Antithrombin III

pro th rom bin * th rom b in

fib rinog en

F ibrin m onom er

F ib rin po lym erC L O T

*X a

X

X III X IIIa

*IX a

IX

*X Ia

X I

*X IIa

X IIW O U N D surface

*ka llik rein

k in inog en (H M W K )

prekallik re in

Va

V IIIa V III

V

Intrinsic p a thwa y

C o m m o np a thwa y

= C a lcium & P L com plex

* = ac tive serine p ro tease

Protein C system

pro th rom bin * th rom b in

fib rinog en

F ibrin m onom er

F ib rin po lym erC L O T

*X a

X

X III X IIIa

*IX a

IX

*X Ia

X I

*X IIa

X IIW O U N D surface

*ka llik rein

k in inog en (H M W K )

prekallik re in

Va

V IIIa V III

V

Intrinsic p a thwa y

C o m m o np a thwa y

= C a lcium & P L com plex

* = ac tive serine p ro tease

Thrombin + thrombomodulin

Protein CaProtein C + protein S

Cleaves Factor Va and VIIIa

Thrombin-activatable fibrinolysis inhibitor (TAFI)

Thrombin + thrombomodulin

Removes the terminal lysine on the fibrin molecule, renders the clot more susceptible to lysis by plasmin

Degradation of the Fibrin Clot Natural part of hemostasis Fibrin fibrils in the clot are dense,

dissolution occurs at “coiled coils” to form oligomers which are digested into smaller units

Highly regulated in terms of gene expression Plasmin

Tissue plasminogen activator (t-PA) urokinase streptokinase

Plasminogenesis

C O O H

S

SArg

Va l

C O O H

S

S

Arg

Va l

p la sm inogen

t-PA(end o th e liu m )

p la sm in

NH 2NH 2

(k id n ey )u ro k in a se

(e x o g e n o u s)s tre p to k in a se

F ib rin c lo tF ib rin fragm en ts

2-an tip la sm in

Plasmin

Serine protease formed from plasminogen Plasminogen found in plasma and

extracellular space and has high affinity for fibrin

Inactive and requires activation to plasmin by urokinase and t-PA

Formation of plasmin is highly regulated Cleaves fibrin into degradation products. Circulating plasmin is inhibited by α2-

antiplasmin. Forms complex with plasmin and prevents it from

binding to fibrin

Tissue Plasminogen Activator Serine protease released from ECs in response

to injury (in response to thrombin and some vasoactive peptides)

Chiefly responsible for conversion of plasminogen to plasmin

Secretion highly regulated at transcriptional level

Major binding is to fibrin clots and extracellular matrix

Highly specific ( site of clot formation ) Inhibited by plasminogen activator inhibitor-1

(PAI-1) Recombinant protein used clinically to inhibit

thrombosis

Urokinase

Serine protease secreted as pro-urokinase Produced by endothelial cells, fibroblasts, and

monocytes/macrophages Potent plasminogen activator but non-specific secreted as one chain: fragments in urine

generated by plasmin Functions to degrade ECM, enabling cells to

migrate Half life of only 7 minutes Inhibited by plasminogen activator-2 (PAI-2) synthesis tightly regulated by cytokines and

inflammatory mediators Used clinically (e.g. Abbokinase)

Streptokinase

Protein isolated from certain types of streptococci bacteria

Potent plasminogen activator Less selective than t-PA Can result in circulating plasmin Can produce degradation of fibrinogen

as well as fibrin May result in formation of plasmin in

excess of that inhibited by α2-antiplasmin and result in bleeding

BECAUSE OF THE COMPLEX NATURE OF HEMOSTASIS, POTENTIAL

INTERFERENCE IN THE PROCESS CAN OCCUR AT MANY LEVELS.

HEMOSTATIC DEFECTS

CONGENITAL Coagulation Factor deficiency

Hemophilia von Willebrand’s disease Factor XI,II, V, X, XIII deficiency

Platelet function defects Glanzmann’s thrombastenia Bernard-Soulier syndrome Storage pool disease

HEMOSTATIC DEFECTS

Major surface protein abnormality Glanzmann’s thrombastenia

Glycoprotein IIb / IIIa Absence of platelet aggregation

Bernard-Soulier syndrome Glycoprotein Ib / IX / V Absence of platelet adhesion

HEMOSTATIC DEFECTS

ACQUIRED Platelet abnormalities quantitative defects

failure of production Bone marrow disorder

shortened survival ITP / DIC

Sequestration hypersplenism

Conditions of Excess Bleeding Hemophilia ( inherited sex-linked rec.

