A.23.inhalational anesthetics Flashcards
what is the blood/gas partition coefficient?
it’s a pharmacokinetic parameter
the ratio of–> concentration of an anesthetic in the blood phase (bound, inactive form) to the concentration of the anesthetic in the gas phase (free active form)
when is the blood/gas coefficient low?
nitrous oxide
drug is less blood soluble
equilibrates faster with blood
rapid onset and recovery from anesthesia
when is the blood/gas coefficient high?
halothane
drug is more blood soluble
slower onset and recovery from anesthesia
parameters affecting the kinetics of inhaled anesthetics?
the partial pressure of inspired gas
ventilation rate
pulmonary blood flow
how does the partial pressure of inspired gas affect the kinetics of inhaled anesthetics?
↑ partial pressure of the gas in the lung–> ↑ rapid achievement of anesthetic effect
how does ventilation rate affect the kinetics of inhaled anesthetics?
↑ ventilation rate–> faster onset of the anesthesia
how does pulmonary blood flow affect the kinetics of inhaled anesthetics?
↑ pulmonary blood flow–> slower onset of anesthesia
what is the minimum alveolar anesthetic concentration? (MAC)
measure of drug potency (ED50)
the alveolar concentration at which 50% of patients do not respond to a surgical stimulus
what affects the MAC?
the ↑ lipid soluble anesthetic the ↓ MAC –> the greater potency
when are MAC values low?
in elderly, infants, opiates or sedative-hypnotics
are MAC valures additive?
yes
what is the clinically used gas?
nitrous oxide (N₂O)
list the volatile liquids
Desflurane Isoflurane Sevoflurane Halothane Enflurane
which agent has the highest B/g coefficient?
halothane–> 2.3
which agent has the lowest B/g coefficient?
Desflurane–> 0.42
which agent has a MAC value of >100%?
N₂O
what is the fraction metabolized by the liver for N₂O?
none
what is the second gas effect in N₂O?
due to the rapid diffusion of N₂O in the alveoli there a ↑ concentration of a second agent
what are the potential SE of N₂O?
risk of spontaneous abortion (trigger uterine contraction)
potential drug of abuse (‘laughing gas’)
diffusional hypoxia
MAC value of desflurane
6.5%
fraction metabolized by the liver of desflurane
<0.1%
MAC value of isoflurane
1.4%
fraction metabolized by the liver of isoflurane
<2%
fraction metabolized by the liver of sevoflurane
2-5%
MAC value of sevoflurane
2%
what agent causes nephrotoxicity?
sevoflurane
*enflurane
what agent causes hepatotoxicity?
halothane
what agent causes arrhythmias?
isoflurane
halothane
what agent has a potential risk for malignant hyperthermia?
halothane
what agent causes bronchospasm?
desflurane
isoflurane
what agent causes peripheral vasodilation?
isoflurane
