Local Anesthesia Flashcards
What is pKa?
pH at which there is 50% dissociation of the proton
Where are amide LAs metabolised?
The Liver
Where are ester LAs metabolised?
Hydrolysed by pseudo-cholinesterase in the plasma membrane
What is the active form the LA?
RNH+
T/F: RNH+ diffuses through the nerve sheath
False: The uncharged RN base defuses through the nerve sheath
Why is it difficult for LA to work in an infected space?
Bacteria produce H+ which favours equilibrium to form the charged RNH+ OUTSIDE the nerve sheath, meaning less RN can diffuse through the nerve sheath
T/F: the higher the pKA the longer the onset of LA
True
Procaine pKa 9.1, onset = 14-18 minutes
Mepivicaine pKa 7.6, onset = 2-4 minutes
What is the onset duration for Lignocaine (Xylocaine)?
2-4 minutes
What is the onset duration for Mepivicaine (Scandonest)?
2-4 minutes
T/F: Articaine is indicated for IANB
False, although it is indicated for us in the USA
What are additives to LA?
1, Methylparabens (Bacteriostatic agent, preservative)
- Bisulphite (Prevents oxidation of vasoconstrictor and lowers pH (may cause allergies)
- Sodium Chloride (isotonic solution)
- Sodium Hydroxide (increases pH of solution producing more RN)
- Distilled water (increases volume)
- Adrenaline/similar compounds (vasoconstrictor)
What is the role of vasoconstrictors in LA?
- Decrease blood flow
- Slows absorption of LA into blood stream
- Maintain higher local concentrations of LA
- Increases duration of LA action
- Reduces bleeding
What are the 3 structural components of an LA molecule
Lipophilic End
Intermediate Chain
Hydrophilic End
Presence of positive aspiration is indication of what?
- Fast and Bright Red: hit an artery
2. Small and Blue-ish: hit a vein
T/F: 30 Gauge is the thickest needle?
False, it is the thinnest and used in intra-periodontal ligament infilitration
What is a 25 Gauge needle used for?
Gow-Gates Block
Which direction should the bevel be facing when administering an periosteal infiltration?
Away from the operator
What is the topical anesthetic applied in SADS?
Ziagel (50mg/g) Topical Lignocaine
What is the LA toxicity dosage for 2% lignocaine for a 20kg child
2 Carpules
2% of 2.2ml Cartridge = 44mg
Toxicity dosage 4.4mg/kg
4.4 X 20kg = 88mg / 44mg = 2 carpules
What is the LA toxicity dosage for 3% scandonest for a 20kg child
3% of 2.2ml Cartridge = 66mg
Toxicity dosage 4.4mg/kg
4.4 X 20kg = 88mg / 66mg 1.3 carpules
What are the likely causes of LA toxicity?
- Rapid IV Injection
- Administering too large a dose
- Rapid absorption from site of administration
- Inability to biotransform the drug normally
- Inability to excrete the drug normally
What is Methemoglobinemia?
Formation of methemoglobin rather than haemoglobin which contains ferric iron that reduces the RBC capacity to carry oxygen.
Can be triggered and acquired through especially articaine, benzocaine, and prilocaine
What is the likely cause of trismus when administering an IANB?
Injecting too medially / inferiorly into the medial pterygoid muscle
What is the likely cause of sloughing when administering LA?
Result of too much vasoconstrictor. Superficial epithelium has as a lack of oxygen so dies and desquamates.
What are alternatives to IANB if the patient is unable to open wide enough or landmarks are unclear?
- Gow-Gates Mandibular Block
- Akinosi Closed Mouth Technique
- Intra-osseous
- Intra-pulpal (if pulp already exposed)
A patient went home after LA and dental treatment, and all of a sudden, bloody nose from nostril of same side as labial 22 infiltration. What happened?
Vasoconstrictors - increased blood pressure, but then followed by dilation, increased blood flow to superior labial artery leading to Littles/Kisslebach’s area?
