Nitrous oxide/Propofol - Anaesthetics Flashcards
history of nitrous oxide
often used recreationally
1842 - ether was used in surgery
1844 - NO used in dental surgery
is anaesthesia reversible
YES
3 main effects of anaesthesia
hypnosis
amnesia
immobility
effect of anaesthesia on brain activity
slows brain activity (EEG)
hypnosis
loss of consciousness/perceptive awareness
amnesia
loss of memory formation
immobility
no movement in response to painful stimuli
3 good stages of anaesthesia
1 - analgesia
2 - excitement, increased muscle tone, HR and BP
3 - anaesthesia
4th bad stage of anaesthesia
too much leads to cessation of breathing
in medical practice –> 3 stages of inducing anaesthesia
induction
maintenance
recovery
induction stage of anaesthesia in medical practice
give patient propofol
maintenance stage of anaesthesia
give patient nitrous oxide or a volatile anaesthetic, or O2
recovery stage of anaesthesia in medical practice
take mask off patient
characteristics of a good anaesthetic
fast induction, fast recovery non-flammable able to adjust length of anaesthesia regular breathing/HR cheap easy to store no undesired effects
common side effect of anaesthesia
nausea
2 classes of anaesthetics
intravenous
inhalants
examples of intravenous anaesthetics
barbiturates ketamine propofol benzodiazepine midazolam
examples of inhalant anaesthetics
NO (ether or chloroform)
isoflurane
seroflurane
desflurane
why is propofol good
rapid acting and rapid elimination
MAC stands for
Minimum Alveolar Concentration
what is the MAC
the minimum concentration of the gas in the lungs that is required to cause immobility in 50% of patients in response to a surgical/pain stimulus
what is the MAC used for
to compare the potency or strength of anaesthetic vapours
what two things are tested when measuring the MAC
hypnosis –> loss of ‘righting’ reflex (standing up)
immobility –> loss of withdrawal reflex
Cp50
a measure of anaesthetic potency
the concentration of agent in the blood required to cause immobility in 50% of patietns
are you awake in MAC and Cp50 tests
yes
volatile anaesthetics above 1atm
do not initiate immobility in 50% of patients
what is the correlation for anaesthetics called
meyer-overton (1899)
axis for meyer-overton correlation graph
MAC on y-axis
olive oil: gas partition coefficient
smaller MAC correlates with
high potency
high olive oil: gas partition
means it is better at dissolving into lipids
what does the MO correlation show
that all the anaesthetics have a hydrophobic site of action
what is the unitary theory
the suggestion that anaesthetics work on the protein hydrophobic site and share common molecular mechanisms
what are the assumptions behind the unitary theory
that anaesthetics will dissolve in neuronal lipid membranes to affect neuronal activity
what are the problems with the unitary theory
- mutations in proteins could impair anaesthetic effects
- new anaesthetics are less potent than predicted
- enantiomer pairs of chiral anaesthetic molecules have different properties
anaesthetic binding site on GABA A receptors
different to GABA site, BZD site and neurosteroid site
example of a neurosteroid
alphaxolone
example of old volatile anaesthetic
halothane
why was halothane discontinued
caused liver problems
examples of new anaesthetics
isoflurane
desflurane
seroflurane
uses of volatile anaesthetics in medicine
used in combination with nitrous oxide and O2 during maintenance stage
effects of volatile anaesthetics
strong immobilisation, amnesic and hypnotic effects
which receptors do volatile anaesthics act on
GABA
other receptor potentiation
glycine receptors can also be activated –> contributes to immobility
K2p channels
receptor inhibition by anaesthetics
Na+ channels
glutamate receptor
K2p channels
2 pore domain
“leak” potassium channels
role of N2O
used in maintenance
weak anaesthetic effects
activates K2p channels
inhibits nAchR- channels
whats different about ketamine to N2O
ketamine can induce anaesthesia by itself
inhibits NMDA receptor channels
importance of spinal cord and anaesthetics
spinal cord contains targets for the immobilisation effects of anaesthetics
if isoflurane is applied to the spinal cord
the MAC is lower
effect of application of GABA antagonists
decrease potency of some anaesthetics e.g. propofol and barbiturates (not ketamine)
main phsyiological effects of GABA A receptor potentiation
hypnosis
amnesia
main physiological effect of glycine receptor potentiation
immobilisation
main physiological effect of NMDA receptor inhibition
analgesia
