title: Revisiting Hartert's 1962 Calculation of the Physical Constants of Thrombelastography.
abstract: Thrombelastography (TEG)/thromboelastometry (ROTEM) devices measure viscoelastic clot strength as clot amplitude (A). Transformation of clot amplitude into clot elasticity (E with TEG; CE with ROTEM) is sometimes necessary (eg, when calculating platelet component of the clot). With TEG, clot amplitude is commonly transformed into shear modulus (G; expressed in Pa or dyn/cm2) as follows: G = (5000 × A)/(100 - A). Use of the constant "5000" stems from Hartert's 50-year-old calculation of G for a normal blood clot. We question the value of calculating G as follows: (1) It may be questioned whether TEG/ROTEM analysis enable measurement of elasticity because viscosity may also contribute to clot amplitude. (2) It has been suggested that absolute properties of a blood clot cannot be measured with TEG/ROTEM analysis because the strain amplitude applied by the device is uncontrolled and changes during the course of coagulation. (3) A review of the calculation of G using Hartert's methods and some updated assumptions suggests that the value of 5000 is unreliable. (4) Recalculation of G for the ROTEM device yields a different value from that with Hartert TEG, indicating a degree of inaccuracy with the calculations. (5) Shear modulus is simply a multiple of E/CE and, because of the unreliability of G in absolute terms, it provides no additional value versus E/CE. The TEG and ROTEM are valuable coagulation assessment tools that provide an evaluation of the viscoelastic properties of a clot, not through measuring absolute viscoelastic forces but through continuous reading of the clot amplitude relative to an arbitrary, preset scale.
authors.affiliation: 1 CSL Behring, Vienna, Austria.
authors.forename: Gerald
authors.initials: G
authors.lastname: Hochleitner
authors.affiliation: 2 Meridian HealthComms, Cheshire, United Kingdom.
authors.forename: Ken
authors.initials: K
authors.lastname: Sutor
authors.affiliation: 2 Meridian HealthComms, Cheshire, United Kingdom.
authors.forename: Caroline
authors.initials: C
authors.lastname: Levett
authors.affiliation: 3 Leyser Lab GmbH, Steinefrenz, Germany.
authors.forename: Harald
authors.initials: H
authors.lastname: Leyser
authors.affiliation: 4 Ludwig Boltzmann Institute for Experimental and Clinical Traumatology and AUVA Research Centre, Vienna, Austria.|5 Department of Anesthesiology and Intensive Care, AUVA Trauma Hospital of Klagenfurt, Austria.
authors.forename: Christoph J
authors.initials: CJ
authors.lastname: Schlimp
authors.affiliation: 4 Ludwig Boltzmann Institute for Experimental and Clinical Traumatology and AUVA Research Centre, Vienna, Austria.|6 CSL Behring, Marburg, Germany.|7 Department of Anesthesiology, Perioperative Care and General Intensive Care, Paracelsus Medical University, Salzburg University Hospital, Salzburg, Austria.
authors.forename: Cristina
authors.initials: C
authors.lastname: Solomon
mesh_terms: D004548:Elasticity / Q000502:physiology*; D006801:Humans; D055595:Mechanical Phenomena; D008962:Models, Theoretical; D013916:Thrombelastography / Q000379:methods*; D013927:Thrombosis / Q000473:pathology*; D055682:Viscoelastic Substances
chemical_list: D055682:Viscoelastic Substances
keywords: bleeding; hemostasis; in vitro diagnostic systems