الفهرس 
Physiology of Coagulation Process
Tissue factor pathway (extrinsic):Only 14 pages are availabe for public view
Abstract
The mechanisms of hemostasis are complex. While
one can evaluate traditional models of coagulation, in
reality the process of clot formation occurs on multiple
levels with complicated feedback systems that are not well
represented in the typical coagulation cascade. This process
is even more complex in the parturient, where changes such
as physiological anemia and fluctuating coagulation factor
concentrations alter the balance between bleeding and clot
formation in preparation for peripartum blood loss.
Although thrombosis is certainly of concern in the
otherwise healthy parturient, those who also have a
coagulation disorder can be difficult to classify on the
spectrum between thrombotic and hemorrhagic risk.
It is important that anesthetists who care for pregnant
patients have an understanding of these changes in
coagulation; not only to ensure the safety of neuraxial
anesthesia, the cornerstone anesthetic for both labour and
Caesarean delivery, but also for the management of
hemorrhage, which is common in the parturient.Thromboelastography and rotational
thromboelastometry are point-of-care tests used to measure
whole blood coagulation, including fibrinolysis.
Thromboelastography is useful because it is sensitive to, all
the cellular and plasma factors in whole blood involved in
clot formation and degradation. It is widely used within a
number of hospital settings including intensive care and
among patients undergoing liver and cardiac surgery.
Although attempts at establishing peripartum reference
ranges for rotational thromboelastometry have been made,
these ranges have not yet been widely accepted or
validated.
As women become hypercoaguable as pregnancy
progresses, a shift toward hypercoagulability as measured
by thromboelastography and rotational thromboelastometry
has been reported in uncomplicated pregnancies as
pregnancy advances.
The pregnant patient with coagulation defects or
receiving anticoagulant medications presents a unique
challenge to the anesthetist. Globally, postpartum
hemorrhage (PPH) is the leading cause of maternal
morbidity and mortality.In addition to concerns of peripartum hemorrhage, one
must be aware of bleeding consequences, factor
replacement strategies, and anticoagulation on the safety
profile of neuraxial anesthesia. The risk of spinal or
epidural hematoma in these patients has not been quantified
fully, but is nevertheless a factor that one must consider on
an individual basis in determining whether neuraxial
anesthesia is appropriate.