Inhaled Anesthetics Flashcards
Nitrous oxide has ____ potency and _____ solubility
Low and Poor
What is the blood-gas partition coefficient?
A ratio of how soluble a substance is in blood compared to air.
If a gas has a blood-gas partition coefficient of 1.7 that means:
The gas is 1.7 times more soluble in blood than air at equilibrium
Since the drug is highly soluble, it will have a longer induction time
As the gas-blood partition coefficient increases, the MAC will generally ______
decrease
High Solubility = ____ induction
Low Solubility = ______ induction
High = Slow induction
Low = Fast induction
Fluorination increases ______ and decreases ______
Increases potency
Decreases flammability
This is why modern inhaled anesthetics are ethers but they are not flammable
What is MACBAR?
MAC required to block adrenergic response
It’s approximately 1.5 MAC
What is the MACAWAKE for Des/sevo/iso?
Approximately 0.33 MAC
When we say a gas has a MAC of 6%, it’s 6% of what?
It’s 6% of 1 ATM (760 mmHg)
So 6% is a partial pressure of 45.6mmHg
How will metabolic acidosis impact MAC?
decreases MAC
Acute alcohol use _____ MAC
Chronic alcohol use _____ MAC
Acute decreases
chronic increases
Will pregnant women have a higher or lower MAC?
Usually lower, because they have a higher level of circulating endorphins
How does serum sodium impact MAC?
Hypernatremia increases MAC
hyponatremia decreases MAC
In animals without brains, how is MAC impacted?
It isn’t, which suggests MAC is spinal cord mediated
Why does chronic meth use decrease MAC?
Depleted norepinephrine levels in the brain mean there’s less stimulation to overcome
Acute meth use will _____ MAC
increase
More norepinephrine stimulation to overcome
What is vapor pressure?
the pressure at which you have equal vaporization and condensation
What is the impact of pressure on vaporization?
Pressure reduces vaporization even at higher temperatures in which the substance would usually vaporize
What does it mean if a substance has a high vapor pressure?
That it really wants to vaporize
BECAUSE if it’s prone to vaporize, a lot more of its molecules will have to be vaporized before an equal number will begin condensing
What does high volatility mean?
That a substance really wants to evaporate
High volatility = high vapor pressure
When the vapor pressure is equal to the atmospheric pressure, you have reached:
the boiling point
Why don’t you have to adjust the dial for Sevo or Iso at altitude?
The percentage delivered at altitude is significantly higher than at 1 ATM, HOWEVER the partial pressure really isn’t
Since partial pressure is what we actually care about, there isn’t a huge need to adjust the dials
Why do you have to adjust Des at altitude, but not Iso or Sevo?
Unlike Sevo or Iso, Des is in a controlled, heated environment where it will always give off a set percentage
What determines how the rate of anesthetic onset?
The rate of rise of the partial pressure in the alveolus
NOT determined by how much of the anesthetic is absorbed in the blood
How does cardiac output influence rate of onset of inhaled anesthetics?
The more blood moving through the lungs, the higher the amount of solubility, which means onset will be slower
this means a high CO will increase the time it takes
A low CO will decrease the time it takes
The partial pressure in the lung is equal to the partial pressure in the ______
brain
What is the FA/FI curve representing?
How long it takes for the alveolar anesthetic concentration to equal the inspired anesthetic concentration
If I have the dial set to 2.1%, how long it takes for the exhaled concentration to reach 2.1%
What is the concentration effect?
Hypothetically, you would think that FA/FI would reach 1 at the same rate no matter what percentage we’re going for
If you give 6% it should take x amount of time for FA to reach 6%, and if we gave 60% it should take the same amount of time.
But it doesn’t. When you give a higher concentration of gas, the FA/FI reaches 1 much, much faster
Since Nitrous is the only gas we routinely use where we give large amounts, it’s the only gas effected by concentration
What is the metabolism rule of 2s?
Percent that is metabolized:
Halothane 20%
Sevo 2%
Iso 0.2%
Des 0.02%
In the CO2 absorber, Sevo can form _____ and Des can form ______
Sevo can form Compound A
Des can form carbon monoxide
What is the MAC of Sevo?
2%
What is the MAC of Des?
6.6%
What is the MAC of Iso?
