Inhalation Agents: MAC Flashcards
the ideal inhaled anesthetic
- 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
effects of increased fluorination
- nonflammable
- decreased solubility ***
- decreased potency
- less toxic due to resistance to degradation
- decreased percentage metabolized
MAC is
minimum alveolar concentration (partial pressure) of an inhaled agent at 1 atmosphere that prevents skeletal muscle movement in response to a noxious stimulus in 50 percent of patients (ED50, potency)
____ greater concentration than MAC produces immobility in ___ of patients
10-30%
90-95%
what portion of the central nervous system determines MAC
spinal cord
____ is decreased resulting in immobility
spinal cord
perfusion of the brain alone with ordinary concentration does not produce ____
immobility (took up to 3-6X MAC)
use minimal alveolar concentration because alveolar reflects
the concentration at the cord or the brain most accurately
with alveolar concentration you must allow
for equilibration (generally about 10-15 min)
alveolar concentration is dependent on
agent (3-4 time constants)
as age increase, MAC
decreases 6% per decade
___ decreases MAC in all ages, but more so in the elderly
nitrous oxide
MAC is greatest in patients
less than a year of age
MAC decreases in nearly
50% in the elderly years
MAC from greatest to least
infants > children > neonates > adults
60% nitrous oxide causes about a ____ reduction in MAC normally
60%
more so in elderly
____ reduction causes MAC reduction
body temperature
MAC of desflurane is decreased almost in half by
a 10 degree C decrease in temp
MAC of ___ is not affected by body temperature
nitrous oxide
pregnancy decrease MAC due to
increased concentrations of progesterone
MAC decreases ___ through early postpartum and normalizes within ___
30%
12-72 hours
decreased CNS ___ decreases MAC
Na
possible causes of decreased CNS Na leading to decreased MAC
dehydration, absorption of irrigant
drugs that decrease MAC
- opioids
- benzodiazepines
- barbiturates and propofol
- acute ETOH injection
- local anesthetics
- nitrous oxide
- clonidine and dexmedatomidine
- some beta-blockers
- some calcium-channel blockers
- adenosine
opioids have a ___ effect on MAC
ceiling
benzodiazepine decrease in MAC is
dose-dependent
the local anesthetic ___ IV decreases MAC
lidocaine
nitrous oxide effects on MAC
0.5 MAC of N2O plus 0.5 MAC of isoflurane are additive to 1 MAC of either drug alone
clonidine and dexmedetomidine decrease MAC by
decreasing central nervous system catecholamines and by hyperpolarization of CNS cell membranes
factors that decrease MAC
- neuraxial opioids
- PaO2 < 38 mmHg
- BP < 40 mmHg
- cardiopulmonary bypass
factors that increase MAC
- red hair
- drug induced increases in CNS catecholamine levels
- hyperthermia
- hypernatremia
red hair increased MAC due to
excess pheomelanin production (19%)
drugs that increase MAC
- cocaine
- ketamine
- amphetamines
factors that do not alter MAC
- gender
- duration of anesthesia (isoflurane decreases)
- body mass
- arterial PaO2 > 50 mmHg
- atrial PaCO2 < 80 mmHg
- Hct > 10%
- BP > 40 mmHg
MACawake is
the average of the concentrations immediately above and below those permitting voluntary response to command
MAC__ usually exceeds MAC___
awake
amnesia
MACawake is affected by
age (decreases) and inhalation agent
the ratio of MACawake/MAC is not affected by
age as both decrease
for desflurane, isoflurane, and sevoflurane, MACawake is
about 1/3 of MAC
for halothane, MACawake is
more than 50% of MAC
for nitrous oxide, MACawkae is
more than 60% of MAC
the higher the MACawake/MAC ration, the __ the recovery
faster
the higher the MACawake/MAC ration, the poorer the
amnestic value
___ minimally affect MACawake
low dose opioids
low dose opioids ___ the MACawake/MAC ratio so, __
increases
awakening should be more quickly
MACawake does not ensure return of
esophageal sphincter tone or return of pharyngeal function
concentration of inhaled agent may require levels of __ for patient safety
less than 0.1 MAC
MAC TE
MAC to allow tracheal stimulation (intubation)
to allow tracheal stimulation there needs to be:
- no coughing or bucking during suctioning of pharynx
- no movement or coughing within 1 min of extubation
- no breath holding or larygnospasm after extubation
MAC TE is __ or __ MAC
equal to or exceeds MAC
MAC bar
minimum alveolar concentration that blocks autonomic response to surgical stimulus
MAC bar with 60% nitrous oxide for deflurane
1.3 MAC (1.9 MAC total)
MAC bar with 60% nitrous oxide for isoflurane
1.3 MAC (1.9 MAC total)
MAC bar with 60% nitrous oxide for sevoflurane
2.2 MAC