Local Anesthesia

Question 1

Definition of LA

Answer 1

Reversible loss of sensation in a circumscribed area of the body caused by depression of excitation in nerve endings or an inhibition of conduction processes in peripheral nerves

Question 2

Role of LA

Answer 2

Decrease intraoperative and postoperative pain
Decrease amount of GA used
Increase patient cooperation
Diagnostic testing/examination

Question 3

Methods of administration

Answer 3

Topical
Infiltration
Regional nerve block
Intra-ligamentary injection

Question 4

Trigeminal nerve anatomy

Answer 4

Divided into V1, V2 (maxillary) and V3 (mandibular)
Max is sensory
Mand is mixed

Question 5

Which nerves to block?

Answer 5

Teeth behind mental nerve: block IDN, lingual nerve (inner gums) and long buccal nerves (outer gums)

Teeth in front of mental nerve: block IDN and lingual nerve

To check if IDN block is working, check lip
To check if long buccal nerve block is work, check cheek

Question 6

Maxillary nerve branches

Answer 6

Max enters pterygopalatine fossa via foramen rotundum, connects to parasympathetic pterygopalatine ganglion

Splits into:

= Lateral nasal nerves

= Nasopalatine nerve

= Greater palatine (mucosa of hard palate and palatal gingiva of maxillary alveolar process)

= Lesser palatine (soft palate)

= Posterior superior alveolar (runs over max tuberosity to supply max molars and buccal gingiva)

= Zygomatic

= Infraorbital nerve
> Middle superior alveolar (max premolars and gingiva)
> Anterior superior alveolar (max canines and incisors)

= Inferior palpebral

= Superior labial

Question 7

Mandibular nerve branches

Answer 7

Through foramen ovale into infratemporal fossa

Anterior
- Sensory: Buccal
- Motor: Pterygoid, deep temporal, masseter

Posterior
- Sensory:
> Inferior alveolar (forms alveolar plexus to innervate dentition and gingiva), giving rise to mental nerve (arises from mental foramen and innervates skin and mucosa of lower lip and buccal gingiva)
> Auriculotemporal (TMJ, skin of temporal and auricular region, sympathetic fibers for parotid gland)
> Lingual (anterior 2/3 sensory of tongue, recall post 1/3 is glossopharyngeal, taste is chorda tympani of facial, motor is hypoglossal)
- Motor: Mylohyoid and anterior belly of digastric

Question 8

Pterygomandibular space relations

Answer 8

A triangular space

Medially: medial pterygoid
Cranially: lateral pterygoid
Laterally: mandibular ramus
Posterior: parotid

Question 9

Ideal LA properties

Answer 9

Water soluble, stable, readily biotransformable
Non-irritating to nerve
Low systemic toxicity
Short induction
Adequate duration
No post anesthetic side effects
Non allergenic

Question 10

LA structure

Answer 10

Weak bases, containing aromatic group (lipophilicity), intermediate ester/amide chain, amine group (hydrophilicity)

Formulated as HCl salt for solubility and stability, but uncharged form is required to traverse tissue to site of action

Question 11

Amide vs Ester LAs

Answer 11

Amides metab in liver by CYP enzymes, contraindicated in liver disease, transplant, and must give lower dose to avoid toxicity

Esters metab in plasma by pseudocholinesterase, but more allergenic (PABA) and some pts have atypical pseudocholinesterase deficiency (can lead to toxicity)

Question 12

Amide LAs

Answer 12

Articaine (used in children as better bone penetration in more porous bones of children)

Bupivacaine (4-6h, used in long surgeries)

Dibucaine

Etidocaine

Lidocaine (for pregnant patients)

Mepivacaine (commonly used except for pregnant patients)

Prilocaine

Ropivacaine

Question 13

Ester LAs

Answer 13

Butacaine
Cocaine
Benzocaine
Hexylcaine
Tetracaine
Procaine
Chloroprocaine
Propoxycaine

Don’t use cos allergic reactions are more common, if need can use topically as penetrates faster

Question 14

LA MoA

Answer 14

Blocks sodium channels by binding to specific sites on channel proteins, thus inhibiting influx and depolarization of membrane in response to APs to prevent propagation of AP

Blocks generation and propagation of impulses in excitable tissues reversibly

Question 15

Factors affecting toxicity

Answer 15

Uptake into circulation:
Vascularity
Vasodilation
LA properties (protein binding, lipid solubility, pKa)

Question 16

Factors affecting uptake into nerves

Answer 16

Distance to nerve
Lower pKa = more rapid onset as more LA in non-ionized form to diffuse through
Increased lipid solubility = increased potency
Local pH

