Inhalational Agents Flashcards
First Ether demonstration
1846 – William Morton Massachusetts General Hosp.
everyone was exposed to ether lol
Vapor
gaseous phase
at a temp where the substance can be either liquid or solid
below its critical temp
Potent inhaled are mostly in the liquid state at which T and atm?
room temperature (20 C)
atmospheric pressure (760 mm Hg)
Heat of vaporization
calories required: 1 g liquid —> vapor
(w/o changing temperature)
Boiling point
temperature at which vapor pressure equals atmospheric pressure (760 mmHg)
Desflurane VP
669 mmHg
Variable bypass vaporizer mechanism
total gas flow is divided in two streams by a variable resistance proportioning valve
small amount enters a vaporizing chamber, acts as carrier gas
majority travels through a bypass line.
DES DOES NOT USE THIS
Tech 6 Vaporizer (Desflurane)
39 C
Raises Vapor Pressure = no need for carrier gas
Dual circuit: fresh/diluted gas separate from vaporizing pressure
Desflurane added directly to fresh gas
vaporizer dial: delivers concentration
T/F
In a Tec 6 Vaporizer, fresh gas mixes with the desflurane.
False
Fresh gas and IA mix = variable BP
Tec 6: Des directly added to fresh gas
this is the main difference btwn VB and tec 6
T/F
The Tec 6 does not use a carrier gas mechanism.
True
Tec 6 increases the vapor pressure, so that a carrier gas is not needed.
The perfect IA
doesn’t exist lol
Ideal IA
-non-pungent
-non-flammable
-fast induction
-fast wake-up
-no harmful metabolites
Nociception
CNS and PNS processing of noxious stimuli
T/F
Gases can provide muscle relaxation
true
most noxious stimulation from anesthesia
intubation
General anesthesia
reversible state of “loss of sensation”
Which phases are affected by the pharmacodynamics and pharmacokinetics of the inhalational anesthetics?
induction
maintenance
emergence (redistribution)
all 3
An Anesthetic state is obtained with a combination of… (3)
amnesia, analgesia and lack of response to noxious stimuli
don’t rely on one agent
Balanced anesthesia
Myer-Overton Theory
(IA)
high lipid solubility = high potency
higher solubility = lower MAC
Mac determines potency
depth of anesthesia is determined by the number of anesthetic molecules that are dissolved in the brain
Unitary Hypothesis
All inhalational anesthetics work via a similar mechanism of action but not all the same sites
IA MoA bottom line
don’t know for sure where/how they work
Enhancing inhibitory sites/receptors (GABA, Glycine)
Inhibits excitatory channels (Glutamine)
Inhibits calcium channels (Ca2+) & K
Immobility is mediated principally by the effects of inhalationals on the ___.
spinal cord
The ultimate effect of an IA depends on…
reaching a therapeutic level in the CNS/Brain/Spinal Cord
Sites of Anesthetic Action
Unconsciousness
Reticular activating system (Cortex, thalamus, brainstem)
Sites of Anesthetic Action
Analgesia
Spinothalamic tract
Sites of Anesthetic Action
Amnesia
Amygdala, hippocampus
Sites of Anesthetic Action
Immobility
Ventral horn
(immobility: spinal cord mediated)
_____ activity causes motor effects.
SPINAL CORD
T/F
Sevo stinks.
False
T/F
Des smells good.
False
pungent
Most polluting IA
Desflurane
Most expensive IA
Desflurane
Which IA works on one specific site of action?
None currently only act on 1 site
T/F
Ideally, IAs should not be water-soluble.
True
LESS W. SOLUBLE = GOOD
we don’t want it to stay in the blood; we can use pressure to get it in there
N2O has a ___ smell.
sweet
SEDLINE monitoring
gives 4 leads of EEG
Looks at both frontal lobe hemispheres
Lots of blue = asleep
Burst suppression
flat EEG; too much anesthetic
Amnesia and LOC occur at (lower/higher) levels while immobility occurs at much (lower/higher) levels.
Amnesia & LOC = lower doses
Immobility = higherrrr
Which route allows us to physically observe all Guedel stages?
