inhaled anesthetics 1 Flashcards
name this agent and how many atoms
sevoflurane (7 fluorine atoms)
fluoromethyl 2,2,2 trifluoro 1 trifluoromethyl ethyl ether
in an atmospheric temperature, the ethers and alkane exist as
liquids
name the ethers (R-O-R)
desflurane
isoflurane
sevoflurane
enflurane
methoxyflurance
ether
name the alkanes (R-H)
halothane
chloroform
name the gases
nitrous oxide
cyclopropane
xenon
name this agent and how many atoms
desflurane
difluoromethyl 1,2,2,2 tetrafluoroethyl ether
6 fluorine atoms
name this agent and how many atoms
isoflurane
5 fluorine atoms + 1 chlorine atoms
1 chloro 2, 2, 2, trifluoroethyl difluoromethyl ether
the addition of a chlorine atom increases potency as well as blood and tissue solubility
which anesthetic agents have chiral carbons
desflurane and isoflurane
which anesthetic agent does not have a chiral carbon
sevoflurane
desflurane full fluorination has the following effects
decreased potency (and decreased oil:gas solubility)–> increased MAC
increased vapor pressure (decreased intermolecular attraction) –> requires heated vaporizer
increased resistance to biotransformation (decreased metabolism) –> decreased trifluoroacetate makes an immune mediated hepatitis extremely unlikely
name this agent and its atoms
halothane
2 bromo 2 chloro 1, 1, 1, trifluoroethane
(presence of a bromide atom and lack of an ether bridge are dead giveaways)
name its agent
nitrous oxide
definition of vapor pressure
vapor pressure is directly proportional to
pressure exerted by vapor in equilibrium with its liquid or solid phase inside of a closed container
temperature (increased vapor pressure, increased temperature)
vapor pressure is less than
atmospheric pressure
boiling occurs when
vapor pressure equals atmospheric pressure
atmospheric pressure is directly proportional to
boiling point
increased atmospheric pressure, increased boiling point
daltons law of partial pressure
the sum of total gas pressure in a container is equal to the sum of partial pressures exerted by each gas
partial pressure of particular gas equation
vol% x total gas pressure
ex) 6% desflurane at sea level delivers a total partial pressure of 45.6mmHg (.06 x 760mmHg)
two inalational agents that become unstable in desiccated soda lime and what they can produce
desflurane and isoflurane –> can produce carbon monoxide (des more than iso)
sevoflurane
vp
bp
molecular weight (g)
preservative
stable in hydrated CO2 absorber
stable in dehydrated CO2 absorber
toxic byproduct
vp 157
bp 59
molecular weight (g) 200
preservative no
stable in hydrated CO2 absorber no
stable in dehydrated CO2 absorber no
toxic byproduct compound A
desflurane
vp
bp
molecular weight (g)
preservative
stable in hydrated CO2 absorber
stable in dehydrated CO2 absorber
toxic byproduct
vp 669
bp 22
molecular weight (g) 168
preservative no
stable in hydrated CO2 absorber yes
stable in dehydrated CO2 absorber no
toxic byproduct carbon monoxide
isoflurane
vp
bp
molecular weight (g)
preservative
stable in hydrated CO2 absorber
stable in dehydrated CO2 absorber
toxic byproduct
vp 238
bp 49
molecular weight (g) 184
preservative no
stable in hydrated CO2 absorber yes
stable in dehydrated CO2 absorber no
toxic byproduct carbon monoxide
nitrous oxide
vp
bp
molecular weight (g)
preservative
stable in hydrated CO2 absorber
stable in dehydrated CO2 absorber
toxic byproduct
vp 38,770
bp -88
molecular weight (g) 44
preservative no
stable in hydrated CO2 absorber yes
stable in dehydrated CO2 absorber yes
toxic byproduct none
blood: gas partition coefficient=
anesthetic dissolved in blood / anesthetic inside alveolus
describe low blood: gas solubility
less likely to be taken up by blood
as a result, more agent is available to exert a partial pressure in the alveoli and brain
describe high blood: gas solubility
more likely to be taken up by blood
less of the agent is available to exert a partial pressure in the alveoli and brain
blood: gas partition coefficient of sevoflurane
0.65
blood: gas partition coefficient of desflurane
0.42
blood: gas partition coefficient of isoflurane
1.46
blood: gas partition coefficient of N2O
0.46
first gas on Fa/Fi curve and order from top to bottom
N2O
desflurane
sevoflurane
isoflurane
halothane
(shows when FA will = FI)
plateau is steady state
FA (uptake) is dependent upon 2 things
delivery from anesthesia machine to alveoli
rate of transfer from alveoli to blood
what are factors in delivery from anesthesia machine to alveoli for FA
- setting on the vaporizor
- time constant on the delivery system
- anatomic dead space
- alveolar ventilation
- volume of the FRC
what are factors in rate of transfer from alveoli to blood for FA
