local anaesthetics Flashcards by Elena Kit

Describe the mechanism by which amide-linked local anaesthetics reach their target. (4 marks)

LA binds to a site in the Na+ channel by going through the myelin sheath
LA blocks the channel and prevents Na+ influx
This blocks action potential generation and propagation = PREVENTS DEPOLARISATION
Block persists so long as a sufficient number of Na+ channels are blocked

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How do local anaesthetics block the action potential of cells? (1 mark)

by blocking the voltage gated Na+ channels

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Describe which part of the action potential is affected by a local anaesthetic (1 mark)

DEPOLARISATION region as sodium channels are blocked

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Explain why the pKa of different types of amide local anaesthetics is relevant to their use.
(1 Mark)

affects the ability to enter lipid membranes of nerve fibres and bind to plasma proteins

the lower pKa = the easier to cross and reach the target

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List a pathological event that may influence your choice of local anaesthetic based on the pKa.
(1 Mark)

acidosis

the extracellular pH is lowered, making the local anesthetic molecule more protonated and therefore less able to cross the cell membrane and bind to the ion channels in their charged form. This reduces the effectiveness of the local anesthetic, and it may be necessary to choose an anesthetic with a lower pKa value, such as lidocaine or prilocaine, which are less affected by changes in pH.

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What is pterygomandibular raphae?

fibrous band of tissue

connects bony projection on the sphenoid bone to the mandible

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Where is ptergomandibular raphae located and how would you identify it in a patient?

in the mandibular trigone, which is a triangular space located between the medial pterygoid muscle, the mandible, and the buccinator muscle.

ask the patient to open their mouth wide and place their finger inside the mouth, just behind the most distal mandibular molar tooth.
ask to close their mouth slowly while maintaining the position of their finger.
then can palpate the fibrous band of tissue running posteriorly from the pterygoid hamulus to the mandible.

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Name a topical anaesthetic. (1)

Benzocaine

e.g. xylonor gel

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What technique would you use to anaesthetise maxillary teeth? (1)

Infiltration

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Which aspect of apex of tooth would you placed needle in maxillary teeth (1)

insert needle in a sulcus in the reflected mucosa just DISTAL TO THE APEX OF THE TOOTH required to be anaesthetised = TOWARD PALATAL ROOT OF THE TOOTH

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Innervation of this nerve? (1)

A-delta, C, A-beta, A-alpha

Superior alveolar nerve

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What structures pass through the mandibular foramen? (1)

inferior alveolar nerve
mylohyoid nerve

inferior alveolar artery and vein

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Infiltration on buccal side of lower tooth also given. Which sensory nerve supplies this region? (1)

buccal nerve, branch of mandibular of trigeminal

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Why is no infiltration given on the lingual gingivae? (2)

lingual nerve is a branch of inferior alveolar, IDB ALREADY does that

risk of injury to the lingual artery

rich blood supply so might be ineffective

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Name three types of local anaesthetics used for injections. (3)

amides and esters

lidocaine
articaine
prilocaine (e.g. citanest)
bupivacaine

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Functions of vasoconstrictor. (2)

Most local anaesthetics are vasodilators
Increased blood flow will increase ‘wash-out’ of LA
To increase duration of action, LA preparations often include a vaso-constrictor:
- Adrenaline
- Felypressin (synthetic vasopressin)
Vasoconstrictors act on receptors on vascular smooth muscle

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Example of vasoconstrictor. (1)

Adrenaline
Felypressin

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Mechanism of action of an amide anaesthetic

The anaesthetic binds to SODIUM CHANNELS and prevents sodium influx.
This blocks action potential generation and propagation.

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Part of action potential affected in amide anaesthetics

DEPOLARISATION region as sodium channels are blocked

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What location is affected to cause anaesthesia (Na channels)

H-gate of voltage gated sodium channels

Anaesthetic used in a healthy individual

Lidocaine 2% with 1:80,000 parts adrenaline

Why do you need to consider pKa

pKa is related to pH by the Henderson hasselbach equation: pH = pKa + log [base]/[acid]
The action of anaesthetics is dependent on pH as the active form of the drug B.H+ cannot cross the cell membrane and needs to break down to B and H+. This reaction is dependent upon the hydrogen concentration of the surrounding tissue as an increase in hydrogen ion concentration shifts the reaction towards increasing the active but non-diffusable B.H+.

What pathological condition affects pKa

Inflammation causes DECREASE in pH

what are the 3 components of LA ?

