Mod IX: Normal Neuro Physiology

Question 1

Clinical Neuroanesthesia

Learning objectives

Answer 1

Review of neurophysiology

^{Cerebral blood flow}

^{Brain metabolism}

^{CSF and intracranial pressures}

Review of pathophysiology

Effects of Anesthesia on the Brain

Anesthesia for specific procedures

^{Craniotomy for supratentorial tumors}

^{Posterior fossa craniotomies}

^{Epilepsy surgery}

^{Cerebral aneurysm clipping / coiling}

Monitoring for Neuro Procedures

^{SSEPs / MEPs}

Question 2

_{Cerebral Blood Flow}

The brain is Very vascular - What % of TBW is it? What % of CO does is receive?

Answer 2

Brain only constitutes 2% of TBW, yet

Receives 15% of cardiac output

Question 3

_{Cerebral Blood Flow}

What % of total body O2 consumption does the brain receive?

Answer 3

20% of total body O2 consumption

Question 4

_{Cerebral Blood Flow}

What are the normal CBF for adult, child and infant?

Answer 4

Infant: 40 mL/ 100 g/min

Child: 95 mL/ 100 g/min

Adult: 50 ml/g/min

Question 5

_{Cerebral Blood Flow}

What the major determinant of CBF?

Answer 5

CMRO2 or Functional state of the brain

(such as lower consumption during sleep)

Question 6

_{Cerebral Blood Flow}

T/F: CBF declines with advanced age

Answer 6

True

Question 7

_{Cerebral Blood Flow}

How does ↑ metabolic rate (CMRO2) affect CBF?

Answer 7

↑ blood flow

Regional &/or global

Mechanism not known

Question 8

_{Cerebral Blood Flow}

How does ↑PaCO2 affect CBF?

Answer 8

Causes vasodilatation = ↑ blood flow

↑ CO2 tension from 40 to 80 mmHg doubles blood flow

↓ CO2 tension from 40 to 20 mmHg cuts flow in half

Question 9

_{Cerebral Blood Flow}

How long do changes to CBF caused by changes CO2 tension last?

Answer 9

Changes last 6 to 8 hours & blood flow returns to normal

_{(Will be useful to understand how we use hyper and hypoventilation to contraol the size of the brain)}

Question 10

_{Cerebral Blood Flow}

Autoregulation allows CBF to remain constant between which MAP ranges?

Answer 10

60 to 150 mmHg

Question 11

_{Cerebral Blood Flow}

Which risk is associated with MAP < 40 mmHg?

Answer 11

Cerebral ischemia

Question 12

_{Cerebral Blood Flow}

MAP > 150 mmHg could have cerebral sequelae?

Answer 12

Disruption of the BBB

Question 13

_{Cerebral Blood Flow}

Which could impair autoregulation of CBF?

Answer 13

Trauma

Hypoxia

Ischemia

Hypercapnia

Certain anesthetic agents

Question 14

_{Cerebral Blood Flow}

Chronic HTN shifts autoregulation curve to the:

Answer 14

Right

This means that the pt can tolerate much higher MAPs

but cannot tolerate lower MAP ranges

For example, while a normal person can tolerate MAPs as low as 60 mmHg, their autoregulation may end at 80 mmHg

Question 15

_{Cerebral Blood Flow}

How does PaO2 affect CBF?

Answer 15

PaO2 has little effect on CBF until <50 mmHg then dramatic increased in CBF b/c the brain may become ischemic or anoxic

Question 16

_{Cerebral Blood Flow}

Neurogentic factors/systems influence CBF?

Answer 16

Adrenergic

Cholinergic

Serotonergic

Question 17

_{Cerebral Blood Flow}

Neurogentic factors such as adrenergic, cholinergic, & serotonergic systems influence CBF. Mainly on which type of blood vessels

Answer 17

Larger blood vessels

Question 18

_{Cerebral Blood Flow}

How does ↓ hematocrit affect CBF?

Answer 18

↓ viscosity = ↑ CBF

Question 19

_{Cerebral Blood Flow}

How does Hypothermia t affect CBF?

Answer 19

Hypothermia = ↓ CMRO2 = ↓ CBF

Question 20

_{Cerebral Blood Flow}

How does Hyperthermia affect CBF?

Answer 20

Hyperthermia = ↑ CMRO2 = ↑ CBF

Question 21

_{Brain Metabolism}

Principle substance used for energy production in the brain is

Answer 21

Glucose,

Brain uses 20-25% of glucose required by the body

Glucose + O2 = ATP

Question 22

_{Brain Metabolism}

What’s Metabolic rate of brain for the Adult and for the child?

