“Monro-Kellie Doctrine” by Lisa DelSignore for OPENPediatrics

Monro-Kellie Doctrine by Dr. Lisa Delsignore. So the first thing I'd like to talk about
is the principles behind brain swelling in terms of the Monro-Kellie Doctrine, which
you may be familiar with. Essentially this doctrine states that the
cranial compartment is incompressible, so the volume inside is a fixed volume. There are three things inside the cranium
that make up its volume, brain tissue, blood, and CSF. Because the volume is fixed, these three things
maintain an equilibrium such that when the volume of one component increases the volume
of another decreases. For example, when a lesion, such as an epidural
hematoma, adds to the brain volume, there are compensatory decreases in CSF and Venus
volume, as you can see here.

However, at a critical point, the CSF and
blood buffers are not able to compensate for changes in cranial compartment volume. That is, when the volume increases too much,
usually at volumes greater than 100 to 120 mL, the intracranial pressure begins to rise
as well, as you can see here. At this point, the intracranial pressure begins
to skyrocket with changes in intracranial volume. And what we're trying to prevent here is reaching
that critical point where brain swelling increases so much that the intracranial compartment
is unable to maintain its pressure. And this is important because the amount of
intracranial pressure that we see is directly related to the cerebral perfusion pressure,
which is the driving pressure the brain is seeing in terms of delivering oxygen and other
key nutrients to it. And cerebral perfusion pressure is defined
as the equation, as you can see here, mean arterial pressure minus the intracranial pressure. So for any constant mean arterial pressure,
you can see that as the intracranial pressure starts to rise, your cerebral perfusion pressure
starts to drop, which means that the brain will start to see less nutrients, less oxygen,
which can have deleterious effects on the brain in terms of ischemia and cell death.

And typically, when we talk about managing
cerebral perfusion pressure, we think about minimum targets by age. And we'll get into this a little bit in a
few minutes. But you can see here that less than 4 years
of age, we try to target cerebral perfusion pressure around 50 millimeters of mercury. Anywhere between 4 to about 10 years of age,
we target around 60 millimeters of mercury as a minimum target. And greater than 9 years we start to think
of them more as like an adult and target cerebral perfusion pressure around 70 millimeters of
mercury..

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