LA

Question 1

what is the mode of action of LA?

Answer 1

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.

Question 2

How does LA enter a nerve membrane?

Answer 2

They are soluble in fat and in a non-charged state

Question 3

What happens to the charge of an LA once it enters the nerve membrane?

Answer 3

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.

Question 4

How can LA exist as both lipid soluble and charged molecule?

Answer 4

because it is a weak base in solution, some molecules are charged and some are uncharged.

Question 5

What 2 factors govern the proportion of charged and uncharged molecules, following injection?

Answer 5

• pH of the region

- dissociation constant of LA molecule (pKa)

Question 6

What does a low pH mean for LA molecules?

Answer 6

less uncharged LA molecules are present in the solution

Question 7

What does a low pKa mean for LA molecules?

Answer 7

the more uncharged La molecules are present in solution

Question 8

Where does LA work on A fibres?

Answer 8

nodes of Ranvier

Question 9

Where does LA work on C fibres?

Answer 9

along the whole length of the cell, they are unmyelinated

Question 10

How does infiltration anaesthesia differ from block anaesthesia?

Answer 10

infiltration: injected into highly vascular region

block anaesthesia: injected directly into nerve

Question 11

What does analgesia mean?

Answer 11

loss of PAIN sensation accompanied by loss of other forms of sensibility

Question 12

What does anaesthesia mean?

Answer 12

loss of ALL FORMS of sensation, including pain, touch, temperature, pressure, and impaired motor function

Question 13

What are the 3 components of LA equipment?

Answer 13

• needle
• cartridge
• syringe

Question 14

What are the 2 types of needles used?
what is their length?
what is their gauge?

Answer 14

LONG. YELLOW

length: 35mm
gauge: 27

SHORT. BLUE

length: 20mm
gauge: 30

Question 15

What does the LA cartridge consist of?

Answer 15

• glass cylinder
• plunger (rubber, can be latex free)
• cap

Question 16

What must the user of LA cartridge check?

Answer 16

• content
• concentration of anaesthetic and vasoconstrictor
• expiry date
• batch number
• damage: cracked, cloudy

Question 17

What is the most common volume of LA in the UK?

Answer 17

2.2ml

Question 18

What does the aspirating technique do?

how do you do it?

Answer 18

• aids in determining if tip of needle is in a blood vessel.

- aspirate twice in 2 planes

Question 19

What are the 6 constituents within an LA cartridge?

Answer 19

1- La agent
2- vasoconstrictor
3- reducing agent
4- preservative
5- fungicide
6- vehicle

Question 20

What are the 3 advantages of a vasoconstrictor?

Answer 20

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

Question 21

What are the 9 properties to consider with LA?

Answer 21

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

Question 22

what are the 2 classes of local anaesthetics?

Answer 22

1- esters

2- amides

Question 23

Where are esters metabolised?

example?

Answer 23

in the plasma. This is a rapid process

example: benzocaine

Question 24

where are amides metabolised?

example?

Answer 24

transported to the liver for breakdown. This is a more complex and slower process.
example: lidocaine

Question 25

In the UK, what class of drug are local anaesthetics? amides or esters?

Answer 25

amides

Question 26

What are the 2 vasoconstrictors generally used in LA?

Answer 26

• adrenaline (epinephrine)

- Felypressin (Octapressin)

Question 27

What does the reducing agent do?

Answer 27

sodium meta-bisulphate.
This competes for available oxygen and prevents the vasoconstrictor becoming unstable/oxidising.
Vasoconstrictors will turn brown when oxidised.

Question 28

What does the preservative do?

Answer 28

caprylhydro-cuprienotoxin.

maintains stability of the LA solution.

Question 29

what does the fungicide do?

Answer 29

thymol

prevents the solution becoming cloudy due to proliferation of minute fungi.

Question 30

what is the vehicle of a LA?

Answer 30

this is what the LA and its’ additives are dissolved in.

This is modified Ringers solution, isotonic solution.

Question 31

What are the 4 main types of LA used in dentistry?

what are the brands for each one?

Answer 31

1- Lidocaine (Xylocaine)
2- Prilocaine (Citanest)
3- Mepivacaine (Scandonest)
4- Articaine (Septanest)

Question 32

What does Lidocaine contain?

Answer 32

2% Lidocaine hydrochloride

1 : 80,000 arenaline

Question 33

What does Prilocaine contain

Answer 33

3% Prilocaine

0.03 iu/ml Octapressin

Question 34

What does Mepivacaine contain?

Answer 34

3% Mepivacaine

no vasoconstrictor

Question 35

What does Articaine contain?

Answer 35

4% Articaine
1 : 100,000 adrenaline
1 : 200,000 adrenaline

Question 36

What is the maximum dose of LA per kg of body weight?

Answer 36

about one tenth of a cartridge.

So for 10kg, 1 cartridge is the maximum