1.15%
Why do inhalational agents drop the MAP?
Reduced SVR, NOT reduced CI
Volatile anesthetics are coronary vaso ______
dilators IN THE EPICARDIUM
What is coronary steal?
You’d think vasodilating the coronary vessels would be helpful in patients who have some blockages
BUT in those patients with partial blockages, they’re already vasodilated at the site of ischemia and vasoconstricted at other sites, allowing for increased flow through the partial occlusion
if you give an anesthetic agent, it vasodilates all the arteries, and the beneficial action of dilating the partially occluded artery decreases. You wind up stealing blood from the ischemic area.
DOES NOT HOLD UP IN THE RESEARCH
How do inhaled anesthetics impact the ECG?
Prolong QT
What do you do if a patient has a long QT at baseline?
Pretreat with beta blockers prior to anesthetizing
What effects on respiration do inhaled anesthetics cause?
Increased RR
Decreased Vt
Combination results in increased dead space, reducing alveolar ventilation
How do volatile anesthetics impact apneic threshold?
Increased
It will take a higher CO2 concentration in the arteries to spark apneic breathing mechanisms
What is the impact of volatile anesthetics on cerebral perfusion?
Increased
Blood flow goes up and metabolism goes down, which can cause increased ICP
Can be mitigated by increasing RR
Sevo
List the ethers
Des/Iso/Sevo
Enflurane
Methoxyflurane
Ether
How can you identify an ether?
The ether bridge:
C - O - C
List the alkanes
Halothane
Chloroform
List the gases
Nitrous Oxide
Xenon
Desflurane
Isoflurane
What effect does adding the Cl atom to Isoflurane have on its actions?
Increases potency by making the molecule heavier
increases blood and tissue solubility
Halothane
The absence of an ether bridge and presence of a Bromine are dead giveaways
Desflurane is fully flurinated. How does this impact its effect?
Decreased potency
Increased vapor pressure
Increased resistance to biotransformation
What does it mean for a gas to be stable?
ability to resist being broken down and metabolized
Des and Iso can become unstable in ______ producing ______
Desiccated soda lime
CO
VAPOR PRESSURE
SEVO/DES/ISO/NITRO
Sevo: 157
Des: 669
Iso: 238
Nitrous: 38,770
BOILING POINT
SEVO/ISO/DES/NITROUS
Sevo: 59
Iso: 49
Des: 22
Nitrous: -88
BLOOD:GAS COEFFICIENT
SEVO/DES/ISO/NITROUS
Nitrous
Des
Sevo
Iso
The VRG contains which organs?
Brain
Heart
Liver
Kidneys
Endocrine Glands
How does FRC effect wash in?
If your FRC is increased, that means there is more space to fill with gas, and the wash in will take longer
If your FRC is decreased, there is less space to fill with gas, and the wash in will be shorter
HEPATIC BIOTRANSFORMATION
DES/SEVO/ISO/NITROUS
Which anesthetic gases produce TFAs?
Primarily halothane (halothane hepatitis)
but also des and iso
Des and Iso are low in number, but since halothane hepatitis is immune mediated, if a patient had halothane hepatitis, they really should be re-exposed to any amount of TFAs
What are the metabolites of Sevo, and what can they cause?
Free Fluoride Ions
Hypothetically they can cause high output renal failure that looks like DI
But there’s no evidence of this in humans
What are the metabolites of Nitrous?
None. It isn’t metabolized in the body
_______ accelerates the production of Compound A from Sevoflurane
Desiccated soda lime
If a 40-year-old patient receives 1% Sevo (0.5 MAC) for 2 hours, what is the MAC - hrs?
2hours at 0.5 MAC = 1 MAC hour
What are the FDA guidelines surrounding FGF with Sevo?
FGF should not be less than 1 L/min for up to 2 MAC hours
For more than 2 MAC hours, FGF should not be lower than 2 L/min
Which P450 enzyme is primarily responsible for halogenated anesthetic metabolism in the liver?
CYP2E1
The concentration effect is also known as:
overpressuring
the higher the concentration of anesthetic, the faster its onset of action
What causes the concentration effect?
