Inhaled Anesthetics I Flashcards
Name the ethers
des
iso
sevo
enflurane
methoxyflurane
ether
name the alkanes
halothane
chloroform
name the gases
nitrous oxide
xenon
cyclopropane
inhaled anesthetics can be broken down into what three groups?
ethers
alkanes
gases
in what state of matter are the ethers and alkanes at room temp and atmospheric pressure? what about the gases?
liquid
gas
which two inhaled anesthetics are almost identical?
Des and Iso. Des is just fully fluorinated so the chlorine from iso has been replaced with another fluorine
how many fluorines in each inhaled agent? what other important elements does each agent have, if any?
Iso 5 and 1 chlorine
Des 6
Sevo 7
halothane 3 and 1 bromine
which inhaled anesthetics have chiral carbons?
des and iso
what does the addition of a chlorine atom to an inhaled anesthetic do?
increases potency and blood gas solubility
what are the effets of full fluorination?
decrease potency
increase MAC
increase vapor pressure > requires heated vaporizer (tech 6)
^ resistance to biotranformation
when does evaporation occur?
when temperature of liquid is less than boiling point. vapor pressure is also less than atmospheric pressure
when does boiling ocur?
when vapor pressure = atmospheric pressure
how does atmospheric pressure (altitude affect boiling point?
at higher atmospheric pressure boiling point is higher. at lower atmospheric pressure (high altitude) boiling point is lower
how is depth of anesthesia from an inhaled agent assessed?
by the partial pressure of the agent, not the volume %!
when is the volume % vs partial pressure of inhaled agents clinically relevant?
Only at elevation, and only for desflurance. conventional variable bypass vaporizers automatically adjust for altitude. the Tech 6 vaporizer does not. atmospheric pressure is lower at elevation so a set percent of a lower pressure is an overall lower dose of anesthetic agent.
when is there a risk of compound a production from sevo?
when sodalime is in use regardless of whether or not it is desiccated or not. more compound a produced with desiccated soda lime though
what happens when des or iso become unstable in soda lime? when does this happen? which one creates more CO?
they can produce carbon monoxide. only in desiccated soda lime. Des produces more.
Does Nitrous oxide have any dangerous by products? when?
no, it is always stable regardless of CO2 absorber status.
do any inhaled anesthetics have preservatives?
no, all preservative free
polar solutes dissolve in what kind of solvents?
hydrophillic
non polar solutes dissolve in what kidn of solvents?
lipophilic
What are the vapor pressures of the inhaled anesthetics?
Sev: 157
Des: 669
Iso: 238
N20: 38770
what is the boiling point of each inhaled anesthetic? in degrees C
Sevo 59
Des 22
Iso 49
N20 -88
What is the molecular weight in g of each inhaled anesthetic?
sevo 200
des 168
iso 184
N20 44
Blood gas solubility for each inhaled agent
des 0.42
N20 0.46
Sevo 0.65
iso 1.46
how does blood gas solubility of the inhaled agents affect onset of action?
the lower the solubiltity the faster the onset
Exception: N20 is faster than Des because of the concentrating effect. Basically just the sheet ammount of N20 diffusing out of the lung
what is wash in?
gas washing into alveoli
what is uptake?
gas taken up from alveoli into blood
does a greater ammount of anesthetic agent dissolved in the blood = greater effect on the brain?
No! it’s an increased partial pressure of the agent that exerts an increased effect on the brain
what can increase the rate of FA/FI?
greater wash in or decreased uptake
what can decrease rate of FA/FI?
decreased wash in or increased uptake
what can increase wash in?
high FGF
high alveolar ventilation
Low FRC (from decreased tv?)
low time constant
low anatomical dead space
what can decrease wash in?
low fgf
low alveolar ventilation
high FRC (why?) decreased Tv I think
high time constant
high anatomical dead space
what will decrease uptake of inhaled agents?
low solubility
low CO
low PA-PV difference
what will increase uptake or inhaled agents?
high solubility
high CO
high PA-PV difference
VRG as percent of body weight, % blood flow, and what organs make it up?
