Advanced Trauma Life Support ATLS Student Course Manual 2018

PHYSIOLOGY REVIEW 107
Intracranial Pressure
Elevation of intracranial pressure (ICP) can
reduce cerebral perfusion and cause or exacerbate
ischemia. The normal ICP for patients in the
resting state is approximately 10 mm Hg. Pressures
greater than 22 mm Hg, particularly if sustained
and refractory to treatment, are associated with
poor outcomes.
Monro–Kellie Doctrine
n FIGURE 6-3 Unequal pupils: the left is greater than the right.
The Monro–Kellie Doctrine is a simple, yet vital concept
that explains ICP dynamics. The doctrine states that
the total volume of the intracranial contents must
remain constant, because the cranium is a rigid
container incapable of expanding. When the normal
intracranial volume is exceeded, ICP rises. Venous
blood and CSF can be compressed out of the container,
providing a degree of pressure buffering (n FIGURE 6-5
and n FIGURE 6-6). Thus, very early after injury, a mass
such as a blood clot can enlarge while the ICP remains
normal. However, once the limit of displacement of
CSF and intravascular blood has been reached, ICP
rapidly increases.
Cerebral Blood Flow
TBI that is severe enough to cause coma can markedly
reduce cerebral blood flow (CBF) during the first few
hours after injury. CBF usually increases over the next
2 to 3 days, but for patients who remain comatose, it
n FIGURE 6-4 Lateral (Uncal) Herniation. A lesion of the middle
meningeal artery secondary to a fracture of the temporal bone
may cause temporal epidural hematoma. The uncus compresses the
Advanced Trauma Life Support for Doctors
upper Student brain Course stem, Manual, involving 9e the reticular system (decreasing GCS),
the oculomotor American College nerve of Surgeons (pupillary changes), and the corticospinal
Figure# 06.04
tract Dragonfly in the midbrain Media Group (contralateral hemiparesis).
12/02/2011
ion associated with contralateral hemiparesis is the
classic sign of uncal herniation. Rarely, the mass lesion
pushes the opposite side of the midbrain against
the tentorial edge, resulting in hemiparesis and a
dilated pupil on the same side as the hematoma.
Physiology Review
Physiological concepts that relate to head trauma
include intracranial pressure, the Monro–Kellie
Doctrine, and cerebral blood flow.
n FIGURE 6-5 Volume–Pressure Curve. The intracranial contents
initially can compensate for a new intracranial mass, such as a
subdural or epidural hematoma. Once the volume of this mass
reaches a critical threshold, a rapid increase in ICP often occurs,
which can lead to reduction or cessation of cerebral blood flow.
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