Aromatic (hydrophobic)
Ester/amide
Amine (hydrophilic)

The hydrophilic portion
The lipophilic portion
The intermediate chain

esters - cocaine, benzocaine

amides - lignocaine, articane, prilocaine

Maxillary buccal infiltration i. Where is the needle place in relation to the apex of the premolar (1 mark) ii. What type of nerve fibres are anaesthetised (1 mark) iii. What branch of the trigeminal nerve innervates the maxilla (1 mark)

i) Needle is in distal direction, superior to the tooth apex into the maxillary mucobuccal fold II) superior alveolar nerve (middle branch) iii) Maxillary of trigeminal nerve

a patient is undergoing an inferior alveolar nerve block for a restorative procedure, for which teeth is this form of LA appropriate?

lower/mandibular molars mental nerve block is for 1st premolar to incisors

what is the pterygomandibular raphe?

thick, fibrous band of tissue

what structures enter the mandible at the mandibular foramen?

the inferior alveolar nerve

sometimes needle feels odd when encounter the lingual of the mandible. what is this?

may have hit the lingual plate of the mandible, that has blood vessels the needle should be repositioned and redirected to avoid the lingual plate

before injecting the anaesthetic solution, the dentist allows the syringe plunger to retract slightly. why is this done?

to aspirate = ensure that LA is not going into the blood vessel

when the anaesthetics is injected, the tip of needle will lie in the pterygomandibular space. between which part of the mandible and which muscle does this region lie?

between the ramus of the mandible and the medial pterygoid

the dentist might also infiltrate local anaesthetics into the mucosa on the buccal side of the lower tooth. which sensory nerve supplies the region?

buccal nerve, only sensory branch of trigeminal

why is no infiltration of the gingival necessary on the lingual side?

it is innervated by lingual nerve which is branch of inferior alveolar so IDB already does that

once the IDB been administered, dentist waits few minutes for it to work. what are signs it started working? what is the anatomical basis of this sign?

tongue and lower lip should feel numb rubbery, tingly, swollen feeling in the area = overall loss of sensation reduced pain this is due to blocking sodium channels in the nerve cells so nerve impulses are stopped

in this patient, IDB doesn't work as planned. instead, corner of the mouth starts to droop. what has happened?

most likely been injected into parotid = facial nerve is impacted = facial palsy

when the corner of the mouth starts to droop, what is an immediate concern?

facial palsy ensure airway is not compromised

what clinical test you perform to check for palsy?

blink or close the eye

Where is LA deposited during infiltration?

Deposited around terminal branches of nerves

Where is the needle place in relation to the apex of the premolar?

distal to the apex

What branch of the trigeminal nerve innervates the maxilla?

Maxillary branch V2 -> Superior alveolar nerve. PSA, MSA, ASA

Name 3 types of LA

* Lignocaine 2% lignocaine HCl + 1:80,000 adrenaline * Prilocaine 4% prilocaine HCl + felypressin * Articaine 4% + adrenaline 1:100,000

Which of the muscles of mastication can cause trismus by accidentally hit it by the needle?

medial pterygoid

Where is LA deposited during dental block?

LA solution desposited around the nerve trunk

contradictions to lidocaine

heart block and no pace-maker allergy to LA (or to corn) hypotension impaired liver function.

contradictions to articaine

Avoid in sickle cell patients (and other haemoglobinopathies) Metabolised in liver and plasma, excreted in kidney More potent than lidocaine 1.5 x avoid in liver and kidney patients

dangers of adrenaline in LA

CARDIO-VASCULAR DISEASE AVOID OR USE < 3 X 2.2ml CARTRIDGES HYPERTHYROIDISM (THYROID CRISIS) PHAEOCHROMOCYTOMA (HYPERTENSION) RENAL IMPAIRMENT DRUG INTERACTIONS 1. MONO AMINE OXIDASE INHIBITORS 2. TRICYCLIC ANTIDEPRESSANTS (amitriptyline, clomipramine, lofepramine) 3. β BLOCKERS 4. NON- POTASSIUM SPARING DIURETICS 5. HALOTHANE (G.A. AGENT) 6. COCAINE

a patient has lost function in one side of their face after administration of LA, you suspect it is facial palsy but how do you ensure that they are not having a stroke?

If patient CAN move eyebrow, they are experiencing facial palsy If patient CANNOT move eyebrow they may be having a stroke

a patient comes into your surgery and requires LA for a procedure. After taking a history you see that they are on Propranolol, how does this affect the type of LA you administer?

on beta-blockers, avoid LA containing adrenaline if possible. beta-blockers block out adrenaline and reduce LA efficacy. if not possible keep dosage to a minimum.

A patient enters your surgery and lets you know that they suffer from Haemophillia, how does this affect their treatment?

cannot perform IDB as a hematoma can occur in the retromolar and pterygoid area