IA
(IV occurs too quickly)
Guedel’s Stage I
I: induction to loss of consciousness
Guedel’s Stage II
Delirium + “excitement” period
pupils dilated
disconjugate gaze
increased RR/HR
High risk of laryngospasm/bronchospasm
b/c reflexes come back but cant control
Caution when removing airway
Minimal extra touching/stimulation
Why is Guedel stage II assoc. w/ risk of laryngospasm/bronchospasm?
reflexes come back but cant control
Guedel’s Stages III
Surgical plane, fixed gaze, constricted pupils
WE LIKE!
Guedel’s Stage IV
Overdose
absent/shallow/irregular RR
-hypoTN/profound CV collapse
-dilated/unresponsive pupils
almost ded lol
T/F
Pts pass thru all Guedel stages into anesthesia and on emergence.
True
I to IV and back up to I
Which Guedel stage is assoc. w/ disconjugate gaze?
II
Vital capacity breathing IA
exhale completely and take deepest breath –> speeds induction
(VC: the volume of exhaled air after maximal inspiration)
Nitrous can help speed induction through…..
the second gas effect
Tidal Volume breathing IA
TV: breathing normal tidal volumes
Slower than IV
Gradual increase of a high concentration
Humans have a constant gas flow of
2-3 L/min
If using TV breathing with IA, how long until total plane of anesthesia?
9 mins
Which technique reaches total plane of anesthesia faster?
VC
TV
VC
T/F
VC breathing IA is the quickest way to reach total plane of anesthesia.
False
IV is quickest
however, VC is faster than TV (diff is small)
Agents for Inhalational Induction
N2O/O2 (70%:30%) and Sevoflurane (7-8%) until induced
⭐️
Can you use Desflurane for a mask induction?
Not reccomended; pungent, coughing
T/F
Volatile agents can also relax airway smooth muscle and produce bronchodilation
True
benefits of not provoking an irritant response
Less:
breath holding
coughing
secretions
laryngospasm
T/F
IAs can break status asthmaticus.
False
cannot drive enough
IA advantages
Less traumatic
No IV access
Short pediatric case
Bronchodilator effect
IA Disadvantages
Smell/Irritant
Excitatory stage (II)
Delayed airway
(b/c have to wait until stage II over)
Gas bypassing scavenger system
⭐️
Minimum Alveolar Concentration (MAC)
inhalational anesthetic/alveolar [ ] at which 50% of the population will not move to painful or noxious stimulus (e.g., surgical incision)
⭐️
MAC is a direct measure of…
the potency of the volatile anesthetic
⭐️
The IA [ ] in the alveoli is equal to…
The IA [ ] in the brain
⭐️
Lower MAC = (more/less) potent
more
lower dose necessary to achieve [ ] = more potent
⭐️
MAC mirrors ____ partial pressure
brain
⭐️
T/F
MAC values are additive
True
0.5 MAC of N2O + 0.5 MAC of Sevoflurane = effect of 1.0 MAC anesthetic
T/F
MAC
Young/healthy pts need lower
False
they need more
⭐️
MAC-BAR
MAC needed to
Block Autonomic Responsiveness to painful stimuli
1.5-2.0 MAC
⭐️
Typical MACBAR values
about 1.5-2.0 MAC
(varies according to resource)
⭐️
MAC-awake
alveolar concentration at which patient opens their eyes
0.4-0.5 = unconsciousness
0.15 = regain
⭐️
MAC value of LOC
0.4-0.5 = unconsciousness
⭐️
MAC value to regain consciousness
0.15
⭐️
MAC value: awareness/recall
(Not the same as MAC awake)
0.4-0.5
⭐️
MAC value that will prevent movement in 95% of surgical patients
1.2-1.3
T/F
MAC is the IA/alveolar [ ] that will block autonomic response to pain.
False
MAC: 50% won’t move to painful/noxious stimulus
MACBAR: MAC that
Blocks Autonomic Responsiveness to pain
⭐️
Know dis
IA potency
most to least potent
Iso > Sevo > Des > N2O
“I’m So Dead Now”
Desflurane:
potency
lipophilicity
onset
clearance
less potent
high lipophilic
fast onset
fast expiratory clearance
T/F
higher MAC = higher lipid solubility
False
higher MAC = LOWER lipid sol.
