1. local anaesthesia in dentistry Flashcards
What is local anaesthesia?
“a loss of sensation in a circumscribed area of the body by a depression of excitation in nerve endings or an inhibition of the conduction process in peripheral nerves”
DEFINITION OF LOCAL ANALGESIA
Localised loss of Pain sensation
DEFINITION OF LOCAL ANAESTHETIC
A drug which reversibly prevents transmission of nerve impulses in the region applied without affecting consciousness
Why Use LA?
✓ Controlling operative pain
✓ The control of postoperative/post-surgical pain
✓ Control of operative haemorrhage
✓ As a diagnostic tool
✓ Symptomatic relief of orofacial pain
Why Master LA?
✓ The most common procedure/ drug you will use
✓ One of the most feared / anxiety inducing procedures
✓ Fundemental to the practice of dentistry.
✓ Anaesthetists as well as dentists
✓ Duty of care to ensure optimal pain control for patients.
✓ Early control of acute pain can shape its subsequent progression
types of LA consent
- Implied
- Verbal
- Written
- Explain LA procedure, benefits & risks
physiology
- Voltage-gated sodium channels are required for action potential generation
- Action potentials are required to signal information in all (most) nerves
how does LA prevent information being signalled to nerves
what is differential block? (what does it affect and depend on?)
*Affects small diameter axons preferentially
*Affects un-myelinated axons preferentially
*Affects those axons on the outside more
*Depends on the type of sodium channel
*Therefore C>Aδ>Aβ>Aα
PHARMACOLOGY OF SPECIFIC BINDING THEORY
MECHANISM OF ACTION
- Injected as acidic ionised water soluble hydrochloride salt
- pH rises molecule dissociates to non-ionised free base
- Lipid soluble free base diffuses through membrane
- Once inside the nerve pH is lower#
- Molecule re-ionises and blocks sodium channel
pH (make Q’s)
LAs cannot block sodium channels from outside the axon
- Only uncharged LA can cross the axon membrane
- Most LAs are weak bases pKa 8-9 (except benzocaine)
- pKa = pH at which 50% LA charged & 50% not charged
- LA + H+ LAH+
what is henderson hasselbalch equation?
chemistry / structure of LA
Types of LA used in Dentistry & Pharmacokinetics
- what they consist of (structure)?
- amides and esters metabolised by?
classifications of LA and examples
AMIDES:
- Lidocaine
- Prilocaine
- Bupivicaine
- Articaine
ESTERS:
- Cocaine
- Benzocaine
ACTION OF LA
1- Speed of action depends on?
- Tissue pH and pKa of aneasthetic
- Diffusion to site
- Nerve morphology
- Concentration
- Lipid solubility
ACTION OF LA
2 - Rate of diffusion away from the
nerve depends on
- Protein binding
- Concentration of anaesthetic
- Lipid solubility
ACTION OF LA
3 - Duration of action increased by
addition of
- Vasoconstrictor e.g. adrenaline
What’s in the LA Solution ?
- Function of each?
Common Injectable Formulations in the UK
(2.2ml cartridges)
a) generic name
b) conc
c) vasoconstriction
d) brand name
Common Topical ( surface ) Anaesthetics (with %)
- Benzocaine 20%
- Xylocaine 4%
- Lignocaine ointment 5% or spray 10%
- EMLA – lignocaine 2.5% & prilocaine2.5%
- Oraqix TM mixture of 5% prilocaine & lidocaine. Periodontal probing & scaling
- Ethyl Chloride Spray
features of an Ideal Local Anaesthetic
- 100% effective
- Safe with no side effects
- Painless and easy to administer
- Quick effect
- Last only for duration of procedure (?)
- Well localised
- Cheap
features of 2% lidocaine with 1:80000 adrenaline ( EPINEPHERINE)
- Most popular local anaesthetic agent
- Safe and effective
- Good vasoconstrictor properties
- Cheap to use
- Adrenaline should be used with care in pts who have had a recent MI, cardiac arrhymia,intravascular injection must be avoided
features of 3% Prilocaine with felypressin or 4% Prilocaine (Plain)
- Marketed as Citanest with Octapressin
- Theoretical risk of inducing labour in late pregnancy/associated with methemoglobinemia as adverse reaction.
- Use if do not wish to use adrenaline containing LA/allergy to lignocaine(rare)or if allergy to latex as non latex bung
- Felypressin vasoconstrictor effect not as good as adrenaline, less effective at reducing operative bleeding and less depth and duration of anaesthesia.
