inhalation anesthesia Flashcards
covalent bonds involves
sharing of electron pairs
all commonly used inhalation agents are ___ or _____
ethers or aliphatic hydrocarbons
anesthesia affect is lost if the chain exceeds
4 carbon atoms
modern inhaled agents are ____ hydrocarbons with exception to ___
halogenated, N20 (Nitrous Oxide)
heavier halogenated agent ___ potency
increases
ceiling effect of affection of F to ether
becomes more potent, then its as a strong convulsant, finally changes to inert compound with full fluorination
lipid solubility is ___ proportional to potency
directly
increase potency, ___ MAC
decrease
increase lipid solubility, ___ potency
increase
increasing # of halogenated agents, ___ arrhythmias
increase
MAC is ___ proportional to potency
indirectly
more hydrogens, ____ flammable
more
more halogens, ____ flammable
less
more halogens, ____ stable
more
one with all the same __ is ___ stable than one with different ___
halogens, more, halogens
why is des metabolized a 1/10th that of iso
because it contains F as its only halogen and thus strongly tests biodegradation
flammability is ___ and chemical stability ____ by substitution hydrogen atoms with halogens
reduced, enhanced
are inhaled anesthetics ionized or non-ionized?
non-ionized
4 elements of general anesthesia
unconsciousness, amnesia, analgesia, immobility
increase lipid solubility, ___ MAC
decrease
decrease temp, ____ anesthetic requirement
decrease (think slowed metabolism)
how is immobility measured?
MAC
what is the site of action for immobility?
dorsal horn of spinal cord
immobility is lost if length exceeds ____ carbon atoms
4-5
what is the site of action for amnesia
limbic system - hippocampus/amygdala
what is the reliable measure for amnesia?
none - but can use BIS or EEG
how is analgesia measured in immobile / unconscious pt
cannot be directly measured. HR and BP are suggestive
CNS depression occurs in 2 ways
enhancement of inhibitory channels & blocking excitatory channels
as the number of F atoms is increased, metabolism
decreases
metabolism of inhalation agents is thru
phase 1 oxidation (hepatic)
percentage of halothane metaboized
45% (large amt! caused hepatitis)
at equilibrium, partial pressures are equal where
Palveoli = Pblood = PCNS
the more blood soluble the drug,
the more drug wants to stay in blood thus slow to move to brain/CNS
N20 is low blood:gas soluble so induction will be
fast
blood solubility is important for ___ and ___
induction and emergence
the higher the blood solubility, the ____ the uptake
slower
with a slower uptake, your patient will go to sleep faster or slower
slower
how does the rate of metabolism and excretion of an inhaled agent compare to the rate of delivery to and removal from the lungs
it is minimal - so you can control your agent and have effects in seconds/mins
what is involved in enhancement of inhibitory channels (movement in and out of neuron)
hyperpolarization of neuron - Cl- enters thru GABA or glycine, slows down transmission. effux of K+
how does blocking excitatory channels work
prevents depolarization of neuron, blockage of glutamate and NMDA
how many flourines does iso have
5
how many flourines does des have
6
how many flourines does sevo have
7
as temp increases, vapor pressure ____
increases
at equilibrium, the pressure exerted by molecular collisions of the gas against the container walls is the
vapor pressure
daltons law
sum of partial pressures
anesthetic gases equilibrate based on
partial pressures
solubility is the tendency of a gas to
equilibrate with a solution
henrys law explains
why anesthetic gas wants to equilibrate with alveoli, blood, CNS. “At a constant temperature, the amount of a given gas that dissolves in a given type and volume of liquid is directly proportional to the partial pressure of that gas in equilibrium with that liquid”
solubility coefficient measures
v dissolved/v liquid at 37*…. balances between gas above and how much is dissolved in liquid below.
concentration of each gas in a mixture depends on what two things
1) its partial pressure in the gas phase and 2) its solubility within that solution
there is no gas phase at what interface
blood - target tissue (liquid phase that equilibrates
equilibrium happens fastest in which organs
vessel rich
what happens when an agent builds up in the fat
longer emergence. wake up is long with sevo and iso in the obese, shorter with des
how do we evaluate our inhaled anesthetics
end-tidal concentration
end tidal concentration doesnt account for
whats hanging around in your brain and fatty tissue
which agent is metabolized the least
des
the speed of an inhaled anesthetic is determined by its solubility and expressed as
blood: gas solubility coefficient
what are the two most soluble volatile anesthetics
iso , halo
oil:gas coefficient is related to an agent’s
potency
the slowest induction is possible with
halo, increased cardiac output state
calculate the partial pressure of 6% des at sea level
.06 x 760= 45.6
why measure alveolar concentration?
the concentration of an agent inside the alveoli is proportional to its concentration inside the blood and this is proportional to the anesthetic inside the brain. while we cannot directly measure the anesthetic in the brain, we use alveolar concentration as a surrogate. (APEX)
the vessel rich group accounts for only __ % of body weight, yet it receives ___% of the cardiac output
10, 75 (apex)
whats the primary mechanism by which inhalation anesthetic is removed from the body
exhalation thru the lungs. hepatic is a secondary mechanism. (apex)