Littles area is very small and delicate, so large excess blood flow can cause a rupture and then a nose bleed.
Injecting too Lateral for an IANB will result in what?
Hitting the mandible too early
Injecting too Deep for an IANB will result in what?
Piercing the parotid gland. Temporary facial paralysis by anesthetizing the facial nerve
If the pterygotemporal depression is not particularly obvious on a patient, what alternative landmark would you use for an IANB?
Finger on the coronoid notch, move medially towards the internal oblique ridge. Inject slightly laterally of this landmark
What is an alternative to injecting palatal infiltrations for children?
Alternative is to inject via interdental papilla on buccal end.
Palatal infiltrations are very painful for kids.
What is the angulation for a maxillary infiltration?
Follow the curvature of the maxilla in order to inject as close to the apex of the root
Which needle should be used for an infraorbital block?
27 Short
What is the target anatomy for a greater palatine block?
The greater palatine foramen around the maxillary 7s
Where is an mandibular infiltration indicators?
Anterior teeth only, as posterior buccal bone is too thick for effective diffusion
What are the superficial landmarks for the IANB?
- Pterygomandibular Fold (Raphe underneath)
- Coronoid Notch (Thumb)
- Pterygotemporal depression (between fold and tendon of temporalis)
- Buccal Fibrous Pad (not always present)
What is the angulation of the syringe for an IANB
Approximately against the 2nd molar of the opposing arch
How deep should the syringe go?
2.5mm of the 4mm long syringe
Injecting too Low for an IANB will result in what?
Insufficient diffusion of LA because of the lingula
Possibly trismus by injecting into the medial pterygoid muscle
What sort of procedures are indicated for a long buccal block
Soft Tissue Surgery on buccal surfaces of the mandibular posteriors
Placement of rubber dam
Lignocaine Hydrochloride 2% + Adrenaline (1:80000) is known by what brand names
Lignospan Special
Xylocaine
When is lignocaine indicated?
When vasoconstriction is needed
Pregnant Patient
When is lignocaine contraindicated?
CVS Issues
Medications that interact with adrenaline
Liver Dysfunction
LA Hypersensitivity
How long does lignocaine provide anesthesia?
Pulp: 60min (Infil), 90 min (Block)
Tissues: 2.5hr (Infil), 3hr (Block)
Mepivacaine 3% is known by what brand name?
Scandonest
Carbocaine
Polocaine
When is Mepivacaine indicated?
Rapid Onset needed
Infiltration + Regional anesthesia
Paediatrics
Geriatrics
When is Mepivacaine contraindicated?
CVS Issues
Liver Dysfunction
How long does Mepivacaine provide anesthesia?
1-2.5 hrs maxilla
2.5-5.5 hrs mandibular
Articaine 4% is known by what brand names
Septocaine
Septanest
Astracaine
Articadent
What is Articaine indicated for?
Lowest toxicity risks
Patients with liver issues (shortest half life)
Infiltrations
What is Articaine contraindicated for?
CVS issues
Risk of paresthesia in IANB if the nerve is damaged
Prilocaine 3% with Octapressin (Felypressin) is known by what brand name?
Citanest
Prilocaine
What is Prilocaine indicated for?
Rapid Onset
Vasoconstriction
CVS issues
If patient has interactions with adrenaline
What is Prilocaine contraindicated for?
Pregnant Patients
After an IANB, the patient calls you and complains that the jaw feels sore. What 2 things could this be?
- Normal soreness from piercing the buccinator muscle during the IANB
- Block was done incorrect, too medially, and resulted in trismus
Mandibular Prognathism can do what to the success of the IANB?
Patients with class III have a lingula positioned higher than the coronoid notch
What are several anatomical reasons that an IANB was unsuccessful?
- Duplicate Mandibular Canals
- Accessory Nerve Supply
- Accessory Foramina
- Obstruction (Eagle’s Syndrome)
- Crossover of mental nerve fibres
- Edentulous Patkients: loss of some I/O landmarks
