C h a p t e r 1 2
Disorders of Hemostasis
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are more directly related to the bleeding problems that
occur. The bleeding may be present as petechiae, pur-
pura, oozing from puncture sites, or severe hemorrhage.
Uncontrolled postpartum bleeding may indicate DIC.
Microemboli may obstruct blood vessels and cause tis-
sue hypoxia and necrotic damage to organ structures,
such as the kidneys, heart, lungs, and brain. As a result,
common clinical signs may be due to renal, circulatory,
or respiratory failure; acute bleeding ulcers; or con-
vulsions and coma. A form of hemolytic anemia may
develop as red cells are damaged passing through vessels
partially blocked by thrombus.
The treatment of DIC is directed toward managing
the primary disease, replacing clotting components, and
preventing further activation of clotting mechanisms.
Transfusions of fresh-frozen plasma, platelets, or fibrin-
ogen-containing cryoprecipitate may correct the clot-
ting factor deficiency. Heparin may be given to decrease
blood coagulation, thereby interrupting the clotting
process. Heparin therapy is controversial, however, and
the risk of hemorrhage may limit its use to severe cases.
It typically is given as a continuous intravenous infusion
that can be interrupted promptly if bleeding is accen-
tuated. Tissue factor pathway inhibitors, antithrombin,
protein C concentrates, and anti-inflammatory cyto-
kines such as interleukin-10 are being evaluated in clini-
cal trials as potential therapies.
R E V I EW E X E R C I S E S
1.
A 55-year-old man has begun taking one 81-mg
aspirin tablet daily on the recommendation of
his physician. The physician had told him that
this would help to prevent heart attack and
stroke.
A.
What is the action of aspirin in terms of heart
attack and stroke prevention?
B.
The drug clopidogrel (Plavix) is often
prescribed along with aspirin to prevent
thrombosis in persons with severe
atherosclerotic disease who are at risk for
myocardial infarction or stroke. Explain the
rationale for using the two drugs.
2.
The drug desmopressin acetate (DDAVP), which
is a synthetic analog of arginine vasopressin,
increases the half-life of factor VIII and is
sometimes used to treat bleeding in males with
mild hemophilia.
A.
Explain.
3.
A 29-year-old new mother, who delivered her
infant three days ago, is admitted to the hospital
with chest pain and is diagnosed as having venous
thrombosis with pulmonary emboli.
A.
What factors would contribute to this woman’s
risk of developing thromboemboli?
4.
The new mother is admitted to the intensive
care unit and started on low–molecular-weight
heparin and warfarin. She is told that she will be
discharged in a day or two and will remain on the
heparin for 5 days and the warfarin for at least 3
months.
A.
Use Figure 12-3 to explain the action of heparin
and warfarin. Why is heparin administered
for 5 days during the initiation of warfarin
treatment?
B.
Anticoagulation with heparin and warfarin is
not a definitive treatment for clot removal in
pulmonary embolism, but a form of secondary
prevention. Explain.
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Disseminated intravascular coagulation (DIC) is
characterized by widespread coagulation and
bleeding in the vascular compartment. It begins
with massive activation of the coagulation
cascade and generation of microthrombi that
cause vessel occlusion and tissue ischemia. Clot
formation consumes all available coagulation
proteins and platelets, and severe hemorrhage
may occur.
SUMMARY CONCEPTS
■■
Bleeding disorders or impairment of blood
coagulation can result from defects in any of the
factors that contribute to hemostasis: platelets,
coagulation factors, or vascular integrity.
■■
Disorders of platelet plug formation include a
decrease in platelet numbers due to inadequate
platelet production (bone marrow dysfunction),
excess pooling of platelets in the spleen,
excess platelet destruction (thrombocytopenia),
abnormal platelet function (thrombocytopathia),
or defects in vonWillebrand factor.
■■
Impairment of blood coagulation can result
from deficiencies of one or more of the known
clotting factors. Deficiencies can arise because of
acquired disorders (i.e., liver disease or vitamin K
deficiency) or inherited disorders (i.e., hemophilia
A or vonWillebrand disease).
■■
Bleeding may also occur from structurally weak
vessels that result from impaired synthesis of
vessel wall components (i.e., vitamin C deficiency,
excessive cortisol levels as in Cushing disease,
or the aging process) or from damage by genetic
mechanisms (i.e., hemorrhagic telangiectasia) or
the presence of microthrombi.
