Disseminated intravascular coagulation is a clinicopathological
diagnosis21 of a disorder that is defined
by the International Society on Thrombosis
and Hemostasis (ISTH) as “an acquired syndrome
characterized by the intravascular activation of coagulation
with loss of localization arising from
different causes.” This condition typically originates
in the microvasculature and can cause damage
of such severity that it leads to organ dysfunction
(Fig. 2). It can be identified on the basis of a
scoring system developed by the ISTH (Table 2).
Disseminated intravascular coagulation usually
presents as hemorrhage, with only 5 to 10% of
cases presenting with microthrombi (e.g., digital
ischemia) alone. Whether the condition presents
with a thrombotic or bleeding episode depends
on its cause and host defenses. Sepsis is the
most common cause of disseminated intravascular
coagulation in critical care; systemic infection
with a range of bacteria from Staphylococcus
aureus to Escherichia coli is known to be associated
with this condition. The complex pathophysiology
is mediated by pathogen-associated molecular patterns,
which generate an inflammatory response
in the host through signaling at specific receptors.
For example, signaling by means of toll-like
and complement receptors initiates intracellular
signaling, which results in the synthesis of several
proteins (including proinflammatory cytokines).
These proteins trigger hemostatic changes,
leading to the up-regulation of tissue factor22
and impairment of physiologic anticoagulants
and fibrinolysis. Tissue factor plays a critical role
in this process, as shown in meningococcal septicemia,
in which the level of tissue factor on monocytes
at presentation may be predictive of survival.
23 Another study of meningococcal sepsis
showed that a large amount of tissue factor was
found on monocyte-derived circulating microparticles.
24 The up-regulation of tissue factor activates
coagulation, leading to the widespread deposition
of fibrin and to microvascular thromboses and
may contribute to multiple organ dysfunction.
Complex abnormalities of the physiologic anticoagulants
occur, and pharmacologic doses of
activated protein C, antithrombin, and tissue