Local Anesthetics Flashcards
How does LA function?
Inhibits neural conduction by inhibiting Na ion influx
How does LA prevent Na ion influx?
LA diffuses across neural membrane into axoplasm
They enter the Na channels preventing them from assuming an active position
What are the three components of LA molecules ?
Lipophilic aromatic ring
Intermediate ester or amide chain
Terminal amine
What is the function of aromatic ring?
Improves lipid solubility
For local anaesthetics what is the benefit of greater lipid solubility ?
Enhances the potency of the LA since more can diffuse across the membrane
Why are inflamed tissues more difficult to anaesthetise ?
Inflamed tissues have an acidic environment favouring the water soluble configuration of LA over the lipid soluble
LA needs to be lipid soluble form to be able to cross nerve membrane
Which LA would be more effective in inflamed tissues?
Mepivicane since it has a pKa of 7.6
What is the pKa ?
pH at which 50% of molecule exists in water soluble state and 50% in lipid soluble state
The intermediate section of LA determines what?
Either amide or ester
Where the LA is metabolised
Where are esters metabolised?
Blood plasma esterases
Where are amides metabolised?
Liver
LA most commonly used are what group?
Amides
Esters only really in topicals
Why is bupivicaine so long acting ?
Greatest affinity of all LA to bind to alpha-1-acid glycoprotein making it more bioavailable
What is the risk of using bupivicaine?
Painful upon injection
Why is articaine more effective than lidocaine ?
- Produced at higher concentration
- Has thiopene ring making it greater lipid soluble
Why does articaine have a reduced risk of systemic toxicity compared to lidocaine ?
Articaine has a reduced half life 20 mins vs lidocaine 90 mins
What are the benefits of vasopressors added?
Local haemostasis
Delay absorption
Name two alternative methods for ID block delivery
Gow Gates
Akinosi technique
What nerves are blocked with the Gow-Gates technique ?
All sensory division of Mandibular nerve
-IDN
-buccal
-lingual
-mylohyoid
In the Gow Gates method where is the LA delivered ?
Adjacent to head of condyle
Approach from contra lateral side
What are the landmarks for delivering a Gow Gates block?
Imaginary line from Corner of mouth to intertragic notch
How is the akinosi technique delivered ?
Closed mouth
Parallel to occlusal plane
Level of the mucogingical junction of maxillary teeth
What is a risk of the akinosi technique compared with Gow Gates?
There is no boney contact made with akinosi
What LA delivery methods exist ?
Infiltrations
Blocks: mental nerve, IDN, Gow Gates, Akinosi
Intraligamentary
Intrapulpal
Intraosseous
What is the benefit of the akinosi over the Gow Gates?
Akinosi there is sensory and motor branch blocks this means the patient can open widely
When giving an intraligamentary injection what would you expect to see happening to the tissues ?
Blanching which occurs due to back pressure
Why is back pressure required for intraligamentary injections?
Because this allows the LA to be forced into the narrow spaces achieving anaesthesia
Which gingival surfaces of the tooth should you direct the needle when giving an intraligamentary?
Mesial
Distal
Lingual
T/F intrapulpal anaesthesia can be achieved with saline
T
Intrapulpal works by delivering back pressure and LA is not required for this
In order to deliver an Intrapulpal injection what size hole should be made into the pulp roof?
The smaller the better as this allowed greater back pressure to be achieved
Which part of the bone are intraosseous injections delivered?
Cancellous bone
