Intracranial Pressure Concepts Michelle Hill RN, BSN, CNRN, CCRN, SCRN Clinical Nurse Educator Neurocritical Care

Objectives Review intracranial pressure concepts (ICP) Discuss cerebral hemodynamics Discuss herniation syndromes Discuss management of increased ICP Discuss types of ICP monitoring devices

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 mmHg Moderate elevation ICP = 15 – 40 mmHg Severe elevation ICP > 40 mmHg Intracranial hypertension: ◦ICP >20mmHg for >5 minutes

Monroe-Kellie Doctrine Used to explain why ICP exists Skull 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 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 Symptoms Cheyne-Strokes Apneustic Hyperventilation 6

Herniation or ICP? Progressive deterioration in LOC ◦Caudal displacement of the diencephalon and midbrain Pupillary dilitation, B/L ptosis, impaired upward gaze Extension to pain Respiratory irregularity 7

What Causes Increased ICP-Brain Space-occupying masses ◦Abscesses ◦Tumors ◦Aneurysms ◦Trauma-hematoma Cerebral Edema ◦Vasogenic (extracellular) ◦Cytotoxic (intracellular)

More causes of Increased ICP-Blood Stroke Trauma Conditions that increase blood flow ◦HTN ◦PaCO2 ◦Anesthetic agents Decreased venous return ◦HOB flat ◦Trach ties ◦Neck flexion

More 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) Required to provide oxygenation to the brain tissue Approximate CBF is 55mL/100g of brain tissue per minute mL/min to the whole brain Brain receives 20% of total cardiac output and uses 20% of oxygen consumed in the basal state.

Cerebral 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 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) 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 Pressure CPP = MAP – ICP More important than ICP value Normal CPP range is 70 – 100 mmHg ◦CPP < 60 = ischemia ◦CPP < 40 = infarct ◦CPP – 0 = brain death

Compensatory 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-CSF Cerebrospinal Fluid Component – Displacement of CSF into the spinal subarachnoid space – Decreased production of CSF

Compensatory 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-Brain Brain Tissue Component ◦Supratentorial  Subfalcine (1)  Uncal (2) ◦ Loss of consciousness ◦ Ipsilateral pupil dilation ◦ Contralateral hemiparesis ◦Infratentorial (3)

Compensatory 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 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 flow Widened pulse pressure ◦Elevated BP increases CO Bradycardia ◦Pressure on the Vagal control in the Medulla ◦Becomes decreased but bounding to pump blood upward

Management of ICP Basic measures ICP monitor Mannitol Hyperventilate 22

Management 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 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 death Brain death is the legal definition of death Spinal reflexes may still be present Brain Death Protocol

References 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: /s