inhalational agents - history and MAC Flashcards
ideal inhaled anesthetic characteristics:
- nonflammable
- easily vaporized at ambient temperature
- potent
- low blood solubility to assure rapid induction and recovery from anesthesia
- minimal metabolism
- compatible with epinephrine
- skeletal muscle relaxation
- suppresses excessive sympathetic nervous system activity
- not irritating to airways
- bronchodilation
- absence of excessive myocardial depression
- absence of cerebral vasodilation
- absence of hepatic and renal toxicity
the modern drugs were possible because with the _________ ________, development of the ________ _______, came advances in discoveries ________ _______.
manhattan project
atomic bomb
in fluorine chemistry
after 1950, all introduced drugs except ____ ______ ______ have contained _______
ethyl vinyl ether
fluorine
first of the modern agents was ______, but limited use due to ______
Fluroxene
PONV
halothane - an alkane - advantages:
nonflammable
less pungent
less soluble
decreased toxicity
halothane - an alkane - disadvantages:
decreased CO
increased arrhythmias
(hepatotoxicity)
enflurane - methyl ethyl ether
[Discovery #]
still has chlorine #347
isoflurane -
isomer #469
desflurane #653 - couldnt be used in ______ _______ due to its ______ _______ near atmospheric pressure at 699 and ______ ________ making it more expensive
conventional vaporizers
vapor pressure
low potency
sevoflurane - no perceived need, more __________ and _______ to synthesize
expensive
difficult
effects of increased fluorination
- nonflammable
- decreased solubility (main advantage)
- decreased potency/increased MAC
- less toxic due to resistance to degradation: desflurane = yes, sevoflurane = no
- decreased percentage metabolized
MAC
minimal alveolar concentration (partial pressure) of an inhaled agent at 1 atm that prevents skeletal muscle movement in response to a noxious stimulus in 50% of patients
10-30% greater concentration than MAC produces immobility in
90-95% of patients
why 50% immobile versus 95% immobile?
less variability
takes fewer subjects to determine MAC
what portion of the CNS determines MAC?
- spinal cord excitability is decreased resulting in immobility
- perfusion of the brain alone with ordinary concentrations does NOT produce immobility (took up 3-6X MAC)
alveolar reflects the _______ at the ______ or the ______ most accurately
concentration at the cord or the brain
must allow for ____________ (generally about ____-____ minutes)
equilibration
10-15 minutes
dependent on agent -
[alveolar reflects concentration at cord or brain]
3-4 time constants
as age increases,
MAC decreases about 6% per decade
N2O decreases MAC in ____ _____, but more so the ______
all ages
the elderly
MAC is greatest in patients less than _____________ and decreases by nearly ________ in the elderly years
less than a year of age
50%
MAC greatest to least populations
infants > children > neonates > adults
reduction caused by __________ is further enhanced with _______ patients
N2O
older
___% N2O causes about a ___% reduction in MAC normally - more so in the ________
60%
60%
elderly
____ __________ reduction causes MAC reduction
body temp
MAC of __________ is decreased almost in half by a 10 degree C decrease in temp
desflurane
MAC of _______ is not as affected
[w/body temp reduction]
N2O
pregnancy ________ MAC due to increased concentrations of _________
decreases
progesterone
MAC decreases nearly ______ through early postpartum, normalizing within ____-____ _____
30%
12-72 hours
Decreased CNS Na leads to _______ MAC
decreased
possible CNS Na causes:
dehydration, absorption of irrigant
MAC and opioid effects
synergistic effect
_____ dose opioids (fent 3mcg/kg) cause ____ decrease in MAC
small dose opioids
big decrease in MAC
opioids have a
ceiling effect on MAC
benzos cause a
dose dependent decrease in MAC
barbiturates, propofol, and acute ETOH ingestion cause
decrease in MAC
local anesthetics
lidocaine IV decreases MAC
N2O - 0.5 MAC of N2O + 0.5 MAC of isoflurane are __________ to ___ MAC of either drug alone
additive
1 MAC
_________ and ________ decrease MAC by decreasing CNS catecholamines and by hyperpolarization of CNS membranes
clonidine and precedex
some ______ _______ and some _______ _______ decrease MAC
[drug classes]
beta blockers
calcium-channel blockers
Adensosine
decreases MAC
factors that decrease MAC (4)
- neuraxial opioids
- PaO2 < 38mmHg
- BP < 40 mmHg
- cardiopulmonary bypass
red hair
increased MAC due to excess pheomelanin production - 19%
drug induced increases in CNS catecholamine levels:
cocaine, ketamine, amphetamines
_______ and _______ increase MAC
hyperthermia and hypernatremia
factors that do NOT alter MAC
- gender
- duration of anesthesia *iso decreases
- body mass
- arterial PaO2 > 50 mmHg
- arterial PaCO2 < 80 mmHg
- hematocrit > 10%
- BP > 40 mmHg
loss of ________ and the __________ (MAC) are not a “single continuum of increasing anesthetic depth but rather two separate phenomena”
consciousness and the immobility
MACawake
the average of the concentrations immediately above and below those permitting voluntary response to command
MACawake usually exceeds ___________
MACamnesia
MACawake is affected by _____ (______) and ______ ______
age (decreases) and inhalation agent
the ratio of MACawake/MAC is not affected by age as _____ _______
both decrease
for des/iso/sevo, MACawake is about
1/3 of MAC
for halothane, MACawake is more than
50% of MAC
for N2O, MACawake is more than
60% of MAC
comparison of MACawake/MAC is important. the higher the ratio, the ______ ___ ______, and the higher the ratio, the poorer the ______ _______
the faster the recovery
the poorer the amnestic value
low dose opioids (2-3 mcg/kg of fent) minimally affects _________. however, it does bring MAC down so the ratio of MACawake/MAC becomes higher and awakening should be more _______.
MACawake
quickly
MACawake does not ensure return of ______ ______ ______ or return of ________ ________
esophageal sphincter tone or return of pharyngeal fxn
concentrations of inhaled agent may require levels of less then _________ for patient safety
0.1 MAC
_________ ________ is impaired even at very low concentration - lower than MAC awake.
sphincter tone
MACte - to allow for ______ ______
tracheal stimulation
MACte - no _________ or _________ during suctioning of pharynx
coughing or bucking
MACte - no movement or coughing within ___ ____ of ______
1 minute of extubation
MACte is equal to or _______ MAC
exceeds
MACbar - minimum alveolar concentration that ______ _______ _______ to surgical stimulus
Blocks Autonomic Responses
with 60% N2O - des 1.3 MAC (________) - iso so 1.3 MAC (______)
des (1.9 MAC total)
iso (1.9 MAC total)
fentanyl of 1.5-3mcg/kg decreases it to 0.4 MAC (des) ________MAC total and 0.55 MAC (iso) ________MAC total.
[w/ 60% nitrous oxide]
des 1.0 MAC total
iso 1.15 MAC total
sevo 2.2 MAC (“less potent”) - with 67% N2O, _______ (2.2 MAC total) - with fent 3mcg/kg alone decreases it by ______
1.45 MAC
83%
[the info here is incorrect and she acknowledged that this info is an error]
MAC should be 1.53
The percentage is off as well!
