Transcript The Normal Hemostatic Process

HEMOSTASIS
HEMOSTASIS COMPONENTS
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Vessel wall
Platelets
Coagulation enzymes
Fibrinolytic system
Control mechanisms, including inhibitors
NOTE: Normal hemostasis involves the complex interaction of the vessel wall, circulating proteins and biochemical mediators,
cells, promoters and inhibitors. Activation of hemostasis usually begins with damage to the vessel wall, exposing the
subendothelium. Conversely, the intact vessel wall helps to maintain fluidity of blood, not simply through being a passive
container wall, but also by synthesizing chemicals and proteins that actively contribute to the process. When the vessel wall is
damaged, platelets are at the forefront of defense by sticking to the damaged area. The clotting enzymes contribute by
developing a fibrin mesh that holds the platelets in place. Control mechanisms come into play to limit hemostatic process to the
are of injury. Otherwise the whole body would “clot up” at the slightest stimulus.
Sequence of Changes With
Vascular Injury
• Injury to vessel wall (endothelium) with resultant
exposure of subendothelium
• Platelet adhesion mediated by HMW vWF
• Simultaneous activation of clotting enzymes
• Platelet aggregation via fibrinogen receptors on
platelets
• Anchoring of platelet plug by cross-linked fibrin
NOTE: Let’s expand on the sequence of events that occur when a vessel wall is injured and define a few basic terms. Injury
exposes the subendothelial collagen and the soluble substances that are normally between the subendothelium and
collagen.
Normal Hemostasis
Vessel Wall
Exposed collagen
Contraction
vFW
large multimers
Platelet
adhesion
Platelet
Aggregation
Tissue TPL
Activation of
Coagulation
Thrombin
Definitive
Hemostatic
Plug
1º Hemostatic
Plug
This slide gives a diagrammatic representation of the
whole process and the functional interrelationships.
We will now go on to dissect the various components
of this process in more detail.
Limiting Reactions
Platelet Components
Canaliculus
Alpha granules
Dense Granules
Actin
RECEPTORS
vWF
Fibrinogen
Clotting Factors
Platelet Granules
• Alpha granules
– vWF
– Fibrinogen
– PF4
– Beta thromboglobulin
– PDGF
• Dense granules (delta)
– ADP
– Serotonin
Platelet Role in Hemostasis
• vFW binding sites- platelet adhesion
• Fibrinogen binding sites- platelet aggregation
• Multiple binding sites for coagulation
factors - enhances appropriate steric
relationships
Production of multiple chemical mediators
Binding sites for chemical mediators
First, lets look more closely at the role of platelets. They play multiple roles in the hemostatic process, and, contrary to the
view held 30 years ago, when they were thought to a small part of the process, many would now consider them to have a
central role. We already have alluded to this by indicating that the first step after injury is platelet adhesion to the
subendothelium. This is mediated by subendothelial HMW vWF binding to specific receptor sites on the platelet
membrane. In, addition there binding sites that play a role in virtually every step of the process. Also. chemical mediators
are synthesized by internal organelles, and they contain a contractile protein that is responsible for clot retraction. The
coagulation enzymes are present in relative low concentrations in plasma. Binding of certain of these factors to specific
receptors on the surface of activated platelets allows them to line up in appropriate steric configuration, catalyzing the
process and limiting the reactions to the area of injury.
von Willebrands Factor
• Synthesized in megakaryocytes and
endothelial cells - approx. 230,000 M.W.
• Macromolecular multimer plasma:
M.W. 1 x 106 - 10 X106. Plasma carrier
of Factor VIII, stabilizes it
• Large molecular forms:
a. Most effective in platelet adhesion
b. Predominate in endothelial cells and
subendothelium
Coagulation Cascade
TISSUE FACTOR
APTT
CONTACT ACTIVATION
FXII, FXI, FLETCHER,
FITZGERALD FACTORS
IX
FACTOR VII
VIIa (ACTIVATED)
IX
IXa
PT
PHOSPHOLIPID
( XI?)