Question 17

Duration of action

Answer 17

Short acting: 60-180 mins
Intermediate: 120-240 mins
Long-acting: 240-540 mins

Question 18

Maximum safe doses of LAs in healthy adults

Answer 18

Procaine: 500mg
Articaine: 500
Tetracaine: 100 topical
Lidocaine: 500
Lidocaine (plain): 300
Mepivacaine: 300
Bupivacaine: 90

Question 19

Henderson Hasselbach equation

Answer 19

Determines how much LA is non-ionized vs ionized, based on tissue pH and anaesthetic pKa

Nonionized diffuses into nerve
Ionized form takes action

Local pH lower (infected tissue): less non-ionized form to cross into nerve, less effective

Question 20

Vasoconstrictors

Answer 20

Prolongs length of action and depth of action
Reduces LA toxicity
Hemostatic by decreasing blood flow

Question 21

Adrenergic agent actions

Answer 21

Alpha: vasoconstriction
Beta1: cardiac smooth muscle chronotropy and inotropy
Beta2: bronchodilation

Dont use in CVS, pregnant and pedo patients

Question 22

Vasoconstrictor concentrations

Answer 22

1:50,000 = 0.02mg/ml
1:80,000 = 0.0125mg/ml
1:100,000 = 0.01mg/ml
1:200,000 = 0.005mg/ml

Max dose in healthy pt approx 0.2mg
Max dose in pt w significant CV history approx 0.04mg

So can calculate max number of carpules, 1 carpule is 1.8cc
1:100,000 = 0.01mg/ml
0.01mg x 1.8cc = 0.018mg
0.04/0.018 = 2.22 carpules so max 1:100,000 carpules for pt with CV history is 2!!

Question 23

Adrenaline systemic effects

Answer 23

Increased BP
Arrhythmia
Fear
Sweating
Anxiety

Question 24

Contraindications to vasoconstrictors

Answer 24

Unstable angina
Recent MI
Recent bypass surgery
Untreated/uncontrolled severe hypertension
Untreated/uncontrolled congestive heart failure

Question 25

Maximum LA dosage calculations

Answer 25

% means g/dL
So 1% = 1g/dL = 10g/L = 10mg/mL

1 carpule = 1.8cc = 1.8mL, so 1 carpule of 2% lidocaine contains 20 x 1.8 = 36mg of LA

Max dose is 7mg/kg, so multiply by pt weight (e.g. 616mg for 88kg), and divide by LA weight per carpule (17 carpules for 88kg)

Question 26

Needle types

Answer 26

Gauge: larger gauge number = smaller needle diameter, use 27 or 30

Length: long for blocks, short for infil

Question 27

LA steps

Answer 27

Use sharp sterile needle
Check flow of LA
Position pt
Dry with gauze to apply topical anesthetic (20% benzocaine or lidocaine)
Communicate w pt
Hand rest
Make injection site tissue taut, insert needle into mucosa with bevel toward bone
Advance slowly while injecting slowly
Aspirate
Inject slowly, withdraw slowly
Observe and record amount and type of LA given

Question 28

EMLA

Answer 28

Eutectic mixture of local anesthetics

Cream of lidocaine (2.5%) and prilocaine (2.5%)

Penetrates skin to 5mm within 1h to permit superficial procedures

Question 29

Commonly used LA mixtures

Answer 29

Lignocaine (2%) with 1:80,000 adrenaline

Prilocaine (3%) with felypressin 0.03

Mepivacaine (2%) with adrenaline (2%) or 3% without adrenaline. 1.5-2min onset, 1.9h half life, operating time of 1.5-2h. Max 6.6mg/kg and 400mg, Liver metab, kidney clearance.

Bupivacaine (0.5%) with epi (1:200,000) is long acting, half life 2.7h, working time 6-8h. Max 1.3mg/kg, total max 90mg. Metab in liver. Most cardiotoxic so aspirate to prevent accidental vascular injection

Lidocaine (2%) with epi (1:80,000/100,000/200,000), 2-4 min onset and 1.6h half life, max 7mg/kg and 500mg or 4.4mg/kg without VC. Liver metab, kidney clearance.

