Transcript How Vasoactive Meds Affect Cerebral Hemodynamics

Anesthesia Medication
Effects on Cerebral
Hemodynamics
CBF:
CBF:
CBV:
CBF:
CBV:
ICP:
CBF:
CBV:
ICP:
Ischemia:
CBF:
CBV:
ICP:
Ischemia:
CBF:
Site of autoregulation
CBV:
ICP:
Ischemia:
CBF:
Site of autoregulation
Site of medication effects
CBV:
ICP:
Ischemia:
CBF:
Site of autoregulation
Site of medication effects
Difficult to measure
CBV:
ICP:
Ischemia:
CBF:
Site of autoregulation
Site of medication effects
CBV:
Difficult to measure
Varies to a lesser degree than CBF
ICP:
Ischemia:
CBF:
Site of autoregulation
Site of medication effects
CBV:
Difficult to measure
Varies to a lesser degree than CBF
ICP:
CSF, CBV, Brain Tissue
Ischemia:
CBF:
Site of autoregulation
Site of medication effects
CBV:
Difficult to measure
Varies to a lesser degree than CBF
ICP:
CSF, CBV, Brain Tissue
Ischemia:
Focal vs global
Affects all above variables
MAP- ICP
CBF:
_____________
Resistance
MAP- ICP
CBF:
Directly Proportional
_____________
Resistance
MAP- ICP
CBF:
Directly Proportional
_____________
Resistance Inversely proportional
Normal Values:
CBF:
Normal Values:
CBF:
15-20% of CO
Normal Values:
15-20% of CO
CBF: 750 mL/min
Normal Values:
15-20% of CO
CBF: 750 mL/min
50 mL/100g/min
Normal Variation:
CBF:
Normal Variation:
BP above autoregulation range
CBF:
CBF
Normal Variation:
CBF:
BP above autoregulation range
CBF
BP below autoregulation range
CBF
Questions
Answers
Question #1: A) Brain Tissue
◦The 3 components that make up ICP are
brain tissue, CSF, and CBV. Brain tissue
accounts for 80% of ICP while CSF and CBV
account for 10% each.
Answers
Question #2: B) Blood flow of 50 ml/min/100 g
of tissue
◦Normal ICP is <15 and the brain normally
receives 15-20% of cardiac output. The typical
total blood flow to the brain is 750 ml/min or
50 ml/min/100 g of tissue. Cerebral Ischemia
begins when blood flow drops below 20 and
infarct begins at 6 ml/min/100 g of tissue.
Answers
Question #3: C) Increased cerebral vascular
resistance
◦Hypercarbia and hypoxia both would
increase CBF due to increased metabolic
demand. Increased cerebral vascular
resistance would have an inverse effect on
CBF.
