Inhaled anesthetics Flashcards
Solubility:
-The affinity for an anesthetic in blood compared to ___ or in blood compared to ___.
air
tissue (fat, muscle)
___ = State of equal partial pressures, NOT ___
Equilibrium
-concentration
While the blood does carry the anesthetic to its effect site (___). Blood is also a pharmacologically ___. The size of this reservoir is determined by ___.
Solubility of an anesthetic in the blood is described using ___.
- brain and spinal cord
- inactive reservoir
- solubility
- Blood Gas Partition Coefficients
Think of this not as a pulsating transport system but rather as a holding pool for gaseous agents?
Blood
The higher the ___, the more that gas goes into the inactive reservoir.
solubility coefficients
Partition Coefficients aka ???
- Solubility is expressed in terms of ___.
- The ___ determine how the anesthetic will partition itself btw the gas and blood phase at equilibrium.
- Partition coefficients exist btw ___ and also btw ___.
Oswaldt Solubility Coefficients
- partition coefficients
- coefficients
- blood and gas
- blood and organs (fat)
MOST SOLUBLE? will have more gas in the inactive blood reservoir than we will have with a lower soluble anesthetic. Will exert its activity on the brain slower.
**Remember ___ will change the amount that can be dissolved in something.
Halothane (2.4)
**temperatures
Will determine the alveolar concentration of an inhalation agent?
Solubility
Determine how the anesthetic agent partitions into gas phase (alveoli) and blood phase (reservoir)?
Solubility coefficients
Eventually equilibrium is reached and there is no longer a gradient. Can take ___ for the anesthetic to equilibrate with the fat compartment.
24-48 hours
Clinical impact of a lower hematocrit (anemic patient)?
Faster induction
fewer binding sites for the anesthetic in the blood
Uptake and Solubility:
Solubility will determine how quickly the concentration in the alveoli (___) reaches the concentration set inspired (___).
The faster these 2 values approximate equality, the faster the ??
FA
FI
uptake to the brain and the induction
*Relationship btw FA and FI:
Alveolar concentration will approach inspired rate varies for each agent.
- Expressed as a ratio of ___ divided by ___ over ___.
- ___ agents have the fastest rate of the alveolar gas matching the inspired concentration over time.
alveolar fraction
inspired fraction
time
Least soluble agents
FA/FI Curves ~ same shape for all agents (not the same curve):
1) initial rapid rise to? uptake by?
2) less rapidly to? uptake by?
3) continues more slowly thereafter
**This is a RATIO, highest possible value is one and we are at equilibrium at that point. Goal is for ___ to reach/approach ___.
1) first “knee” - vessel rich group (VRG)
2) second “knee” - muscle group (MG)
FA
FI
FA/FI Curves:
____ agents will have fastest rate of rise.
*Will have a slower induction when the B/G solubility is 1.4 vs 0.42.
Least soluble agents
N2O has a B/G of 0.47, yet there is a more rapid rate of rise with N2O than with desflurane which is 0.42. Why?
Concentration effect
N2O has a higher solubility than desflurance but this is because we can deliver N2O in a very high concentration (up to ?) also due to the second gas effect. Desflurane can only be delivered up to ?
80%
6%
The lower the solubility, the more rapid rate of rise. This makes sense since a higher solubility will go into the blood aka the inactive reservoir. The ___ is what makes the difference and the ___ is what determines what goes into this region.
___ is what you set as the concentration on the dial.
- alveolar region
- solubility
- FI
- Uptake = Influence on FA/FI:
- Uptake opposes the effect of ___ (which increases the ___).
- If FA removes 1/2 of anesthetic in lung - FA would be ___ of FI.
- If FA removes 2/3 of anesthetic in lung - FA would be ___ of FI.
ventilation (FA)
- 1/2
- 1/3
Tissue uptake of the agent will decrease the ___ and therefore it will decrease relative to the ___.
The degree to which the ___ is decreased depends on percentage of uptake into the blood and tissues.
*Tissue solubility coefficients determines this uptake.
alveolar concentration
inspired concentration
alveolar concentration
Washout of Anesthetic - Effect of Solubility on FA/FI:
-The higher the solubility the ___ the increase in alveolar concentration rise toward inspired concentration.
- Reason: soluble anesthetics require that a large amount of anesthetic be dissolved in the ___ before the Pa and PA partial pressures equilibrate.
- Greater solubility = greater uptake = less of a ___ buildup in the alveoli.
Slower
- blood (inactive reservoir)
- pressure
Determines how the anesthetic will partition itself btw the blood phase and air phase when equilibrium is reached?
Solubility
Goal = ???
To accomplish this desire high percentage of ___ in the ___.
Alveoli are the windows to the brain!
-Thus with a 0.5 solubility = faster induction compared to 2.0.
Fast Induction
- Gas
- lungs
Impact of High Solubility on Induction:
- Since ___ mirrors brain concentration and the more soluble agent has a ___ - induction is slower with more soluble agents.
- Likewise a low solubility agent demonstrates a fast induction because very little anesthetic must dissolve in the blood reservoir before partial pressures equilibrate.