- Blood:Gas solubility
- CO
- Pa-Pv difference
factors that increase wash in for gas
high FGF
high alveolar ventilation
low FRC
low time constant
low anatomic dead space
factors that decrease wash in for gas
low solubility
low CO
low Pa-Pv difference
Fi=
concentration of anesthetic leaving the vaporizor
FA=
partial pressure of anesthetic inside the alveoli
surrogate for concentration of inhaled anesthetic in the brain
FA
alveolar partial pressure ~ blood partial pressure ~ brain partial pressure
solubility of anesthetic gas in relation to onset
low solubility –> decreased uptake into blood –>increased rate of rise –> faster equilibration of FA/Fi–> faster onset
high solubility–> increased uptake into blood –> decreased rate of rise —> slower equilibration of FA/Fi–> slower onset
factors that decrease wash in for gas
low FGF
low alveolar ventilation
high FRC
high time constant
high anatomic dead space
factors that increase wash in for gas
high solubility
high CO
high Pa-Pv difference
Name the 4 tissue groups
how much CO each receives
% body mass
organs included in each group
rate of anesthetic uptake into the tissues is dependent upon
- tissue BF
- solubility coefficient (solubility of anesthetic in tissue)
- arterial blood: tissue partial pressure gradient
the vessel rich group consists of (5)
heart, brain, kidneys, liver, endocrine gland
first group to equilibrate with FA
vessel rich group
inhaled anesthetics are eliminated from the body in 3 ways
- elimination from alveoli (primary mechanism)
- hepatic biotransformation (secondary mechanism, P450 system)
- percutaneous loss (minimal and not clinically significant)
hepatic biotransformation % of each gas from least to most
N2O: 0.004%
Desflurane 0.02%
Isoflurane 0.2%
Sevoflurane 2-5%
Halothane 20%
byproduct of halothane
trifluoroacetic acid (TFA), responsible for halothane hepatitis
metabolic byproducts of desflurane and isoflurane
inorganic fluoride ions and TFA
metabolic byproducts of sevoflurane
inorganic fluoride ions. maybe responsible for high output renal failure that does not respond to vasopressin.
is N2O metabolized in the body
nah
what do desflurane and isoflurane produce in desiccated soda lime
carbon monoxide
what does sevoflurane produce in hydrated OR desiccated soda lime
compound A
minimum FGF with sevo per the FDA
minimum FGF 1L/min for up to 2 MAC hours and 2L/min after 2 MAC hours
FGF <1L/min are not recommended at any time
define the concentration effect
the higher the concentration of anesthetic delivered to the alveolus, the faster the onset on action (also called over pressuring)
temporarily reduces alveolar volume
only applies to induction
nitrous oxide is ______ times more soluble in the blood than nitrogen
34x
describe the concentrating* effect
explains why nitrous oxide achieves the fastest rate of FA/Fi even though desflurane is soluble in the blood. The sheer volume of nitrous oxide movement more than compensates for the difference in blood solubility
define ventilation effevt
the greater the alveolar ventilation, the greater the rate of rise for FA/Fi
difference between concentration effect and second gas effect
concentrating effect deals with single gas while second gas effect is when N2O is co administered
how does the second gas effect work
- when N2O and the second gas are introduced into the alveolus, rapid uptake of N2O causes alveoli to shrink temporarily
- reduction of alveolar volume and augmented tracheal inflow causes a relative increase in concentration of second gas (ex: iso)
- pp of alveolar O2 also increases as alveolus shrinks. this is also a transient effect
- end result: alveolar concentration of other gases is higher than if they were administered alone
gas containing areas of body can absorb how many liters of N2O within the first two hours of administration?
30L
define diffusion hypoxia
when you shut off N2O, N2O that has accumulated in the body transfers to the alveoli for elimination in the first 1-5 min. can temporarily dilute alveolar O2 and CO2 concentrations leading to diffusion hypoxia and hypocarbia (reduced stimulus to breathe)
in the presence of right to left shunt (bypassing lungs), which agents will be most affected
agents with lower solubility will be most affected
desflurane is affected the most with the lowest B:G partition coefficient (.42) and isoflurane is affected the least because it has the highest B:G partition coefficient (most soluble)
in the presence of left to right shunt, how is FA/Fi affected
it isn’t
in the presence of left to right shunt, how is IV induction affected
slower IV induction (recirculated in lungs)