IXa
TFPI
INHIBITION OF
VIII
CLOTTING
VIII
FACTOR X
THROMBOMODULIN
PROTEIN C
Xa
V, Ca
FACTOR II
FIBRINOGEN
PLATELET
ACTIVATION
IIa
FIBRIN MONOMERS
FACTOR XIII
IN VITRO
PT
APTT
CROSS-LINKED FIBRIN
(STABLE FIBRIN CLOT)
Coagulation Cascade- PT
TISSUE FACTOR
APTT
CONTACT ACTIVATOR
FXII, FXI, FLETCHER,
FITZGERALD FACTORS
IX
FACTOR VII
VIIa (ACTIVATED)
IX
IXa
PT
PHOSPHOLIPID
( XI?)
IXa
TFPI
INHIBITION OF
VIII
CLOTTING
PHOSPHOLIPID
VIII
FACTOR X
THROMBOMODULIN
PROTEIN C
Xa
V, Ca
FACTOR II
FIBRINOGEN
PLATELET
ACTIVATION
IIa
FIBRIN MONOMERS
(ENDPOINT)
FACTOR XIII
IN VITRO
PT
APTT
CROSS-LINKED FIBRIN
(STABLE FIBRIN CLOT)
Coagulation Cascade- APTT
TISSUE FACTOR
APTT
CONTACT ACTIVATOR
FXII, FXI, FLETCHER,
FITZGERALD FACTORS
IX
FACTOR VII
VIIa (ACTIVATED)
IX
IXa
PT
PHOSPHOLIPID
( XI?)
IXa
TFPI
INHIBITION OF
VIII
VIII
CLOTTING
FACTOR X
THROMBOMODULIN
PROTEIN C
Xa
V, Ca
FACTOR II
FIBRINOGEN
PLATELET
ACTIVATION
IIa
FIBRIN MONOMERS
(ENDPOINT)
FACTOR XIII
IN VITRO
PT
APTT
CROSS-LINKED FIBRIN
(STABLE FIBRIN CLOT)
Control Mechanisms
• Intact endothelial cells
– Chemical mediators
– Membrane bound receptors
– Synthesizes activators of fibrinolysis
• Circulating inhibitors
– Protein C “system”
• Fibrinolytic system
– Endothelial component
– plasma protein component
Intact Endothelium Limits
Hemostasis
INHIBITS PLATELET ACTIVATION
INACTIVATES Va +
VIIIa
NO PGI2 ADPase
FIBRINOLYSIS
INACTIVATES
PAI
PLASMINOGEN
PROTEIN S
PROTEIN C
INHIBITS Xa + THROMBIN
PROTEIN Ca
THROMBIN
ATIII
+
THROMBOMODULIN
Subendothelium
vFW
multimers
PLASMIN
HEPARAN
PLASMINOGEN
ACTIVATORS (tPA)
(uPA)
Intact Endothelium Limits
Hemostasis – Fibrinolysis
INHIBITS PLATELET ACTIVATION
PLASMINOGEN
INACTIVATES Va +
VIIIa
NO PGI2 ADPase
FIBRINOLYSIS
INACTIVATES
PAI
PROTEIN S
PROTEIN C
INHIBITS Xa + THROMBIN
PROTEIN Ca
THROMBIN
ATIII
+
THROMBOMODULIN
Subendothelium
vFW
multimers
PLASMIN
HEPARAN
PLASMINOGEN
ACTIVATORS (tPA)
(uPA)
Intact Endothelium Limits Hemostasis
“Protein C System”
INHIBITS PLATELET ACTIVATION
FIBRINOLYSIS
INACTIVATES
PAI
PLASMINOGEN
INACTIVATES Va + VIIIa
NO PGI2 ADPase
PLASMIN
INHIBITS Xa + THROMBIN
PROTEIN S
PROTEIN C
PROTEIN Ca
THROMBIN
ATIII
+
THROMBOMODULIN
Subendothelium
vFW
multimers
HEPARAN
PLASMINOGEN
ACTIVATORS (tPA)
(uPA)
Intact Endothelium Limits Hemostasis Chemical Mediators
INHIBITS PLATELET ACTIVATION
INACTIVATES Va +
VIIIa
NO
PGI2 ADPase
FIBRINOLYSIS
INACTIVATES
PAI
PROTEIN S
PROTEIN C
PLASMINOGEN
INHIBITS Xa + THROMBIN
PROTEIN Ca
THROMBIN
ATIII
+
THROMBOMODULIN
Subendothelium
vFW
multimers
PLASMIN
HEPARAN
PLASMINOGEN
ACTIVATORS (tPA)
(uPA)
Production of Coagulation
Factors
• Synthesized in the liver– All except Factor VIII
– Vitamin K dependent
• II, VII, IX, and X
• Protein C, Protein S
• Factor VIII- unknown
Vitamin K Dependent Enzymes:
Factors II, VII, IX, X
• Synthesized in liver
• Serine proteases, inactivated by AT3
• Activation on surface of biologic
membranes
• Have an affinity for binding calcium
Coagulation Cascade- PT
TISSUE FACTOR
APTT
CONTACT ACTIVATOR
FXII, FXI, FLETCHER,
FITZGERALD FACTORS
IX
FACTOR VII
VIIa (ACTIVATED)
IX
IXa
PT
PHOSPHOLIPID
( XI?)