CBF Autoregulation
Overview
Intrinsic factors
Extrinsic factors
Ischemia
CBF Autoregulation
Overview
MAP 50-150
CBF Autoregulation
Overview
MAP 50-150
Rapid change will still affect CBF
CBF Autoregulation
Overview
MAP 50-150
Rapid change will still affect CBF
Disrupted by :
volatile anesthetics
CBF Autoregulation
Overview
MAP 50-150
Rapid change will still affect CBF
Disrupted by :
volatile anesthetics
HTN
CBF Autoregulation
Overview
MAP 50-150
Rapid change will still affect CBF
Disrupted by :
volatile anesthetics
HTN
CBF Autoregulation
Overview
Pt’s Baseline MAP
determines the patient’s
autoregulation range
CBF Autoregulation
Intrinsic Factors
Myogenic response
CBF Autoregulation
Intrinsic Factors
Myogenic response
Nitric Oxide
CBF Autoregulation
Intrinsic Factors
Myogenic Response
Nitric Oxide
Autonomic Innervation
CBF Autoregulation
Intrinsic Factors
Myogenic Response
Nitric Oxide
Autonomic Innervation
CBF Autoregulation
Extrinsic Factors
PaCO2
CBF Autoregulation
Extrinsic Factors
PaCO2
Metabolism
CBF Autoregulation
Extrinsic Factors
PaCO2
Metabolism
CBF Autoregulation: Extrinsic
Factors
PaCO2:
Most potent vasodilator
CBF Autoregulation: Extrinsic
Factors
PaCO2:
Most potent vasodilator
Direct relationship to CBF
CBF Autoregulation: Extrinsic
Factors
PaCO2:
Most potent vasodilator
Direct relationship to CBF
CO2 Responsiveness Preserved
with anesthetics
CBF Autoregulation: Extrinsic
Factors
Metabolism (CMRO2):
Direct relationship to CBF
CBF Autoregulation: Extrinsic
Factors
Metabolism (CMRO2):
Direct relationship to CBF
Main factor is brain activity
CBF Autoregulation: Extrinsic
Factors
Metabolism (CMRO2):
Direct relationship to CBF
Main factor is brain activity
Main controllable factor
intraop is temperature
CBF Autoregulation: Extrinsic
Factors
Metabolism (CMRO2):
Direct relationship to CBF
Main factor is brain activity
Main controllable factor
intraop is temperature: 7% per
1deg C
CBF Autoregulation: Extrinsic
Factors
Metabolism (CMRO2):
Direct relationship to CBF:
Flow-Metabolism Coupling
CBF Autoregulation
Ischemia
Focal vs Global
CBF Autoregulation: Focal
Ischemia
Cerebral Steal:
CBF Autoregulation: Focal
Ischemia
Cerebral Steal:
1. Focal Ischemic areas are
maximally dilated
CBF Autoregulation: Focal
Ischemia
Cerebral Steal:
1. Focal Ischemic areas are
maximally dilated
2. General Cerebral
Vasodilation
CBF Autoregulation: Focal
Ischemia
Cerebral Steal:
1. Focal Ischemic areas are
maximally dilated
2. General Cerebral
Vasodilation
Reduces net blood flow to ischemic
areas
CBF Autoregulation: Focal
Ischemia
Inverse Steal:
CBF Autoregulation: Focal
Ischemia
Inverse Steal:
1. Focal Ischemic areas are
maximally dilated
CBF Autoregulation: Focal
Ischemia
Inverse Steal:
1. Focal Ischemic areas are
maximally dilated
2. General Cerebral
Vasoconstriction
CBF Autoregulation: Focal
Ischemia
Inverse Steal:
1. Focal Ischemic areas are
maximally dilated
2. General Cerebral
Vasoconstriction
increases net blood flow to
ischemic areas.
Questions
Answers
Question #1: D) 50-150
◦While some texts have varying values of
cerebral autoregulation, most sources
agree on the value of 50-150 in the
healthy patient.
Answers
Question #2: B) PaCO2
◦While isoflurane and nitrous oxide are
cerebral vasodilators, the most potent
cerebral vasodilator is PaCO2. High PaO2
is a vasoconstrictor.
Answers
Question #3: C) Vasoconstriction of nonischemic brain tissue
◦In focal ischemia a small area of brain tissue is
receiving too little blood flow. Desirable effects
to reduce the damage would be vasoconstriction
of non-ischemic tissue and vasodilation of
ischemic tissue. This process is referred to as
inverse steal.
