Inhaled Anesthetics Flashcards
What is MAC-awake?
the alveolar concentration where a patient opens his or her eyes
~0.4-0.5 MAC for induction
~0.15 MAC for recovery
What is MAC-bar?
the alveolar concentration required to block the autonomic response following a supramaximal painful stimulus
~1.5 MAC
What is a MAC-hour?
one times the minimum alveolar concentration that prevents movement in response to a noxious stimulus in 50% of subjects administered for 1 hour
Sevo @ 2 MAC x 1 hour
Sevo @ 1 MAC x 2 hours
What factors increase MAC?
chronic alcohol consumption
increased CNS neurotransmitters
hypernatremia
infants 1-6 months
hyperthermia
red hair
What factors decrease MAC?
acute alcohol intoxication
IV anesthetics
N2O
opioids
alpha-2 agonists
lithium
lidocaine
hydroxyzine
hyponatremia
prematurity
older age (6% decrease per decade after 40)
hypothermia
hypotension
hypoxia
anemia
CPB
metabolic acidosis
postpartum (24-72 hours)
PaCO2 >95
What factors have no effect on MAC?
hyper/hypo kalemia
hyper/hypo magnesemia
hyper/hypo thyroidism
gender
PaCO2 15-95
hypertension
What was the first inhaled anesthetic used on a wide scale?
ether
How was the first inhaled anesthetic administered?
using a drop mask
Why was ether a bad anesthetic?
strong emetic properties, airway irritant, and highly flammable
Why is halogenation a good thing?
increases stability aka not flammable
forms on 3 sides of ethers
Which halogenation is the most stable?
fluorination
Which was the first halogenated ether?
halothane
Which is the most potent inhalation agent in history?
methoxyflurane (MAC 0.16%)
Why was methoxyflurane a bad anesthetic?
high metabolism leading to high output renal failure, pungent, respiratory depressant
When is methoxyflurane used today?
Penthrane inhaler as an emergency analgesic
Why was enflurane a bad anesthetic?
caused Ethrane shakes, tonic-clonic seizure with deep anesthesia and PCO2 <30
Why was cyclopropane a bad anesthetic?
powerful respiratory depressant, sensitized myocardium, emetic, explosive
What receptor does Xenon inhibit?
NMDA
What is the MAC and B:G of Xenon?
MAC 71%
B:G 0.11
Why is Xenon a good anesthetic?
rapid induction and emergence
good analgesic
no CV depression
cerebral autoregulation
no hepatic or renal metabolism/toxicity
no MH trigger
does not sensitize myocardium
What are the disadvantages of Xenon?
increased CBF
increased PVR
cost and availability
Which gas lasts the longest in the environment?
desflurane
Which gas accounts for the most greenhouse gas emissions of all the anesthetic gases?
nitrous oxide
What is directly proportional to potency?
O:G
What is inversely proportional to MAC?
O:G
Does a lower body temperature lead to a slower or faster induction?
slower
What three things lead to increased alveolar concentration?
increased gas flow, increased concentration, increased RR
Does a lower B:G coefficient lead to slower or faster induction?
faster
Does increased CO lead to slower or faster induction?
slower
Does a lower B:G coefficient lead to a slower or faster emergence?
faster
What does decreasing CO2 do to clearance of inhaled anesthetics?
decrease clearance due to decreased cerebral perfusion
What is the MAC, B:G, and O:G of desflurane?
6.6%
0.42
19
What is the MAC, B:G, and O:G of sevoflurane?
2%
0.65
55
What is the MAC, B:G, and O:G of isoflurane?
1.2%
1.46
91
What is the MAC, B:G, and O:G of halothane?
0.75%
2.3
225
What is the MAC, B:G, and O:G of nitrous oxide?
104%
0.47
1.4
What is the MAC, B:G, and O:G of enflurane?
1.68
1.8
???
Which of the modern anesthetics has the fastest induction and emergence?
nitrous oxide (B:G 0.47)
Which of the modern anesthetics has the slowest induction and emergence?
isoflurane (B:G 1.46)
Which of the modern anesthetics is the most potent?
isoflurane (O:G 91)
Which of the modern anesthetics is the least potent?
nitrous oxide (O:G 1.4)
xenon (O:G 0.14)
Which of the modern anesthetics has the lowest molecular weight?
nitrous oxide (44 g)
Which of the modern anesthetics has the highest vapor pressure and why does it matter?
desflurane (VP 667 mmHg)
needs special vaporizer (heated)
Which of the modern anesthetics has the lowest boiling point and why does it matter?
nitrous oxide
stored as a compressed liquid
List the anesthetics in order from least to most in terms of liver metabolism.
nitrous oxide, desflurane, isoflurane, sevoflurane, halothane