Des
Dial for 1 MAC
VP
Dial 6.6
VP 669
N2O
Dial for 1 MAC
VP
Dial 104
VP 38,770
Iso
Dial for 1 MAC
VP
Dial 1.17
VP 240
Sevo
Dial for 1 MAC
VP
Dial 1.8
VP 157
No Change in MAC
Duration of anesthesia
Anesthetic metabolism
Hyperkalemia
Hyper/Hypocarbia
Gender
Thyroid function (not directly)
Metabolic alkalosis
T/F
Thyroid fxn directly alters MAC.
False
not directly
Increases MAC
Hyperthermia
Excess catecholamines (MAO inhibitors, cocaine, ephedrine, levodopa, amphetamine abuse)
Excess pheomelanin production (true redhead)
Hypernatremia
Chronic ethanol abuse
We would expect a (higher/lower) MAC in a chronic drinker.
higher
Hypernatremia (increases/decreases) MAC. Hyponatremia (increases/decreases) MAC.
HyperNa = increase MAC
HypoNa = decrease MAC
“MAC is high in sodium”
Ephedrine (increases/decreases) MAC.
increases
Decreases MAC
Hypothermia
Benzos
> 40Y
Pregnancy
Alpha agonists (Precedex)
Acute alcohol ingestion
Hyponatremia
Induced hypotension (MAP<50)
Lots of drugs (Lidocaine, Lithium, Ketamine, opioids, benzos)
Severe anemia/traumatic blood loss
We would expect a trauma pt w/ blood loss to have (increased/decreased) MAC.
decreased
We would expect a pregnant pt to have (increased/decreased) MAC.
decreased
d/t uterine atony & increased Vd
Opioids and benzos (increase/decrease) MAC.
decrease
HypoTN (increases/decreases) MAC.
decreases
MAP <50
T/F
All IAs are rapid acting.
True
Only true gas
N2O; rest are mixed
Potent inhaled anesthetics are vapors of
volatile liquids
Why do IAs diffuse rapidly?
nonionized
low molecular weights
Major advantage of IAs
delivered to the bloodstream via the lungs
Know dis too
ugh
T/F
IAs are heavily metabolized by the body.
False
Which IA is metabolized by the body the most?
Sevo
Inhaled gases quickly transfer bidirectionally (when dial is at ___) via…
dial = 0
lungs <—>bloodstream <—> CNS
⭐️
Gases are delivered and removed by…
ventilation thru the lung
T/F
Plasma and tissues have a high capacity to absorb the anesthetic
False
low capacity
bidirectional flow
high vaporizer [ ] = into lungs
low vaporizer [ ]= exhausted out of pt as they expire
When does
PCNS = PBlood = PAlveolar ?
at equilibrium
EtCO2 constant
Constant rate of EtCO2 = reached equilibrium
(assuming no changes in ____)
delivery
Expired [ ] is measured from…
venous blood returning to alevolus
increases the speed of onset of inhaled anesthetics
High inspired concentration (FI)
High alveolar minute ventilation
Low blood solubility
High MAC
Higher gas delivery = (higher/lower) FI
higher
Why do we want low blood solubility for faster IA onset?
Low blood solubility: will not sit in blood; will cross into brain rapidly
higher blood solubility = will sit in blood; requires saturating systemic circulation (wait longer)
Lower blood solubility is preferred with IAs.
How do we get into into circulation to reach the brain?
drive across capillary membrane with high alveolar [ ]
T/F
The high water solubility of IA’s allow them to act quickly.
False
Their low blood solubility allows fast onset
IA’s do not sit in blood and cross into brain quickly
FGF
fresh gas flow
flowmeter settings & vaporizer [ ]
FI
definition
depends on…
inspired gas concentration
FGF, breathing circuit volume & circuit absorption
The common gas outlet sensor senses the:
FGF
FI
FA
Fa
FI
inspired gas concentration
T/F
FA can be measured directly.