) Hemophilia A (classic)- deficiency of

Factor VIII (85%) Hemophilia B – deficiency of Factor IX

(15%) Spontaneous bleeding

Joints frequently, crippling arthropathies Retroperitoneal hematoma Gastrointestinal/ genitourinary

NORMAL PLATELET FUNCTION

Conditions of Excess Bleeding von Willebrand’s disease

Autosomal dominant Low level of vWF

CARRIER FOR FACTOR VIII NORMAL PLATELET ADHESION

ABNORMAL PLATELET FUNCTION Easy bruising and mucosal bleeding

Menorrhagia is common

Conditions of Excess Bleeding

Thrombocytopenia Most common abnormality of hemostasis in

surgical patients Platelets fall from normal 150-400,000 to <

100,000/µl Massive blood loss Heparin induced Impaired platelet function Vit b12 / folic acid def ITP hypersplenism

Conditions of Excess Bleeding

Coagulopathy of liver disease Vitamin K deficiency

Required by liver for formation of prothrombin and Factors VII, IX, X and protein C

Leads to serious bleeding tendencies

Conditions of Clotting Dysfunction Thromboembolic conditions

Can result when endothelial surface is compromised or BF is slow

Associated with atherosclerosis, infection, or trauma

Femoral venous thrombosis When BF is slow (bed ridden, prolonged sitting) Clot grows and large piece can break off Can pass through right side of heart to lodge in

pulmonary arteries (pulmonary embolism) If large enough can be fatal

COAGULANTS

Thrombosis Inappropriate activation of hemostatic

mechanism; Venous –associated with stasis of blood

with small platelet component Arterial – associated with artherosclerosis

with large platelet component

COAGULANTS

Vitamin K Essential for the formation of clotting

factors (II, VII, IX and X) Given orally or thru IV (Natural Vit K

requires Bile-acid while Menadiol Na Phosphate does not but takes longer to act)

USE – bleeding 2o to oral anticoagulants, babies, Vit. K deficiencies

COAGULANTS

Antifibrinolytic Agent Tranexamic acid (Inhibit plasminogen

activation),for conditions with bleeding or risk of bleeding,life-threatening bleeding following thrombolytic drug administration and hereditary angioedema.

Aprotinin-inhibits proteolytic enzymes, used for hyperplasminemia due to fibrinolytic overdose & during cardiac

surgery

Conditions of Clotting Dysfunction Disseminated intravascular coagulation

Clotting activated in widespread areas Often from severe trauma or shock

(endotoxin) Plugging of vessels limits oxygen delivery lethal in ~85% of the cases

ANTICOAGULATION AND

BLEEDING

Prevention of Blood Clotting Critical for clots to dissolve or not form

when not neededEndothelial cell surface-

Most important factor – integrity prevents contact activation of intrinsic clotting system by collagen

Charged EC glycocalyx repels platelets and clotting factors

Thrombomodulin-EC membrane protein, binds thrombin to slow clotting process. Thrombomodulin-thrombin complex activates a protein C which inactivates Factors V and VIII.

Removal of Thrombin (blocks common pathway) Fibrin – absorbs 85-90% of thrombin by

absorption into fibers Anti-thrombin III – binds remaining

thrombin

Prevention of Blood Clotting

Vitamin K cycle (post-translational carboxylation)

NH

R

R

C H C H2 C H2

C = O

-C O 2

NH

R

R

C H C H2 C H

C = O

-C O 2

-C O 2

K (re d )

carboxylase

epoxidereductase

vitam in Kreductase

coum arin sK (e p o x )

K (o x )

C a

G L U res id u e

G L A res id u e

O + C O2 2 H O + H2+

D ie t Factors VII, IX, X and prothrombin

Anticoagulants for Clinical Use

Heparin Coumarins Aspirin

Cyclooxygenase inhibitor Prevents formation of thromboxane A2 and

activation of platelets Calcium-deionizing agents

Sodium, ammonium and potassium citrate combines with calcium in blood

Several factors require calcium for activation Used in test tubes to prevent clotting

Antithrombin III

pro th rom bin * th rom b in

fib rinog en

F ibrin m onom er

F ib rin po lym erC L O T

*X a

X

X III X IIIa

*IX a

IX

*X Ia

X I

*X IIa

X IIW O U N D surface

*ka llik rein

k in inog en (H M W K )

prekallik re in

Va

V IIIa V III

V

Intrinsic p a thwa y

C o m m o np a thwa y

= C a lcium & P L com plex

* = ac tive serine p ro tease

ANTICOAGULANT

Heparin -binds to antithrombin III Combines with anti-thrombin III and

increases activity 100-1000X Immediate effect ,half life of 60-

90min Monitor by aPTT

ANTICOAGULANT

Low molecular weight heparin- 4-6 kDa

Selective Xa inhibitor More favorable antithrombotic

effect,less bleeding,highly predictable bioavailability

Longer half life

ANTICOAGULANTS

Coumarin derivatives- warfarin,acenocoumarol,phenprocoumon

Block coagulation factors(2,7,9,10) Warfarin decreases formation of Factors VII,

IX and X by the liver Competes with vitamin K for reactive sites

Restoration after coumarin tx- 3-5 days Prothrombin time INR- corrects the differences of the

various thromboplastin activity. INR=1 no anticoagulation

ANTICOAGULATION

Antiplatelet Drugs Aspirin Dipyridamole Thienopyridine Derivatives Glycoprotein IIB/IIIA receptor antagonists Other antiplatelet drugs

