Inhalational agents - Uptake and Distribution Flashcards
Process of getting the anesthetic agent from the anesthetic machine to the patient’s CNS (5)
Vaporizer
Circuit
Alveoli
Blood / arterial
Brain (CNS)
Series of ___ ___ ___to move agent through barriers to the CNS
partial pressure gradients
Series of partial pressure gradients:
PA —— Pa ——- Pbr
Partial pressure of anesthetic vapor ___ every step.
[Uptake and distribution]
decreases
Partial pressure between alveolar, and ___equilibrates quickly
[Uptake and distribution]
arterial
___ ___ ___equilibrates rapidly with that in the brain.
[Uptake and distribution]
Arterial partial pressure
We know that ___ ___ don’t produce unconsciousness directly
[Uptake and distribution]
alveolar concentrations
However, alveolar concentration is a great estimate of ___/___ ___ which we can not directly measure
[Uptake and distribution]
CNS/brain concentrations
Thus, we use alveolar concentration as a “___ for CNS/brain concentration.
[Uptake and distribution]
stand-in”
FGF (fresh gas flow) is determined by the ___ and ___ settings.
vaporizer, flowmeter
FI (Inspired gas concentration) is determined by 1. ___ 2. ___ 3. ____
FGF rate, breathing-circuit volume and circuit absorption
FA (alveolar gas concentration) is determined by 1. uptake (=(lambda)b/g x C (A-V)xQ 2. ___ and 3. the concentration effect and second gas effect
Ventilation
Uptake equation:
=(lambda)b/g x C (A-V)xQ
The concentration effect and second gas effect:
a. concentrating effect b) augmented inflow effect
Fa (arterial gas concentration) is affected by ___/___mismatching
ventilation/perfusion
Inhalation anesthetic agents must pass through many barriers between the ___ ___ and the brain.
anesthesia machine
The vapor pressure of isoflurane is ___ (33% of atmospheric pressure).
242 mm Hg
The MAC of isoflurane:
1.17%
The vaporizer of isoflurane is dialed to deliver about ___
2%
The concentration must be diluted out; that starts in the ___.
vaporizer
In the circuit, there is the ___ ___and the ___ that is being rebreathed
fresh flow, gas
This dilutes out the ___ ___ more.
inspired agent
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Flows are fresh gas flow (FGF), ___ , and ____ ___.
[path of anaesthetic]
alveolar ventilation (VA), cardiac output (CO)
Measurements are delivered (Set) concentration,___ ___, ___ ___, and ___ ___ expressed as partial pressure, tension, or fraction so that tissue concentration equals arterial concentration at equilibrium
[path of anaesthetic]
inhaled concentration, alveolar concentration, and tissue concentration
The rise and fall in alveolar partial pressure precedes that of other tissues
The rise and fall in ___partial pressure precedes that of other tissues.
alveolar
Inspired or inhaled partial pressure ___
(PI)
A high PI initially offsets the impact of ___ and speeds ___ (rise in PA and thus Pbr)
uptake, induction
Concentration effect – the higher the ___, the more rapidly the PA approaches the PI
PI
Second-gas effect – “high- ___ uptake of one gas to ___ the rate of increase of the PA of a concurrently administered ‘companion’ gas”
volume, accelerate
As equilibrium is achieved and uptake is slowed, the PI must be ___ to maintain a constant Pbr.
reduced
The greater the concentration of inhalation agent delivered to the circuit, the greater the ___ ___between the vaporizer and the alveoli, and the faster the rise in alveolar concentration.
concentration gradient
N2O is higher because it’s the partial pressure of the anesthetic agent in the blood that equates to a greater effect
Alveolar concentration is determined by a balance between the delivery of anesthetic to the ___and removal of the drug from the ___ into the blood (uptake).
alveolus, alveolus
Greater alveolar ventilation promotes delivery of ___ ___ to offset uptake
[Factors determining PP gradient from machine to alveoli (input)]
anesthetic agent
More rapid ___ with greater alveolar ventilation
[Factors determining PP gradient from machine to alveoli (input)]
induction
___induction with decreased alveolar ventilation
[Factors determining PP gradient from machine to alveoli (input)]
Slower
The effect of increasing ventilation will be most obvious in raising the FA/FI for more ___anesthetics, as they are more subject to ____.
[Factors determining PP gradient from machine to alveoli (input)]
soluble, uptake
Spontaneous ventilation.
Anesthetic agents impact their own uptake due to the ___-___ ___effects on alveolar ventilation.