IXa
TFPI
INHIBITION OF
VIII
CLOTTING
PHOSPHOLIPID
VIII
FACTOR X
THROMBOMODULIN
PROTEIN C
Xa
V, Ca
FACTOR II
FIBRINOGEN
PLATELET
ACTIVATION
IIa
FIBRIN MONOMERS
(ENDPOINT)
FACTOR XIII
IN VITRO
PT
APTT
CROSS-LINKED FIBRIN
(STABLE FIBRIN CLOT)
Coagulation Cascade- APTT
TISSUE FACTOR
APTT
CONTACT ACTIVATOR
FXII, FXI, FLETCHER,
FITZGERALD FACTORS
IX
FACTOR VII
VIIa (ACTIVATED)
IX
IXa
PT
PHOSPHOLIPID
( XI?)
IXa
TFPI
INHIBITION OF
VIII
VIII
CLOTTING
FACTOR X
THROMBOMODULIN
PROTEIN C
Xa
V, Ca
FACTOR II
FIBRINOGEN
PLATELET
ACTIVATION
IIa
FIBRIN MONOMERS
(ENDPOINT)
FACTOR XIII
IN VITRO
PT
APTT
CROSS-LINKED FIBRIN
(STABLE FIBRIN CLOT)
Prothrombin Time
• Poor reproducibility from lab to lab in US
– No good assayed standards
– Many manufacturers
– Many chemically different reagents
– Many different types of instruments
– Poor lot-to-lot reproducibility even from same
manufacturer
Reporting Protime Results
• Each laboratory must establish it’s own normal
range using the instrument and reagents that it
is using
• It may have to be redone with each new lot of
reagents, certainly, at least rechecked and
verified- insist on it from the laboratory you use
• Results should be expressed in seconds, not
INR
• Results should be compared to the normal
range. The true “Control” value is meaningless
for clinical use.
Prothrombin Time
• “The INR is the answer to our prayersHallelujah”- NOT!!
– Poor calibration by reagent manufacturers
is the weak link in the chain
– Intended only for inter laboratory
comparisons in patients who are on steady
state anticoagulation with coumadin: at
least two weeks of therapy, ambulatory,
normal activity and diet
– Widely misapplied to express protime
results in all other situations
Bleeding Time
• Widely misused as a screening test for
platelet function abnormalities
• Can predict trends when used to study
large populations
• Cannot predict bleeding risk in
individual patients - use for this
purpose has been discredited
Screening for Hemostatic
Defects
• PT, APPT- sensitivity is too poor to pick
up mild defects
• Bleeding time- poorly reproducible, too
many false positives and false
negatives, Most common cause of a
prolonged bleeding time- improperly
performed
• Best screen: good history
Screen for Platelet
Abnormalities
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No good tests, history
Immediate bleeding
Mucous membrane bleeding
Easy bruising
Petechiae
Screen for Clotting Factor
Deficiencies
• Delayed onset of bleeding
• Large ecchymoses or hematomas
• Bleeding into joints
Screening History for Bleeding
Problems
• Do you think you have a bleeding problem?