FA
lower FA
___ solubility coefficient = quicker induction and fasterrrr emergence!
LOW
In theory use of a moderately soluble agent Halothane B/G 2.4 would result in slow rise of ___ and slow induction.
In practice, this effect is compensated for by increasing the ___ used for ___.
Use of high delivered concentrations is known as = ___. Use a much higher concentration at induction than during maintenance phase.
FA
concentration
induction
Overpressure
Impact of Solubility on Emergence:
The ___ the B/G solubility coefficient - the shorter time emergence will take.
~Clinical application - turn off the agents sooner. Also begin to decrease the concentration delivered earlier with a ___ agent compared to one with ___.
lower
very soluble agent
lower solubility
(Halothane - 2.4 off sooner than Desflurane - 0.42)
\_\_\_ = parallels induction with respect to solubility concepts. \_\_\_ = slower time to awaken, more left in the reservoir (blood) when the gas is turned off.
Emergence
Higher Solubility
Elimination is more rapid with a ___ agent. Turn off agent - 0% delivered and administer 100% oxygen.
less soluble
Quadrupling CO with no change in solubility will ___ FA/FI.
~Clinical example - patient in liver failure and is fluid overloaded will see a ___ in rate of induction.
~If CO decreased and no change in solubility ___ rate of induction as FA/FI ratio ___.
decrease
decrease
increase
increases
___ CO slows induction - greater effect with ___ soluble agent.
Increased
highly
The a-v difference reflects uptake of anesthetic by the?
tissues
This anesthetic has an extremely low uptake in the fat, lowest fat/blood partition coefficient - 2.3 (also lowest with brain to blood - 1.1)?
Normal range for lean tissue (brain) - ?
Normal range for fat coefficients (usually high) - ?
Nitrous oxide
- 1-2
- 27-67
0 uptake into the ___ - receives 0% of the CO.
Vessel poor group (VPG)
FA/FI Curves - Impact of Tissue Uptake:
1) ___ = a-v difference = 0 as no agent occupies the alveoli - no uptake
2) ___ = uptake by VRG balances input “quasi-equilibrium”
3) ___ = decreased uptake by VRG, MR group uptake
4) ___ = occurs in ___ - uptake by MRG slows
1) Initial steep rise
2) First knee
3) Slower second rise
4) Second knee
4-8 minutes
___ - partial pressure, concentration going to the brain
___ - concentration inspired, this is altered by changes in ___
___ - show the rate at which the alveolar concentrations approaches inspired concentrations
FA
FI
-Fraction delivered
FA/FI curves
Represents the partial pressure of anesthetic going to the brain?
The alveolar partial pressure = the arterial partial pressure = the brain partial pressure.
Based on this assumption PA is used to estimate???
FA
depth of anesthetic
recovery from anesthesia
anesthetic potency or MAC
We use a much higher concentration (%) at __ than during __ phase.
induction
maintenance phase
The concentration that will produce absence of movement in 50% in response to a noxious stimulus?
Minimum Alveolar Concentration (MAC) (ED50 of inhalation agents)
Increase in ventilation (2-4 L/min to 8 L/min) will increase FA/FI more for a ___!!! this will help speed its induction rate
Highly soluble agent
- N2O (low solubility) FA rapidly rises to FI even at alveolar ventilation (2L/min). Curve not capable of increasing no matter what the ventilation is.
- Ether (high solubility) doubling vent = FA/FI increases 2x
Ventilation Perfusion Abnormalities: will have a greater effect with the ???
Ex: Main stem intubation causes a ___ d/t ___.
less soluble agents
slower induction
dilutional effect
Shunting effects are greater with the ??? impact much larger on these.
Lower soluble agents
___ agents washout first!
As duration of anesthesia lengthens - washout ___ due to more anesthetic in the reservoirs.
Least soluble
prolonged
The higher the B/G solubility coefficient the ___ emergence will take.
Longer
___ = is where 50% of the population will respond to a verbal command, still have an anesthetic agent on board but they are still responsive. 50% of people will respond to you.
MAC awake
1) ___ solubility = slower increase in alveolar concentration (FA) toward inspired (FI).
2) Elimination (washout) more rapid with ???
3) Changes in ventilation or CO have less of an impact on depth of anesthetic with ___ agents vs. ___ agents.
1) Higher
2) Low solubility
3) lower solubility vs. higher solubility
Want patients breathing at the end, to breathe off the anesthetics. Emergence is a lot tougher than induction. Emergence want to washout the gas and want their physiological drives to kick back in, need to allow CO2 to build up. When trending towards the end of the case need to begin the washout process, start decreasing our agent. Want to reach ___ at the end of the procedure.
MAC awake
- If changes in anesthetic depth need to be made to compensate for surgical stimulus - faster with a ___ agent.
- Changes in ventilation or CO influence anesthetic depth to a greater degree with ___.
- The ___ the solubility the smaller influence of ventilation/perfusion inequalities on arterial anesthetic pressure.
- less soluble agent
- soluble agents
- greater
