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Flashcards in Neurophysiology Deck (62):
1

3 main components within the cranial vault that can cause ICP?

1. CSF (obstruction, overproduction, decreased clearance) 2. Blood volume (hypotension, high CVP) 3. Brain tissue (edema)

2

What does cerebral perfusion pressure equal?

CPP = MAP - ICP (or CVP whichever is higher)

3

What is a normal ICP?

< 10 mmHg

4

What MAP range is cerebral vascular resistance auto-regulated?

70 mmHg to 150 mmHg, above that, cerebral vascular resistance cannot increase anymore to restrict pressure dependent increase in flow

5

How does cerebral vascular resistance change with hypercarbia?

CVR and flow increases in a linear fashion until > 80 mmHg where the curve starts to flatten, and gets flat at 120 mmHg

6

How does cerebral vascular resistance change with hypoxia?

Little effect until PaO2 drops below ~50 mmHg and then rises exponentially; no effect between 60 mmHg and 300 mmHg

7

How do volatile anesthetics affect cerebral blood flow and cerebral metabolic rate?

VA's "uncouple" flow from consumption in that O2 consumption decreases and CBF (and therefore oxygen delivery) increases

8

What is the normal cerebral metabolic rate (CMRO2)?

3.5 cc/ 100g/ min

9

What is the normal cerebral blood flow?

50 cc/ 100g/ min

10

How much CSF does an average adult have at any one time? How much CSF is produced per day?

~150 cc, 500cc produced per day

11

What happens in the brain when the ICP is 30?

CPP decreases -> decreased blood flow -> decreased O2 delivery -> ischemia -> cellular break down -> edema -> increased ICP -> decreases CPP more

12

What does dexamethasone do to CSF production and absorption?

Decreases production, decreases absorption in animal studies

13

How does mannitol work?

Increases serum osmolality -> fluid shift into intravascular space -> increased UOP

14

What do you worry about with mannitol and intracranial hematomas?

Decreased brain swelling can cause a hematoma that was being tamponaded by the swollen brain tissue to expand

15

What happens to cerebral blood flow with 1 MAC of sevoflurane?

Increases about 20%

16

How does propofol affect cerebral blood flow and cerebral consumption of oxygen?

Decreases both

17

What happens in reverse steal of the brain?

Normal brain vasculature vasocontricts to stimulus (i.e. propofol) while ischemic brain cannot response -> normal brain is underperfused

18

How does hypercarbia affect cerebral blood flow?

Changes the H+ concentration

19

Mechanisms of action for cerebral ischemia with a PaCO2 less than 20?

1. Decrease in cerebral blood flow 2. Left shit in the oxyhemoglobin dissociation curve

20

Which anesthetic agents decrease cerebral metabolic rate of O2?

Most anesthetic agents except ketamine and N2O

21

Does hypothermia uncouple CMRO2 and CBF?

No, it just decreases both of them

22

Is autoregulation affected by high doses of propofol?

No, but propofol does decrease CBF, cerebral blood volume, and ICP

23

How does thiopental affect CMRO2 and CBF?

Decreases it in a dose dependent manner until 50%

24

What IV induction agent do you worry about in patients with seizures?

Etomidate (can be epileptogenic in patients with seizure disorders)

25

Which narcotic can provoke seizures in patients with epilepsy?

Alfentanil

26

Do volatile anesthetics impair autoregulation and if so, which ones more than the others?

Yes in a dose-dependent manner Sevoflurane impairs less than iso or des, halothane impairs it the most

27

How does nitrous affect CMRO2, CBF, and ICP?

Increases all three of them

28

What level of consciousness do you see when an EEG shows delta waves? theta waves? alpha waves? beta waves?

Delta: deep sleep Theta: first stage of sleep/drowsiness Alpha: relaxed bu alert Beta: Highly alert

29

Which volatile anesthetic has epileptiform discharge during induction and at 2 MAC?

Sevoflurane and Enflurane (not clinically significant)

30

Blood flow to the brain comes what what two main arteries?

Internal carotid (80%) and vertebrobasilar system (20%)

31

What are the main areas of aneurysms in the brain?

Anterior communicating artery (25%) MCA (25%) Internal carotid artery between posterior communicating and anterior choroidal arteries (22%) Basilar bifurcation (7%) Internal carotid bifurcation (4%)

32

Put these in order of most to least sensitive for detecting VAE: TEE, PA pressures, ETN2, Precordial doppler

TEE > Doppler > PA pressure changes > ETN2

33

What are the first steps needed after diagnosis of a VAE?

