ROTEM, TEG measures and graphically displays the changes in viscoelasticity at all stages of the developing and resolving clot. These include the time until initial fibrin formation, the kinetics of fibrin formation and clot development, the ultimate strength and stability of the fibrin clot, and fibrinolysis.
The Sonoclot system is also a viscoelastometric device used for measuring coagulation and platelet function. It provides information on haemostasis including coagulation, fibrin gel formation, clot retraction (platelet function) and fibrinolysis.
The Sonoclot test is performed by placing whole blood into a pre‑warmed cuvette in which a vertically vibrating probe is suspended. As the blood clots, increased viscosity causes changes in the mechanical impedance that is exerted on the probe. Clot formation is displayed in real time on a computer which is connected to the device via USB. The Sonoclot device generates both a qualitative graph known as the Sonoclot signature, and quantitative results on the clot formation time (activated clotting time and the rate of fibrin polymerisation or clot rate). These help to identify coagulopathies including platelet dysfunction, factor deficiencies, anticoagulant effect, hypercoagulable tendencies and hyperfibrinolysis.
The Sonoclot assays include:
SonACT, which measures large‑dose heparin management without aprotonin
kACT, which measures large‑dose heparin management with or without aprotonin
aiACT, which measures large‑dose heparin management with aprotonin
gbACT+, which measures overall coagulation and assesses platelet function in non‑heparinised patients
H‑gbACT+, which measures overall coagulation and assesses platelet function in the presence of heparin.
The comparator for this assessment is a combination of clinical judgement and standard laboratory tests. Standard laboratory coagulation analyses include prothrombin time which is also used to measure prothrombin ratio and international normalised ratio, activated partial thromboplastin time, activated clotting/coagulation time, platelet count and plasma fibrinogen concentration.
Standard laboratory tests were not developed to predict bleeding or guide coagulation management. They are able to identify when blood is not clotting properly, but they are not able to identify what part of the clotting process is disrupted. Standard laboratory tests are performed on platelet‑poor plasma (blood plasma with low number of platelets) and therefore do not reflect the true physiological clotting process. Moreover, they are performed at 37oC, which limits the detection of coagulopathies induced by hypothermia. Standard laboratory tests are unable to provide information on clot formation over time or on fibrinolysis, and so cannot detect hyperfibrinolysis.
After a blood sample is taken, standard laboratory tests usually take between 40 and 90 minutes to give a result. This turnaround time may be too long for the results to reflect the current coagulation status of the patient.