False
End tidal detection of returning volatile thru expiratory limb
FA
definition
depends on…
alveolar gas
uptake, ventilation, the concentration effect & second gas effect
Fa
definition
depends on…
arterial gas
affected by ventilation-perfusion mismatch
We want our Et [ ] to equal ___ for that particular agent.
1 MAC
FA (alveolar gas) reflects [ ] in ….
brain and spinal cord
not to be confused with Fa (arterial gas)
T/F
FA (alv. gas) is always less than the vaporizer [ ].
True
~0.4-0.6 less
adjust vaporizer [ ] so that Et correlates with 1.0 MAC
Gives info on MAC
FA or Fa
FA (alveolar gas)
T/F
Fa tells us how much gas is being absorbed.
False
FA (alveolar gas) does
arterial gas [ ] in blood/cap bed on the other side of avleolus that’s picking up the gas
Fa
Goal of Inhalational Anesthesia
anesthetic state in the CNS/Brain
optimal and constant partial pressure of anesthetic in the brain (Pbr)
Increased Induction or Fast Recovery
High fresh gas flow
Small breathing circuit
Less absorption
Organ of uptake for inhalation agents is the
LUNGS
Target Organs
Brain and spinal cord
⭐️
Solubility in the ___ determines speed of onset
blood
(not lipid solubility!)
When we talk about solubility with IAs, we are referring to (blood/lipid) solubility.
blood (water)
insoluble= faster; crosses into brain
soluble= slower; stays in blood
Faster induction is achieved with an (insoluble/soluble) IA.
insoluble
taken up much slower by the blood faster induction
does not want to enter/stay in blood
Solubility of an anesthetic is expressed as
Partition Coefficients
Partition Coefficients
ratio
IA [ ] in blood phase : gas phase
(at equilibrium between the two phases)
Higher blood : gas coefficient means
highly blood soluble
Most to least blood soluble
Halo > Iso > Sevo > N2O > Des
“Hate Ice So No 2 Drinking”
Overpressure technique
speeds induction for blood soluble agent
increase inhaled [ ]
speeds up equilibrium
Which has faster induction/wakeup?
Iso or Des
Desflurane
0.42 (Poor bld Solubility)
Rapid induction/wakeup
⭐️
T/F
Insoluble IAs have faster onset.
True
insoluble IA = not water soluble
will not sit in blood
crosses into brain
Parallels anesthetic requirements
Oil:Gas Partition Coefficients
B/c brain & SC = lots of lipids
⭐️
Potency of volatile agents correlates w/
physical property of lipid solubility
**potency = lipid sol.
onset = w. sol
⭐️
T/F
higher MAC = higher B:G coefficient
False
higher MAC = lower B:G coefficient
Decrease in potency is associated with
a decrease in the oil:gas partition coefficient
How does increased CO affect IA uptake?
higher CO = higher lung blood flow
more rapid uptake
more removed from alveolar [ ]
constantly have to refresh [ ]
Increased CO = (shorter/longer) induction time
longer induction time
**longer time for IA to reach equilibrium (alveoli & brain)
(high/low) solubility agents are more effected by changes in CO.
High
(high/low) solubility agents are rapid onset regardless of CO changes.
low
Decreased CO = ___ PA (Alveolar blood flow)
Slow flow = pick up more
A-vD
tissue uptake of inhaled anesthetics
never will be 1:1 d/t tissue extraction!
Transfer of anesthetic from blood to tissue is determined by:
Tissue solubility
Tissue blood flow (perfusion)
Arterial blood/tissue partial pressure difference
The brain and spinal cord are vessel (rich/poor)
Rich
(VRG/VPG) gets IA first
VRG
Inhalational agents are very (blood/lipid) soluble
lipid
Greater affect on emergence than induction d/t…
Diffusing out of tissues
(reservoir for drug)
(Fat/blood) equilibrates slower due to ___.
Fat
perfusion
(fat is vessel poor)
What do this graph tell us?
