Egar Video #3 MAC Flashcards
MAC-bar
minimum alveolar concentration that blocks the adrenergic or autonomic reponse
MAC-awake
The end tidal anesthetic concentration that suppresses appropriate response to command in 50% of subjects
Why do we use 50% response
It is the easiest response to determine with the least number of experimental subjects
tells us where the 90% is
MAC
The minimum alveolar concentration of anesthetic (at one atmosphere) that abolishes movement in response to a noxious stimulus in 50% of subjects
What part of the central nervous system mediates the capacity of inhaled anesthetics to produce immobility?
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
What is the effect of IV anesthetics such as propofol on the brain and the spinal cord?
Propofol works mainly on the brain w/ min effect on the cord
why is it alveolar concentration? (MAC: Minimal Alveolar concentration)
It most accurately reflects the brain or spinal cord concentration
What do you have to do to ensure that MAC is reflecting spinal chord cocentration?
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
For the commonly inhaled anesthetics, on average how long does it take to achieve equilibration between the spinal cord and the alveoli?
10-15 minutes
Determination of MAC in Animals
2.1% end-tidal sevoflurane: no movement
1.9% end-tidal sevoflurane: movement
MAC = 2.0%
how to determine MAC in humans?
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
Determining MAC in humans using ____ stimulation
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%
Different inhaled agents and their MACs for humans
Agents given with O2 need higher percentages, compared with agents given with N2O
Factors that DO NOT change MAC
Gender
Body mass
across species
Increase in ____ doesn’t not effect MAC
Duration
Physiologic Factors that Decrease MAC
Increase age
decrease body temp
decreased CNS sodium
Pregnancy
as you ____ in age, there is a ______ MAC
increase ; decrease
____ the body temp, ____ the MAC requirement
lower ; less
Gender affects MAC in the sense that ____ lowers MAC
pregnancy
Decreased CNS sodium, _____ MAC requirements
Decreases
What alters Na levels: dehydration, SIADH, fluid overload, Mannitol infusion (decreases Na in the cord)
how does alcohol affect MAC?
- helps differentiate between acute vs chronic alcohol use
Chronic alcohol requires ____ MAC
increased
Use of Opiods ____ MAC
decreases
The effect of opiods on MAC is ______
synergistic