CBF and Anesthetics
Inhaled Anesthetics
IV General Anesthetics
CBF and Anesthetics: Inhaled Anesthetics
CBF and Anesthetics: Inhaled Anesthetics
Decrease CMRO2
CBF and Anesthetics: Inhaled Anesthetics
Decrease CMRO2 which
CBF
CBF and Anesthetics: Inhaled Anesthetics
Are direct cerebral vasodilators
which
CBF
CBF and Anesthetics: Inhaled Anesthetics
Net effect determined by:
CBF and Anesthetics: Inhaled Anesthetics
Net effect determined by
balance of MAP and
CBF and Anesthetics: Inhaled Anesthetics
Net effect determined by
balance of MAP and MAC
MAP- ICP
CBF:
Directly Proportional
_____________
Resistance Inversely proportional
MAP- ICP
CBF:
Directly Proportional
_____________
Resistance Inversely proportional
MAP- ICP
CBF:
Directly Proportional
_____________
Resistance Inversely proportional
MAP- ICP
CBF:
Directly Proportional
_____________
Resistance Inversely proportional
MAP- ICP
CBF:
Directly Proportional
_____________
Resistance Inversely proportional
CBF and Anesthetics: Inhaled Anesthetics
Over 1 MAC, cerebral
vasodilation greatly increases
CBF and Anesthetics: Inhaled Anesthetics
Over 1 MAC: cerebral
vasodilation greatly increases
& autoregulation is impaired
CBF and Anesthetics: Inhaled Anesthetics
Over 1 MAC: cerebral
vasodilation greatly increases
& autoregulation is impaired
BUT
CBF:
Site of autoregulation
Site of medication effects
CBV:
Difficult to measure
Varies to a lesser degree than CBF
ICP:
CSF, CBV, Brain Tissue
Ischemia:
Focal vs global
Affects all above variables
CBF and Anesthetics: Inhaled Anesthetics
Inhaled Anesthetics within normal
ranges in patients with normal
intracranial compliance and PaCO2 will
have minimal cerebral hemodynamic
changes
Questions
Answers
Question #1: C) Sevoflurane
◦All volatile anesthetics impair cerebral
autoregulation at anesthetic levels.
Barbiturates and propofol preserve it.
Answers
Question #2: D) Halothane
◦All volatile anesthetics have the potential
of increasing ICP, but halothane increases
CBF the most. Other volatile anesthetics
would be more appropriate in this
scenario.
Answers
Question #3: C) Isoflurane
◦Isoflurane is unique in that it is the only
volatile agent that facilitates the absorption
of CSF and has a favorable effect on CSF
dynamics.
Answers
Question #4: D) All of the above
◦Nitrous has the potential to increase ICP
substantially. The other volatile
anesthetics increase ICP as well, but not to
the same degree as nitrous.
Answers
Question #5: C) A decrease in CMRO2 and
an increase in CBF
◦Volatile anesthetics can produce what is
referred to luxury perfusion, a beneficial
effect during global ischemia that reduces
CMRO2 and increases CBF.
Answers
Question #6: A) Isoflurane
◦The mechanisms by which iso, sevo, and
des decrease CMRO2 is similar, but iso is
the one that reduces CMRO2 the most.
CBF and Anesthetics
Inhaled Anesthetics
IV General Anesthetics
CBF and Anesthetics: IV General Anesthetics
CBF and Anesthetics: IV General Anesthetics
Just as with Inhaled Anesthetics,
CO2 responsiveness is preserved
CBF and Anesthetics: IV General Anesthetics
Just as with Inhaled Anesthetics,
CO2 responsiveness is preserved
Unlike Inhaled Anesthetics,
autoregulation is also preserved
CBF and Anesthetics: IV General Anesthetics
All Gen Anesthetics except
Ketamine reduce CMRO2, which
reduces CBF
CBF and Anesthetics: IV General Anesthetics
All except Ketamine reduce
CMRO2, which reduces CBF
Many have direct cerebral
vasoconstriction
CBF and Anesthetics: IV General Anesthetics
Net Effect:
Substantial Reduction in CBF (4050%)…
CBF and Anesthetics: IV General Anesthetics
Net Effect: Substantial Reduction
in CBF (40-50%) IF MAP IS
MAINTAINED within
autoregulation range…
CBF:
Site of autoregulation
Site of medication effects
CBV:
Difficult to measure
Varies to a lesser degree than CBF
ICP:
CSF, CBV, Brain Tissue
Ischemia:
Focal vs global
Affects all above variables
CBF and Anesthetics: IV General Anesthetics
Net Effect: Reduction in CBF (4050%) leads to moderate reduction
in ICP (20-30%)
Questions
Answers
Question #1: D) Propofol
◦Of the drugs on the list propofol is the
only drug that decreases CBF and CMRO2.
