Uptake and Distribution- Pharmacokinetics of Volatile Agents Flashcards by Lauren Ranson

process of getting the anesthetic agent from the anesthetic machine to the patient’s CNS

vaporizer
circuit
alveoli
blood/arterial
brain (CNS)

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the series of partial pressure gradients to move agent through barrier to the CNS

PA—–Pa—–Pbr

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partial pressure between alveolar and arterial equilibrate

quickly

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arterial partial pressure equilibrate __ with the brain

rapidly

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alveolar pressure don’t produce __ directly

unconsciousness

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we use alveolar concentration as

a stand-in for CNS/brain concentration

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fresh gas flow is determined by

the vaporizer and flowmeter settings

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Fi (inspired gas concentration) is determined by

FGF rate, breathing-circuit volume, and circuit absorption

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FA (alveolar gas concentration) is determined by

uptake, ventilation, and the concentration/second gas effect- concentrating agent and augmented inflow effect

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Fa (arterial gas concentration) is affected by

ventilation/perfusion mismatching

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a high inspired or inhaled partial pressure (PI) initially offsets

the impact of uptake and speeds induction (rise in PA and thus Pbr)

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concentration effect

the higher the PI, the more rapidly the PA approaches the PI

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second-gas effect

high volume uptake of one gas to accelerate the rate of increase of the PA of a concurrently administered “companion gas”

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as equilibrium is achieved and uptake is slowed, the __ must be reduced to maintain a constant __

Pbr

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greater alveolar ventilation promotes

delivery of anesthetic agent to offset uptake

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___ induction with greater alveolar ventilation

more rapid

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__ induction with decreased alveolar ventilation

slower

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the effect of increasing ventilation will be most obvious in raising the FA/FI for

more soluble anesthetics, as the are more subject to uptake

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anesthetic agents impact their own uptake due to the

dose-dependent depressant effects on alveolar ventilation

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if controlled ventilation is used there is potential for

overdose

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time constant is

the time required for flow through a container to equal the volume of the container

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time constant =

capacity (L) / flow (L/min)

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time constant is the amount of time in minutes required for

a 63% turnover of gas within a container

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application of time constant is in

the rate of alveolar rise in anesthetic concentration

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time constant multiple 1

63%

time constant multiple 2

86%

time constant multiple 3

95%

time constant multiple 4

98%

time constant multiple 5

99.5%

vessel rich group receives __ of CO

75%

lean muscle receives __ of CO

19%

fat receives __ of CO

vessel poor group receives __ of CO

__ takes away from what is going to the alveoli

the volume of gas in the circuit

___ negates what the machine takes away from the alveoli

higher fresh gas flows (5-10 L/min)

__ in the rubber/plastic components of breathing system slows the rise of the PA initially

solubility of an agent

circle system allows

rebreathing of previously exhaled gas

exhaled gas contains

lower concentration of agent during the initial uptake phase because some is taken out by the body

the agent concentration coming in the fresh gas from the machine is

diluted down by mixing with the exhaled gas

in non-rebreathing circuits, exhaled gas is

no rebreathed and high flow are required

in non-rebreathing circuits, the concentration of agent in the circuit is

very close to the concentration set on the vaporizer dial

in non-rebreathing circuits, is the gas is soluble in the material of the circuit or system, some agent will

be lost to these materials

functional residual capacity is composed of

the residual volume and the expiratory reserve volume

the larger the FRC, the __ the induction of the anesthetic agent

slower

__ have smaller FRC than adults as a percent of TLV, more volume changed with

neonates each respiration and faster induction with anesthetic agent than adults

solubility is

blood:gas partition coefficient

solubility definition

a distribution ratio describing how the anesthetic distributes itself between two phases at equilibrium (steady state)

the lower the solubility, the __ the rate of rise of the PA toward the PI

faster

partition coefficients are

temperatrue dependent

decreased temperature causes

increased solubility

increased temperature causes

decreased solubility

the initial steep rise of FA/FI is due to

unopposed filling of the alveoli by ventilation

CO (pulmonary blood flow) affects uptake by

carrying away agent from the alveoli and preventing the rise in PA

increased CO leads to

greater uptake/removal of agent from the lungs and slowed induction

the rate of increase of __ is affected more by CO

more soluble agents

the increase in CO will __ induction and the rise in PA

slow

during uptake, __ will remove the anesthetic agent that is delivered

the vessel rich group

the mixed venous blood returning to the lungs has

a lower partial pressure of agent

the gradient between the alveolar partial pressure and the venous blood is __ encouraging __

great diffusion out of the alveoli

as saturation of the VRG increase, ___ becomes smaller and the __ rises

gradient PA

arterial partial pressure is __ then ETgas

less

___ enhances the difference in Pa and ETgas

right to left shunt

lower Pa with

right to left shunt, especially with less soluble agents

__ poorly estimates __, with right to left shunt

PA Pa

V/Q mismatch is seen with

bronchial intubation or right to left intracardiac shunt

factors determining transfer of agent from arterial blood to brain

1. brain:blood partition coefficient 2. cerebral blood flow 3. arterial to venous partial pressure difference

vessel rich group includes

1. brain 2. heart 3. kidney 4. splanchnic 5. liver 6. endocrine

muscle group contains

muscle and skin

vessel poor group contains

1. bone 2. ligament 3. cartilage

rapid increase in FA/FI thats

faster induction

to have faster accumulation/onset/wash-in you need

1. higher FGF 2. higher alveolar ventilation 3. decrease FRC 4. smaller time constant 5. smaller amount of anatomic dead space

to increase FA/FI decrease amount of uptake

1. gas with lower solubility 2. low CO 3. difference between arterial pressure and venous pressure smaller

to decrease rate of FA/FI meaning slower onset/build up

1. decrease FGF 2. decrease AV 3. higher FRC 4. higher time constant 5. higher amount of anatomic dead space

decrease FA/FI meaning slower induction with increased uptake

1. higher solubility 2. higher CO 3. higher difference in Pa/Pv

elimination generally =

reverse of uptake

slower awakening with

higher soluble, longer duration of exposure, higher concentration

elimination via

exhalation predominantly so increase alveolar ventilation

factors associated with increased rate of recovery

1. elimination of rebreathing 2. high FGF 3. low anesthesia-circuit volume 4. low absorption by anesthesia circuit 5. decreased solubility of agent 6. high cerebral blood flow 7. increased alveolar ventilation

implication for rapid recovery

1. airway protection/oxygenation 2. rapid movement through the 0.1 MAC concentration that causes enhanced perception of pain 3. return to normal CV function 4. turnover more rapid 5. quicker discharge from PACU 6. quicker return to normal activities

changes in compartments in elderly

decreases in lean body mass and increases in body fat

volume of distribution in elderly

of central compartment is smaller (plasma volume) for volatiles is larger (especially more lipid soluble agents)

elderly clearance

decreased due to impaired pulmonary gas exchange

elderly CO

reduced

reduced CO in elderly leads to

reduced tissue perfusion, increased time constants, altered regional distribution of anesthetics

does switching to a less soluble agent at the end of a case help?

no, it is additive or even synergistic effect regarding return to mental function