intracranial dynamics
TRANSCRIPT
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
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