Ketamine, halothane, and nitrous oxide all
increase CBF.
Answers
Question #2: D) All of the above
◦Ketamine increases CBF, CMRO2, and ICP.
Answers
Question #3: A) Barbiturates have a more
global reduction in CBF and CMRO2 than
etomidate
Answers
Question #4: A) Decrease cerebrovascular
resistance.
◦Like most other IV anesthetics barbiturates
increase cerebrovascular resistance through
a decrease in CMRO2.
Vasoactive Meds and CBF
Vasodilators
Vasopressors
Vasoactive Meds and CBF: Vasodilators
All common vasodilators cause
cerebral vasodilation
Vasoactive Meds and CBF: Vasodilators
Includes SNP, NTG, hydralazine,
adenosine, and Calcium channel
blockers
Vasoactive Meds and CBF: Vasodilators
Some antihypertensives have no
effect on cerebral vasculature,
including ACE inhibitors such
enalapril
Vasoactive Meds and CBF: Vasodilators
Beta blockers (propranolol,
labetalol) may have small decrease
CMRO2, leading to small decrease in
CBF
Vasoactive Meds and CBF: Vasodilators
Evidence is not available for all
antihypertensives
Vasoactive Meds and CBF: Vasodilators
Net Effect:
Vasoactive Meds and CBF: Vasodilators
MAP- ICP
CBF:
Directly Proportional
_____________
Resistance Inversely proportional
Vasoactive Meds and CBF: Vasodilators
MAP- ICP
CBF:
_____________
Resistance
Vasoactive Meds and CBF: Vasodilators
MAP- ICP
CBF:
_____________
Resistance
Vasoactive Meds and CBF: Vasodilators
MAP- ICP
CBF:
_____________
Resistance
Vasoactive Meds and CBF: Vasodilators
MAP- ICP
CBF:
_____________
Resistance
Vasoactive Meds and CBF: Vasodilators
MAP- ICP
CBF:
_____________
Resistance
Vasoactive Meds and CBF: Vasodilators
Net Effect:
CBF
CBF:
Site of autoregulation
Site of medication effects
CBV:
Difficult to measure
Varies to a lesser degree than CBF
ICP:
CSF, CBV, Brain Tissue
Ischemia:
Focal vs global
Affects all above variables
Vasoactive Meds and CBF: Vasodilators
Net Effect: moderate dosedependent
CBF leading to
small to moderate
ICP
Vasoactive Meds and CBF: Vasodilators
Net Effect: moderate dosedependent
CBF leading to
small to moderate
ICP
Vasoactive Meds and CBF: Vasodilators
Much greater risk in patient with
neurologic injury
Vasoactive Meds and CBF: Vasodilators
Much greater risk in patient with
neurologic injury: especially focal
ischemia. Why?
Vasoactive Meds and CBF: Vasodilators
Vasodilators can directly cause
cerebral steal, regardless of
decrease in MAP.
Vasoactive Meds and CBF: Vasodilators
PaCO2 responsiveness is generally
intact with vasodilators.
Vasoactive Meds and CBF: Vasodilators
All vasodilator effects, including
cerebral steal, can be mediated or
exacerbated by PaCO2.
Vasoactive Meds and CBF: Vasodilators
All vasodilator effects can be
mediated by:
Hypocapnia
Vasoactive Meds and CBF: Vasodilators
All vasodilator effects can be
mediated by:
Hypocapnia
Slower Induction of Hypotension
Vasoactive Meds and CBF
Vasodilators
Vasopressors
Vasoactive Meds and CBF: Vasopressors
Vasoactive Meds and CBF: Vasopressors
In general, vasopressors do no affect
cerebral vasculature directly
Vasoactive Meds and CBF: Vasopressors
In general, vasopressors do no affect
cerebral vasculature directly.
