1. Anesthesia Medication Effects on Cerebral Hemodynamics

2. CBF:

3. CBV:

4. CBF: CBV:ICP:

5. CBF: CBV:ICP:Ischemia:

6. CBF: CBV:ICP:Ischemia:

7. CBF: CBV:ICP:Ischemia: DECREASE INCREASE

8. CBF: CBV:ICP:Ischemia: Site of autoregulation

9. CBF: CBV:ICP:Ischemia: Site of autoregulation Site of medication effects

10. CBF: CBV:ICP:Ischemia: Site of autoregulation Site of medication effects Difficult to measure

11. CBF: CBV:ICP:Ischemia: Site of autoregulation Site of medication effects Difficult to measure Varies to a lesser degree than CBF

12. CBF Autoregulation

14. CBF: CBV:ICP:Ischemia: Site of autoregulation Site of medication effects Difficult to measure Varies to a lesser degree than CBF Brain Tissue, CSF, CBV

15. CBF: CBV:ICP:Ischemia: Site of autoregulation Site of medication effects Difficult to measure Varies to a lesser degree than CBF Brain Tissue, CSF, CBV Focal vs global Affects all variables

16. CBF: (MAP-ICP)= CPP _____________ Resistance

17. CBF: MAP- ICP Directly Proportional _____________ Resistance

18. CBF: MAP- ICP Directly Proportional _____________ Resistance Inversely proportional

19. CBF: MAP- ICP Metabolism _____________(CMRO2) Resistance

20. CBF: Normal Values:

21. CBF: Normal Values: 15-20% of CO

22. CBF: Normal Values: 15-20% of CO 750 mL/min

23. CBF: Normal Values: 15-20% of CO 750 mL/min 50 mL/100g/min

24. Questions

25. Question #1 In the normal patient, what is the largest component of the cranial vault? A. Brain Tissue B. CSF C. CBV D. MAP

26. Answer Question #1: A) Brain Tissue ◦The 3 components that make up the cranial vault are brain tissue, CSF, and CBV. Brain tissue accounts for 80% of the space while CSF and CBV account for 10% each. However, when ICP is altered it is typically caused by a change in CBV.

27. Question #2 Which of the following parameters is true for the normal patient? A. 35% of cardiac output to the brain B. Blood flow of 50 ml/min/100 g of brain tissue C. ICP of 17 mmHg D. Both A and B

28. Answer Question #2: B) Blood flow of 50 ml/min/100 g of brain tissue ◦Normal ICP is <15 and the brain normally receives 15-20% of cardiac output. The typical 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 ml/min/100 g and infarct begins at 6 ml/min/100 g of tissue.

29. Question #3 All of the following increase CBF, except: A. Hypercarbia B. Hypoxia C. Increased cerebral vascular resistance D. They all increase CBF

30. Answer Question #3: C) Increased cerebral vascular resistance ◦Both hypercarbia and hypoxia increase CBF. Hypoxia increases CBF by causing an increased metabolic demand. Hypercarbia has a direct vasodilatory effect on the cerebral vasculature. Increased cerebral vascular resistance would decrease CBF.

31. CBF Autoregulation OverviewIntrinsic factorsExtrinsic factorsIschemia

32. CBF Autoregulation Overview MAP 60-150

33. CBF Autoregulation Overview MAP 60-150 Rapid change will still affect CBF

34. CBF Autoregulation Overview MAP 60-150 Rapid change will still affect CBF Disrupted by : volatile anesthetics

35. CBF Autoregulation Overview MAP 60-150 Rapid change will still affect CBF Disrupted by : volatile anesthetics HTN

36. CBF Autoregulation Overview Pt’s Baseline MAP is the best indicator of their autoregulation range

37. CBF Autoregulation

40. Intrinsic Factors Myogenic Response

41. CBF Autoregulation Extrinsic Factors PaCO2

42. CBF Autoregulation Extrinsic Factors PaCO2 Metabolism

43. CBF Autoregulation Extrinsic Factors PaCO2 Metabolism

44. CBF Autoregulation: Extrinsic Factors PaCO2: Most potent vasodilator

45. CBF Autoregulation: Extrinsic Factors PaCO2: Most potent vasodilator Direct relationship to CBF

46. CBF Autoregulation: Extrinsic Factors PaCO2: Most potent vasodilator Direct relationship to CBF CO2 Responsiveness Preserved with anesthetics

47. CBF Autoregulation: Extrinsic Factors Metabolism (CMRO2): Main controllable factor intraop is temperature

48. CBF Autoregulation: Extrinsic Factors Metabolism (CMRO2): Main controllable factor intraop is temperature: 7% change per 1 deg C

49. CBF Autoregulation Ischemia Focal vs Global

50. CBF Autoregulation: Focal Ischemia Cerebral Steal:

51. CBF Autoregulation: Focal Ischemia Cerebral Steal: * Focal Ischemic areas are maximally dilated

52. CBF Autoregulation: Focal Ischemia Cerebral Steal: * Focal Ischemic areas are maximally dilated * Cerebral Vasodilation