10% body mass
75% blood flow
brain
heart
kindeys
liver
endocrine glands
Muscles as percent of body weight, % blood flow, and what organs make it up?
50% body mass
20% CO
skeletal muscle
skin
Fat as percent of body weight, % blood flow, and what organs make it up? What is special about fats function with inhaled agents?
20% body mass
5% CO
functions has high capacity sink that can store large amounts of volatile agent
VPG as percent of body weight, % blood flow, and what organs make it up?
20% Body Mass
< 1% CO
tendons ligaments cartilage and bone
how does N20 distribute throughout the body?
uptake by any group (VRG, muscle, fat, VPG) is minimal and partitions nearly the same into all compartments.
where does N20 diffuse quickly?
int ogas containing compartments like GI tract and middle ear
How are volatile agents eliminated from body?
- from alveoli
- hepatic biotransformation
- percutaneous loss - not clinically relevant
how much hepatic metabolism occurs for each inhaled agent?
Rule of 2s “NDISH”
N20 0.04%
Des 0.02%
Iso 0.2%
Sevo 2-5%
Halothane 20%
what hepatic enzyme metabolism inhaled agents?
CPY450 system
specifically CYP2E1
by products of hepatic metabolism is each inhaled agent?
Iso and Des fluoride ions and trifluoracetic acid
Halothane: trifluoroacetic acid
Sevo: fluoride ions
what is one concern regarding sevos metabolic by product effect on the body?
because sevo has relatively high hepatic metabolism (2-5%) there is theorectical concern about fluoride induce high output renal failure. To-date this concern seems unfounded in humans.
What is the concentration effect?
AKA “overpresuring”
the higher the concentration of inhaled agent delivered the faster the onset.
this is likely only clinically relevant for N20.
the higher the solubility of the agent the greater the effect of the concentration effect will be.
what is the Conentrating effect? not to be confused with concentration effect.
Because N20 is 34x more soluble in blood than nitrogen, way more N20 leaves alveloi than Nitrogen leaves blood to come into alveoli
this leads to shrinking alveoli
leads to relative increase in FA of VA
This is why N20 has faster onset than Des even though Des has lower solubility in blood.
augmented gas inflow effect
this happens right after conentrating effect
becasue alveoli shrank > increased tracheal inflow of anesthetic in next breath > increases alveolar ventilation > ^FA of VA
does concentration effect apply to induction or emergence?
only to induction
what is the ventilation effect?
increased ventilation > ^ FA/FI
when sponaneously breathing, as anesthetic depth ^ ventilation decreases.
this can be thought of as a protective mechanism to prevent risk of anesthetic overdose.
what is the 2nd gas effect? what gasses are most affected?
admin of 1 gas speeds the onset of another gas during INDUCTION
rapid uptake of N20 > alveoli shrink temporarily > decreased alveolar volume > increased tracheal inflow > realative ^ in concentration of 2nd gas
the effect is greater in gases with higher blood gas solubilties
describe diffusion hypoxia from nitrous oxide? what are the related reccomendations?
body can store up to 30L of N20 after 2hrs, when N20 is shut off all of this N20 diffuses back into the alveoli causing diffusion hypoxia and hypocarbia.
classic teaching says use 100% fio2 when N20 is turned off to mitigate this risk.
newer evidence says user lower Fi02 to prevent resorption atelectasis and improve post-op gas exchange.
how to L-R cardiac shunts affect IV and inhalation inductions?
IV: slower because IV agent is recirculated in the lungs
Inhalation: no meaningful effect
how to R-L cardiac shunts affect IV and inhalation inductions? Which VAs are affected the most?
IV: faster becasue you bypass lungs and go straight to brain
Inhaled: slower less blood go through lungs. agents with low solubility are affected the most. high solubility agents somewhat offset this effect.
name some R-L shunt conditions
tetraology of fallot
foramen ovale
eisenmergers syndrome
tricuspid atresia
ebstein anomaly
