Neurophysiology

Question 1

Cerebral Vascular Blood Supply

Answer 1

Anterior - internal carotid artery

Posterior - vertebral arteries x2

Question 2

Circle of Willis

Answer 2

Located at base of brain

Forms an anastomotic ring includes vertebral (basilar) & internal carotid flow

Question 3

What site do aneurysms & atherosclerosis commonly occur?

Answer 3

Middle cerebral artery

Question 4

CBF

Answer 4

Cerebral blood flow varies based on metabolic activity
10-300 mL/100g/min
Average CBF = 50 mL/100g/min

Adult averages 750 mL/min
Receives 15-200% CO

Question 5

Gray Matter CBF

Answer 5

80mL/100g/min

Question 6

White Matter CBF

Answer 6

20mL/100g/min

Question 7

EEG Activity

Answer 7

20-25mL/100g/min = cerebral impairment
15-20mL/100g/min = flatline EEG
< 10mL/100g/min = irreversible brain damage

Question 8

NIRS

Answer 8

Near infrared spectroscopy
Normal = 80%
Reflects venous Hgb absorption
NOT pulsatile arterial blood flow

Neuro events associated w/ rSO2 <40% or >25% change from baseline

Question 9

CPP

Answer 9

Cerebral perfusion pressure
MAP - ICP = CPP
CVP ≈ ICP

↑CPP = cerebral vasoconstriction (↓CBF)
↓CPP = cerebral vasodilation (↑CBF)

Question 10

Normal ICP

Answer 10

ICP < 10mmHg (5-15mmHg)

Question 11

Normal CPP

Answer 11

80-100mmHg

Question 12

Cerebral Autoregulation

Answer 12

Myogenic - smooth muscle intrinsic response

Metabolic - tissue demand decreases arteriole tone & increases blood flow

Question 13

CBF remains constant b/w what MAPs?

Answer 13

60-100mmHg

MAP > 150-160mmHg potentially results in cerebral edema & hemorrhage

Question 14

What effects CBF?

Answer 14

PaCO2
PaO2
Temperature
Viscosity
Age
Autonomic

Question 15

PaCO2 impact on CBF

Answer 15

CBF α PaCO2 b/w 20-80mmHg

Blood flow changes 1-2mL/100g/min per 1mmHg PaCO2 change

Question 16

_____ metabolic acidosis has _____ effect on CBF

Answer 16

Acute metabolic acidosis has minimal effect on CBF
HCO3¯ does NOT acutely effect CBF
- Unable to passively cross the blood-brain barrier
- 24-48hrs CSF HCO3¯ compensates via active transport to buffer PaCO2 (PACU or ICU)
- Hypo/hypercapnia are diminished

Question 17

PaCO2 < 25mmHg

Answer 17

CBF α PaCO2
Effects attenuated at PaCO2 < 25mmHg (ceiling effect)
Left shift on oxyhemoglobin curve
Alkalosis causes ↑Hgb oxygen-affinity

Question 18

PaCO2 AFTER Surgery

Answer 18

After sustained hyperventilation/hypocapnia
CSF acidosis → increase CBF
↑CBF ↑ICP
SLOWLY restore/increase PaCO2 back to baseline

Question 19

PaO2 impact on CBF

Answer 19

50 to > 300mmHg minimal influence on CBF

< 50mmHg rapidly ↑CBF

Question 20

PaO2 < 60mmHg

Answer 20

Vasodilation mediated via

• Release neuronal nitric oxide
• Open ATP-dependent K+ channels
• Rostral ventrolateral medulla
• Cerebral O2 sensor stimulation ↑CBF but not CMRO2

Question 21

Temperature Impact (Cooling)

Answer 21

CBF ↓5-7% per 1°C
Cerebral metabolic rate ↓6-7% per 1°C
↓CMRO2 7% per 1°C

Question 22

Viscosity Impact

Answer 22

Hct determines viscosity
↓Hct ↓viscosity ↑CBF
↓O2-carrying capacity → impaired oxygen delivery to brain tissue

Question 23

Optimal cerebral oxygen delivery hematocrit = ___ %

Answer 23

30%

Question 24

Sympathetic impact on CBF

Answer 24

Vasoconstriction

Question 25

Parasympathetic impact on CBF

Answer 25

Vasodilation

Question 26

Age Impact

Answer 26

Progressive loss neurons Loss myelinating fibers Synapses loss ↓CBF & CMRO2 by 15-20% at 80yo

Question 27

Brain normally consumes ___ % total body oxygen

Answer 27

20% (60% used to generate ATP)

Question 28

Cerebral Metabolic Rate

Answer 28

CMRO2 3-3.8 mL/100g/min = 50mL/min | 80% O2 consumed in the gray matter

Question 29

Cerebral perfusion interruption = unconsciousness w/in ___ seconds

Answer 29

10 seconds | O2 not restored w/in 3-8 minutes → ATP depletion → irreversible cellular injury

Question 30

What areas are most sensitive to hypoxic injury?