ANTICOAGULATION

Antiplatelet Drugs Aspirin

Inhibits cyclooxygenase irreversibly Inhibits TXA2 Main drug – acute MI, High-risk for MI,

after coronary artery Bypass, after angioplasty, unstable coronary syndromes,TIA and AF if oral anticoagulant

is contraindicated

ANTICOAGULATION

Antiplatelet Drugs Dipyridamole

Phosphodiesterase inhibitor Additive effect to aspirin Less effective than aspirin Headache but no excess risk of bleeding

ANTICOAGULATION

Antiplatelet Drugs Thienopyridine Derivatives

Inhibits ADP-dependent aggregation Orally given, additive with aspirin Ticlopidine slow onset, unwanted effects-

blood dyscrasias (neutropenia) Clopidogrel – same as Ticlopidine except

for neutropenia

ANTICOAGULATION

Antiplatelet Drugs Glycoprotein IIB/IIIA Receptor Antagonists

Abciximab – for angioplasty patient as adjunct to heparin and aspirin, reduces restenosis, Tirofiban – an oligopeptide

Abciximab - Risk of bleeding & immunogenicity limits its use

They inhibit diverse agonists (e.g. ADP, TXA2 etc. )

ANTICOAGULATION

Thrombolytic agents- plasminogen activators.

Recombinant endogenous plasminogen activators(recombinant tPA)

Streptokinase- exogenous source bleeding

ANTICOAGULATION

Fibrinolytic Drugs Streptokinase

Protein extracted from cultures of streptococci

Activates plasminogen, given IV Additive with aspirin Action blocked by antistreptococcal

antibodies Allow 1 year before it can be used again

ANTICOAGULATION

Fibrinolytic Drugs Alteplase, Duteplase and Reteplase

Recombinant tPA (plasminogen activator) ‘Clot-selective’ – fibrin bound plasminogen Not antigenic-substitute for patients w/ ab

for streptokinase Reteplase –longer half-life, bolus

admn.simple

Tests of hemostasis

Primary deficiency/ defect in one component

Pharmacologic therapy Anticoagulant/ antiplatelet

Comorbid condition Thrombocytopenia Sepsis/ hepatic disease

Tests of hemostasis

Careful review of patient’s clinical history most important/ initial approach

Drug use Basic laboratory tests

Platelet count Prothrombin time ( PT ) or INR Activated partial thromboplastin time

( aPTT ) Bleeding time ( BT ) and clotting time

( CT )

Evaluation of surgical patient Patients history Questions to ask

Prolonged bleeding or swelling after biting the lip or tongue

Bruises without apparent injury Prolonged bleeding after dental extraction Excessive menstrual bleeding Bleeding problems associated with major and minor

operations Medical problems receiving a physician’s attention

within the past 5 years Medications including aspirin or remedies for

headache taken within the past 10 days Relative with a bleeding problem

Four levels of concern

Level I Hx(-); Sx (m) no test

Level II Hx(-); Sx (M) platelet ct

PTT

Level III Hx (suggestive) PT, PTT, BT, CT, pltelet ct

Level IV Hx(+)Hematologic consultation

Platelet dysfunction

Normal 150,000 to 400,000 /ul Clinical signs of thrombocytopenia

< 100,000 / ul Increased bleeding complications in major

surgical procedures < 50,00 / ul

Increased bleeding complications in minor surgical procedures

< 20,000 / ul SPONTANEOUS HEMORRHAGE

Platelet dysfunction

Bleeding time ( BT ) Evaluate platelet , vWD and vascular

dysfunction Several methods

Ivy test = 7mins

Clotting time ( CT ) … + Aspirin use

Clotting dysfunction

PT reagent contains thromboplastin and calcium + plasma =

clot PT measures

Factors I, II, V, X and VII Factor VII extrinsic pathway

Abnormal coagulation due to Vit K deficiency warfarin / coumadin therapy

Clotting dysfunction

Variations in thromboplastin activity from different sources PT value is adjusted = INR

ISI ( international sensitivity index ) Value for each batch of thromboplastin Optimal reagent has as ISI of 1.3 to 1.5

INR = ( PTpatient / PTnormal )ISI

INR- corrects the differences of the various thromboplastin activity. INR = 1.0 is NORMAL

Clotting dysfunction

aPTT reagent contains Phospholipid substitutes, activator and

calcium + plasma = clot aPTT measures

Factors I, II and V of the common pathway Factors VIII, IX, X and XII

intrinsic pathway Heparin therapy

HEMOSTASIS

RENE PSA MENDOZA, MD, MHSA

Associate Professor, Department of Surgery

FEU-NRMF Institute of Medicine