Answer 22

Child 5.2 mL O2/min/100g brain tissue

Adult 3.5 mL O2/min/100g brain tissue

Question 23

_{Brain Metabolism}

What’s the largest energy requirement for the brain?

Answer 23

Pumping ions across cell membranes is the largest energy requirement for the brain

Question 24

_{Brain Metabolism}

Write the Fick’s Equation - What’s the major tenant of the Fick’s Equation?

Answer 24

Fick’s Equation: CMRO2 = CBF x (Ca02 – Cv02)

So the oxygen consumption of the brain is directly related to the CBF and the oxygen content in the blood

Question 25

_{Cerebrospinal Fluid} Where is CSF formed? at what rate?

Answer 25

In the **Choroid plexus** of the cerebral ventricles At the rate of **0.4 mL/min**

Question 26

_{Cerebrospinal Fluid} What's the chemical characteristic of CSF?

Answer 26

Is a ultrafiltrate of plasma with active and passive transport of ions and metabolites

Question 27

_{Cerebrospinal Fluid} Total volume of CSF is

Answer 27

between **100 and 150 mL**

Question 28

_{Cerebrospinal Fluid} How often is CSF volume replaced?

Answer 28

3 to 4 times a day

Question 29

_{Cerebrospinal Fluid} How does CSF flows? What's its function?

Answer 29

Out to **subarachnoid space** of the brain and spinal cord **Through ventricles** _Provides cushioning_

Question 30

_{Cerebrospinal Fluid} How is CSF reabsorbed?

Answer 30

**Arachnoid villi** The reabsorbed into _venous blood_

Question 31

_{Cerebrospinal Fluid} Which two barriers maintain the difference between CSF & blood composition?

Answer 31

Blood-brain barrier Blood-CSF barrier

Question 32

_{Intracranial Pressure (ICP)} What are the Three major intracranial components

Answer 32

**Brain** ^{80 to 85% of the volume Composed of neurons, glia, and interstitial fluid} **CSF** ^{7 to 10% of the volume} **Cerebral blood volume** ^{5 to 8% of the volume}

Question 33

_{Intracranial Pressure (ICP)} What % of the volume that make up ICP is represented by the brain?

Answer 33

80 to 85% of the volume Composed of neurons, glia, and interstitial fluid

Question 34

_{Intracranial Pressure (ICP)} What % of the volume that make up ICP is represented by the CSF?

Answer 34

7 to 10% of the volume

Question 35

_{Intracranial Pressure (ICP)} What % of the volume that make up ICP is represented by the Cerebral blood volume?

Answer 35

5 to 8% of the volume

Question 36

_{Intracranial Pressure (ICP)} What's Normal ICP

Answer 36

\< 10mmHg

Question 37

_{Intracranial Pressure (ICP)} When a small ↑ in the volume of one component of the cranial vault is noted, what comepensates for ↑ in pressure?

Answer 37

**Elasticity** or C**ompliance** to the components Once this compliance is exhausted, small ↑ results in large ↑ in ICP.

Question 38

_{Intracranial Pressure (ICP)} Which two major deleterious effects can increased ICP cause?

Answer 38

Reduced blood flow to the brain leading to ischemia Brain herniation

Question 39

_{Intracranial Pressure (ICP)} How does Reduced blood flow to the brain affect CPP?

Answer 39

Compromised Cerebral perfusion pressure (CPP)

Question 40

_{Intracranial Pressure (ICP)} How is CPP calculated? What happens to CPP when ICP is increased and MAP remains constant?

Answer 40

CPP = MAP-ICP so if you have ↑ ICP and MAP remains constant, you get ↓ CPP If ↓ CPP enough, you get brain ischemia

Question 41

_{Intracranial Pressure (ICP)} In which areas can Brain herniation occur?

Answer 41

Across the meninges Down spinal canal Through an opening in the skull

Question 42

_{Intracranial Pressure (ICP)} What can brain herniation lead to? ultimately...

Answer 42

Can lead to rapid neurologic deterioration and death

Question 43

_{Intracranial Pressure (ICP)} What are the causes of ↑ ICP?

Answer 43

**Increased CSF volume** D/t Blockage of circulation or absorption **Increased blood volume** D/t Vasodilatation or hematoma **Increased Brain tissue** D/t Tumor or edema