• Does anyone in your family have a bleeding
problem?
• Easy bruising?
• Previous hemostatic challenges:
o Major surgery
o Trauma
o Extraction of impacted teeth
Bleeding Problems
• Pre-operative screening
• Patient with suspicious history
• Actively bleeding patient
Pre-operative Screening
• Most common hereditary bleeding
problems?
• Acquired bleeding problems?
• Sensitivity of screening tests?
Hereditary Bleeding Disorders
• von Willebrand’s disease - platelet
function
• Storage pool disease (delta granule
deficiency) - platelet function
• Factor VIII deficiency (Hemophilia A)
• Factor IX deficiency (Christmas disease)
• Factor XI deficiency
Patient with Suspicious
History
• Refer to laboratory or specialist that
specializes in bleeding disorders.
Actively Bleeding Patient
• Focal bleeding - catgut insufficiency
• Generalized bleeding o Thrombocytopenia
o Vitamin K deficiencies - common
o DIC - most over-diagnosed cause of bleeding in
the acute care/ICU setting. Primary fibrinolysis rare
Acquired Bleeding Problems
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drug-induced platelet function defects
Thrombocytopenia
vitamin K deficiency
Liver disease
Coagulation inhibitors
Post viral
Misc. others
Idiopathic
Vitamin K Deficiency
• Appropriate clinical setting:
a. Poor or no oral intake
b. Broad spectrum antibiotics
• Prolonged PT, PTT with a normal
platelet count and fibrinogen presumptive diagnoses of Vitamin
K deficiency
Acute DIC:
A clinical-pathologic Dx
• Severely, acutely ill patient (not
clinically stable).
• Decreasing platelet count and/or
fibrinogen.
Acute DIC Principles
• Most over-diagnosed cause of bleeding in
a hospital/ICU setting.
• Should be approached as a diagnosis of
exclusion
• If it is the only diagnosis you can think of,
you are over your head. GET HELP
• Vitamin K deficiency is much more
common.
• Many other factors are more likely to be
the cause of thrombocytopenia.
Possible DIC
• Run all tests on the same specimen:
PT, PTT, Fibrinogen, FDP Platelets
(Factor V, Factor VIII).
• It may take sequential testing to
establish diagnosis.
Sources of Vitamin K
• Diet- Fresh, green leafy vegetables
• Synthesis by bacteria in the intestinal track
• Typical ICU/acutely ill, hospitalized patient
– No or poor oral intake
– Broad spectrum antibiotic therapy
– Increased vitamin K requirement because
of illness
• Result: Acquired vitamin K deficiency within
two to three days of admission
Vitamin K Dependent Factors
• II, VII, IX, X
• PT - II, VII, X
• APTT - II, IX, X
Vitamin K Deficiency vs.
Acute DIC
Vitamin K
DIC
PT
Prolonged
N or prolonged
APT
Prolonged
N or prolonged
FDP
Normal
Usually elevated
Fibrinogen
Normal
N or decreased
*Platelets
Normal
Usually decreased
Elevated Levels of FDP
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Recent surgery
Acute thromboembolic event
Renal failure
Hepatic failure
Acute myocardial infarction
DIC
TTP/HUS
Primary fibrinolysis
Suggested Approach to the Bleeding
Hospitalized Patient
• Draw PT, APTT, FDP, fibrinogen and platelet
count on same specimen as a panel. Do
not try to use values drawn at different times.
• Immediately give Vitamin K
• Redraw panel in 4-6 hours.
o K deficiency should show some degree of
correction of PT and APTT within this time period
o DIC should manifest itself by a decreasing
fibrinogen without any significant correction of PT<
APTT
Diagnostic Approach to
Thrombocytopenia
• Good history; medication - don’t forget
heparin; Acuteness of onset; Underlying
diseases
• Physical - splenomegaly
• Examination of blood smear by an
experienced individual; platelet morphology,
Other hematologic abnormalities
• Bone marrow examination - almost never
helpful in the absence of other hematologic
abnormalities