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Intracranial Pressure

Terry Coyne MBBS, FRACS

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Raised ICP • Definitions

• Causes

• Consequences

• Therapy

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What its all about

• Cerebral blood flow (CBF) sufficient to meet cerebral metabolic oxygen demand (CMRO2)

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Cerebral Perfusion Pressure (CPP)

= Mean Arterial Pressure (MAP) – ICP

Normal ICP <10-15 mm Hg

Normal CPP > 50 mm Hg

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Cerebral Autoregulation

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Monro-Kellie Doctrine

• The skull is an inelastic closed compartment

• Intracranial compartment contains

brain

blood (intra- & extra-vascular)

CSF

other – tumour, abscess, etc

- extracellular fluid (vasogenic

edema)

• Sum of these is constant – if one increases, another must decrease, or else ICP increases

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ICP Curve

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Consequences of Raised ICP

• Global - CPP

• Compartment - herniation

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Causes of Raised ICP

• Too much:

brain – cytotoxic edema

blood – intracranial haemorrhage

- venous sinus thrombosis

CSF – hydrocephalus

• Other – tumour, abscess

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Effects of Raised ICP

Early on

Headache – positional

val salva

early morning

Nausea/vomiting

Changed level of consciousness

Any focal symptom/deficit

Papilloedema

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Effects of Raised ICP

• Generalised – low CPP, generalised loss of brain function – decreased level of consciousness

• Herniations

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Herniations

• Subfalcine – not generally clinically significant

• Tentorial – 3rd nerve palsy (dilated pupil)

- lateral brainstem (pyramidal tracts) compression – contralateral weakness

- PCA occlusion - hemianopia

- cardio-respiratory centre

destruction - death

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Herniations

• Foramen magnum

“Cushing’s triad”

bradycardia

hypertension

irregular respirations

(decreased level of consciousness)

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Raised ICP Management

• Treat cause (remove clot/tumour, V-P shunt for hydrocephalus)

• Less blood volume – head up

- neck not kinked

- low pCO2 (hyperventilation)

• less brain – mannitol

- dexamethasone (vasogenic edema)

• less CSF – CSF drain

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Extradural haematomas

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Raised ICP Management

More sophisticated (Neuro ICU)

• Change the rigid box (decompressive craniotomy)

• Modulate CPP

• Reduce CMRO2 – sedation

- thiopentone

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Raised ICP Management

• GP management

• ABC’s – prevent hypoventilation

- maintain pO2, BP (CPP)

dexamethasone if vasogenic edema

eg 4mg q6h

- 20% mannitol (eg 300 mls)

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Thank you