Gas builds in alveoli the fastest
When gas is turned off:
-[ ] drops rapidly in alveoli and VRG
-[ ] in muscle and fat are now higher
shows why effects of gases are still evident on emergence
FA/FI
Ratio
alveolar [ ] anesthetic/inspired anesthetic over time
⭐️
alveolar fraction is directly proportional to…
the partial pressure of the anesthetic in the brain (CNS)
3 time constants = __% of max theoretical value of anesthetic
95
Anesthetic [ ] in gas circuit follows which order of kinetics?
first
How to lower number of time constant
higher gas flow
decrease FRC (supine)
low dead space
How can we increase the FI?
Increase the fresh gas flow
Increase the ventilation
Decrease the Functional Residual Capacity (FRC)
T/F
Supine pts will experience Equilibrium of FA/FI faster.
True
Supine = decreases FRC
decreased FRC = increased FI
Uptake (increases/declines) as the tissues become saturated
declines
Augmented gas flow
absorbed gas replaced by FGF (new gas)
we refresh by giving FGF plus IA
⭐️
achieves a faster rate of rise of FA/FI
N2O
Desflurane is less soluble in blood, but the volume of Nitrous compensates for the minimal difference in solubility
Second Gas Effect
Uptake large volume of first/primary gas (ie: Nitrous) from alveoli
sharper increase in PA of second gas
Factors that are responsible for the concentration effect also control
the second gas effect
Factors responsible for the [ ] effect & control the second gas effect
Increasing ventilation
Concentrating the IA
Second Gas Effect is associated with which law?
Fick’s Law of Diffusion
all about [ ] gradients
V/Q mismatch may occur in
R mainstem bronch intubation
T/F
Ventilation/Perfusion mismatch can affect the uptake and distribution of the inhaled anesthetics
True
Longest recovery time (gas)
Iso
“Iso slow”
⭐️
Concentration of Inhaled anesthetics in the tissues at the end of anesthetic depends on…
the solubility of the agent and time of administration
⭐️
Exhaled gases from the patient containing anesthetic will be rebreathed unless
fresh gas low rates are >5L/min
T/F
Return of spont. breathing can cause increase in expired IA
True
spont breathing has greater lung recruitment
T/F
During emergence, can permissively let CO2 climb to trigger brainstem breathing reflexes
True
esp sleep apnea
T/F
Recovery is exact mirror of induction
True
T/F
Long induction = long recovery
True
Primary factor in recovery/exhalation
Anesthetic solubility
others:
circuit volume
increased CBF
CO
increase ventil8n & FGF
non-pungent
Sevoflurane, Halothane, and Nitrous
“Smells Hella Nice”
pungent
Isoflurane
Desflurane
“I’m Dead”
⭐️
dose dependent IA changes in resp parameters
Increase: RR, PaCO2
Decrease: TV, MV
IAs (increase/decrease) MV.
decrease
gradually
How IA affects respiratory parameters
increased:
RR
PaCO2
Decrease:
TV
MV
How do IAs increase PaCO2?
Dose dependent depression of the ventilatory response to hypercarbia
⭐️
T/F
all IA’s cause bronchodilation
true
Which IA should we not give to a smoker?
Des
airway irritant
Inhalationals (except N2O)
CV effects
reduce MAP, CO, and CIndex in (dose-dependent)
Reduce BP –> decrease in SVR (relaxes vascular smooth muscle)
N2O
hemodynamic effects
Activates SNS
increases SVR, CVP & art.pressures
Nitrous + inhalationals
CV effects
increase SVR
help support BP
balance each other out:
N20 inc HR but temper with IA
can increase HR and BP due to the sympathetic stimulation
!!! Desflurane
Isoflurane
has an irritant effect (gas)
Des
“Stop it, Des irritating me”
minimal effect on HR (inhaled agent)
Sevoflurane
“Sevo the heart saver”
Use ___ to blunt tachycardic effects of some IAs
opioids
T/F
IAs lower the CO.
False
Cardiac Output is well preserved with minimal effect
T/F
IAs decrease SVR, leading to hypoTN.
True
T/F
IAs are coronary vasodilators.
True
T/F
IAs cause myocardial depression.
