Local Anaesthesia Flashcards
what is anaesthesia
Anaesthesia: Loss of all sensation
what is analgesia
Analgesia: loss of pain sensation
what is local anaesthesia
Local anaesthesia: a method of anaesthesia that acts in a local area of the body and does not result un a loss of consciousness
anaestheseia comes in 4 forms in dentistry what are they
topical
infiltration
reginal anaesthesia
supplementary techniques
when applying LA via infiltration, where is the target site
apex of tooth
what determines infiltration effectiveness
determined by the permeability of the tissues (especially bone) through which the solution has to pass
will infiltration mechanism work on very dense outer cortical bone with lidocaine
will not work
will infiltration mechanism work on very dense outer cortical bone with articaine
may work
why do divergent roots make infiltration harder
the divergent roots are further away from the point of injecting, making it harder for the LA to reach the apex of the root
which nerves are commonly blocked by a regional block anaesthesia
- Inferior alveolar (dental)
- Mental and incisive
- Lingual
- Long buccal
- Greater palatine
- Naso-palatine
what is in a LA cartridge
- usually 2.2ml or 1.8ml
- anaesthetic agent (lidocaine, articane)
- vasoconstrictor (adrenaline)
- stabilizer/preservative
- isotonic carrier medium
what is the biggest name of anaesthesia manufacturer
septodont
when a LA drug name ends with Plain, what does that indicate
no vasoconstrictor present
what is the function of the lipophilic head
Lipophilic head: the head is what combines to the phospholipid bilayer
what is the function of the hydrophilic tail
Hydrophilic tail: having a tendency to mix with, dissolve in, or be wetted by water.
what is the function of the intermediate chain
Intermediate chain: all local anaesthetic has an intermediate chain which links an amine to a aromatic ring
what are the types Ester LA
procaine
benzocaine
what are the types of amide LA
- Lidocaine
- Prilocaine
- Mepivacaine
- Bupivacaine
- Articane
how do local anaesthetics work
- They work during action potentials, during the initial opening of the Na+ channels
- Depolarisation
- Reversibly block Na+ channels
- LA diffuses into the axon membrane (lipophilic head)
- Compresses the channels, which then closes the sodium ion channels
is an example of what theory
membrane expansion theory
- LA passes through the phospholipid bilayer.
- LA binds to the sodium channels
- Inactivates the sodium ion channels
is an example of what theory
specific receptor theory
what two states does a LA exist in
charged
uncharged
what is the pKa of a drug
the pKa value is one method used to indicate the strength of an acid.
pKa is the negative log of the acid dissociation constant or Ka value.
The lower the value indicates, more the acid fully dissociates.
what state must the LA be in to bind to the sodium channels
charged
what state must the LA be in to pass through the axon membrane
uncharged
which LA has a quicker onset and why
Lidocaine (pKa= 7.7)
procaine (pKa=9.1)
Lidocaine
if the LA has a low pKa value (range = 2-14) it will have an increase in more uncharged drugs this will allow the LA to pass through the nerve membrane rapidly.
H+ ions determine the pH.
if there is a low pH (increase in H+), how will that affect the action of LA
an increase in H+ ions results in the excess binding of LA, which results in more charged particles.
this makes the speed of onset slow.
which LA has a high lipid solubility
articaine
which nerve types are easier to block
small nerves
what are the types of LA
lidocaine
prilocaine
mepivacaine
bupivacaine
articaine
what is articaines USP
diffusability
what is the gold standard for LA
Lidocaine
absorption of the drugs is dependant on what
dose
vasoactivity of a drug
vascularity of the tissue
vasodilator effect vs use of vasoconstrictor
if a tissue is highly vascularised, how would that affect LA
ther will be an increase in uptake of the LA
what is esterase
enzyme found in plasma and breaks down the ester bonds (the chain that links the aromatic head to the tail). The breaking down of the LA allows them to become smaller which results in the excretion of them.
where is articaine metabolised
plasma
where is prilocaine metabolised
lungs
where is amidase base LA metabolised
liver
what is the purpose of vasoconstrictors in LA
- Increases speed of onset
- Counteract vasodilatory effects of the LA agent
- Extends duration of anaesthesia
- Improves depth of anaesthesia
- Lower blood levels of LA (blood flow reduced in site)
- Reduced haemorrhage (bleeding)
there are two types of vasoconstrictors, what are they
- Sympathomimetic amines: adrenaline
- Synthetic polypeptides: felypressin
whats used as an antagonist to adrenaline
phentolamine
what is the function of phentolamine
is used to reverse LA. It counteracts vasocontriction, which increases local blood flow and vasodilation = allowing LA to be taken up.
what is the absolute maximum dose for Lidocaine
300mg
when would you not use lidocaine/adrenaline
if patient has:
- Unstable angina
- Severe cardiac dysrhythmia
- Allergy to any components
- Avoid or reduce dose with other cardiac conditions
which LA would you use if you wished to avoid adrenaline
prilocaine/octapressin
which LA would you not use for someone pregnant
Octapressin
what LA would be a good alternative to inferior alveolar blocks
Articaine
when should you consider reducing the dose of LA
- Liver disease – impaired metabolism
- Beta blockers
- Calcium channel blockers
- Drug abuse
