Pharmacokinetics & Inhaled Anesthetics
UPDATED Exam Questions and
CORRECT Answers
Fluorination of gases - CORRECT ANSWER - -to decrease flammability
-decrease lipid solubility facilitates rapid induction and prompt recovery
- more resistant to metabolism
Fluorine is a Halogen
-All inhalation anesthetics in current clinical use are halogenated ethers, except for halothane
(which is a halogenated hydrocarbon or haloalkane), nitrous oxide, and xenon.
1st general anesthetic - CORRECT ANSWER - Diethyl ether (CH3CH2OCH2CH3)
Anesthetics and low FGF rates - CORRECT ANSWER - -less soluble anesthetics are better
with low flow rates bc their poor solubility permits better control of the delivered concentration.
-there is less depletion of these so fewer molecules need to be added to the returning rebreathed
gases (conservation)
Xenon - CORRECT ANSWER - -an inert gas with anesthetic properties, but clinical use is
hindered by high cost
-nonexplosive, nonpungent, odorless, not metabolized and low toxicity.
-not harmful to the environment
-similar to N20, can result in air bubble expansion
-exerts NMDA antagonism, neuroprotective
MAC 63-71%
b:g 0.115 (the lowest of any VAs)
,Nitrous Oxide (N2O) - CORRECT ANSWER - -Low molecular weight, odorless to sweet
smelling, gas at room temperature
-low potency and poor solubility (b:g 0.46)
-usually administered in combo with opioids or other gases /VAs to produce general anesthesia
- non flammable gas, but supports combustion
-caution: high absorption in gas-containing spaces, potential increase in PONV, inactivate vit
B12.
SVP (none bc gas at room temp)
MAC 105
b:g 0.46
Halothane - CORRECT ANSWER - -halogenated alkane
-clear, sweet non pungent odor, nonflammable, liquid at room temp
-intermediate solubility, high potency
SVP 244
MAC 0.75
b:g 2.54
Enflurane - CORRECT ANSWER - -halogenated methyl ethyl ether
-clear, non-flammable, liquid, pungent ethereal odor
-intermediate solubility, high potency
SVP 172
MAC 1.63
b:g 1.9
Isoflurane - CORRECT ANSWER - -halogenated methyl ethyl ether
,-isomer of enflurane, but more stable
-clear, non-flammable, liquid, pungent ethereal odor
-intermediate solubility, high potency
SVP 240
MAC 1.17
b:g 1.46
Desflurane - CORRECT ANSWER - -fluorinated methyl ethyl ether
-differs from isoflurane only by a substitution of a F atom for a Cl- atom on the alpha-ethyl
component
-fluorination rather than chlorination increases vapor pressure (decreases intermolecular
attraction), enhances stability and decreases potency
-would boil at room temp, requires a special vaporizer
-pungent, airway irritation
-CO produced when degragated
-rapid achievement of alveolar partial pressure and prompt awakening
SVP 669
MAC 6.6
b:g 0.42
Sevoflurane - CORRECT ANSWER - -fluorinated methyl isopropyl ether
-prompt induction and recovery
-non pungent, minimal odor, the least airway irritation among VAs
-bronchodilation similar to isoflurane
-good for inhalation inductions
-least likely to form CO
, -differs from all the other VAs that are metabolized with intermediates with potential
hepatotoxicity and cross-sensitivity between them
-does produce Compound A, which can be nephrotoxic, but at levels far below toxic levels
SVP 170
MAC 1.8
b:g 0.69
Pharmacokinetics of IAs - CORRECT ANSWER - 1) absorption/uptake from alveoli into
pulmonary capillary blood
2) distribution in the body
3) metabolism
4) elimination, primarily via lungs
-may be influenced by aging (decreased lean body mass, increased body fat, impaired pulmonary
exchange, reduced CO) and opposite effects in very young
Partial Pressure gradients - CORRECT ANSWER - -Gases diffuse down partial pressure
gradients from high to low across many barriers (alveoli, capillaries, brain cell membranes)
-equilibration does NOT mean equal concentrations in two separate areas
-the goal of anesthesia is to achieve a constant and optimal brain partial pressure of the inhaled
anesthetic
Factors that determine partial pressure gradients: machine to alveoli - CORRECT ANSWER -
Inspired partial pressure (Pi)
alveolar ventilation
characteristics of the anesthetic breathing (delivery) system [gas inflow and volume of the
system]
functional residual capacity
UPDATED Exam Questions and
CORRECT Answers
Fluorination of gases - CORRECT ANSWER - -to decrease flammability
-decrease lipid solubility facilitates rapid induction and prompt recovery
- more resistant to metabolism
Fluorine is a Halogen
-All inhalation anesthetics in current clinical use are halogenated ethers, except for halothane
(which is a halogenated hydrocarbon or haloalkane), nitrous oxide, and xenon.
