intracranial pressure concepts

Intracranial Pressure Intracranial Pressure ConceptsConcepts

Michelle Hill RN, BSN, CNRN, CCRN, SCRNClinical Nurse Educator

Neurocritical Care

ObjectivesObjectives

Review intracranial pressure concepts (ICP)

Discuss cerebral hemodynamicsDiscuss herniation syndromesDiscuss management of increased ICPDiscuss types of ICP monitoring devices

Intracranial Pressure (ICP)Intracranial Pressure (ICP)

Intracranial pressure is the pressure exerted by the intracranial contents of brain tissue, blood, and cerebrospinal fluid (CSF) within the skull.

Fluctuates within a normal range.Normal ICP = 0 – 15 mmHgModerate elevation ICP = 15 – 40 mmHgSevere elevation ICP > 40 mmHgIntracranial hypertension:

◦ICP >20mmHg for >5 minutes

Monroe-Kellie DoctrineMonroe-Kellie Doctrine

Used to explain why ICP existsSkull is a rigid, non-distendable box containing 3

volume components:◦ 80 % brain tissue◦ 10% blood◦ 10% CSF

As long as these volumes remain the same, the pressure within the box is unchanged

Signs and Symptoms of Increased ICPSigns and Symptoms of Increased ICP

Headache (Worse in morning)

Vomiting without nausea Change in LOC Change or loss of

motor/sensory function Pupillary changes Respiratory changes Papilloedema Cushing’s Response

◦ Increased systolic blood pressure

◦ Widened pulse pressure◦ Bradycardia

Respiratory Signs and SymptomsRespiratory Signs and Symptoms

Cheyne-StrokesApneusticHyperventilation

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Herniation or ICP?Herniation or ICP?

Progressive deterioration in LOC◦Caudal displacement of the diencephalon and

midbrainPupillary dilitation, B/L ptosis, impaired

upward gazeExtension to painRespiratory irregularity

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What Causes Increased ICP-BrainWhat Causes Increased ICP-Brain

Space-occupying masses◦Abscesses◦Tumors◦Aneurysms◦Trauma-hematoma

Cerebral Edema◦Vasogenic (extracellular)◦Cytotoxic (intracellular)

More causes of Increased ICP-BloodMore causes of Increased ICP-Blood

StrokeTraumaConditions that increase blood flow

◦HTN◦PaCO2◦Anesthetic agents

Decreased venous return◦HOB flat◦Trach ties◦Neck flexion

More Causes of Increased ICP-CSFMore Causes of Increased ICP-CSF

Increases in CSF volume◦Obstruction of CSF pathways

Non-Communicating hydrocephalus◦Decreased CSF absorption

Communicating hydrocephalus Subarachnoid hemorrhage

◦Overproduction of CSF Choroid plexus papillomas

Cerebral Blood Flow (CBF)Cerebral Blood Flow (CBF)

Required to provide oxygenation to the brain tissue

Approximate CBF is 55mL/100g of brain tissue per minute

450-1000mL/min to the whole brainBrain receives 20% of total cardiac output

and uses 20% of oxygen consumed in the basal state.

Cerebral Blood Flow RegulationCerebral Blood Flow Regulation

Autoregulation◦Ability of an organ to maintain a constant blood

flow◦Major homeostatic and protective mechanism◦Provides a constant CBF by adjusting the

diameter of blood vessels.

Cerebral Blood FlowCerebral Blood Flow

Arterial carbon dioxide pressure affects the CBF by affecting the arterioles of the brain.

PaCO2 > 45 mmHg causes inappropriate vasodilation of the arterioles which ↑ CBF.

PaCO2 < 35 mmHg causes constriction of the arterioles which ↓ CBF.

PaO2 <50 mmHg also causes cerebral vasodilation.

Cerebral Perfusion Pressure (CPP)Cerebral Perfusion Pressure (CPP)

CPP is the blood pressure gradient across the brain

CPP is the difference between the mean arterial pressure (MAP) and the intracranial pressure (ICP)

Any blood coming into the brain must overcome the ICP to enter the intracranial contents and perfuse brain cells.

