PowerPoint Presentation Introduction This section will address the
concepts of intracranial dynamics
Objectives Describe the relations of intracranial concepts Discuss
cerebral blood flow hemodynamics Identify normal and abnormal
cerebral blood flow Describe cerebral autoregulation mechanisms
Discuss normal cerebral metabolism Identify the impact of cerebral
ischemia
Key Points Intracranial Pressure Cerebral blood flow
Metabolism
Title Speaker Bio
Karen March MN, RN, CNRN, CCRN alumnus, is an Advanced Practice
Nurse from Sammamish, Washington. She began her career as a
Neuroscience critical care nurse in 1974 after graduating from the
Hospital of the University of Pennsylvania School of Nursing with
a
diploma in nursing. She worked in the Neurosurgical/Surgical ICU
for 11 years during which time she obtained her BSN from Widner
University in Chester, Pennsylvania.
Your Instructors
Karen March’s qualifications: Karen March MN, RN, CNRN, CCRN
alumnus, is an Advanced Practice Nurse from Sammamish, Washington.
She began her career as a neuroscience critical care nurse in 1974
after graduating from the Hospital of the University of
Pennsylvania School of Nursing with a diploma in nursing. She
worked in the Neurosurgical/Surgical ICU for 11 years during which
time she obtained her BSN from Widner University in Chester,
Pennsylvania.
Title
Your Instructors Karen March’s qualifications con’t: • Master
degree in nursing (MN) as a CNS from University of Washington
(1988) with a thesis
focusing on the Effect of Backrest Position on Increased
Intracranial Pressure & Cerebral Perfusion Pressure
• Post-masters Karen worked as a Neuroscience CNS at Harborview
Medical Center followed by Director of Clinical Development at
Integra Lifesciences
• Currently is a global consultant for neuroscience education •
Adjunct faculty and clinical faculty at the University of
Washington School of Nursing • Expertise in Neurotrauma and
Neurocritical Care having published numerous articles and
chapters over 35 years • Volunteers for more than a decade helping
to develop the neurosciences and critical care
in Africa
Title
Your Instructors
Rachel Malloy, MSN, RN, CNRN, SCRN is a native of Kansas City,
Missouri. She began her nursing career 20 year ago after graduating
with her Bachelor in Science in Nursing From Research College of
Nursing in Kansas City, MO.
The majority of her experience is in neurocritical care, diagnostic
medicine and imaging and stroke. In 2011, she began working in
Industry as a clinical resource and educator working with neuro
programs across the nation.
Title
About Rachel Malloy, MSN, RN, CNRN, SCRN Rachel’s qualification
con’t
Master of Science in Nursing with an education focus from Research
College of Nursing in Kansas City, MO with a thesis focusing on
Guidelines for Use of Human Patient Simulators
Certified Neuroscience Registered Nurse Stroke Certified Registered
Nurse Post Graduate Fellowship in Neurovascular Education and
Training in Stroke
Management and Acute Reperfusion Therapy Expertise in principles of
intracranial dynamics, cerebral monitoring, imaging and
stroke Rachel speaks locally, nationally and internationally on a
variety of topics including cerebral dynamics, neuroimaging,
traumatic brain injury, correlative assessment and stroke.
Title Intracranial Dynamics
• The interaction between intracranial content that may compromise
perfusion and produce ischemia
• Three primary components of Intracranial dynamics include: •
Intracranial pressure • Cerebral blood flow • Metabolism
• May be impacted by systemic and intracranial pathology
Title Intracranial Dynamics
Intracranial Pressure (ICP) • Intracranial Pressure reflects the
dynamics relationship
between the intracranial contents and the pathophysiology that may
exhaust its compensatory mechanism
• Mass occupying lesions • Edema • Blood • Hydrocephalus •
Ischemia
Title Intracranial Dynamics
1,400 mls 150 mls 150 mls
Title Intracranial Dynamics
Title Intracranial Dynamics
Volume Pressure Relationship
Compensatory mechanisms to maintain a constant intracranial volume
include the following: Displacement of venous blood through the
jugular and scalp veins Displacement of intracranial CSF through
the foramen magnum into the spinal subarachnoid space Decreased
production of CSF
Cerebral vasodilatation = increases cerebral blood volume Cerebral
vasoconstriction = decreases blood volume
Manipulation of these factors may be used to treat elevated ICP
When compensatory mechanisms are exhausted, brain parenchyma and
arterial blood supply are the last components to be displaced
resulting in elevated ICP Untreated ICP results in intracranial
hypertension, cerebral hypoperfusion, ischemia, brain herniation,
and death
Title Intracranial Dynamics
Compliance
Compliance
• Compliance is the adaptive capacity of the intracranial contents
• Compliance is represented by the formula: C = V/P
• Factors affecting compliance • Amount of volume increase • Time
period over which the volume increases • Volume and characteristics
of the intracranial contents themselves
• Compliance is said to be high when the intracranial contents will
accommodate a large mass with very little change in pressure
Title Intracranial Dynamics
Elastance • Elastance is the inverse of compliance and is what is
measured clinically. Elastance is the change in pressure observed
for a given change in volume. It is a feature of brain tissue and
is represented by the formula E = P/V
• Volume Pressure Index or VPI reflects brain elastance. It
represents the magnitude of response to an increase in
volume.
