wk1- intro to LA Flashcards
uses for LA
- diagnostic
- therapeutic
- surgery
LAs that podiatrist can use
bupivocaine 0.5% or less
levobupivacaine of 0.5% or less
lidocaine of 2% or less
prilocaine 2% or less
modes of delivery of LA
- topical
- infiltrative
- ring block
- peripheral nerve block
- EMLA
- iontophoresis
podiatrists with ESM can do what with LAs
prescribe
give treatment dose
administer
purchase
possess
dispose
what LAs do podiatrists with ESM have access to
methoxyflurane- more of an analagesic
tetracaine
bupivacaine
levobupivacaine
lidocaine with or without adrenaline
prilocaine
ropivacaine
what LA does EMLA consist of
prilocaine
what is iontophoresis
topical anaesthesia via an electric current
what does LA do to the body
reversible loss of sensation in an area of the body
how does LA work
they block sodium ion channels so sodium cannot flow into neurons
this inhibits the transmission of APs along individual neurons
anatomy of LA (3 things and what do they determine?)
aromatic ring- confers lipid solubility
intermediate linkage- permits classification and mode of metabolism (amide or ester)
terminal amine- charged or uncharged to make it water or lipid soluble
types of LA
amide
ester
ester
metabolism, toxicity, allergy, stability, onset of action, pKa
M: rapid by protein cholinesterase
T: less likely
A: more likely
S: photo/temp labile
O: slower
pKa: higher (8.5-8.9)
amide
metabolism, toxcity, allergy, stability, onset, pKa
M: slower, by the liver
T: more likely
A: less likely
S: very stable
O: moderate to fast
Pka: Close to 7.4
types of esters
cocaine
chloroprocaine
tetracaine
types of amides
bupivacaine
lidocaine
ropivacaine
unpronated LA molecules can what
pass through cell membranes because theyre lipophilic
define pKA
pH where drug is 50% ionised and unionised
if the pka is low what does that mean for the LA drug in the body
lower the pKa, more drug present in unionised form, the faster the onset of drug
what nerve fibers are effected by LA, what order is sensation lost
greatest effect is on automatic and small myelinated nerve fibers than large myelinated fibres
C-unmyelinated,
B-unmyelinated,
A delta (small myelinated)
order of nerve sensation loss
- pain
- temp
- touch
- deep pressure
- motor
how many nodes have to be blocked
more than 1 as AP can skip over a blocked node called saltatory conduction
what makes onset of time faster?
the closer the pKa is to tissue pH (7.4), the more unionised form which causes a faster rate of onset
LAs onset time, fastest to slowest
mepivacaine
lidocaine/prilocaine
bupivacaine/ropivacaine
what speeds up onset?
alkalinisation (eg bicarbonate solution added to an LA)
important characteristics of LAs
- onset
- duration
3.toxicity - distribution
- regression