Cerebral Perfusion PressureCerebral Perfusion PressureCPP = MAP – ICPMore important than ICP value

Normal CPP range is 70 – 100 mmHg◦CPP < 60 = ischemia◦CPP < 40 = infarct◦CPP – 0 = brain death

Compensatory MechanismsCompensatory Mechanisms

These are protective mechanisms to assure that the brain is receiving adequate perfusion

If one of the intracranial volumes increases another must decrease to avoid increase in ICP◦ CSF◦ Blood◦ Tissue

Compensatory Mechanisms-CSFCompensatory Mechanisms-CSF

• Cerebrospinal Fluid Component–Displacement of CSF into the spinal

subarachnoid space–Decreased production of CSF

Compensatory Mechanisms-BloodCompensatory Mechanisms-Blood

Blood component◦Vasoconstriction of the blood vessels of

cerebral structures (carbon dioxide) Decrease in the intracranial blood volume

◦Increased venous outflow Corrected with positioning

Compensatory Mechanisms-BrainCompensatory Mechanisms-Brain

Brain Tissue Component◦Supratentorial

Subfalcine (1) Uncal (2)

◦Loss of consciousness◦ Ipsilateral pupil

dilation◦Contralateral

hemiparesis

◦Infratentorial (3)

Compensatory MechanismsCompensatory Mechanisms

Success of compensatory mechanisms is dependent upon several factors:◦Rate of expansion of the volume causing

increased ICP◦Compliance of the brain◦Location of the expanding volume

Cushing’s ResponseCushing’s Response

Elevated BP◦ Ischemia in Medullary vasomotor center-increase in

systemic arterial pressure◦ Intraluminal blood pressure must be higher than the ICP

for continued blood flowWidened pulse pressure

◦ Elevated BP increases COBradycardia

◦ Pressure on the Vagal control in the Medulla◦ Becomes decreased but bounding to pump blood upward

Management of ICPManagement of ICP

Basic measuresICP monitorMannitolHyperventilate

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Management of ICPManagement of ICP

Craniectomy: excision of a portion of the skull without replacement◦ Skull bone can be stored in the patient’s abdomen◦ Considered a life-saving measure for maximal cerebral

swelling

Brain DeathBrain Death

It is the complete and irreversible cessation of all brain function

Absence of brain function and all brain stem reflexes

Cerebral blood flow is 0 in brain deathBrain death is the legal definition of deathSpinal reflexes may still be presentBrain Death Protocol

ReferencesReferences Dunn, L. (2002). Raised Intracranial Pressure. Journal of Neurology,

Neurosurgery and Psychiatry. 73 (suppl 1). i23-i27. Germon, K. (1988). Interpretation of ICP pulse waves to determine

intracerebral compliance. Journal of Neuroscience Nursing, 20, 344–351. Hickey, J. V. (2009). The Clinical Practice of Neurological and

Neurosurgical Nursing (6th ed.). Philadelphia: Lippincott. March, K. (2004). Intracranial Pressure Concepts and Cerebral Blood

Flow. In M. K. Bader & L. R. Littlejohns, AANN Core Curriculum for Neuroscience Nursing (4th ed., pp. 87–114). Philadelphia: Saunders.

Slazinski, T., Anderson, T., Cattell, E., Eigsti, J., Heimsoth, S., Holleman, J. & et.al. (2011). Care of the patient undergoing intracranial pressure monitoring/external ventricular drainage or lumbar drainage. American Association of Neuroscience Nurses Clinical Practice Guideline Series.

Stevens, R., Huff, J., Duckworth, J., Papangelou, A., Weingert, S. & Smith, W., (2012). Emergency Neurological Life Support: Intracranial Hypertension and Herniation. Neurocritical Care. DOI: 10.1007/s12028-012-9754-5