Neuro Anesthesia

Question 1

At what rate is CSF produced? min? hour? day?

Answer 1

0.3cc/min, 20cc/hour, 500cc/day

Question 2

Where is CSF produced?

Answer 2

primarily in the choroid plexuses of the cerebral (mainly lateral) ventricles.

Question 3

At what rate is CSF reabsorbed?

Answer 3

It is reabsorbed at a rate of 0.3-0.4cc/min into the venous system by the villi in the arachnoid membrane

Question 4

What are some drugs that can decrease CSF production?

Answer 4

carbonic anhydrase inhibitors (acetazolamide), corticosteroids, spironolactone, loop diuretics (lasix), isoflurane, and vasoconstrictors

Question 5

What is the normal volume of CSF at any given time?

Answer 5

100-150cc

Question 6

What is the average normal amount of cerebral blood flow?

Answer 6

50ml/100g/min or ~750ml/min on average

Question 7

CBF represents approximately _____% of the cardiac output and consumes _____% of the oxygen.

Answer 7

15-20%; 20%

Question 8

CBF rates below what limit, are considered to be associated with cerebral impairment?

Answer 8

below 20-25ml/100gm/min

Question 9

What change in CBF occurs with every 1mmHg change in PaCO2?

Answer 9

for every 1 mmHg change in PaCO2, there is a corresponding change in CBF by 1-2ml/gm/min

Question 10

CBF is directly proportionate to PaCO2 during a CO2 range of ____ to ____ mmHg.

Answer 10

20-80mmHg

Question 11

How much of a change in CBF occurs with every 1 degree Celcius reduction in temperature?

Answer 11

5-7%; Hypothermia decreases both CMRO2 and CBF

Question 12

How much does CMRO2 decrease with every each reduction in temperature by 1 degree Celcius?

Answer 12

7%

Question 13

What is the formula for CPP?

Answer 13

CPP= MAP-ICP (or cerebral venous pressure, whichever is greater)

Question 14

What is the normal range for CPP?

Answer 14

80-100mmHg

Question 15

In what direction is the cerebral perfusion pressure autoregulation curve shifted in chronic hypertensive patients?

Answer 15

to the right

Question 16

What are some factors that can impair cerebral perfusion autoregulation?

Answer 16

in the presence of intracranial tumors or volatile anesthetics

Question 17

What effect does hematocrit have on CBF?

Answer 17

CBF increases with decreasing viscosity (hematocrit); optimal cerebral oxygen delivery occurs at Hct between 30-34%

Question 18

What area of the brain has the most neuronal activity?

Answer 18

cerebral cortex…. in the grey matter; hence the phrase… increasing cortical activity (which can increase CBF)

Question 19

What is the normal range for ICP?

Answer 19

5-10 mmHg

Question 20

What occurs if ICP exceeds 30mmHg?

Answer 20

CBF progressively decreases and a vicious cycle is established: ischemia causes brain edema, which further increases ICP, which in turn causes more ischemia.

Question 21

Periodic increases in arterial BP with a reflex slowing in the HR is called the _________ response. It can be correlated with abrupt increases in ICP lasting ____ to _____ minutes.

Answer 21

Cushing response; 1-15min

Question 22

What are some s\s of increased ICP?

Answer 22

n\v, mental status change, visual changes, neck stiffness, HTN, bradycardia, dilated pupils, respiratory changes (late and unreliable sign)

Question 23

What may a CT/MRI show if the patient has an increase in ICP?

Answer 23

midline shift, cerebral edema, mass lesions, abnormal ventricular size, obliteration of basal cistern

Question 24

What are some ways in which the body compensates for increased ICP?

Answer 24

displacement of CSF from cranial to spinal compartment, increase CSF absorption, decrease CSF production, decrease in total cerebral blood volume

Question 25

What are some anesthetic considerations to reduce the cerebral blood volume?

Answer 25

hyperventilation (PaCO2 20-25mmHg), excessive < than 20mmHg CO2 can cause cerebral ischemia, prevent straining or coughing, elevation of the head to encourage venous drainage

Question 26

Name some ways (both medications and surgical interventions) to reduce CSF.

Answer 26

ventriculostomy or lumbar subarachnoid catheter, use acetazolamide (diamox), hypertonic saline and mannitol may give immediate reduction in CSF, osmotic diuretic (20% mannitol 0.5gm/kg; thought to reduce cerebral swelling by osmotic dehydration), loop diuretics (lasix 0.5mg/kg), and steroids (decadron: 10mg), barbiturates (methohexital and thiopental: potent cerebral vasoconstrictors that decrease cerebral blood volume while decreasing cerebral metabolic rate)

Question 27

What types of drugs offer cerebral protection?

Answer 27

barbiturates, etomidate, propofol, and isoflurane (all may offer protection against focal ischemia and incomplete global ischemia by producing complete electrical silence of the brain and eliminated the metabolic cost of electrical activity.... but they have no effects on basal energy requirements); CCB's (nicardipine/cardene and nimodipine: may be beneficial in reducing neurologic injury following hemorrhagic and ischemic strokes)

Question 28

What intervention will effectively decrease both basal and electrical metabolic requirements throughout the brain?

Answer 28

hypothermia; metabolic requirements continue to decrease even after complete electrical silence; THE MOST EFFECTIVE METHOD FOR PROTECTING THE BRAIN DURING A FOCAL AND GLOBAL ISCHEMIA

Question 29

What are the main ways to offer cerebral protection?

Answer 29

use the right neuroprotective drugs to decrease CBF, CMRO2, etc; hypothermia; maintain adequate CPP (BP, ICP, O2 carrying capacity, Hct 30-34%); tight glucose control (hyperglycemia aggravates neurologic injuries; and the brain uses glucose for energy to function, so hypoglycemia can cause neuronal cell death)

Question 30

What effect does volatile anesthetics have on CBF if used above 0.6MAC?

Answer 30

cerebral vasodilation, decreased cerebral vascular resistance, and resulting dose dependent increases in CBF despite concomitant decreases in CMRO2

Question 31

What is the only IV anesthetic that dilates the cerebral vasculature and increases CBF?

Answer 31

Ketamine

Question 32

What effect does muscle relaxants have on CBF and CMRO2?

Answer 32

NONE!; sux can cause a transient increase in CBF and CMRO2

Question 33

What are some pre-op considerations and pre-medications prior to a craniotomy?

Answer 33

assess for s\s of increased ICP; neurologic assessment and documentation of mental status and any deficits; review CT and MRI for any brain edema, ventricular size, or midline shift > than 0.5cm; pre-medication is best avoided when increased ICP is suspected; corticosteroids and anticonvulsants should be continued up until the time of surgery

Question 34

What is the goal for induction of anesthesia during a craniotomy?

Answer 34

induction without increasing ICP or compromising CBF; HTN, hypotension, hypoxia, hypercarbia, and coughing should be avoided

Question 35

What are some drugs that can be used for IV induction of a craniotomy?

Answer 35

thiopental, propofol, and etomidate; these are unlikely to cause an increase in ICP

Question 36

How can you blunt the hemodynamic response to laryngoscopy prior to a craniotomy?

Answer 36

pre-treat with lidocaine, labetalol, opioids, and/or esmolol