[Factors determining PP gradient from machine to alveoli (input)]
dose-dependent depressant
If controlled ventilation is used, there is potential for ___.
[Factors determining PP gradient from machine to alveoli (input)]
overdose
The lowering of alveolar partial pressure by uptake can be ___ by increasing alveolar ventilation.
[Factors determining PP gradient from machine to alveoli (input)]
countered
In other words, constantly replacing anesthetic taken up by the ___ ___ results in better maintenance of alveolar concentration.
[Factors determining PP gradient from machine to alveoli (input)]
pulmonary bloodstream
The effect of increasing ventilation will be most obvious in raising the ___/___for more soluble anesthetics, as they are more subject to uptake.
[Factors determining PP gradient from machine to alveoli (input)]
FA/FI
Maintaining____ventilation is important with inhalation induction to avoid overdose.
[Factors determining PP gradient from machine to alveoli (input)]
spontaneous
This protective mechanism (spontaneous ventilation) is lost with ___ or ____ventilation
[Factors determining PP gradient from machine to alveoli (input)]
mechanical, controlled
Higher rates of ___ ___keep the concentration gradient maximized and thus the diffusion of anesthetic from the alveoli into the ____ is maximized.
[Factors determining PP gradient from machine to alveoli (input)]
alveolar ventilation, blood
____ is a limiting factor to this overdose possibility.
[Factors determining PP gradient from machine to alveoli (input)]
PaCO2
Greater ventilation leads to hyperventilation – decreased PaCO2 –___ ___– reduction of delivery of agent to the ___.
[Factors determining PP gradient from machine to alveoli (input)]
cerebral vasoconstriction, brain
Time constant: The time required for___ through a container to ____ the volume of the container.
flow, equal
Time constant = ___/___
[equation]
capacity (L) / flow (L/min)
The amount of time, in minutes, required for a ___turnover of gas within a container.
[Time Constant]
63%
In two time constants there is an ___ turnover of gas.
[Time Constant]
86%
(That is 63% + 63% of the remaining 37%. )
In ___time constants there is a 95% turnover of gas.
[Time Constant]
three
(That is 86% + 63% of the remaining 14%.)
Normally the wash in of new gas into the lungs is greater than ___ complete in ___ minute.
[Time Constant]
80%, 1
Minute ventilation (and alveolar ventilation) is more important than the ___.
[Time Constant]
tidal volume
Alveolar ventilation is (___-___) x RR = approx. (450-150) x 14 = 4200 mL/min
[Time Constant]
TV-Vdead
If the container capacity is 5 liters and the new gas flow into the container is 10 L/M, then the time constant is ___minutes. And the gas in the container will be ___turned over in 2 minutes.
[Time Constant]
0.5, 98%
If the container is 5 L and the fresh gas flow is 1 L/min, the time constant is
If the container is 5 L and the fresh gas flow is 1 L/min, the time constant is ___ minutes and the gas in the container will be turned over 98% in ___minutes.
[Time Constant]
5, 20
Practically use this concept to understand how long it takes to change the concentration in the ___ after changing the concentration on the ___
[Time Constant]
circuit, vaporizer
We can adjust flow, not the ___, increasing flow will ___up how fast the gas is turned over.
[Time Constant]
capacity, speed
Time constant multiples
1……………………..___
2……………………..___
3……………………..___
4……………………..___
5……………………..___
63%, 86%, 95%, 98%, 99.5%
Vessel-rich (brain, heart, liver, kidney, endocrine) – small capacity w ___ flow – short time constant – equilibrates more ___
[Time Constant]
high, rapidly
Vessel-rich: Receives __% of CO (only __% body mass)
[Time Constant]
75%, 10%
Lean muscle (muscle, skin) – large capacity w ___ flow – longer time constant – equilibrates more ___
[Time Constant]
lower, slowly
Lean Muscle receives ___% of CO (___% body mass)
[Time Constant]
19, 50
Fat – medium capacity w ___ flow – longer time constant – equilibrates ___ ___
[Time Constant]
lowest, most slowly
Receives ___% of CO (___% body mass)
[Time Constant]
6%, 20
Vessel-poor (___, ___, ___)
[Time Constant]
bone, ligament, cartilage
Vessel-poor receives ___% of CO (___% body mass)
[Time Constant]
0, 20
The volume of the gas in the ___ takes away from what is going to the ___.
[Factors determining partial pressure gradient from machine to alveoli (Input)]
circuit, alveoli
Higher fresh gas flows (___-___L/min) from the machine ___ this effect.
