Inhalation Agents Flashcards
Uptake
removal from the lungs
Increase in uptake
delay anesthetic action
Increase of Input of anesthetic
Help speed up anesthetic action and fall asleep
The more dissolved in the blood
the more time patient takes to fall asleep
Blood solubility
affects delivery.
Vehicle absorption and elimination
Lungs
Desflurane and N2O
minimal metabolism
Measurable
Inspired concentration
and expired concentration
At equillibration of FA/FI
any changes in the machine occurs quickly in the brain
N2O is the only gas
at room temperature
The larger breathing circuit
Hinders anesthetic, can work against wor
Fraction inspired
The gas then enters the inspiratory limb of the circuit to be inspired
by the patient
Fraction alveolar FA.
The inspired concentration is then taken into the lungs through spontaneous or controlled ventilation and transferred to the alveoli
VA are respiratory
Depressant
Too much anesthetics
breathing will decline, protecting mechanism of the patient
**2 effects of VA:
Myocardial depressant
Respiratory depressants
The more soluble in the BLOOD
the longer time to fall asleep
BLOOD GAS PARTITION of Des
1.4
BG partition of 0.5 (fills in quicker)
At equillibration, for every 2 molecules in alveolar gas, 1 moleculres will be in the blood
BG partition of 1.5 (fills in slower)
2 molecules in alveolar gas, 3 molecules in the blood.
Partial pressure determined by
Solubility in blood and solubility in the tissues.
Relationships
FD> FI > FA> pressure arterial > pressure brain> Pressure venous
Agents with a low blood to gas partition coefficient equilibrate_________ than do agents with a high blood to gas partition coefficient if other variable are held constant.
more rapidly
Mass spectometry
How much in and how much out
FA/FI has to be close to
1
ISoflurane very
1.5
Des, Nitrous, Sevo
fast onset and offset
Each 1% of agent at normal atmospheric pressure represents 1% of
760 mm Hg or
7.6 mm Hg pressure
A blood gas solubility of 1.0 indicates that at equilibrium a concentration of anesthetic in arterial blood of 1% would mean
that the concentration in the lung would be 1%
If the blood to gas partition coefficient is 2.0, the concentration in the blood must
equal 2% to achieve a concentration in the lung of 1%.
iF B/G partition is 0.5 , how many molecules would it take for 1 molecule in blood
4
follows Formulae
• Uptake=
cardiac output (Q) X concentration gradient
(alveolar to venous partial pressure difference) X
blood to gas solubility (λ)
Higher cardiac output in VA
slower induction time
For induction though, higher CO
Faster induction time
Alveolar-venous measure
Venous measure how much in the tissue
Alveolar
Sevo, NITROUS , DESp
Poorly soluble
less uptake into blood
fall asleep faster
Sevo, NITROUS , DESFlurane
Poorly soluble
less uptake into blood
fall asleep faster
Increasing FD:
overpressuring
Increasing the concentration on the
vaporizer to supraphysiologic levels
(Caution is warranted)
Increasing FGF
Increasing the fresh flow rates via
anesthesia machine
Increasing alveolar ventilation
Increasing rate and/or tidal volume
(note tidal volume must not exceed
dead space)
Concentrating effect
The administration of a gas in high
concentrations will increase its own
concentration and the rate of rise in
FA/FI
Second gas effect
The administration of a gas in high
concentration will increase the rate
of rise of the FA/FI of companion
gas
Risk of DELIVERING TOO MUCH ANESTHETIC
Hypotension
Delivery high to low
FD >FI>FA>Pa>Pbr>Pv
B/G partition less than 1
Faster sleep
For example, isoflurane has a blood-gas partition coefficient of 1.4. This means that,
at equilibrium, the isoflurane concentration in the
blood would be 1.4 times the concentration in the gas (alveolar) phase
The principle objective is to achieve
a constant and optimal brain partial pressure of the inhaled anesthetic
The alveolar partial pressure (PA) of the inhaled anesthetic
mirrors
the brain partial pressure (Pbr)
Transfer of inhaled anesthetic from machine to alveoli (anesthetic input) FIAC
- Inspired partial pressure
- Alveoli ventilation
- Characteristics of breathing system
- Functional residual capacity
Ratio that determines delivry
Alveolar ventilation
Functional Residual Capacity
Transfer of inhaled anesthetic from alveoli to arterial blood
•
**Blood gas partition coefficient
• Cardiac output
• Alveolar-to-venous partial pressure difference
Transfer of inhaled anesthetic from arterial blood to brain (anesthetic loss)
- Brain:blood partition coefficient
- Cerebral blood flow
- Arterial-to-venous pressure difference
The PA and ultimately the Pbr of an inhaled
anesthetic are determined
by input (delivery) into alveoli MINUS (uptake) loss of the drug from alveoli into arterial blood.
**Inhaled partial pressure (PI) is high during initial
administration to offset _____________.it is then decreased during maintenance to match the ____________
uptake from alveoli into arterial blood (similar to administering IV loading dose);
Decreased uptake as tissues accumulate anesthetic.
Initial fraction of VA, More important for drugs that are MORE SOLUBLE (HIGHER PARTITION COEFFICIENT)
ISOFLURANE
A high PI delivered from the anesthetic machine is required during_______• This will help__________
• With time, as uptake into the blood
decreases, the PI should be
- initial administration to offset the impact of uptake.
- accelerate induction of anesthesia.
- decreased to match the decreased anesthetic uptake and therefore maintain a constant optimal Pbr.
what is the second gas effect?
Ability of high volume uptake of one gas (first-gas) to accelerate the rate of increase on PA of a concurrently administered companion gas (second gas).
Simultaneous administration of slower agent, such as halothane with a faster drug such as
nitrous oxide (in high concentrations) can speed the onset of the slower agent.
Controlled ventilation of the lungs that results in
hyperventilation and decreased venous return will________
accelerates the rate of increase in PA by virtue
of increased input (increased VA) and decreased
uptake (decreased cardiac output).
OIL: GA
Affect potency
KNow B/G partition
Sevo des, nitrous, iso
Opiates __________MAC
decrease