53. CBF Autoregulation: Focal Ischemia Cerebral Steal: * Focal Ischemic areas are maximally dilated * Cerebral Vasodilation Redirects blood flow away from ischemic areas

54. CBF Autoregulation: Focal Ischemia Inverse Steal:

55. CBF Autoregulation: Focal Ischemia Inverse Steal: * Focal Ischemic areas are maximally dilated

56. CBF Autoregulation: Focal Ischemia Inverse Steal: * Focal Ischemic areas are maximally dilated * Cerebral Vasoconstriction

57. CBF Autoregulation: Focal Ischemia Inverse Steal: * Focal Ischemic areas are maximally dilated * Cerebral Vasoconstriction directs blood flow toward ischemic areas.

58. Questions

59. Question #1 In the normal person, cerebral autoregulation maintains a constant CBF between what MAP values? A. 45-100 mmHg B. 50-115 mmHg C. 55-125 mmHg D. 60-150 mmHg

60. Answer Question #1: D) 60-150 mmHg ◦While some sources have varying values of cerebral autoregulation, most have the low value of between 50 and 60 in the healthy patient.

61. Question #2 What is the most potent cerebral vasodilator? A. PaO2 B. PaCO2 C. Isoflurane D. Nitrous Oxide

62. Answer Question #2: B) PaCO2 ◦While isoflurane and nitrous oxide are cerebral vasodilators, the most potent cerebral vasodilator is PaCO2. High PaO2 is a vasoconstrictor.

63. Question #3 In the case of focal ischemia, which of the following would be a desirable effect to reduce damage? A. Vasodilation of non-ischemic tissue B. Vasoconstriction of ischemic tissue C. Vasoconstriction of non-ischemic tissue D. None of the above

64. Answer Question #3: C) Vasoconstriction of non- ischemic brain tissue ◦In focal ischemia a small area of brain tissue is receiving too little blood flow. The process of inverse steal involves vasoconstriction of non- ischemic tissue and vasodilation of ischemic tissue.

65. CBF and Anesthetics Inhaled AnestheticsIV General Anesthetics

66. CBF and Anesthetics: Inhaled Anesthetics

67. Decrease CMRO2 (except N2O)

68. CBF and Anesthetics: Inhaled Anesthetics Decrease CMRO2 which CBF

69. CBF and Anesthetics: Inhaled Anesthetics Are direct cerebral vasodilators which CBF

70. CBF and Anesthetics: Inhaled Anesthetics Net effect determined by MAC

71. CBF: MAP- ICP Metabolism _____________(CMRO2) Resistance

72. CBF: MAP- ICP Metabolism _____________(CMRO2) Resistance

73. CBF: MAP- ICP Metabolism _____________(CMRO2) Resistance

74. CBF: MAP- ICP Metabolism _____________(CMRO2) Resistance

75. CBF: MAP- ICP Metabolism _____________(CMRO2) Resistance

76. CBF: MAP- ICP Metabolism _____________(CMRO2) Resistance

77. CBF and Anesthetics: Inhaled Anesthetics Over 1 MAC, cerebral vasodilation greatly increases

78. CBF and Anesthetics: Inhaled Anesthetics Over 1 MAC: cerebral vasodilation greatly increases & autoregulation is impaired

79. Autoregulation & Volatiles

83. CBF and Anesthetics: Inhaled Anesthetics Over 1 MAC: cerebral vasodilation greatly increases & autoregulation is impaired

84. CBF: CBV:ICP:Ischemia: Site of autoregulation Site of medication effects Difficult to measure Varies to a lesser degree than CBF Brain Tissue, CSF, CBV Focal vs global Affects all above variables

85. CBF and Anesthetics: Inhaled Anesthetics Inhaled Anesthetics in normal patients with normal PaCO2 will cause minimal ICP changes

86. CBF and Anesthetics: Inhaled Anesthetics Inhaled Anesthetics in patients with reduced intracranial compliance can greatly increase CBV and ICP.

87. Questions

88. Question #1 A trauma patient comes into the OR with suspected head injury. Which volatile anesthetic would be least appropriate for anesthesia maintenance? A. Sevoflurane B. Isoflurane C. Enflurane D. Halothane

89. Answer Question #1: 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.

90. Question #2 Which volatile anesthetic would increase CSF absorption? A. Desflurane B. Sevoflurane C. Isoflurane D. Volatile anesthetics do not increase CSF absorption

91. Answer Question #2: 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.

92. Question #3 Which of the following inhalation agents have been shown to increase ICP? A. Nitrous oxide B. Sevoflurane C. Isoflurane D. All of the above

93. Answer Question #3: 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.

94. Question #4 During global ischemia, what is a potentially beneficial effect that can be induced by volatile anesthetics? A. An increase in CMRO2 with an increase in CBF B. An increase in CMRO2 with a decrease in CBF C. A decrease in CMRO2 with an increase in CBF D. A decrease in CMRO2 with a decrease in CBF

95. Answer Question #4: C) A decrease in CMRO2 and an increase in CBF ◦Volatile anesthetics can produce what is referred to as luxury perfusion, a reduced CMRO2 with an elevated CBF. This can be particularly beneficial during global ischemia.

