Hemostasis, platelets and Blood management Julie Wegner, PhD, CP Midwestern University Glendale, AZ

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Why do patients bleed? Macrovascular Microvascular –Inability to generate thrombin Insufficient clotting surface (platelets) Insufficient substrates (clotting factors) Inhibitors (anticoagulants, antithrombotic agents) –Clot not strong enough Insufficient thrombin generation Weak fibrin-platelet mesh (platelets, fibrinogen) –Clot vulnerable to lysis

Hemostatic components Clot location Substrates for: thrombin generation fibrin formation Generating environment Provide substrate Provide protection Clot formation requirements Platelets Endothelium WBC RBC Procoagulant factors Intrinsic Extrinsic Anticoagulant factors Antithrombotic factors Endothelium Subendothelium

Cell-based model

Platelet contribution Initiation and propagation Serial samples Cancer patients Correlations: platelet count vs. MA r=0.7 vs. R r=-0.7 vs.  r=0.8 Roeloffzen WWH et al. Thrombocytopenia affects plasmatic coagulation as measured by thromboelastography. Blood Coag Fibrinolysis 2010 (in press).

Platelet cascade Adhesion

Thrombin generation and hemostasis Insufficient clotting surface Insufficient substrates Presence of inhibitors

Central role of thrombin From: Crawley JTB et al. The central role of thrombin. J Thromb Haemost. 2007; 5(Suppl 1):

Thrombin generation kinetics T1 = lag phase T2 = maximum rate of TG T3 = Peak [thrombin] T4 = Total free thrombin (AUC)‏ Fibrin cross linking Lateral aggregation TG = thrombin generation, AUC = area under the curve = endogenous thrombin potential (ETP)‏ from: Wolberg AS. Blood Rev

From: Vanschoonbeek K, Feijge MAH, van Kampen RJW et al. Initiating and potentiating role of platelets in tissue factor-induced thrombin generation in the presence of plasma: subject-dependent variation in thrombogram characteristics. J Thromb Haemost. 2004; 2: Thrombin generating surface Thrombin generation and platelet #

Bollinger D et al. Br J Anaesthesiol 2009; 102:793 TG and [substrate] PPP (50%) 1.No change in lag time 2.Slight decrease rate TG 3.Decrease peak TG

1.Decrease coagulation factors FV and FVII ~ 28%  Dilution FII and FX ~ 44%  Dilution + consumption 2.Thrombin potential – [FX] and [FII]-dependent 3.Blood loss vs. thrombin potential (r = -0.75*)

Post-op bleeding: Hemodilution vs. consumption? Hemodilution  global (cells and factors) Consumption → global? –Importance of adequate anticoagulation 480 sec: clots vs consumption?

Heparin and thrombin generation From: Tanaka KA, Katori N, Szlam F, Sato N, Kelly AB, Levy JH. Effects of tirofiban on haemostatic activation in vitro. Br J Anaesth. 2004; 93: Peak thrombin  Max. rate thrombin generation  Lag time 

Reversing heparin effect Is more protamine always good? Fine tuning protamine –‘excess’ protamine:  TG –‘excess’ protamine: Increased time to clot Decreased clot strength Enhanced vulnerability to fibrinolysis Ni Ainle F et al. Blood 2009; 114:1658 TF Celite Nielsen VG. Ann Thorac Surg 2006; 81:1720

Weak clots Insufficient thrombin generation Insufficient substrate (fibrinogen) Weak fibrin-platelet mesh (platelets)

Clot quality and [thrombin] Wolberg, AS. Thrombin generation and fibrin clot structure. Blood Review 2007; 21: Fiber thickness Fiber weave Thick Thin LooseTight Clot strength LowHigh

Anesth Analg In press Plateau effect 1 g/L 120 x 10 9 /L Bleeding Depends on clot strength (MA) fibrinogen levels platelet function 100

Clot strength Fibrinogen vs. platelets Lang T et al. Anesth Analg 2009; 108:751 Velik-Salchner C et al. JTH 2007; 5:1019

Clot vulnerability to lysis Importance of clot strength in hemostasis

Holly, J. Cardiometabolic Risk Syndrome Part V: Fibrinolytic Dysfunction Fibrinolysis endothelium contact activation TAFI Thrombin I

Clot quality: Clot structure and local [thrombin] Wolberg, AS. Thrombin generation and fibrin clot structure. Blood Review 2007; 21: Clot strength LowHigh Fibrinolysis vulnerability HighLow

Colloid solutions (HES) do not activate fibrinolysis, but they do make clots more vulnerable to fibrinolysis

Summary Variability in hemostasis –One size fits all? –Monitoring Thrombin generation –Multiple roles –Rate and peak vs. total thrombin Clot structure –Thrombin –Platelets –Fibrinogen Clot structure and fibrinolysis