intracranial pressure and monitoring.pdf

8/17/2019 Intracranial Pressure and Monitoring.pdf

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Intracranial Pressure

The Good, Bad & Ugly

4/19/2011 1ENMU-Roswell

ALL NUMBERS GIVEN ARE ISH…

4/19/2011 ENMU-Roswell 2

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


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


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


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


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


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


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)


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


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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…


More ICP (Bad)

Equals Less LOC

(Also Bad)


What Is Normal ICP?

0 to 15mm Hg in an adult (depends on

where you look)

Most text list it as < 15mm Hg


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


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…


Of Course…


If you feel up to it, there is always

surgery…

Surgery by numbers?

A Little Bit About ICP

Monitoring


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?


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