[Factors determining partial pressure gradient from machine to alveoli (Input)]
5-10, negates
Solubility of an agent in the ___/___ components of the breathing system slows the rise of the PA initially
[Factors determining partial pressure gradient from machine to alveoli (Input)]
rubber/plastic
___ circuits require higher flows so exhaled gases are not recycled/rebreathed – concentrations in the circuit are typically at or near the % set on the ___.
[Factors determining partial pressure gradient from machine to alveoli (Input)]
Mapleson, vaporizer
Circle system:
Allows rebreathing of previously exhaled gas
Exhaled gas contains ___concentration of agent during the initial uptake phase because some is ___ out by the body
[Circle System]
lower, taken
The agent concentration coming in the fresh gas from the machine is ___ ___by mixing with the exhaled gas.
[Circle System]
diluted down
A relatively ___ flow will eventually eliminate this. A relatively ___flow will magnify the dilution effect.
[Circle System]
high, low
___ gas is not rebreathed, and ___ flows are required.
[Non-rebreathing Circuits]
Exhaled, high
The concentration of agent in the ___ is very close to the concentration set on the ___ ___.
[Non-rebreathing Circuits]
circuit, vaporizer dial
If the gas is soluble in the material of the circuit or system, some agent will be ___to these materials.
[Non-rebreathing Circuits]
lost
Functional Residual Capacity
Composed:
[Factors determining partial pressure gradient from machine to alveoli (Input)]
the residual volume and the expiratory reserve volume
The larger the FRC, the ___ the induction of the anesthetic agent.
[Factors determining partial pressure gradient from machine to alveoli (Input)]
slower
Neonates have ___ FRC than adults as a percent of ___, more volume changed with each respiration and faster induction with anesthetic agent than adults.
[Factors determining partial pressure gradient from machine to alveoli (Input)]
smaller, TLV
Residual volume cannot be ___ directly.
[Factors determining partial pressure gradient from machine to alveoli (Input)]
ventilated
___ ___ volume is the portion of the lung volume that is possible to ventilate but which was not ventilated during a given breath.
[Factors determining partial pressure gradient from machine to alveoli (Input)]
Expiratory reserve
Solubility – __:___ partition coefficient
Definition: “a ___ratio describing how the anesthetic distributes itself between___ phases at equilibrium (steady state)”
[Factors determining transfer of agent from alveoli to arterial blood (Uptake)]
blood:gas, distribution, two
The ___ the solubility, the faster the rate of rise of the ___toward the PI.
[Factors determining transfer of agent from alveoli to arterial blood (Uptake)]
lower, PA
Remember partition coefficients are ___dependent – decreased temperature causes ___solubility and increased temperature causes ___ solubility.
[Factors determining transfer of agent from alveoli to arterial blood (Uptake)]
temperature, increased, decreased
Each coefficient is the ratio of the ___ of the anesthetic gas in each of ___ phases at steady state.
[Factors determining transfer of agent from alveoli to arterial blood (Uptake)]
concentrations, two
Steady state is defined as equal ___ ___ in the two phases.
[Factors determining transfer of agent from alveoli to arterial blood (Uptake)]
partial pressures
Equilibrium is the ___pressure in both states, blood and gas.
[Factors determining transfer of agent from alveoli to arterial blood (Uptake)]
partition? (Partial)
The more soluble the agent, the more agent has to be dissolved in the blood before the ___ equilibrates with the PA. ___ induction.
[Factors determining transfer of agent from alveoli to arterial blood (Uptake)]
Pa, Slow
The ____ the blood/gas coefficient, the greater the anesthetic’s solubility and the ___ its uptake by the pulmonary circulation.
[Factors determining transfer of agent from alveoli to arterial blood (Uptake)]
higher, greater
As a consequence of this increased solubility, alveolar partial pressure ___to a steady state more ___.
[Factors determining transfer of agent from alveoli to arterial blood (Uptake)]
rises, slowly
The less soluble agent, minimal amounts of agent must be dissolved before ___ is achieved; the rate of rise of PA and Pa and induction are ___.
[Factors determining transfer of agent from alveoli to arterial blood (Uptake)]
equilibrium, rapid
[Factors determining transfer of agent from alveoli to arterial blood (Uptake)]
its the partial pressure of the anesthetic (N2O) in the blood that equate to greater effect
FA rises toward FI faster with ___ ___ (an insoluble agent) than with halothane (a soluble agent).
nitrous oxide, halothane
The initial steep rise of FA/FI is due to ___ ____ of the alveoli by ventilation.
unopposed filling,
The rate of rise slows as the ___-___group—and eventually the muscle group—approach steady-state levels of ____
vessel-rich, saturation.
