LA science 210 Flashcards
physical anaesthesia of surfaces tissues without venopuncture
reducing temperature
ethyly chloride (rarely used)
pharmacological anaesthesia of surface tisseus without venopuncture
topical anaesthesia
intra oral
- will anaesthetise 2-3mm tissue depth
- dry area -> cotton wool roll, 2-5mins
- lidocaine (2% gel, 10% spray, 5% ointment)
- benzocaine (20% flavoured gel)
extra oral
- EMLA cream
- 5% prilocaine (amide) and lidocaine (amide)
- needs to be applied for an hour
- euctectic (semi solid) mix
- Ametop Gel
- tetracaine (amethocaine) 4% gel (esther)
- faster onset than EMLA
non pharmlocological pain control
TENS (transcutaneous Electrical nerve stimulation)
- blocks pain gate to smaller unmyelinated fibres
Hypnosis
- decrease pulse rate
lidocaine
half life 1.5-2hrs
anti-arrythmic drug
contraindications: heart block with no pacemaker, impaired liver function, hypotension
articaine
half life of 20 mins
thiopine ring instead of benzene
hydrolised by blood quicker (less toxic)
good for mandibular infiltrations
contraindications: sickle cella anamia and other haemoglobinopathies
adrenaline effects
avoid intra-arterial injection (aspirate)
adrenline binds to α-receptors in peripheral vasculature - vasoconstriction
tachycardia also present due to β1 adrenergic receptors in heart wall
- increase heart rate and BP
caution with pts on:
- Diuretics adrenaline free to reduce hypokaleaemia chance
- β-blocker pts
LA stop
nerve conduction by blockeing the voltage gated sodium channels
act on the nerve before it reaches the spinal doral horn trigeminal nucleus
order of nerve fibre block
Aδ (sensory- noci, thermo, chemo and mechano)
C (sensory - noci, thermo, chemo)
Aβ (sensory- mechano)
Aα
- group 1 - sensory (proprio)
- motor - skeletal muscle
Aδ nerve fibres
structure and function
myelinated
sensory - mechano-, thermo-, noci- and chemo-receptors
C nerve fibres
structure and functrion
unmyelinated
sensory (noci-, thermo- and chemo-receptors)
autnomic (post-ganglionic)
Aβ nerve fibres
structure and function
myelinated
sensory (mechanoreception)
Aα nerve fibres
structure and function
myelinated
sensory (proprioception)
motor (skeletal muscle)
mode of action of LA
LA binds to sit in the Na+ channel
LA block channel and prevents Na+ influx into cell
- i.e prevents depolarisation
Blocks AP generation and propagation
Block persists so long as sufficient no. of channels blocked
Non- specific!! > Can do the same to myocardium = hypotension + bradycardia
biochemical structure and process of LA
organic molecules in 3 components
- aromatic region (hydrophobic)
- ester/amide bond
- basic amine side chain (hyrophillic)
presented as hydrochloride (B.HCl)
- renders amine base more water soluble
partially dissociated
- pharmocologically active in ionised form
- can cross membrane in un-ionised form only
what axons more susceptible to LA
smaller diameter as they have fewer layers of sodium channels
constituents for LA preparations
LA Base - present as Hydrochloride - inc the anaesthetics solubility in aqueous solution
for dental injections 2-4%
reducing agent - sodium metabisulphide
preservatives and fungicide
+/- vasoconstrictive
LA
ester
benzocaine
LA amides
lignocaine/lidocaine
prilocaine
articaine
bupivicaine
why LA better with vasoconstrictor
most LAs are vasodilators
inc blood flow = inc wash out of LA
to couteract this use vasoconstrictive agent
- adrenaline
- felypressin (synthetic vasopressin)
vasoconstrictors act on
receptors on vascular smooth muscle
- adrenoreceptors
- α receptors = vasoconstriction
- β2 receptors = vasodilation
- β1 receptors = caridac muscle
- positive chronotopic effect (inc rate)
- positive inotropic effect (inc force)
- ADH receptors (Vasopressin)
adrenaline effective on what receptors
α and β receptors
Locally = vasoCONSTRICTIVE (α)
Systemically = Lowers TPR (β > α)
adrenaline inc CO
overall, adrenaline has little/no effect on mean arterial BP
noradrenaline effective on
α more
Locally = vasoCONSTRICTIVE (α)
Systemically = increase TPR (α >β)
noradrenaline inc CO
overall noradrenaline raises mean arterial BP
has minimal effect on CO and HR so can lead to fall in BP
