Egar Video #3 MAC

Question 1

MAC-bar

Answer 1

minimum alveolar concentration that blocks the adrenergic or autonomic reponse

Question 2

MAC-awake

Answer 2

The end tidal anesthetic concentration that suppresses appropriate response to command in 50% of subjects

Question 3

Why do we use 50% response

Answer 3

It is the easiest response to determine with the least number of experimental subjects

tells us where the 90% is

Question 4

MAC

Answer 4

The minimum alveolar concentration of anesthetic (at one atmosphere) that abolishes movement in response to a noxious stimulus in 50% of subjects

Question 5

What part of the central nervous system mediates the capacity of inhaled anesthetics to produce immobility?

Answer 5

the spinal cord

if we severed the connection between the brain and the spinal cord, it doesn’t alter the MAC.

The brain needs higher concentrations to achieve immobility

Question 6

What is the effect of IV anesthetics such as propofol on the brain and the spinal cord?

Answer 6

Propofol works mainly on the brain w/ min effect on the cord

Question 7

why is it alveolar concentration? (MAC: Minimal Alveolar concentration)

Answer 7

It most accurately reflects the brain or spinal cord concentration

Question 8

What do you have to do to ensure that MAC is reflecting spinal chord cocentration?

Answer 8

Allow equilibration between the spinal cord and the alveoli –> results in the direct measure of the partial pressure of the anesthetic at the sight of action

Question 9

For the commonly inhaled anesthetics, on average how long does it take to achieve equilibration between the spinal cord and the alveoli?

Answer 9

10-15 minutes

Question 10

Determination of MAC in Animals

Answer 10

2.1% end-tidal sevoflurane: no movement
1.9% end-tidal sevoflurane: movement

MAC = 2.0%

Question 11

how to determine MAC in humans?

Answer 11

Use 2 patients:
- First patient: 1.1% end tidal isoflurane: movement
- Second patient: 1.2% end tidal isoflurane: no movement
MAC = 1.15%
This is called Dixon up-and-down technique

Question 12

Determining MAC in humans using ____ stimulation

Answer 12

Tetanic Stimulation
example of determining MAC on humans using 1 patient:
- first administer 1.5% of MAC and then produce a tetanic stimulation
- if patient moves, turn up the MAC 2.5% then produce tetanic stimulation and see if patient moves
- MAC for this patient would be 2%

Question 13

Different inhaled agents and their MACs for humans

Answer 13

Agents given with O2 need higher percentages, compared with agents given with N2O

Question 14

Factors that DO NOT change MAC

Answer 14

Gender
Body mass
across species

Question 15

Increase in ____ doesn’t not effect MAC

Answer 15

Duration

Question 16

Physiologic Factors that Decrease MAC

Answer 16

Increase age
decrease body temp
decreased CNS sodium
Pregnancy

Question 17

as you ____ in age, there is a ______ MAC

Answer 17

increase ; decrease

Question 18

____ the body temp, ____ the MAC requirement

Answer 18

lower ; less

Question 19

Gender affects MAC in the sense that ____ lowers MAC

Answer 19

pregnancy

Question 20

Decreased CNS sodium, _____ MAC requirements

Answer 20

Decreases

What alters Na levels: dehydration, SIADH, fluid overload, Mannitol infusion (decreases Na in the cord)

Question 21

how does alcohol affect MAC?

Answer 21

• helps differentiate between acute vs chronic alcohol use

Question 22

Chronic alcohol requires ____ MAC

Answer 22

increased

Question 23

Use of Opiods ____ MAC

Answer 23

decreases

Question 24

The effect of opiods on MAC is ______

Answer 24

synergistic

Question 25

Benzodiazepines does what to MAC?

Answer 25

Decreases
dose-dependent

Question 26

Depressant drugs that decrease MAC

Answer 26

opioids
benzos
barbiturates
propofol
local anesthetics
nitrous oxide

Question 27

Fentanyl synergistically _____ MAC

Answer 27

decreases
Blue dots: patients who moved in response to surgical stimulation

Open squares: patients who didn’t move

As you increase fentanyl levels, MAC for sevo decreases

Question 28

Do muscle relaxants decrease MAC?

Answer 28

yes
MAC is where 50% of patients don’t move to noxious stimulus, therefore muscle relaxants decrease MAC requirements

Question 29

How would you maintain motor movement and get the muscle relaxed?

Answer 29

isolate one extremity from the circulation using a tourniquet or BP cuff

Question 30

______ do not cross the blood brain barrier because they are polar agents

Answer 30

Muscle relaxants, no effect in the brain

Question 31

Drugs that act on receptors the MIGHT effect MAC

Answer 31

Clonidine and dexmedetomadine

Question 32

dexmedetomadine ______ MAC

Answer 32

decreases
can decrease it to 0, dexmedetamodine can be an anesthetic in itself

Question 33

Neurotransmitter Agonists and Antagonists can decrese MAC

Answer 33

Alpha 2 sympathetic agonists
some beta-blockers
calcium channel blockers
adenosine and ATP
false neurotransmitters

Question 34

Why is MAC awake important?

Answer 34

• MAC awake exceeds the MAC for ammnesia (the concentration that suppresses memory)
• determines recovery: at MACawake patient is responding and might be able to maintain airway
  Picture: increased fraction MACawake, increased potential for regurgitation

Question 35

MACawake ______ with increasing age

Answer 35

Question 36

Effect of Isoflurance vs Nitrous Oxide

Answer 36

Question 37

Nitrous Oxide has a _____ MACawake value than Isoflurane

Answer 37

Higher (above 60% of MAC)

This means Nitrous oxide help patients recover quickly and get them through PACU quickly

Question 38

What is the downside of Nitrous Oxide having a high MACawake value?

Answer 38

It is not a very good amnestic agent
Anesthetics need to be given as supplement to prevent patients from moving and remembering