Coagulation Flashcards
Physiology and Pathophysiology of Coagulation
o Stage 1 – Formation of Platelet Plug
• Platelet aggregation initiated by exposure of collagen
• Formation of fibrinogen bridges between glycoprotein IIb/IIIa receptors
• GP receptors must first be activated – stimulated by multiple factors
• Thromboxane, thrombin, collagen-platelet activating factor, ADP
• Plug is unstable and must be reinforced by fibrin
Physiology and Pathophysiology of Coagulation
o Stage 2 – Coagulation
o Production of fibrin which stabilizes the clot
o Production by 2 pathways:
• Intrinsic (contact activation)
• Turned on when blood makes contact with collagen as result from trauma to blood vessel
• Extrinsic (tissue factor)
• Turned on when there is trauma to the vascular wall
• Triggers release of tissue thromboplastin
• Causes conversion of prothrombin to thrombin
• Also causes a number of factors to be activated as well as conversion of fibrinogen to fibrin
• Both pathways meet at Factor Xa
Laboratory Monitoring
• PT (prothrombin time)
• PT (prothrombin time)
o Time it takes plasma to clot after the addition of tissue factor
o Measure extrinsic pathway
o Measured in INR which is a ratio based on the pts time vs. a control.
o Normal INR is 0.8 to 1.2
Laboratory Monitoring
aPTT (patial thromboplastin time)
o Time it takes for plasma to clot, called partial due to absence of tissue factor
o Measure of intrinsic pathway
o Normal is 30 – 50 sec
Three major Groups:
• Anticoagulalants:
o Warfarin, heparin, LMW heparins, bivalirudin, dabigatran
• Antiplatelets:
o ASA, clopridrogel, eptifibatide, dipyridamole
• Thrombolytics (clot dissolver)
o Streptokinase, alteplase
Heparin Info
• Heparin: Produces anticoagulant effects by binding Antithrombin III (AT-III)
o 1,000 times more active in inhibiting thrombin, Factor Xa, Factor IXa, and other substances.
• aPTT monitored frequently and should be 1.5 and 2 times higher than the Pt baseline, between 60-80 seconds.
Low molecular weight Heparin
Differences with Heparin: SQ only o Weight based dosing o BID dosing o 10x less heparin induced thrombocytopenia o 4x longer shelf life o more expensive o no aPTT monitoring.
