Local Anaesthetics Flashcards
Which type of nerve fibre is responsible for only mechanoreception?
A-beta fibres.
Which type of nerve fibre is responsible for chemoreceptors and nociceptors?
A-delta fibres.
Which type of nerve fibre is responsible for dull aching nociception?
C-fibres.
What is the mechanism of action by which local anaesthetics work?
They block voltage gated sodium channels, preventing sodium influx - thus stopping an action potential from being generated.
In which order will nerve fibres be affected by local anaesthetic?
- A-Delta fibres
- C-fibres
- A-Beta fibres
- A-Alpha fibres
What constituents can be found in a typical cartridge of 2% lidocaine?
Lidocaine Hydrochloride
Reducing agent
Preservatives
Vasoconstrictors
Why do local anaesthetics normally contain vasoconstrictors?
LAs tend to be vasodialators, which encourages diffusion of the active molecule.
A vasoconstrictor can be used to keep the LA in the targeted area.
What is the mechanism of action for adrenaline when given systemically - in relation to blood pressure?
Activates a-1 receptors, causing vasoconstriction.
However it also activates b-2 receptors causing vasodialation.
Overall little effect on blood pressure overall.
What is the mechanism of action for adrenaline when given locally?
It triggers both a-1 and b-2 receptors, however when given locally it acts more on a-1 receptors.
This leads to vasoconstriction in the local area.
What is the key clinical distinction between articaine and lidocaine?
Articaine is an ester based LA, lidocaine is an amide based LA.
Amide based LAs are typically safer and more predictable - with a lower chance of allergic reaction.
When is felypressin/octapressin contracindicated for use in LA?
Pregnent women as it may induce labour.
Why might preservatives within LA cartirgdges be of risk ro a patient?
Allergic reactions can happen, and bisulphite can trigger a patients asthma.
How does the gauge of needle relate to the size of lumen?
The lower the gauge, the greater the diameter of the lumen will be - and also the lower the risk of breakage.
What is the purpose of pulling back on the plunger before injecting LA into a patient?
Aspiration - you can check whether you are in a blood vessel before injecting.
What would you do in the event of positive aspiration?
Reposition the needle and aspirate again.
What areas of the mouth does an IDB with a lingual block anaesthetise?
Teeth up to the central incisor.
Buccal and Lingual soft tissue.
Lower lip and chin.
If you wanted to restore a lower 6 and use dental dam, what LA would you perform?
IDB or B/L Infiltrations
Why might a long buccal infiltration be advisable when giving an IDB for working on lower molar teeth?
The IDB isn’t that effective at numbing posterior buccal tissue - so invasive procedures involving the tissue could justify it.
What are the landmarks involved in performing an IDB?
Coronoid notch
Post. border of the mandible
Pterygomandibular raphe
Barrel over opposite premolars
Where is the mental foramen located?
Typically between the apex of the 4 and the 5.
What does a mental block anaesthetise?
Lower teeth 5-1
Labial soft tissues
Lip and chin
What is the target site for a nasopalatine block?
Incisive papilla
What complications can arise from delivering local anaesthetic?
Psychogenic (fainting)
Interaction with drugs
Cross infection issues
Allergy
Collapse
Toxicity
What causes a patient to faint due to psychogenic stress?
Lack of oxygenated blood to the brain.
What are the clinical features of someone experiencing a faint?
Lightheadeness
Pallor
Beads of sweat
Bradycardia
Nausea
Pupil dialation
How do you manage a faint?
Lay flat and raise legs
Loosen neck clothing
Ventilation
Sugar
Which drugs can interact with LA when accidentally injected systemically?
MAOI Anti-deps
Tri-cyclics
B-Blockers
Non-potassium sparing diuretics
Cocaine
Why might a patient have an allergic reaction to an LA injection?
Rarely allergy to the LA itself
Historically due to latex bung
The preservatives/anti-oxidents within the LA.
What are the symptoms of a toxic LA overdose?
Convulsions
Loss of conciousness
Respiratory depression
Circulator collapse
How many mg of lidocaine is there in a 2.2ml cartridge of 2% concentration?
2% = 2g/100ml
= 20mg/ml
Therefore there is 44mg in a 2.2ml cartridge.
What is the maximum safe dose of lidocaine with adrenaline that can be given to a fit and healthy patient?
5mg/kg
or
50mg/10kg
Maximum dose in a 70kg male is 350mg.
What is the maximum number of cartridges of lidocaine with adrenaline that can be given?
1 cartidge per 10kg body weight, approximately 7 in a 70kg man.
What is the maximum dose of 4% articaine that can safely be given to a fit and healthy individual?
7mg/kg
or
70mg/10kg
How many cartridges of articaine can be given to a 70kg male healthy patient?
5.
How many mgs of 4% articaine is there in a 2.2ml cartridge?
88mg.
What is the adrenaline concentration found in 4% articaine cartridges?
1:100,000
What is the adrenaline concentration found in 2% lidocaine cartridges?
1:80,000
What effect does adrenaline have on the sympathetic nervous system?
Increase in:
- HR
- MCF
- MCO
- Systolic BP
Decrease in:
- Diastolic BP
- Bronchial constriction
What is a safe way of using adrenaline containing LAs in patients with cardio-vascular disease?
Use <3 x 2.2ml cartridges
What risk is involved in giving LA to patients with hyperthryoidism?
Thryoid crisis.
What risk is involved in giving LA to patients with phaeochromocytoma?
Hypertension
List the potential local complications of giving LA intra-orally.
Failure to achieve anaesthesia
Prolonged anaestesia
Trismus
Haematoma
Intra-vascular injection
Blanching
Facial paresis
Broken needle
Infection
Soft tissue damage
Why should articaine be avoided when performing an IDB?
There is evidence to suggest that 4% articaine has a higher risk of causing nerve damage than 2% lidocaine.
Why might prolonged anaestesia occur?
Direct trauma from needle
Blunt needle
Chemical trauma from LA
Type of LA used
How might an LA cause trismus?
Most likely damage to medial pterygoid, injection may be too low or forceful.
What causes facial palsy when giving an IDB?
Injecting too far back, and therefore injecting into the parotid gland.
This causes VII-Facial nerve ganglion to be numbed, causing paralysis of one side of the face.
How would you manage someone who has just been given a facial palsy from an IDB?
Reassure patient
Cover eye with pad until blink reflex has returned.
What are the symptoms of an intravascular injection?
Heart palpatations
Anxiousness
Restlessness
Headache
Sweating
Pallor
