title: Real-time measurement of free thrombin: evaluation of the usability of a new thrombin assay for coagulation monitoring during extracorporeal circulation.
abstract: BACKGROUND
  In patients undergoing cardiac surgery with heart-lung machine support, adequate anticoagulation to mitigate blood clotting caused by the artificial surfaces of the extracorporeal circulation (ECC) system is essential. These patients routinely receive heparin, whose effectiveness is monitored by measurements of the activated clotting time (ACT). However, ACT values only poorly correlate with the actual hemostatic status. The aim of our study was to evaluate the detection of free thrombin in heparinized human blood as a monitor of anticoagulation during ECC.
  
  
  METHODS
  Human whole blood was anticoagulated with different concentrations of heparin (0.75, 1, 2 or 3 IU/ml) and circulated in the Chandler-loop model for up to 240 min at 37 °C. Next to ACT, ECC-mediated changes in free active thrombin, prothrombin fragment 1+2 (F1+2) and thrombin-antithrombin-III (TAT) levels were measured before and during circulation. Platelet activation and cell count parameters were further investigated.
  
  
  RESULTS
  Our study shows that detection of ECC-mediated changes in free thrombin is possible in blood anticoagulated with 0.75 or 1 IU/ml heparin, whereas no thrombin was detectable at higher heparin concentrations. Thrombin generation during 240 min of ECC is comparable to F 1+2 and TAT plasma levels during ECC.
  
  
  CONCLUSIONS
  Thrombin is the key enzyme in the coagulation cascade and hence represents a promising marker for monitoring the coagulation status of patients. Although detection of free thrombin was not feasible at high heparin concentrations, the employed test represents an additional test to current laboratory methods investigating blood coagulation at low heparin concentrations.
authors.affiliation: Department of Thoracic, Cardiac and Vascular Surgery, Clinical Research Laboratory, University Hospital Tuebingen Germany. Electronic address: stefanie.krajewski@uni-tuebingen.de.
authors.forename: Stefanie
authors.initials: S
authors.lastname: Krajewski
authors.affiliation: Department of Thoracic, Cardiac and Vascular Surgery, Clinical Research Laboratory, University Hospital Tuebingen Germany.
authors.forename: Sabrina
authors.initials: S
authors.lastname: Krauss
authors.affiliation: Department of Thoracic, Cardiac and Vascular Surgery, Clinical Research Laboratory, University Hospital Tuebingen Germany.
authors.forename: Julia
authors.initials: J
authors.lastname: Kurz
authors.affiliation: Department of Thoracic, Cardiac and Vascular Surgery, Clinical Research Laboratory, University Hospital Tuebingen Germany.
authors.forename: Bernd
authors.initials: B
authors.lastname: Neumann
authors.affiliation: Department of Thoracic, Cardiac and Vascular Surgery, Clinical Research Laboratory, University Hospital Tuebingen Germany.
authors.forename: Christian
authors.initials: C
authors.lastname: Schlensak
authors.affiliation: Department of Thoracic, Cardiac and Vascular Surgery, Clinical Research Laboratory, University Hospital Tuebingen Germany.
authors.forename: Hans P
authors.initials: HP
authors.lastname: Wendel
mesh_terms: D001777:Blood Coagulation / Q000502:physiology*; D001780:Blood Coagulation Tests / Q000379:methods*; D004305:Dose-Response Relationship, Drug; D005112:Extracorporeal Circulation / Q000295:instrumentation / Q000379:methods*; D006487:Hemostasis / Q000502:physiology; D006493:Heparin / Q000494:pharmacology; D006801:Humans; D013917:Thrombin / Q000032:analysis* / Q000378:metabolism
chemical_list: D006493:Heparin; D013917:Thrombin
keywords: Thrombin; aptamer; coagulation; extracorporeal circulation; heparin