True
⭐️
Coronary Steal
Diversion of blood from a myocardial bed with limited or inadequate perfusion to a bed with more perfusion
(Dilation pulls blood away from areas that usually lack oxygenation)
currently debated
T/F
All inhalationals increase Cardiac Blood Flow less than the myocardial oxygen demand
False
increase blood flow more than O2 demand
IA
CNS effects
increases:
CBF (vasodilation cerebral BVs)
ICP (N2O)
decreased:
Cereb. metab rate
How to attenuate increased ICP from IAs.
Hyperventilation
T/F
All volatiles cause dose-dependent:
increase in latency
decrease amplitude in all cortical SEPs
True
“I’m late b/c my cortical sep isn’t working”
IA
OB effects
Mag + too much IA = uterine atony and bleeding!
dose-dependent decreases in uterine smooth muscle contractility and blood flow
⭐️
OB
IAs cause undesired effects for uterus at which flows?
(risk uterine atony from too much relax8n)
Modest: 0.5 MAC
substantial: >1 MAC
OB
We want to keep volatile dosing as low as possible. What can we do to reduce it?
Nitrous
can decrease the need for volatile anesthetics
____ degradation with the older carbon dioxide absorbents = compound A
Sevo
Renal concerns with Compound A
nephrotoxic in rats
IAs are most commonly biodegraded by…
hepatic metabolism
cytochrome P-450 oxidation
**Keep in mind: minimal liver metabolism
Depolarizing and nondepolarizing muscle relaxants have an additive effect/potentiates IA’s; except for ____
Suxx
gone too quick
How do IAs relax skeletal muscle?
Reduced CNS neural activity
Prominent postsynaptic effect at NMJ
Inhalationals ____ recovery from nondepolarizing muscle relaxants
delay
synergsitic effect
Which pt population is prone to emergence delirium with IAs?
Children
Put back to sleep
re-emerge usually w/o stage II
Emergence delirium
duration
how to treat
10-15 minutes
propofol, midazolam, clonidine, dexmedetomidine, ketamine, opioids
T/F
Emergence Delirium can resolve spontaneously
true
Emergence Delirium is more common with ___ and ___ compared to Iso & TIVA.
Des
Sevo
“they be on some Dumb Shit”
Compound A
Degradation of Sevoflurane by strong bases (soda lime) in the CO2 absorbers
increases chances of compound A
low flow rates
closed circuit
warm/dry CO2 absorbents
Induced Nephrotoxicity risk factors
Sevo: >2 MAC hours
FGF <2 L/min
degradation product of volatile agents(especially Desflurane) due to dry/desiccated CO2 absorbents
C. Monox
Monday morning phenomena contributes to ___ production
CO
Dry CO2 absorbers produce ___.
CO
Optimal CO2 absorbent size
2.5 mm
4-8 mesh
CO2 absorber channeling
loose packing allowing exhaled gases to bypass absorber granules in the canister
⭐️
Final Products of CO2 Neutralization
Ca carbonates, water and heat
T/F
Ideal CO2 absorbents have high resistance to gas flow.
False
low resistance
Turns sodalime purple
ethyl violet
T/F
Current CO2 absorbers use NaOH or KOH.
False
contain Calcium or lithium hydroxides
strong bases + sevo = compound A
what kind of compound is Compound A?
vinyl ether
⭐️
Other than turning purple, what indicates our CO2 abs. is exhausted?
rising ETCO2 waveform on capnograph
Why does des need diff vaporizer?
Vapor pressure close to atm
Vapor Pressure
The pressure exerted by a vapor in equilibrium with its liquid or solid phase inside of a closed container
Vapor pressure is ____ proportional to temperature
directly
T/F
All anesthestic gases used today are based off ethers.
False
N2O is not an ether
⭐️
Who dis
Isoflurane
5 fluorine atoms and 1 chlorine atom
⭐️
Who dis
N2O
Who is she?
Sevoflurane
7 fluorine atoms
(sevo=seven)
New phone, who dis?
Desflurane
6 fluorine atoms
⭐️
Which IA is not chiral?
