Hemostasis

• Intrinsic path (PTT): exposed collagen + XII -> XI, IX -> X which activates thrombin to produce fibrin
• Extrinsic path (PT): tissue factor + VII -> activated X -> fibrin.  X is common to both pathways
• XIII crosslinks fibrin to form "plug"
• PT is best single test to evaluate synthetic function of liver
• Banked blood is low in 2,3 DPG which increases HgB affinity for O2 (left shift)
• Cryoprecipitate contains fibrinogen and vwf-VIII; used in vwd, hemophilia A, and DIC if fibrinogen low
• Coumadin inhibits factors 2, 7, 9, 10, protein C & S (vit k dependant)
• Protein C degrades active V and VIII.  Protein S helps protein C
• V and VIII are labile factors, low levels in stored blood
• Factor VIII only factor not made in liver (made by reticuloendothelial system)
• Von Willebrand's Disease: long PTT, long bleeding time, + ristocetin test.  Type I and III have low amounts of vwf, respond to DDAVP; type II is qualitatively poor vwf. (DDAVP causes release of vwf, useful also in pts on ASA or w/poor platelets due to uremia).  Autosomal dominant (only one besides Rosenthal's XI deficiency).  Only inherited coagulopathy with long bleeding time.  Rx with VIII, vwf or cryoprecipitate.

• Glanzman's thrombasthenia: plt's have IIb/IIIa receptor deficiency, decreased aggregation
• Bernard Soulier: Ib deficiency, decrease adherence to exposed collagen

• VII deficiency causes long PT, normal PTT
• Hemophilia A = VIII deficiency, sex linked recessive, replace to 100% levels pre-op.  Have long PTT, normal PT.  Newborn has VIII from mom, may not bleed at circumcision.  Hemophiliac joint - do not aspirate; Ice, range of motion therapy, give factor VIII.
• Hemophilia B = IX deficiency = Christmas disease, also sex linked.  Achieve 50% levels pre-op.
• Lupus Anticoagulant: antiphospholipid antibodies, not necessarily w/Lupus and generally pro-coagulant; DX: long Russel viper venom time; long PTT which does not correct by adding normal plasma.
• Factor XII = Hagemann factor; activated by cardiopulmonary bypass -> need for heparin
• Factor V Leyden = resistance to activated protein C = common cause of DVT
• Plasmin degrades fibrinogen, is inhibited by alpha-2-plasmin inhibitor
• Heparin binds, activated ATIII and inactivates factors 9-12; prolongs PTT; counteract w/protamine.
• e-ACA (epsilon amino-caproic acid) inhibits fibrinolysis, is the Rx for overdose of thrombolytics
• Thrombin time is best to monitor thrombolysis
• DIC: see low platelets, prolonged PT/PTT, low fibrinogen, high fibrin split products
• HIT: 'white clot syndrome', thrombocytopenia due to anti-platelet antibody causing plt aggregation.  Use dextran to anticoagulate.  Generally see after 5 days of heparin, less frequent with LMWH
• Prostacyclin = PGI2: from endothelium. Decrease plts aggregation, vasodilation, bronchial relaxation
• Thromboxane: from platelets. Opposite effects of above.
• Best pre-op test for pt on nsaids/ASA is bleeding time

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