- The concentratingeffect: Nitrous oxide is WAAAAYYY more soluble in the blood than nitrogen, so more air is moving from the alveolus into the blood, and this causes the alveoli to shrink. Smaller alveoli means decreased FRC means faster rate of rise
- Augmented Gas Inflow Effect: Because gas is leaving the alveoli rapidly and reducing alveolar volume, air is sucked down from the upper airways into the alveoli to replace the lost gas. But this really only happens for the first breath or so
What is the ventilation effect?
In spontaneously breathing patients, as you breathe in anesthetic gases, RR and Vt decrease, which in turn decreases the amount of gas inhaled
minimizes the risk of anesthetic overdose
Does the second gas effect have more impact on sevo or iso? Why?
Iso
It produces more of an effect on agents that have higher solubility
In a R to L shunt, the FA/FI of which agents are most effected?
The less soluble it is, the more it’s going to be effected (des is more effected than Iso)
In R to L shunt, the rate of rise for inhaled anesthetics will be ______ and the rate of rise for IV anesthetics will be ______
decreased
increased
List five examples of R to L shunts
Tet of Fallot
Eisenmenger’s Syndrome
Foramen Ovale
Tricuspid Atresia
Ebstein’s Anomaly
How much more soluble than nitrogen is nitrous oxide?
34x
What are the blood:gas solubility coefficients for nitrogen and nitrous oxide?
Nitrogen 0.014
Nitrous Oxide 0.46
Why would it be unwise to give nitrous oxide to a long-term alcoholic?
Nitrous oxide causes Vit B12 deficiency
For people who already have some level of B12 deficiency, this can lead to megaloblastic anemia, neuropathy, and decreased DNA synthesis
Which is inhibitory and stimulatory:
Opening of potassium channels
Opening of Sodium Channels
Opening potassium channels is inhibitory
Opening sodium channels is excitatory
In the brain, the most important site of volatile anesthetic action is the:
GABA-A Receptor
In the spinal cord, the most important site of volatile anesthetic action is:
Glycine receptor stimulation
NMDA receptor inhibition
Sodium Channel Inhibition
GABA-A ACTION IS NOT RESPONSIBLE FOR IMMOBILITY
Inhaled anesthetics cause immobility at the ______
ventral horn of the spinal cord
Who do inhaled anesthetics decrease MAP?
They decrease the amount of intracellular calcium in vascular smooth mm and cardiac myocytes → vasodilation and myocardial depression
What effect do inhaled anesthetics have on an ECG?
Prolong QT because they impair potassium movement out of the cell during depolarization
This means the action duration is much longer, because the cell has a hard time repolarizing
Hence, the QT is prolonged
Which volatile anesthetic decreases SVR the LEAST?
Sevo
Coronary vasodilation is greatest with which anesthetic?
Iso
Then Des, then Sevo
What effect does nitrous have on HR and BP?
Increases both because it activates the SNS
The halogenated agents are broncho_______
dilators
Which inhaled anesthetic impairs hypoxic ventilatory response the least?
Des
Why do inhaled anesthetics impair hypoxic ventilatory drive?
We think it’s because when they’re metabolized they produce a reactive oxidative species that impairs the sensory cells of the carotid body
It makes sense, then, that Sevo (which undergoes the most metabolism) causes the most suppression of hypoxic respiratory drive, and Des (which undergoes the least metabolism) causes the least suppression
Which anesthetic is ideal for patients with sleep apnea or emphysema?
These patients rely on hypoxic ventilatory drive
Where are the carotid baroreceptors located?
the carotid sinus
Where are the carotid chemoreceptors located?
The carotid body
At what MAC is the response to hypoxia impaired?
O.1
BUT this MAC does NOT impair CO2
What MAC is required to produce an isoelectric state?
1.5-2
Motor Evoked Potentials (MEPs) monitor the _________
corticospinal tract
Somatosensory Evoked Potentials (SSEPs) monitor the integrity of the ______
dorsal column
The corticospinal tract is supplied by the _____ arteries
Anterior spinal
The dorsal column is supplied by the ______ arteries
posterior spinal
With EMPs, what are amplitude and latency?
the best anesthetic technique to preserve evoked membrane potentials is:
TIVA without N2O
NOT KETAMINE
What is the maximum MAC you can use if you’re monitoring EMPs?
0.5
