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