Flashcards in Anaesthesia and anaesthetics Deck (39)
How is regional and general anaesthetic administered
regional - intrathecal
general - inhilation / iv
what does local/regional anaesthetic target?
what does general anaesthetic target?
L/R = afferent sensory reflex
G = central neural processing
when would you use local anaesthetic
1. hand/foot/gum - suturing / dental procedures
describe the mechanism for local anaesthetic
Weak bases - cross the membrane uncharged then ionise and block the channel
Lipid soluble/ uncharged - dissolves in the membrane and blocks the channel from within
Lidocaine, Benzocaine, Tetracaine.. what type are they
lido = weak acid
tetra lipid sol
Name the two types of regional anaesthetic and when you would use them
spinal - c section/ bladder surgery (subarachnoid)
epidural - child birth (epidural)
What would you give if a patient is nervous for general anaesthetic and why would they be
patient stays awake - benzodiazepine
what is bupivicaine and how would you administer it? how long would it last?
into epidural space at L4 - lasts 2-3 hours
IV general anaesthetic describe the mode of action
1. Propofol, etomidate, thiopental (barb)
describe the 2 main types
1. at gaba receptor
2. blocks NMDA glutamate receptor
barbiturates ad non barbiturates
inhilation GA - mechanism of action?
1. halothane isoflurane
2. nitrous oxide
1. volatile liquide - act on gaba receptor
2. inorganic gases - unclear
1. loss of consciousness, amnesia, inhib sensory reflexes, skm relax
2. induces sleep
3. eases anxiety WITHout causing sleep
when would you want to put a patient in a medically induced coma
used to protect the brain following major neurosurgey
decreases E requirements of the brain and allows for healing and swelling to go down
what is used to control a medically induced coma
barbiturates / propofol
List the 5 main stages of anaesthesia
3. surgical anaethesia
4. medullary depression
anaesthesia - induction ?
autonomic reflexes progressively depressed
control the airway, 02 levels, vent, and circilation
anaesthesia - stage 1 ?
consciousness NOT lost - thoughts blurred
smell and pain lost by the end
which stage of anaesthesia is child birth limited to ?
anaesthesia - stage 2?
comiting, temp control lost, EEG desynchronised, resp irreg, increased muscle tone, incoherent speech
anaesthesia - stage 3?
slow synchronised EEG , reg slow breathing, reflexes lost, pupils dilates,
anaesthesia - stage 4?
resp arrest, CV collapse, EEG small/ lost
what is boyles apparatus used for?
mixes 02 anaesthetic and ambient air
pros of inhilation anaesthesia
Levels are easily controlled
Rapid elimination from body
Doesn't cause post op resp depression
Few drug interactions
why isnt halothane used?
toxic to liver
what is MAC? what decreases MAC?
the minimum alveolar concentration - potency of inhailed anaesthetic
mix air with N20 and decreases MAC therefor need to use less anaesthetic
Name 3 factors that alter MAC
pregnancy (alcohol abuse, some drugs)
describe the uptake of inhalation anaesthetics
lipid soluble molecules rapidly absorbed across pul memb, pass into blood into tissue, BBB freely permeable to GAs
describe the elimination of inhalation anaesthetics
diffuses out of the brain into muscles and fat
inert therefor undergos little metabolism
eliminated via lungs
rate mirrors uptake
problem with some inhalation anaesthetics during elimination
some are metabolised by liver and some metabolites are toxic
how do inhaled anaesthetics cause anaesthesia
uncharged molecules conc in lipid membrants causing effects on the structure - membrane expansion! effects membrane spanning proteins e.g. ion channels
how are inhilation anaesthesia reversed?
decompression chamber 200 ATM
How long do iv anaesthetics last for?
20 minutes - short acting
when is the ideal time to use IV anaesthetics in anaesthetics
induction - then maintain with GA
negatives and 1 +ve to barbiturates
enter brain quickly,
no analgesia, small therapeutic window ,short lasting, slow metabolism, irritant , resp depression
example of barbiturates
1. examples of 2 non barbiturates used for GA
2. which causes neausea
ketamine and propofol
ketamine causes nausea on recovery
2 main sites of action of general anaesthetics and why they target these areas
RAS - reticular activating system ( medullary area involved in sleep and wake)
hippocampus (inhibit Ach release - amnesic effects)
what is the lipid theory in general anaesthesia
GAs potency directly correlates with lipid solubility (proposed)
How to GAs work..
increased fluidity of membrane..
decrease NT release pre synaptically
decrease excitability post synaptically