1st general anesthetic - CORRECT ANSWER - Diethyl ether (CH3CH2OCH2CH3)
Anesthetics and low FGF rates - CORRECT ANSWER - -less soluble anesthetics are better
with low flow rates bc their poor solubility permits better control of the delivered concentration.
-there is less depletion of these so fewer molecules need to be added to the returning rebreathed
gases (conservation)
Xenon - CORRECT ANSWER - -an inert gas with anesthetic properties, but clinical use is
hindered by high cost
-nonexplosive, nonpungent, odorless, not metabolized and low toxicity.
-not harmful to the environment
-similar to N20, can result in air bubble expansion
-exerts NMDA antagonism, neuroprotective
MAC 63-71%
b:g 0.115 (the lowest of any VAs)
,Nitrous Oxide (N2O) - CORRECT ANSWER - -Low molecular weight, odorless to sweet
smelling, gas at room temperature
-low potency and poor solubility (b:g 0.46)
-usually administered in combo with opioids or other gases /VAs to produce general anesthesia
- non flammable gas, but supports combustion
-caution: high absorption in gas-containing spaces, potential increase in PONV, inactivate vit
B12.
SVP (none bc gas at room temp)
MAC 105
b:g 0.46
Halothane - CORRECT ANSWER - -halogenated alkane
-clear, sweet non pungent odor, nonflammable, liquid at room temp
-intermediate solubility, high potency
SVP 244
MAC 0.75
b:g 2.54
Enflurane - CORRECT ANSWER - -halogenated methyl ethyl ether
-clear, non-flammable, liquid, pungent ethereal odor
-intermediate solubility, high potency
SVP 172
MAC 1.63
b:g 1.9
Isoflurane - CORRECT ANSWER - -halogenated methyl ethyl ether
,-isomer of enflurane, but more stable
-clear, non-flammable, liquid, pungent ethereal odor
-intermediate solubility, high potency
SVP 240
MAC 1.17
b:g 1.46
Desflurane - CORRECT ANSWER - -fluorinated methyl ethyl ether
-differs from isoflurane only by a substitution of a F atom for a Cl- atom on the alpha-ethyl
component
-fluorination rather than chlorination increases vapor pressure (decreases intermolecular
attraction), enhances stability and decreases potency
-would boil at room temp, requires a special vaporizer
-pungent, airway irritation
-CO produced when degragated
-rapid achievement of alveolar partial pressure and prompt awakening
SVP 669
MAC 6.6
b:g 0.42
Sevoflurane - CORRECT ANSWER - -fluorinated methyl isopropyl ether
-prompt induction and recovery
-non pungent, minimal odor, the least airway irritation among VAs
-bronchodilation similar to isoflurane
-good for inhalation inductions
-least likely to form CO
, -differs from all the other VAs that are metabolized with intermediates with potential
hepatotoxicity and cross-sensitivity between them
-does produce Compound A, which can be nephrotoxic, but at levels far below toxic levels
SVP 170
MAC 1.8
b:g 0.69
Pharmacokinetics of IAs - CORRECT ANSWER - 1) absorption/uptake from alveoli into
pulmonary capillary blood
2) distribution in the body
3) metabolism
4) elimination, primarily via lungs
-may be influenced by aging (decreased lean body mass, increased body fat, impaired pulmonary
exchange, reduced CO) and opposite effects in very young
Partial Pressure gradients - CORRECT ANSWER - -Gases diffuse down partial pressure
gradients from high to low across many barriers (alveoli, capillaries, brain cell membranes)
-equilibration does NOT mean equal concentrations in two separate areas
-the goal of anesthesia is to achieve a constant and optimal brain partial pressure of the inhaled
anesthetic
Factors that determine partial pressure gradients: machine to alveoli - CORRECT ANSWER -
Inspired partial pressure (Pi)
alveolar ventilation
characteristics of the anesthetic breathing (delivery) system [gas inflow and volume of the
system]
functional residual capacity