Question 30

LA techniques

Answer 30

Infiltration - directly at tissues, esp for max teeth and secondary injections to block gingival tissues of mand teeth

Blocks - inject near major nerve, esp for mand teeth (IDN for half of anterior 2/3 of tongue, half of floor of mouth, half of all mand teeth)

Question 31

Useful max blocks

Answer 31

Nasopalatine - Palatal gingiva between right and left upper canines, most painful as chance of hitting nerve v high (lateral to incisive papilla, inserted at 45 degree towards posterior of incisive papilla, 6-10mm)

Greater palatine - palatal gingiva of upper premolars and molars without pulpal anesthesia, high pressure as no space for solution, inject slowly (target junction of max alveolar process and hard palate at 2nd or 3rd molar, GP foramen midway between median palatine raphae and lingual gingival margin of molar, insert 90 degrees to palate)

Infraorbital - lower eyelid, side of nose, upper lip, upper central to second premolar and associated gingiva, but central incisor may also be innervated by nasopalatine branches (feel depression of IO foramen by moving down about 10mm from IO rim, insert from mucobuccal fold at apex of 1st premolar)

Posterior superior alveolar - max molars and associated buccal tissues (insert short needle towards height of mucobuccal fold above max second molar, bevel towards bone, 45 degrees to occlusal plane, medially toward midline at 45 degrees to long axis, 16mm penetration)

Middle superior alveolar - max premolars and associated buccal tissues (insert short needle well above apex of max 2nd premolar at mucobuccal fold)

Anterior superior alveolar - max canine and incisors in one quadrant (insert needle in 3-5mm, parallel to long axis of tooth, at mucobuccal fold above apex of max canine)

Question 32

Useful mand blocks

Answer 32

IDN - half of anterior 2/3 of tongue, half of floor of mouth, half of all mand teeth (but may need infil for lower incisors), facial tissues anterior to mand 1st molar, need supplemental buccal nerve block for soft tissues at buccal posteriors (insert long needle at mucous membrane on medial side of ramus between coronoid notch and pterygomandibular raphae, insert until contacting bone then retract a bit, 3/4 needle)

Buccal - tissues distobuccal to most distal mand molar (mucobuccal fold at mand molars, deposit 0.2-0.3ml)

Mental - buccal soft tissue anterior to the mental foramen and the lower lip and chin (insert short needle at mucobuccal fold between 1st and 2nd premolar, target mental foramen, deposit 1/3 to 1/2 cartridge)

Incisive - teeth and facial tissues anterior to mental foramen

Gow-Gates - most of mand nerve, mand teeth to midline, buccal tissues on side of injection, anterior 2/3 tongue and floor of oral cavity, body of mandible and inferior ramus, skin over zygoma, posterior cheek and temporal regions (long needle direct from contralateral corner of mouth, mesiopalatal cusp of max second molar, aim for neck of condyle, advance until bone and deposit, keep mouth open)

Akinosi technique - closed-mouth technique with delayed onset, does not rely on hard tissue landmark to anesthetize mand teeth to midline, body of mand and inferior ramus, buccal tissues in front of mental foramen, lingual soft tissues and periosteum, anterior 2/3 of tongue and floor of oral cavity (parallel to occlusal plane, height of mucogingival junction, advance until level with distal surface of max second molar)

Question 33

Adjunctive strategies

Answer 33

Nerve to mylohyoid - deposit 3/4 on lingual surface of tooth in alveolar mucosa

PDL injection - insert into gingival sulcus 30 degrees towards tooth, advance until resistance is felt, inject for 15s with 0.2ml

Intraosseous injection - for mand infiltration, perforate cortical plate to LA periradicular medullary bone

Question 34

Adjunctive strategies

Answer 34

Nerve to mylohyoid - deposit 3/4 on lingual surface of tooth in alveolar mucosa

PDL injection - insert into gingival sulcus 30 degrees towards tooth, advance until resistance is felt, inject for 15s with 0.2ml

Intraosseous injection - for mand infiltration, perforate cortical plate to LA periradicular medullary bone

Intrapulpal injection

Different anesthetics - articaine (improved anesthetic effect, may become toxic or cause methemoglobinemia)

Question 35

LA complications

Answer 35

Fainting due to fear (give LA when lying down)
Interaction
Cross-infection (use disposable needle)
Allergy (esp esters, skin rashes or bronchospasm. May cause anaphylaxis)
CV collapse due to stress causing arrhythmia or fibrillation of heart
Failure to achieve anesthesia (often due to hot pulp or acute apical abscess, supplement with infil, sedative dressing, other injections)
Hematoma (aspiration!)
Trismus (hematoma in medial pterygoid, dont LA too fast and get positioning right)
Facial paralysis (Specifically IDN block, about 1h)
Needle fracture (dont bend needle)
Systemic toxicity (CNS disturbances like dizziness, tinnitus, irrational behavior, metal taste, seizures, coma, restlessness, tremors and convulsions, treat w benzos, get CV toxicity like systemic vasodilation, hypotension, arrhythmias later)