General Anesthetics Flashcards
what does general anesthesia do?
renders patient unresponsive to painful stimuli through loss of consciousness
what are the five primary effects of general anesthetics?
unconsciousness
amnesia
analgesia
inhibition of autonomic reflexes
skeletal muscle relaxation
what do general anesthetics do to the cardiovascular and respiratory systems?
cardiovascular depression
some: cardiac dysrhythmias
depress respiration
why is balanced anesthesia used?
to achieve goal of safe, effective anesthesia and analgesia
what are the four stages anesthesia?
awake/analgesia
excitement
surgical anesthesia
overdose: medullary paralysis
what are the functional steps in anesthesia?
anesthetic induction
anesthetic maintenance
anesthetic recovery
what is the main effect of general anesthetics?
inhibit synaptic transmission
what are the main targets of anesthetics?
GABAa receptors
glutamate NMDA receptors
glycine receptors
K2P channels
where does general anesthesia act?
in the brain
what are the most sensitive regions to anesthesia?
thalamic sensory relay nuclei and the deep layer of the cortex to which these nuclei project
what are inhalant anesthetics?
volatile anesthetics: gas
what is the mechanism of action for inhalant anesthetics?
general disruption of neurotransmission
what do the main differences in agents of inhalant anesthetics relate to?
pharmacokinetics and adverse effects
what does it mean for something to be a volatile anesthetic?
liquid at room temperature
gas as pressure drops
what are some gas anesthetics?
isoflurane
sevoflurane
how do inhalant anesthetics work?
augment inhibitory activity (GABA receptors) and depress neurotransmission pathways (glutamate/NMDA and other pathways)
how is the potency of inhaled anesthetics defined quantitatively?
minimum alveolar concentration (MAC)
what is the minimum alveolar concentration (MAC)?
concentration of anesthetic gas needed to eliminate movement in 50% of patients with a standardized skin incision
what is the blood:gas partition coefficient?
how much gas dissolves in blood
what is the tissue:gas partition coefficient?
how much gas dissolves in tissues
the _____________ of an individual gas is proportional to its concentration
tension
what determines the flow of an anesthetic gas?
difference in tension between two sites, or the pressure gradient
where are gas anesthetics absorbed and eliminated?
lungs are only quantitatively important route
true/false: anesthetics cross blood-brain barrier quickly, so brain tension follows blood tension
true
what determines distribution of an anesthetic?
blood flow to tissue
capacity of tissue to absorb anesthetic
what is the main factor in determining rate of induction and recovery?
blood:gas partition coefficient
does a lower blood:gas partition coefficient take longer or shorter to induce a response?
shorter
drops alveolar gas concentration if higher
agents with _____ blood and tissue solubility have more rapid elimination
low
why do high tissue solubility anesthetics take longer to recover from?
95% of total amount in body is in fat after a long anesthetic, must come out and does so slowly
what are the physiological factors that influence kinetic behavior of inhaled anesthetics?
alveolar ventilation rate
cardiac output
distribution of anesthetic in body
what is the most commonly used inhalant anesthetic now?
isoflurane
how soluble is isoflurane?
relatively insoluble: relatively rapid induction and recovery
does isoflurane put stress on the liver and kidneys?
not really
does isoflurane impact the cardiovascular system?
dose-dependent cardiovascular depression
generally minimal at doses used for surgery
minimal sensitization of heart to catecholamines
what is a positive of sevoflurane?
very rapid induction and recovery
what are the respiratory and cardiovascular impacts of sevoflurane?
similar to isoflurane
dose-dependent cardiovascular depression
respiratory depressant
what is special about sevoflurane pertaining to toxicity?
reacts with carbon dioxide to make compound A, which is potentially nephrotoxic
what are the advantages of injectable anesthetics?
act more rapidly than inhaled
less menacing than having face mask
rapid induction avoids excitement phase of inhaled
what are the disadvantages of injectable anesthetics?
more difficult to quickly alter dose delivered
elimination slower than inhaled anesthetics, particularly if body tissues become saturated
what are some nonbartituate sedative injectable anesthetic agents?
propofol
etomidate
alfaxalone
what are some dissociative agent injectable anesthetics?
ketamine
tiletamine
what receptors do injectable anesthetics act on?
GABAa
glutamate-NMDA
glycine
AMPA (glutamate) receptors
what drugs act on the GABAa receptor?
barbituates
propofol
etomidate
alfaxalone
what do the injectable anesthetics that act on GABAa receptor do?
enhance inhibitory GABAergic effects
do not bind to GABA binding site
what do barbituates generally do?
depress the CNS
potentiate GABAa-induced increases in chloride conductance (inhibitory receptors)
bind to specific barbituate receptor sites on GABA-sensitive ion channels
are barbituates acidic or basic?
weak acids
do barbituates have a low or high therapeutic index?
low
what can underdosing of barbituates lead to?
stage 2 excitement
is methohexital short acting?
ultrashort acting, rapid recovery
what are the adverse effects of barbituates?
dose dependent depression of all organ systems
respiratory depression
cardiovascular depression
how does propofol act?
primarily through potentiation of GABA pathways
is propofol related to other anesthetics?
no
alkoxyphenol derivative
true/false: propofol accumulates in the body
false: rapidly metabolized so does not
does propofol have analgesic effects?
no
how does propofol affect respiration?
significant respiratory depression
can cause period of apnea on induction
does proopofol have a rapid recovery after prolonged infusion?
yes
what animals can you use propofol in?
dogs and cats
how is propofol metabolized?
glucuronidation
what can repeated use of propofol cause in cats?
heinz body formation
lethargy
malaise
diarrhea
where does alfaxalone (neurosteroid) bind?
GABAa receptor
what is alfaxalone?
ultra-short acting anesthetic
does accumulation of alfaxalone occur?
no
what are the adverse effects of alfaxalone?
respiratory and CV depression
is the NMDA glutamate receptor excitatory or inhibitory?
excitatory (depolarization)
what are the NMDA glutamate receptor antagonists?
ketamine
tiletamine
dissociative anesthetics
what do NMDA glutamate receptor antagonists cause?
stage I and II anesthesia, no stage III
amnesia and paralysis of movement, but do not cause a true and complete loss of consciousness
significant analgesic
what are some body effects of ketamine?
minimal cardiopulmonary depressant effects
apneustic breathing
high muscle tone
how do you recover from ketamine IV?
redistribution
what are the practical considerations of ketamine?
excellent somatic analgesia
some visceral analgesia
poor muscle relaxation
what are some adverse effects of ketamine?
increase CSF pressure
+/- increased seizures
should not be used in combination with xylazine in dogs: severe cardiopulmonary depression
cat eyes remain open
painful on IM injection