anesthesia medication effects on cerebral hemodynamics

Anesthesia Medication Effects

on Cerebral Hemodynamics

Site of autoregulation

Site of autoregulationSite of medication effects


Difficult to measure


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


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

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.

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.

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

MAP- ICP_____________

Resistance


MAP- ICP _____________

Resistance

Vasoactive Meds and CBF: Vasopressors

MAP- ICP _____________

Resistance


With Inhalational Anesthetics at ½ MAC or greater

MAP- ICP _____________

Resistance


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%

anesthesia medication effects on cerebral hemodynamics

Documents

proportionalmap icp

resistancemap icp

medication effectsdifficult

variablesmap icp

brain tissue accounts

brain tissuethe

cbfsite of autoregulationsite

lesser degree