Cardiac output (pulmonary blood flow)
Affects ___ by carrying away agent from the ____ and preventing the rise in PA
[Factors determining transfer of agent from alveoli to arterial blood (Uptake)]
uptake, alveoli
Increased CO leads to ____uptake/removal of agent from the lungs and ___induction.
[Factors determining transfer of agent from alveoli to arterial blood (Uptake)]
greater, slowed
The rate of increase of more soluble agents is affected more: the ___ in CO will slow the induction and the rise in ___.
[Factors determining transfer of agent from alveoli to arterial blood (Uptake)]
increase, PA
Agents that depress CO cause a ____ feedback response that contrasts the negative feedback from spon. vent.
[Factors determining transfer of agent from alveoli to arterial blood (Uptake)]
positive, spon. vent.
The decreased CO results in an increase in ___, which further deepens anesthetic depth and causes further __ ___.
[Factors determining transfer of agent from alveoli to arterial blood (Uptake)]
PA, myocardial depression
As ___ ___ increases, anesthetic uptake increases, the rise in alveolar partial pressure slows, and ___ is delayed.
cardiac output, induction
The effect of changing cardiac output is ___ pronounced for insoluble anesthetics, as so little is taken up regardless of _____ blood flow.
[Factors determining transfer of agent from alveoli to arterial blood (Uptake)]
less, alveolar
Low-output states predispose patients to ___ with soluble agents, as the rate of rise in alveolar concentrations will be markedly increased.
[Factors determining transfer of agent from alveoli to arterial blood (Uptake)]
overdosage, increased
Alveolar-to-Venous Partial pressure gradient:
During uptake the ___ ___group will remove the anesthetic agent that is delivered
[Factors determining transfer of agent from alveoli to arterial blood (Uptake)]
vessel rich
The mixed venous blood returning to the lungs has a ___ partial pressure of agent.
[Factors determining transfer of agent from alveoli to arterial blood (Uptake)]
lower
The gradient between the ___ ___ ___ and the ___ ___is great encouraging diffusion out of the alveoli.
[Factors determining transfer of agent from alveoli to arterial blood (Uptake)]
alveolar partial pressure, venous blood
As saturation of the VRG ___, the gradient becomes smaller, and the ___rises
[Factors determining transfer of agent from alveoli to arterial blood (Uptake)]
increases, PA
After __-___ minutes the vessel rich group begins to saturate, venous blood partial pressure rises and the gradient becomes smaller, uptake slows, and ___rises.
[Factors determining transfer of agent from alveoli to arterial blood (Uptake)]
5-15, PA
Assumption is alveolar PA and arterial Pa are ___
[V /Q Mismatch (Shunt)]
equal
Reality is that arterial partial pressure is less than ___
[V /Q Mismatch (Shunt)]
ETgas
R to L shunt enhances this difference
___ Pa – especially with less soluble agents
PA poorly estimates the___
[V /Q Mismatch (Shunt)]
Lower, Pa
Seen with ___ ___or __to___ intracardiac shunt
[V /Q Mismatch (Shunt)]
bronchial intubation, right-to-left
A bronchial intubation or a right-to-left intracardiac shunt will slow the rate of induction with ___ ___ more than with ___.
[V /Q Mismatch (Shunt)]
nitrous oxide, sevoflurane
The ___ ___ agent has uptake that offsets the dilutional effects of shunted blood on the Pa.
[V /Q Mismatch (Shunt)]
more soluble
Uptake of the poorly soluble agent is ___, and ___effects on the Pa are relatively unopposed.
[V /Q Mismatch (Shunt)]
minimal, dilutional
V/Q mismatch may come from ___, ____, ___(uneven gas distribution)
[V /Q Mismatch (Shunt)]
venous admixture, alveolar dead space, bronchial intubation
Restriction” is:
[V /Q Mismatch (Shunt)]
diffusion between alveoli and arterial – higher before, lower after
Factors determining transfer of agent from arterial blood to brain (uptake) (3)
- Brain:blood partition coefficient
- Cerebral blood flow
- Arterial-to-venous partial pressure difference
Equation:
[Tissue Uptake]
λ x Q x (PA-PV) / PB
λ is ___
[Tissue Uptake]
solubility
Q is __ ___
[Tissue Uptake]
Q is cardiac output
PA is ___ ___ ___
[Tissue Uptake]
alveolar partial pressure
PV is ___ ___ ___ ___
[Tissue Uptake]
mixed venous partial pressure
PB is ___ ___
[Tissue Uptake]
barometric pressure
___ ___ will determine what the loss from the lungs will be.
[Tissue Uptake]
Tissue uptake
Tissue uptake is determined by ? (4)
[Tissue Uptake]
solubility , blood flow, pressure gradients, and tissue mass.
