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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

Alterations in intracranial pressure (ICP)Alterations in intracranial pressure (ICP)

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 1000 liters per day delivered at a pressure of 100 mmHg and at any given time the cranium contains 75 ml (ish)at any given time, the cranium contains 75 ml (ish)

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 brainCerebrospinal fluid

Is constantly secreted, and after circulating,Is constantly secreted, and after circulating, absorbed at an equal rateCSF circulation is slow (500 to 700 ml/day)At a given time the cranium contains 75 ml of CSF

Extracellular and intracellular fluid

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Important Concepts

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Cerebral Perfusion Pressure (CPP)

Cerebral blood flow depends on cerebral perfusion pressureCerebral blood flow controls oxygen and glucose delivery and waste removalIt depends on the pressure gradient across brain

Cerebral perfusion pressure (CPP) and cerebral vascular bed resistanceCPP 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 MAP113 MAP- 80 ICP = 33 CPP (BAD)

Best if > 70 mm Hg< 60 mm Hg = impaired blood flow to brainCan 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 down 25%< 30 mm Hg - Irreversible cerebral< 30 mm Hg Irreversible cerebral ischemiaIf MAP = ICP there is no gradient

Hence, there is no blood flow to the brain and 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

When ICP increases CPP decreasesWhen ICP increases, CPP decreasesAs CPP decreases, cerebral vasodilation occurs

Increases cerebral blood volume (increasing ICP) and further cerebral vasodilation

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Autoregulation OfCerebral Blood Flow

The main regulator of brain blood flow is pressure - dependent activation of smooth muscle 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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SoSo…

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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)

H d d k iti

Agitation

Pain

Coughing andHead and neck position

Changing level of height of bed (especially flat)

External noxious stimuli

Coughing and valsalva maneuver

Seizures

What Can You Do?

Decrease external stimulation

Ensure a quiet environment

Pull slouching patients to the top of the b dbed

Use cervical collar with decreased neck muscle tone

Shut off bright lights

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Treatment

Ventilation:

What is optimal PaO2 level?Keep PaO2 between 90-120mmHg or SPO2

COWhat is the optimal PaCO2

Old method – Keep PaCO2 at 25 mmHg

New method – Keep PaCO2 range 30-35 mmHg

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Treatment

Analgesia and SedationReduces movement

Helps with ventilation

Reduces perceived painReduces perceived pain

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?g y y

A Little Bit About ICP Monitoring

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ICP Monitoring - Indications

Glasgow coma score <8Abnormal CT scan - 50-60% risk

Normal CT Scan, Age > 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

Subdural / subarachnoid monitoringSubdural / subarachnoid monitoring 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 brainObtain CSF cultures

Increased accuracy in ICP monitoring

Accurate and reliable

Clot formation

Hemorrhage risk

Collapsed ventricle

Placement may be impossible

Interventricular Cannula (IVC)

Transport considerationsSystem set-up

Charting ICPg

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?Questions?

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