Inhalation Agents: MAC

Question 1

the ideal inhaled anesthetic

Answer 1

1. nonflammable
2. easily vaporized at ambient temperature
3. potent
4. low blood solubility to assure rapid induction and recovery from anesthesia
5. minimal metabolism
6. compatible with epinephrine
7. skeletal muscle relaxation
8. suppresses excessive sympathetic nervous system activity
9. not irritating to airways
10. bronchodilation
11. absence of excessive myocardial depression
12. absence of cerebral vasodilation
13. absence of hepatic and renal toxicity

Question 2

effects of increased fluorination

Answer 2

1. nonflammable
2. decreased solubility ***
3. decreased potency
4. less toxic due to resistance to degradation
5. decreased percentage metabolized

Question 3

MAC is

Answer 3

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)

Question 4

____ greater concentration than MAC produces immobility in ___ of patients

Answer 4

10-30%

90-95%

Question 5

what portion of the central nervous system determines MAC

Answer 5

spinal cord

Question 6

____ is decreased resulting in immobility

Answer 6

spinal cord

Question 7

perfusion of the brain alone with ordinary concentration does not produce ____

Answer 7

immobility (took up to 3-6X MAC)

Question 8

use minimal alveolar concentration because alveolar reflects

Answer 8

the concentration at the cord or the brain most accurately

Question 9

with alveolar concentration you must allow

Answer 9

for equilibration (generally about 10-15 min)

Question 10

alveolar concentration is dependent on

Answer 10

agent (3-4 time constants)

Question 11

as age increase, MAC

Answer 11

decreases 6% per decade

Question 12

___ decreases MAC in all ages, but more so in the elderly

Answer 12

nitrous oxide

Question 13

MAC is greatest in patients

Answer 13

less than a year of age

Question 14

MAC decreases in nearly

Answer 14

50% in the elderly years

Question 15

MAC from greatest to least

Answer 15

infants > children > neonates > adults

Question 16

60% nitrous oxide causes about a ____ reduction in MAC normally

Answer 16

60%

more so in elderly

Question 17

____ reduction causes MAC reduction

Answer 17

body temperature

Question 18

MAC of desflurane is decreased almost in half by

Answer 18

a 10 degree C decrease in temp

Question 19

MAC of ___ is not affected by body temperature

Answer 19

nitrous oxide

Question 20

pregnancy decrease MAC due to

Answer 20

increased concentrations of progesterone

Question 21

MAC decreases ___ through early postpartum and normalizes within ___

Answer 21

30%

12-72 hours

Question 22

decreased CNS ___ decreases MAC

Answer 22

Na

Question 23

possible causes of decreased CNS Na leading to decreased MAC

Answer 23

dehydration, absorption of irrigant

Question 24

drugs that decrease MAC

Answer 24

1. opioids
2. benzodiazepines
3. barbiturates and propofol
4. acute ETOH injection
5. local anesthetics
6. nitrous oxide
7. clonidine and dexmedatomidine
8. some beta-blockers
9. some calcium-channel blockers
10. adenosine

Question 25

opioids have a ___ effect on MAC

Answer 25

ceiling

Question 26

benzodiazepine decrease in MAC is

Answer 26

dose-dependent

Question 27

the local anesthetic ___ IV decreases MAC

Answer 27

lidocaine

Question 28

nitrous oxide effects on MAC

Answer 28

0.5 MAC of N2O plus 0.5 MAC of isoflurane are additive to 1 MAC of either drug alone

Question 29

clonidine and dexmedetomidine decrease MAC by

Answer 29

decreasing central nervous system catecholamines and by hyperpolarization of CNS cell membranes

Question 30

factors that decrease MAC

Answer 30

1. neuraxial opioids 2. PaO2 < 38 mmHg 3. BP < 40 mmHg 4. cardiopulmonary bypass

Question 31

factors that increase MAC

Answer 31

1. red hair 2. drug induced increases in CNS catecholamine levels 3. hyperthermia 4. hypernatremia

Question 32

red hair increased MAC due to

Answer 32

excess pheomelanin production (19%)

Question 33

drugs that increase MAC

Answer 33

1. cocaine 2. ketamine 3. amphetamines

Question 34

factors that do not alter MAC

Answer 34

1. gender 2. duration of anesthesia (isoflurane decreases) 3. body mass 4. arterial PaO2 > 50 mmHg 5. atrial PaCO2 < 80 mmHg 6. Hct > 10% 7. BP > 40 mmHg

Question 35

MACawake is

Answer 35

the average of the concentrations immediately above and below those permitting voluntary response to command

Question 36

MAC__ usually exceeds MAC___

Answer 36

awake amnesia

Question 37

MACawake is affected by

Answer 37

age (decreases) and inhalation agent

Question 38

the ratio of MACawake/MAC is not affected by

Answer 38

age as both decrease

Question 39

for desflurane, isoflurane, and sevoflurane, MACawake is

Answer 39

about 1/3 of MAC

Question 40

for halothane, MACawake is

Answer 40

more than 50% of MAC

Question 41

for nitrous oxide, MACawkae is

Answer 41

more than 60% of MAC

Question 42

the higher the MACawake/MAC ration, the __ the recovery

Answer 42

faster

Question 43

the higher the MACawake/MAC ration, the poorer the

Answer 43

amnestic value

Question 44

___ minimally affect MACawake

Answer 44

low dose opioids

Question 45

low dose opioids ___ the MACawake/MAC ratio so, __

Answer 45

increases awakening should be more quickly

Question 46

MACawake does not ensure return of

Answer 46

esophageal sphincter tone or return of pharyngeal function

Question 47

concentration of inhaled agent may require levels of __ for patient safety

Answer 47

less than 0.1 MAC

Question 48

MAC TE

Answer 48

MAC to allow tracheal stimulation (intubation)

Question 49

to allow tracheal stimulation there needs to be:

Answer 49

1. no coughing or bucking during suctioning of pharynx 2. no movement or coughing within 1 min of extubation 3. no breath holding or larygnospasm after extubation

Question 50

MAC TE is __ or __ MAC

Answer 50

equal to or exceeds MAC

Question 51

MAC bar

Answer 51

minimum alveolar concentration that blocks autonomic response to surgical stimulus

Question 52

MAC bar with 60% nitrous oxide for deflurane

Answer 52

1.3 MAC (1.9 MAC total)

Question 53

MAC bar with 60% nitrous oxide for isoflurane

Answer 53

1.3 MAC (1.9 MAC total)

Question 54

MAC bar with 60% nitrous oxide for sevoflurane

Answer 54

2.2 MAC