Flood the field, stop N2O, 100% O2, T-berg, positive pressure vent (pressure on SVC), compression of jugular vein, fluids/pressors, aspiration of central line

34

If you have an unruptured aneurysm and surgeon asks for hyperventilation and mannitol, what do you do?

No! Since transmural pressure of the aneurysm is MAP - ICP, once the cranial vault is open, ICP is 0 and then you can do it to prevent rupture since transmural pressure = MAP

35

What ECG changes do you see with subarachnoid hemorrhages?

Sympathetic stimulation can cause dysrythmias (i.e. PVCs, prolonged QT, ventricular tachyarrythmias)

36

What is Cushing's response?

From high ICP: bradycardia, HTN, irregular breathing (Cheyne Stokes)

37

When is the peak time you would expect cerebral vasospasm after SAH?

1 week peak (rarely occurs after 2 weeks): thought to be from oxy-Hgb in subarachnoid space leading to free radical production = decreased NO = more vasoconstriction

38

What is the treatment for cerebral vasospasms?

HHH: Hypertension (SBP ~160), hypervolemia (CVP >8), and hemodilution (Hct of ~30) Nimodipine (CCB)

39

Lucid interval following head trauma, lenticular appearance on CT

Epidural hematoma

40

Associated with old age, crescent shape on CT expanding past skull sutures

Subdural hematoma

41

RBCs in CSF means what?

Subarachnoid hematoma

42

Diffuse bleeding into an area of cerebral contusion is what kind of hemorrhage?

Intracerebral hematoma

43

What is neurogenic pulmonary edema?

ARDS in the setting of TBI

44

Patient after TBI has a sodium of 154 and nearly 200cc of urine in an hour. Diagnosis and treatment?

Diabetes insipidus Tx: DDAVP

45

What is neurogenic diabetes insipidus?

Lack of ADH secretion

46

What is syndrome of inappropriate ADH secretion?

Too much ADH leading to hyponatremia and fluid retention (patients normally euvolemic)

47

What is cerebral salt wasting syndrome?

After brain injury, salt wasting (hyponatremia) poorly responsive to fluid restriction and are often hypovolemic from fluid losses (SIADH patients are euvolemic)

48

Treatment for cerebral salt wasting syndrome?

Replacing fluid loss with NS and generally resolves over days to weeks

49

Treatment for SIADH?

Fluid restriction + salt tablets (symptomatic) + "vaptan" drugs - vasopressin analogues

50

What is the Monro-Kellie hypothesis?

Cranial compartment is incompressible and the volume inside is fixed made up of: blood, CSF, and brain tissues

51

What does line A, B, and C represent?

Q image thumb

A: O2

B: CO2

C: MAP

52

Which actually slightly increases cerebral blood flow: sufentanil, alfentanil, fentanyl, remifentanil

Sufentanil (the rest slightly decreases CBF)

53

The blood brain barrier prevents the passage of: glucose, water, CO2, lipid soluble compounds

Glucose

54

What two drugs decrease CSF production?

Acetazolamide and furosemide

55

Which decreases cerebral blood flow and cerebral metabolic rate: fentanyl, ketamine, isoflurane, lidocaine

Lidocaine (remember that isoflurane and other volatile anesthetics uncouple CMRO2 and CBF)

56

Compared to serum, which is proportionately the lowest in CSF: protein, glucose, sodium, bicarbonate

Protein

57

Class C nerves are used in what?

Nociception and post-ganglionic autonomic system

58

Where are the cell bodies of the first order neurons for pain signaling? 2nd order neurons?

1st: Dorsal root ganglion

2nd: Dorsal horn of the spinal cord

59

What tracts does pain and temperature go up in the spinal cord?

Spinothalamic tract (after crossing over to the contralateral side)

60

What is the precentral gyrus responsible for? Postcentral gyrus?

Pre: motor cortex

Post: sensory cortex

61

What does beta-1 activation do? Beta-2 activation?

1: increased chronotropy/inotropy/lusitropy, lipolysis, renin secretion

2: bronchodilation, smooth muscle relaxation, glycogenolysis

62

How does the SNS affect GU organs? ADH secretion?

Relaxes GU organs (i.e. uterus, etc.) and increase ADH secretion (to increase BP)