Sevo
“Sevo’s So different”
Isoflurane (Forane)
Halogenated methyl ethyl ether
Coronary Steal
Low flow OK, resistant to degradation
B:G Coeff 1.46 (soluble)
Vapor Pressure 238
Decrease MAP (d/t dec. SVR)
Increase CBF
most potent
pungent
Sevoflurane (Ultane)
Fluorinated methyl isopropyl ether
bronchodilator
Minimal sympathetic activation
Compound A
B:G coefficient of 0.65
VP 157
Desflurane (Suprane)
Fluorinated methyl ethyl ether
Carbon Monoxide if dry absorber
Insoluble (faster sleep & wake)
potential irritant over 1 MAC
B:G 0.42
VP 669
SNS stimulation (Increased HR and BP)
T/F
You cannot fill the Tec 6 vaporizer while its in use.
False
Can fill the vaporizer during use
⭐️
T/F
volatiles decrease incidence of PONV.
FALSE
all volatile agents increase PONV
T/F
N2O is a triggering agent for MH.
False
It is not
T/F
N2O does not offer muscle/uterine relaxation, as opposed to other IAs.
True
⭐️
N2O diffusion & solubility
Diffusion into closed spaces
INSOLUBLE
Nitrous is 34x more soluble than N2, both are insoluble (increase in volume and pressure with the closed space)
When to avoid N2O
bowel cases
pneumothorax/blebs
venous air emboli
middle ear surgery
some eye surgeries
T/F
N2O is an analgesic.
True
⭐️
N2O inactivates ________, a key enzyme in folate metabolism. This affects vitamin ____.
methionine synthetase
B12
pic: “inactivation of vitamin B12 by nitrous oxide”
N2O can cause ____ in a noncomplicant airspace, esp it pf does not have a chest tube.
tension pneumothorax
In a fixed/noncompliant airspace, N2O will increase ____.
pressure
In a compliant airspace, N2O will increase ____.
volume
______ effects responsible for PONV
Middle ear
⭐️
best approach to prevent operating room pollution with anesthetic gases and reduce wastage
Shut off FGF (not vaporizer) during intubation or airway instrumentation
⭐️
Diffusion Hypoxiais SPECIFIC TO
N2O
Diffusion Hypoxia
- nitrous stopped abruptly
- reverses prtl pressure gradients
- nitrous: blood –> alveoli
washout of high N2O [ ] lowers alveolar [ ] of oxygen and carbon dioxide
How to avoid diffusion hypoxia
Stop nitrous early
initiate recovery from N2O anesthesia with 100% oxygen rather than less concentrated O2/air mixtures.
how does diffusion hypoxia affect respiratory drive?
decreases
(Diluted PACO2)
MAC of ____ will decrease potential for intraop awareness
0.4 - 0.5
Malignant Hyperthermia
massive release of Ca from sarcoplasmic reticulum
Ryanodyne receptor (RYR1)
Induced by inhalational agents and succinylcholine
T/F
O2 will displace N2O
False
N2O displaces O2
T/F
Early signs of MH include increased temperature.
False
this is a late sign
First sign of MH
unexplained rising EtCO2
Determines bill for gases
FGF
(low/high) solubility needs less FGF.
low solubility = less FGF
T/F
All volatiles are greenhouse gases.
True
How long does Des last in atmosphere?
14 Yrs
chlorofluorocarbon that directly contributes to the destruction of the ozone layer
N2O
atmospheric lifetime of 114 years
N2O
Minimizing IA pollution
✅sevoflurane & isoflurane ❌desflurane & nitrous oxide
Total intravenous anesthesia (TIVA)
Which takes priority when choosing anesthetic?
Environmental effect
Patient Safety
Patient Safety
Earth can’t sue me, but the patient/family sure can
Henry’s Law
More Dissolved gas = higher partial pressure
Graham’s Law
Ideal Gas Law
volume of a gas is directly proportional to mass
entire mixture behaves just as if it were a single gas
LeChatelier’s Law
Fick’s Law of Diffusion
gas: high [ ] area –> low [ ] area proportional to the concentration gradient