Formulas for Volume-Pressure Index and Pressure-Volume Index
Volume-Pressure Index (VPI) Pressure-Volume Index (PVI)
VPI = P V
PVI = ____V____ log Final ICP
Initial ICP The VPI is the rise in ICP produced by injecting 1 ml
fluid in 1 second Normal = 1-2 mmHg/ml After surgery for head
trauma
= 3-4 mmHg/ml Mass lesion = 10-20
mmHg/ml
The PVI is the volume of saline injected or withdrawn that produces
a 10-fold increase in ICP Normal volume = 25 ml
Title Intracranial Dynamics
Volume Pressure Relationship
Title Intracranial Dynamics
Cerebral Blood Flow
• Cerebral blood flow (CBF) is the cerebral perfusion pressure
(CPP) divided by cerebrovascular resistance
• CBF is a function of the following: Influx pressure—systole
pressure Efflux pressure—venous pressure or outflow Vascular
radius—vasoconstriction versus
vasodilatation Blood viscosity
Title Intracranial Dynamics
Cerebral Perfusion Pressure (CPP)
• Cerebral perfusion pressure is an estimate of the pressure it
takes to perfuse the brain
• It is calculated by subtracting the mean intracranial pressure
(MICP) from the mean systemic arterial blood pressure (MSAP)
MAP-ICP= CPP • Normal CPP ~ 80 mmHg in adults
• Target for traumatic brain injury (TBI) 60–70 mmHg • Ischemia
occurs at a CPP < 40 mmHg
• Pediatric CPPs are undetermined, but hypotension is suggested at
or below the fifth percentile of normal systolic pressure for the
age of the child
• ~ 65–70 mmHg for infants, ~ 85 mmHg for adolescents • The
threshold for CPP in pediatric TBI is at 40–50 mmHg
Title Intracranial Dynamics
Autoregulation
Autoregulation
• Autoregulation is the capacity of the cerebral circulation to
alter vascular resistance in order to maintain a relatively
constant CBF over a range of mean arterial pressure (MAP)
• When autoregulation is impaired, cerebral arterioles diameter
changes passively causing an increase or decrease of CBF Vasomotor
(Myogenic, adrenergic)
Red circles illustrate constriction and dilation of blood vessels
with blood pressure and autoregulation.
Title Intracranial Dynamics
• Mechanisms that impact autoregulation are: • Flow-metabolism
coupling • Partial pressure of oxygen (PaO2) • Partial pressure of
carbon dioxide (PaCO2) • Neurogenic regulation • Certain anesthetic
agents
Title Intracranial Dynamics
Cerebral Blood Volume
Cerebral blood Volume
• Cerebral blood volume (or CBV) is the volume of blood present at
a given moment within the cranium
• Cerebral blood volume is determined by cerebral blood flow and
vessel diameter
• Average CBV 3–4 ml/100 g tissue • CBV/unit: gray matter >
white matter
• 1-ml change in CBV may equal up to 7-mmHg change in
pressure
Title Intracranial Dynamics
Cerebral Metabolism
Cerebral metabolism • The brain is 2%–3% of body weight but
receives 15% of the cardiac output, uses 20% of the oxygen, and
consumes 25% of the body’s glucose
• The brain has a very high metabolic function • Most (95%) of the
brain’s energy comes from
aerobic glucose metabolism and the production of adenosine
triphosphate (ATP)
• The brain cannot store energy - glucose or O2
• Dependent on CBF to supply nutrients • Normal cerebral metabolic
rate of oxygen
(CMRO2) is 3–5 ml O2/100 g/min
Glycolysis
Glucose
Cyclic acid cycle
Ischemia Risks
• Ischemia – inadequate CBF to meet the demand of the tissues. •
Ischemic cascade is a series of biochemical reactions that are
initiated in the
brain after seconds to minutes of ischemia • Failure of the
sodium/potassium pump • Increase in excitatory amino acids such as
glutamate and aspartate • Release of inflammatory mediators •
Production of superoxides and free radicals
Title
Summary
• Intracranial pressure is the result of a disproportionate sum of
intracranial volume that can no longer adapt to a change in one or
more of its volumes
• These mechanisms are expressed in the concepts of compliance,
elastance, and volume pressure relationship
• Cerebral blood flow is responsible for the delivery of the
nutrients which the cells need to survive
• Cerebral autoregulation is the mechanism which regulates CBF to
assure that CBF remains constant over a wide range of
situations
• Cerebral perfusion pressure is an estimate of adequate perfusion
• Pathologic states can impair autoregulation and cause increased
intracranial
pressure
Title
Conclusion