___is high solubility for inhaled agents, but has little CO going to it.
[Tissue Uptake]
Fat
___has lower solubility, but higher CO.
[Tissue Uptake]
Brain
Vessel rich groups – ___ of CO
75%
VRG (6)
Brain, heart, kidney, splanchnic, liver, endocrine
Muscle group – 18% of CO
18%
MG:(2)
Muscle, skin
Fat group –___ of CO
5%
Vessel poor group – ___ of CO
2%
VRG: (3)
Bone, ligament, cartilage
The containers and connections depict the structure of the model. The level of filling depicts the ___ ____ in the respective compartments.
[Annotated Gas Man® picture.]
anaesthetic tension
This ___ ___ is the model behaviour in response to all changes made in the input variables up to the present time.
[Annotated Gas Man® picture.]
filling state
Possible input changes are ___, ____, ____, ____
[Annotated Gas Man® picture.]
vaporizer setting, fresh gas flow, alveolar ventilation, and cardiac output
Generally=
[Elimination]
reverse of uptake
Slower awakening
___ soluble
[Elimination]
Higher
Higher soluble
____ duration of exposure
____concentration
[Elimination]
Longer, Higher
Elimination via exhalation predominantly
____alveolar ventilation
[Elimination]
Increase
Recovery from anesthesia depends on ___ ___ ___ CNS/brain tissue.
[Elimination]
lowering the concentration in
Most agents are___ ___ in the brain and the brain receives a large % of CO.
[Elimination]
poorly soluble
Agents with low solubility are not affected by ____ as much as the more highly soluble.
[Elimination]
time
Metabolism can speed ___ of halothane.
[Elimination]
recovery
Elimination of ___
[Factors assoc. with increased rate of recovery]
rebreathing
___ fresh gas flows
[Factors assoc. with increased rate of recovery]
High
Low anesthesia-circuit volume
[Factors assoc. with increased rate of recovery]
Low
___ absorption by anesthesia circuit
[Factors assoc. with increased rate of recovery]
Low
___ solubility of agent
[Factors assoc. with increased rate of recovery]
Decreased
___cerebral blood flow*
[Factors assoc. with increased rate of recovery]
High
____alveolar ventilation
[Factors assoc. with increased rate of recovery]
Increased
Many of the factors that speed induction also speed ____: elimination of rebreathing, high fresh gas flows, low anesthetic-circuit volume, low absorption by the anesthetic circuit, decreased solubility, high cerebral blood flow (CBF), and increased ventilation.
recovery
Airway protection / ____
[Implications for Rapid Recovery]
oxygenation
___ movement through the ___ MAC concentration that causes enhanced perception of pain
[Implications for Rapid Recovery]
Rapid, 0.1
Return to normal ___ function
[Implications for Rapid Recovery]
cardiovascular
___more rapid
[Implications for Rapid Recovery]
Turnover
___ discharge from PACU
[Implications for Rapid Recovery]
Quicker
___ return to normal activities
[Implications for Rapid Recovery]
Quicker
Safety, cost, ____ ____
[Implications for Rapid Recovery]
patient satisfaction
Decreased amount of available drug for ____/____
Eliminate the enhancement of ___
Rapid movement through the 0.1 MAC concentration that causes enhanced ____
[Implications for Rapid Recovery]
metabolism/toxicity, NMB, perception of pain
If a less soluble drug leads to more rapid awakening, why not switch over to des before the end of the case? Additive or even synergistic effect regarding return to mental function.
Changes in compartments – ___ in lean body mass and increases in body fat
[Elderly / age-related changes ]
decreases, increases
Volume of distribution of the central compartment is ___(plasma volume); volume of distribution for volatiles is ____(especially more lipid soluble agents)
[Elderly / age-related changes ]
smaller, larger
___clearance due to impaired pulmonary gas exchange
[Elderly / age-related changes ]
Decreased
[Elderly / age-related changes ]