Including phenylephrine, ephedrine,
norepi-, epi-, dopamine
Vasoactive Meds and CBF: Vasopressors
Their effect depends on their effect
on MAP
Vasoactive Meds and CBF: Vasodilators
MAP- ICP
CBF:
Directly Proportional
_____________
Resistance Inversely proportional
Vasoactive Meds and CBF: Vasopressors
MAP- ICP
CBF:
_____________
Resistance
Vasoactive Meds and CBF: Vasopressors
MAP- ICP
CBF:
_____________
Resistance
With
Inhalational
Anesthetics at
½ MAC or
greater
Vasoactive Meds and CBF: Vasopressors
MAP- ICP
CBF:
_____________
Resistance
With TIVA: no
effect on CBF
Vasoactive Meds and CBF: Vasopressors
Beta-agonists may have a direct
effect on cerebral metabolism
Vasoactive Meds and CBF: Vasopressors
Beta-agonists may cause a direct increase
in cerebral metabolism based on:
Dose
Vasoactive Meds and CBF: Vasopressors
Beta-agonists may cause a direct increase
in cerebral metabolism based on:
Dose
BBB effectiveness
Vasoactive Meds and CBF: Vasopressors
BBB effectiveness:
BBB permeability is increased with
increased stress, sustained hypertension,
hypertonic drugs, fever, sepsis
Vasoactive Meds and CBF: Vasopressors
BBB effectiveness:
Incrs BBB permeability leads to incrs
CMRO2 effect of beta adrenergics
Vasoactive Meds and CBF: Vasopressors
Epinephrine has the greatest
increase in CMRO2.
Vasoactive Meds and CBF: Vasopressors
Epinephrine has the greatest
increase in CMRO2.
Incrs CMRO2 has been shown in
low-doses with intact BBB
Vasoactive Meds and CBF: Vasopressors
Dobutamine has been associated
with 20-30% increase in CMRO2,
leading to incrs CBF
Vasoactive Meds and CBF: Vasopressors
Net Effect:
Vasoactive Meds and CBF: Vasopressors
Net Effect:
Least effect of all medications we
have looked at today
Questions
Answers
Question #1: B) Hydralazine
◦All direct vasodilators and Ca Channel
blockers increase CBF. Propofol decreases
CBF. Lidocaine and dilaudid have minimal
effect on CBF.
Answers
Question #2: C) The oral form has a more
gradual effect on cerebral vasodilation.
◦Gradual increases in cerebral vasodilation
allow for compensatory mechanisms such
as a decrease in CSF and increased venous
shunting out of the intracranial
compartment.
Answers
Question #3: C) Both A and B
◦Normally vasoconstrictors have a minimal
effect of CBF. This changes if MAP is
outside of the patient’s autoregulation
range or if the BBB is not intact.
Answers
Question #4: B) Phenylephrine
◦Beta 1 agonists have minimal, but some
increase in CBF and CMRO2. Pure alpha 1
agonists have no evidence of effect on CBF
or CMRO2.
Answers
Question #5: A) Epinephrine
◦When the BBB is not intact the most
potent beta 1 drugs will increase CBF and
CMRO2 the most.
CBF: Autoregulation
Autoregulation: PACO2. getting pt breathing back… paCO2 52-55. HTN d/t higher PACO2, MAC of
gas, treat with vasodilator, going to compound the incrs CBV. Tolerable on normal pt but minimally
tolerable on head injury.
50 mL/100g/min incrs to 70 mL/100g/min
+40%
In general, the response to PaCO2 is preserved with anesthetics
ICP 8 goes to 9
MAP incrs 65 to 85 +30%