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
its the partial pressure of the anesthetic (N2O) in the blood that equate to greater effect
