intracranial pressure and monitoring.pdf
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Intracranial Pressure
The Good, Bad & Ugly
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ALL NUMBERS GIVEN ARE ISH…
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Neurological
Pathophysiology
Cerebral blood flow (CBF) interrupted by:
Structural changes or damage
Circulatory changes
era ons n n racran a pressure
Three structures in the intracranial space:
Brain tissue
Blood
Water
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Monroe-Kellie Doctrine
The cranial vault is a fixed space consisting of
3 compartments:
Parenchyma (neurons and neuroglial tissue) - 80%
CSF - 10%
Blood - 10%
Therefore, expansion of one compartment
results in a compensatory decrease in another
in order to maintain ICP
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Intracranial Space
Brain tissue
Mostly water, intracellular and extracellular
Blood - Intracranial circulation of blood is about 1000liters per day delivered at a pressure of 100 mmHg and
,
Major arteries in base of brain
Arterial branches, arterioles, capillaries, venules,
veins within brain substance
Cortical veins and dural sinuses
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Intracranial Space
Water in:
Ventricles of brain
Cerebrospinal fluidIs constantl secreted and after circulatin , ,absorbed at an equal rate
CSF circulation is slow (500 to 700 ml/day)
At a given time the cranium contains 75 ml ofCSF
Extracellular and intracellular fluid
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Important Concepts
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Cerebral Perfusion Pressure
(CPP)
Cerebral blood flow depends on cerebralperfusion pressure
Cerebral blood flow controls oxygen andglucose delivery and waste removal
It depends on the pressure gradient acrossbrain
Cerebral perfusion pressure (CPP) and cerebralvascular bed resistance
CPP determined by:Mean arterial pressure (MAP): (Diastolic pressure +⅓pulse pressure) minus intracranial pressure
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Cerebral Perfusion Pressure
Calculate CPPSubtract ICP from MAP
Example:Patient has an ICP of 80 and a MAP of 113
113 MAP
- 80 ICP
= 33 CPP (BAD)
Best if > 70 mm Hg
< 60 mm Hg = impaired blood flow to brain
Can lead to seizure, coma and death
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The Bottom Line…
< 50 mm Hg - Mild cerebral ischemia
< 40 mm Hg - Cerebral blood flow down25%
< - ischemia
If MAP = ICP there is no gradient
Hence, there is no blood flow to the brainand brain death in imminent (seizure – coma
– death)
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Cerebral Blood Flow
As ICP approaches MAP:
Gradient for flow decreases
Cerebral blood flow restricted
,
As CPP decreases, cerebral vasodilation
occurs
Increases cerebral blood volume
(increasing ICP) and further cerebral
vasodilation
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Autoregulation Of
Cerebral Blood Flow
The main regulator of brain blood flow is
pressure - dependent activation of smoothmuscle in the arterioles of the brain. The
more the arteriole is stretched, the more it
contracts, and this lasts as long as the
stretch occurs
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…
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More ICP (Bad)
Equals Less LOC
(Also Bad)
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What Is Normal ICP?
0 to 15mm Hg in an adult (depends on
where you look)
Most text list it as < 15mm Hg
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Factors Which Increase ICP
Hip flexion
(decreases venous
return)
Agitation
Pain
ea an nec pos t on
Changing level of height
of bed (especially flat)
External noxious stimuli
valsalva
maneuver
Seizures
What Can You Do?
Decrease external stimulation
Ensure a quiet environment
Pull slouching patients to the top of the
e
Use cervical collar with decreased neck
muscle tone
Shut off bright lights
Align head and neck
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Treatment
Ventilation:
What is optimal PaO2 level?
Keep PaO2 between 90-120mmHg or SPO2
What is the optimal PaCO2Old method – Keep PaCO2 at 25 mmHg
New method – Keep PaCO2 range 30-35
mmHg
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Treatment
Analgesia and Sedation
Reduces movement
Helps with ventilation
Limits responses to procedures such as
suctioning
A lot of different ones – fentanyl,
midazolam, propofol etc…
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Of Course…
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If you feel up to it, there is always
surgery…
Surgery by numbers?
A Little Bit About ICP
Monitoring
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ICP Monitoring - Indications
Glasgow coma score 40 or BP < 90mmHg or abnormal
motor posturing - 50-60% risk
Normal CT scan with no risk factors - 13% risk
Glasgow coma score 9 to 12If paralytic and/or sedative medications are being used or
abnormal CT scan - 10-20% will deteriorate to severe head
injury
Devices
Interventricular cannula (IVC)
Epidural catheter
devices
Fiber optic transducer tipped probe
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Interventricular Cannula (IVC)
Most commonly used
monitor Placed within the
ventricle
IVC
Interventricular Cannula
(IVC)
AdvantagesDrain CSF to lower
ICP
DisadvantagesInfection
Injury to brain
Obtain CSF cultures
Increased accuracy
in ICP monitoring
Accurate and reliable
Clot formation
Hemorrhage risk
Collapsed ventricle
Placement may be
impossible
Interventricular Cannula
(IVC)
Transport considerations
System set-up
Charting ICP
Drainage orders
Movement
Pressure changes with air transport
Abnormal Wave Forms
P2 > P1 – Autoregulation gone and
things are swirling the drain. “A” waves
are next
Abnormal Wave Forms
Things Are Headed South
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Questions?
4/19/2011 ENMU-Roswell 31
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