96. Question #5 Which anesthetic drug would decrease CMRO2 the most? A. Isoflurane B. Sevoflurane C. Fentanyl D. Meperidine

97. Answer Question #5: A) Isoflurane ◦The mechanisms by which iso, sevo, and des decrease CMRO2 is similar, but iso is the one that reduces CMRO2 the most.

98. CBF and Anesthetics Inhaled AnestheticsIV General Anesthetics

99. CBF and Anesthetics: IV General Anesthetics CO2 responsiveness is preserved

100. CBF and Anesthetics: IV General Anesthetics CO2 responsiveness is preserved Unlike Inhaled Anesthetics, autoregulation is also preserved

101. Autoregulation & Volatiles

102. CBF and Anesthetics: IV General Anesthetics All Gen Anesthetics except Ketamine reduce CMRO2, which reduces CBF

103. CBF and Anesthetics: IV General Anesthetics Many also have direct cerebral vasoconstriction

104. CBF and Anesthetics: IV General Anesthetics Many also have direct cerebral vasoconstriction Global/ Near Global: Barbs, Propofol Regional (Not Uniform): Etomidate

105. CBF: MAP- ICP Metabolism _____________(CMRO2) Resistance

106. CBF: MAP- ICP Metabolism _____________(CMRO2) Resistance

107. CBF: MAP- ICP Metabolism _____________(CMRO2) Resistance

108. CBF: MAP- ICP Metabolism _____________(CMRO2) Resistance

109. CBF: MAP- ICP Metabolism _____________(CMRO2) Resistance

110. CBF: MAP- ICP Metabolism _____________(CMRO2) Resistance

111. CBF and Anesthetics: IV General Anesthetics Net Effect: Substantial Reduction in CBF (30- 60%)…

112. CBF: CBV:ICP:Ischemia: Site of autoregulation Site of medication effects Difficult to measure Varies to a lesser degree than CBF CSF, CBV, Brain Tissue Focal vs global Affects all above variables

113. CBF and Anesthetics: IV General Anesthetics Net Effect: Reduction in CBF (30- 60%) leads to smaller reduction in ICP (10-20%)

114. CBF and Anesthetics: IV General Anesthetics CBF 30-60% CBV 20-40% ICP 10-20%

115. CBF and Anesthetics: IV General Anesthetics CBF 30-60% CBV 20-40% ICP 10-20% with Hypocapnia

116. CBF and Anesthetics: IV General Anesthetics But, in Normocapnia, if MAP falls below autoregulation range, cerebral vasodilation will increase.

117. CBF Autoregulation

118. Questions

119. Question #1 At anesthetic doses all of the following drugs would preserve cerebral autoregulation except: A. Propofol B. Sodium Thiopental C. Sevoflurane D. All preserve cerebral autoregulation

120. Answer Question #1: C) Sevoflurane ◦All volatile anesthetics impair cerebral autoregulation at anesthetic levels. Barbiturates and propofol preserve it.

121. Question #2 Which of the following agents decreases both cerebral blood flow and cerebral metabolism in the normocarbic patient? A. Halothane B. Ketamine C. Nitrous Oxide D. Propofol

122. Answer Question #2: 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.

123. Question #3 Ketamine increases which of the following? A. CBF B. CMRO2 C. ICP D. All of the above

124. Answer Question #3: D) All of the above ◦Ketamine increases CBF, CMRO2, and ICP.

125. Question #4 Which statement best describes the reasoning for using barbiturates over etomidate for cerebral protection in focal ischemia? A. Barbiturates have a more global reduction in CBF and CMRO2 than etomidate B. Etomidate has a more global reduction in CBF and CMRO2 than barbiturates C. Barbiturates have a more focal reduction in CBF and CMRO2 than etomidate D. Etomidate has a more focal reduction in CBF and CMRO2 than barbiturates

126. Answer Question #4: A) Barbiturates have a more global reduction in CBF and CMRO2 than etomidate.

127. Question #5 Barbiturates do all of the following except: A. Decrease cerebrovascular resistance B. Reduce cerebral blood flow C. Reduce cerebral metabolic rate D. Produce hypnosis

128. Answer Question #5: A) Decrease cerebrovascular resistance. ◦Like most other IV anesthetics, barbiturates increase cerebrovascular resistance by direct vasoconstriction as well as by decreasing CMRO2.

129. References Evers, A. S., and Maze, M. (2003). Anesthetic Pharmacology -- Physiologic Principles and Clinical Practice. Churchill Livingston: New York. Morgan, G.E., Mikhail, M.S., & Murray, M.J. (2005). Clinical Anesthesiology 4 th Ed. McGraw-Hill. Stoelting, R. K., and Miller, R. D. (2007). Basics of Anesthesia 5 th Ed. Elsevier: Philadelphia.