Answer 30

Hippocampus & cerebellum

Question 31

What is the primary cerebral energy source?

Answer 31

GLUCOSE Brain glucose consumption 5mg/100g/min 90% metabolized aerobically

Question 32

Hypoglycemia

Answer 32

→ brain injury

Question 33

Hyperglycemia

Answer 33

→ exacerbate hypoxic injury

Question 34

Blood-Brain Barrier

Answer 34

Vascular endothelial cell junctions tight (essentially fused together) - O2, CO2, & lipid-soluble molecules freely cross the blood-brain barrier

Question 35

What impacts molecules/drugs that are able to cross the blood-brain barrier?

Answer 35

``` Size & charge - Ions (electrolytes Na+) Lipid solubility Plasma protein binding Large molecules such as Mannitol ```

Question 36

What causes disruptions to the blood-brain barrier?

Answer 36

HTN, tumor, trauma/stroke, infection, hypercapnia, hypoxia, sustained seizure

Question 37

CSF

Answer 37

Cerebral spinal fluid formed in the choroid plexuses by ependymal cells Replaced 3-4x per day Found in cerebral ventricles, cisterns, & subarachnoid space surrounding the brain & spinal cord Isotonic w/ plasma Serves as a cushion to protect CNS from trauma

Question 38

How many mL CSF produced in adults per hour & day?

Answer 38

21mL/hr | 500mL/day

Question 39

Total CSF Volume

Answer 39

≈ 150mL | 1/2 cranium & 1/2 spinal space

Question 40

CSF Circulation

Answer 40

Lateral ventricles → intraventricular foramina of Monroe → 3rd ventricle → cerebral aqueduct of Sylvius → 4th ventricle → medial (foramen of Magendie) or lateral (foramen of Luschka) apertures → subarachnoid space → arachnoid villi → superior sagittal sinus

Question 41

Cranial Vault

Answer 41

RIGID structure Monroe-Kellie hypothesis Cranial compartment = incompressible Volume inside cranium remains FIXED volume Any increase in one volume requires compensatory decrease in another volume to prevent ↑ICP *Small volume increases are initially well-compensated

Question 42

Brain/Blood/CSF

Answer 42

Brain 80% Blood 12% CSF 8%

Question 43

ICP

Answer 43

Supratentorial CSF pressure measured in the lateral ventricles over the cerebral cortex

Question 44

ICP Compensatory Mechanisms

Answer 44

CSF displacement from cranium to spinal compartment ↑CSF absorption ↓CSF production ↓total cerebral blood volume *Major compensatory mechanisms`

Question 45

Closed Cranium Goals

Answer 45

Maintain CPP | Prevent herniation

Question 46

Open Cranium Goals

Answer 46

Facilitate surgical process | Reverse ongoing herniation

Question 47

Intracranial HTN

Answer 47

Sustained ICP 20-25mmHg

Question 48

Intracranial HTN | Causes

Answer 48

Expanding tissue or fluid mass Interference w/ CSF absorption Excessive CSF production Systemic disturbances promoting edema

Question 49

↑ICP S/S

Answer 49

``` Headache Nausea/vomiting Papilledema Focal neurological deficit ↓LOC Seizures Coma CUSHING TRIAD ```

Question 50

CUSHING TRIAD

Answer 50

1. HTN 2. Bradycardia 3. Irregular respirations

Question 51

Herniation Types

Answer 51

1. Cingulate gyrus under flax cerebri 2. Central 3. Uncal (transtentorial) 4. Cerebellar tonsils through foramen magnum* 5. Upward herniation of cerebellum 6. Transcalvarial

Question 52

Most common herniation type _____

Answer 52

Cerebellar tonsils through foramen magnum

Question 53

Cerebellar Tonsillar S/S

Answer 53

``` No specific clinical manifestations Arches stiff neck Paresthesias in shoulder ↓LOC Respiration abnormalities Pulse rate variations ```

Question 54

Uncal & Central S/S

Answer 54

↓LOC Sluggish pupils or fixed & dilated Cheyne-Stokes respirations Decorticate → decerebate posturing

Question 55

Cingulate Gyrus S/S

Answer 55

Minimal known about S/S

Question 56

Transcalvarial S/S

Answer 56

Potential to occur during surgery

Question 57

Intracranial HTN | Treatment

Answer 57

Brain tissue - surgical mass removal (lobectomy or bone flap) CSF - no effective pharmacological manipulation; drain placement Fluid - steroids; osmotics/diuretics Blood - most amenable to rapid alteration ↓arterial flow or ↑venous drainage (patient positioning) Hyperventilation ↓PaCO2 25-35mmHg CMR pharmacological suppression (i.e. barbiturates or Propofol) or hypothermia (therapeutic cooling)