Neurology- Intracranial Pressure (ICP) Learning Objectives
1) Understand the relationship between ICP, BP, CPP, and Cerebral Blood Flow. Know these structures and their functions
; Choroid plexus: CSF made here. It is an ultra filtrate of plasma and provides metabolic
nutrients to the brain. The most important function is to provide support and buoyancy for the
brain. Total CSF volume is 150cc but turns over 3x/day and so we make about 450cc/day. ; Blood-brain barrier
; Venous sinuses
This important doctrine says that there are only 3 major components of the IC contents: 1- brain 2 – CSF 3 – blood. If all 3 components are in harmony you get normal CSF pressure. If one of them is abnormal the other 2 will try to make room to accommodate the increase pressure and normalize the pressure. This is needed because the brain is enclosed by the skull except for the foramen magnum – hence a herniation site.
Arterial blood pressure and Autoregulation:
Autoregulation curve – the cerebral circulation has an amazing capacity to control the flow of blood into the brain regardless of what is happening in the rest of the body. The cerebral blood
flow is maintained fairly stable for a MABP of 50-150. Beyond MABP of 150 you will get an
increase in cerebral blood flow and will be at risk in developing a hemorrhage.
So, How Are they All Related?
- ICP- Usually 200 mm of Water or 10-15 mm Hg. If it increases, it can reduce cerebral blood
- Cerebral Blood Flow and BP- This is maintained pretty constantly over a wide MABP. - Cerebral Perfusion Pressure (CPP)- Is actually what is measured as a surrogate for Cerebral
Blood flow under conditions where stats are rapidly changing (i.e. ill person with increased
ICP and possible herniation in progress)
o Equation- MABP- ICP
o CPP < 40 considered critical
o CPP Goal- Maintain above 50-55
2) Recognize the Clinical Signs and Symptoms of ICP.
Adults’ Presentation Kids’ Presentation
Acute Increase In ICP HA/Nausea/Vomiting Lethargy and Vomiting
Altered Mentation Bulging Fontanel
Adults’ Presentation Kids’ Presentation
Chronic Increase In ICP HA Failure to Thrive
Lethargy in Varying Degrees Head Circumference Gradually
Cognitive Changes increases th6 Nerve Palsy Fontanel May Bulge
Parinaud’s Disturbances CN Palsies (Again dependent on
Gait Disturbances the etiology)
Some Other Signs/Symptoms Described In Medical Literature
A. Cushing 3 cardinal Symptoms: HTN, Bradycardia, and Respiratory Irregularity
B. Cushing’s Triad’s Classic Case: May also have full blown neurogenic pulmonary edema
C. Symptoms of the NPH are: Gait problems, Dementia, and Urinary incontinence. Know
this triad of SX. These symptoms are all due to the affected frontal lobe
i. A.K.A. Wobbly, Wacky and Wet (I read that in some book)
3) Know the Major Types of Herniation Syndromes and their signs and symptoms.
Herniation can result when a mass (like a tumor or an infarction) reaches a size that causes focal distortion of the brain structures.
The midline structure near #1 is the faux; hence that herniation is also called a sub-faucine herniation, where the mass is so large that it pushes the frontal love from one side of the brain to the other hemisphere.
#2 is a lesion that causes the temporal lobe to herniate down toward the tentorium, hence a transtentorial herniation. It can be bi- or unilateral. It has a very characteristic feature, due to the compression of cranial nerve III. Third nerve palsy -> a big dilated pupil.
#3 is the most fatal. It is transforaminal (smushes the medulla through the foramen magnum).
#4 is relatively rare. Upward herniation of the medulla into the tentorium.
#5 results from a craniotomy and the brain herniates through the opening in the cranium.
4) Know the Major Techniques to reduce elevated ICP and how they work.
A. The Major Techniques to Reduce Elevated ICP are as follows:
i. Intracranial Mass Lesion- Remove the Lesion
ii. Head of the Bed is elevated 30 degrees-Promotes Venous return
iii. Hyperventilation in the Short-term
1. Related to pC02 levels
2. PCO2 is also related to ICP. Decreased arterial CO2 -> increased
constriction of the cerebral blood vessels -> decreased CBF ->
decreased ICP. Decreasing pCO2 (often by hyperventilating the patient)
is a treatment strategy for elevated ICP.
3. Goal- 30 mm Hg
iv. Diuretic Therapy with Mannitol and Furosemide (Lasix)
1. Reduce cerebral edema and pressure
v. Sedation and Paralytic Agents
1. Effective in Vasogenic Edema produced by intracranial tumors
2. Not demonstrated efficacy in cytotoxic cerebral edema
vii. Barbiturate Coma
1. Clinical Efficacy has not been proven
2. General anesthetic helps reduce edema by reducing the metabolism of
viii. Decompressive Craniectomies or Lobectomies
1. Extreme Instances
2. Younger, Healthier Patients are the optimal candidates
B. The Goals in Treating are as follows:
i. Maintain the ICP below 20 mm Hg.
ii. Sustain a cerebral perfusion pressure (CPP) of > 50 mm Hg.
5) Learn the causes for both acute and chronic-elevated ICP A. Acute Causes are as follows:
i. Head Injury
iv. Metabolic Changes
v. Dural Sinus Thrombosis
vii. Certain Tumors
B. Chronic Causes are as follows:
i. Many Tumors
ii. Pseudo-tumor cerebri or Benign Intracranial HTN
iii. Some cases of Hydrocephalus
iv. Chronic Subdural Hematomas
C. Herniation Syndromes and there relative contributions are related to the immediate and
urgent progression of these syndromes.