LA Flashcards
what is the mode of action of LA?
local anaesthetics bind reversibly to specific receptors in Na channels. This prevents the normal passage of ions through the nerve membrane and there is no conduction of impulses.
How does LA enter a nerve membrane?
They are soluble in fat and in a non-charged state
What happens to the charge of an LA once it enters the nerve membrane?
The uncharged LA molecules re-equilibrate inside the aqueous environment of the cell, to charged and uncharged.
The charged molecules then bind to the Na channel.
How can LA exist as both lipid soluble and charged molecule?
because it is a weak base in solution, some molecules are charged and some are uncharged.
What 2 factors govern the proportion of charged and uncharged molecules, following injection?
- pH of the region
- dissociation constant of LA molecule (pKa)
What does a low pH mean for LA molecules?
less uncharged LA molecules are present in the solution
What does a low pKa mean for LA molecules?
the more uncharged La molecules are present in solution
Where does LA work on A fibres?
nodes of Ranvier
Where does LA work on C fibres?
along the whole length of the cell, they are unmyelinated
How does infiltration anaesthesia differ from block anaesthesia?
infiltration: injected into highly vascular region
block anaesthesia: injected directly into nerve
What does analgesia mean?
loss of PAIN sensation accompanied by loss of other forms of sensibility
What does anaesthesia mean?
loss of ALL FORMS of sensation, including pain, touch, temperature, pressure, and impaired motor function
What are the 3 components of LA equipment?
- needle
- cartridge
- syringe
What are the 2 types of needles used?
what is their length?
what is their gauge?
LONG. YELLOW
length: 35mm
gauge: 27
SHORT. BLUE
length: 20mm
gauge: 30
What does the LA cartridge consist of?
- glass cylinder
- plunger (rubber, can be latex free)
- cap
What must the user of LA cartridge check?
- content
- concentration of anaesthetic and vasoconstrictor
- expiry date
- batch number
- damage: cracked, cloudy
What is the most common volume of LA in the UK?
2.2ml
What does the aspirating technique do?
how do you do it?
- aids in determining if tip of needle is in a blood vessel.
- aspirate twice in 2 planes
What are the 6 constituents within an LA cartridge?
1- La agent 2- vasoconstrictor 3- reducing agent 4- preservative 5- fungicide 6- vehicle
What are the 3 advantages of a vasoconstrictor?
1- reduces toxic effect by retarding absorption of constituents
2- confines LA to a localised area: increases depth and duration of anaesthesia
3- produces relatively bloodless field
What are the 9 properties to consider with LA?
1- potency and reliability. Must consistently produce effective local anaesthesia
2-reversibility of action. Must be completely reversible within a predictable time
3-safety. wide margin of safety
4-lack irritation
5-rapid onset
6-duration of effect. recovery of sensation should coincide with completion of treatment
7-sterility. be able to sterilise the instruments
8- have adequate shelf life
9- should be able to penetrate mucous membrane
what are the 2 classes of local anaesthetics?
1- esters
2- amides
Where are esters metabolised?
example?
in the plasma. This is a rapid process
example: benzocaine
where are amides metabolised?
example?
transported to the liver for breakdown. This is a more complex and slower process.
example: lidocaine
In the UK, what class of drug are local anaesthetics? amides or esters?
amides
What are the 2 vasoconstrictors generally used in LA?
- adrenaline (epinephrine)
- Felypressin (Octapressin)
What does the reducing agent do?
sodium meta-bisulphate.
This competes for available oxygen and prevents the vasoconstrictor becoming unstable/oxidising.
Vasoconstrictors will turn brown when oxidised.
What does the preservative do?
caprylhydro-cuprienotoxin.
maintains stability of the LA solution.
what does the fungicide do?
thymol
prevents the solution becoming cloudy due to proliferation of minute fungi.
what is the vehicle of a LA?
this is what the LA and its’ additives are dissolved in.
This is modified Ringers solution, isotonic solution.
What are the 4 main types of LA used in dentistry?
what are the brands for each one?
1- Lidocaine (Xylocaine)
2- Prilocaine (Citanest)
3- Mepivacaine (Scandonest)
4- Articaine (Septanest)
What does Lidocaine contain?
2% Lidocaine hydrochloride
1 : 80,000 arenaline
What does Prilocaine contain
3% Prilocaine
0.03 iu/ml Octapressin
What does Mepivacaine contain?
3% Mepivacaine
no vasoconstrictor
What does Articaine contain?
4% Articaine
1 : 100,000 adrenaline
1 : 200,000 adrenaline
What is the maximum dose of LA per kg of body weight?
about one tenth of a cartridge.
So for 10kg, 1 cartridge is the maximum
