Anesthesia Medication Effects on Cerebral Hemodynamics

Anesthesia Medication Effects

on Cerebral Hemodynamics

Site of autoregulation

Site of autoregulationSite of medication effects

Site of autoregulationSite of medication effects

Difficult to measure

Site of autoregulationSite of medication effects

Difficult to measureVaries to a lesser degree than CBF

Site of autoregulationSite of medication effects

Difficult to measureVaries to a lesser degree than CBF

CSF, CBV, Brain Tissue

Site of autoregulationSite of medication effects

Difficult to measureVaries to a lesser degree than CBF

CSF, CBV, Brain Tissue

Focal vs globalAffects all above variables

MAP- ICP _____________

Resistance

MAP- ICP Directly Proportional_____________

Resistance

MAP- ICP Directly Proportional_____________

Resistance Inversely proportional

Normal Values:

Normal Values:

15-20% of CO

Normal Values:

15-20% of CO750 mL/min

Normal Values:

15-20% of CO750 mL/min50 mL/100g/min

Normal Variation:

Normal Variation:

BP above autoregulation range CBF

Normal Variation:

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.

MAP 50-150

MAP 50-150Rapid change will still affect CBF

MAP 50-150Rapid change will still affect CBFDisrupted by :

volatile anesthetics

MAP 50-150Rapid change will still affect CBFDisrupted by :

volatile anestheticsHTN

MAP 50-150Rapid change will still affect CBFDisrupted by :

volatile anestheticsHTN

Pt’s Baseline MAP determines the patient’s autoregulation range

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 non-ischemic 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.

MAP- ICP Directly Proportional_____________

Resistance Inversely proportional

MAP- ICP Directly Proportional_____________

Resistance Inversely proportional

MAP- ICP Directly Proportional_____________

Resistance Inversely proportional

MAP- ICP Directly Proportional_____________

Resistance Inversely proportional

MAP- ICP Directly Proportional_____________

Resistance Inversely proportional

Site of autoregulationSite of medication effects

Difficult to measureVaries to a lesser degree than CBF

CSF, CBV, Brain Tissue

Focal vs globalAffects all above variables

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.

Site of autoregulationSite of medication effects

Difficult to measureVaries to a lesser degree than CBF

CSF, CBV, Brain Tissue

Focal vs globalAffects all above variables

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.

MAP- ICP Directly Proportional_____________

Resistance Inversely proportional

Vasoactive Meds and CBF: Vasodilators

MAP- ICP_____________

Resistance

Vasoactive Meds and CBF: Vasodilators

MAP- ICP_____________

Resistance

Vasoactive Meds and CBF: Vasodilators

MAP- ICP_____________

Resistance

Vasoactive Meds and CBF: Vasodilators

MAP- ICP_____________

Resistance

Vasoactive Meds and CBF: Vasodilators

MAP- ICP_____________

Resistance

Vasoactive Meds and CBF: Vasodilators

Site of autoregulationSite of medication effects

Difficult to measureVaries to a lesser degree than CBF

CSF, CBV, Brain Tissue

Focal vs globalAffects all above variables

MAP- ICP Directly Proportional_____________

Resistance Inversely proportional

Vasoactive Meds and CBF: Vasodilators

MAP- ICP _____________

Resistance

Vasoactive Meds and CBF: Vasopressors

MAP- ICP _____________

Resistance

Vasoactive Meds and CBF: Vasopressors

With Inhalational Anesthetics at ½ MAC or greater

MAP- ICP _____________

Resistance

Vasoactive Meds and CBF: Vasopressors

With TIVA: no effect on CBF

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%