ORAL SURGERY Local Anesthesia Flashcards
___ is a drug that reversibly blocks the conduction of nerve impulses when applied locally in a concentration without toxic effects. if the concentration is sufficient, motor nerves can be blocked as well
local anesthetics
what is the concept of “critical length” in nerve blockades?
- complete anesthesia occurs when 3 consecutive nodes of ranvier are blocked (assuming myelinated)
- the blockade can be cumulative along the axon length, resulting in gradual reduction in conduction velocity that eventually leads to a complete blockade
T or F:
not all nerves are susceptible to blockade
false, all nerves are susceptible to blockade, regardless of their function
sensations disappear and reappear in a definite order. what is that order?
- pain
- temperature
- touch
- pressure
what is redistribution affected by?
- diffusion away from the site of action
- vascularity of the injection site
- protein binding characteristics of the local anesthetic that are directly related to lipid solubility
if the injection site has increased blood flow, what happens to the duration of action?
shorter
if the local anesthetic has increased protein binding characteristics, what happens to the duration of action?
increased lipid solubility, leading to increased duration of action
duration of action of local anesthetics is directly proportional to ___ and ___
protein binding and lipid solubility
what is the onset of action of a local anesthetic based on?
- pKa
- the lower the pKa (closer to physiologic pH), the faster the onset of action
what are the initial clinical signs and symptoms of mild to moderate local anesthetic toxicity?
talkativeness, apprehension, excitability, slurred speech, dizziness, and disorientation
what are the initial clinical signs and symptoms of severe local anesthetic toxicity?
seizures, respiratory depression, coma, and death
what are allergic responses to local anesthetics due to?
- esters (high incidence of 5% of the population)
- amides (low incidence, <1%)
- metabisulfite (low incidence)
- allergies prior to 1985 may have been due to methylparaben
what is metabisulfite?
- antioxidant in local anesthetics that protects the vasoconstrictor from oxidation
- present only in LA cartridges with a vasopressor (epinephrine or levonordefrin)
methomoglobinemia is essentially unique to which local anesthetic? what dose can cause methomoglobinemia?
- prilocaine
- excess of 600mg (for a 70 kg adult)
- lower dose applies in a patient with hereditary methomoglobinemia
- second most common anesthetic to cause this is articaine
T or F:
when used for inferior alveolar nerve blocks, some local anesthetics are superior to others in terms of efficacy
false, they are all have equal efficacy, there is no one local anesthetic that has been shown to be superior
how have local anesthetic manufacturers adjusted drugs in terms of potency and toxicity?
concentration has been adjusted so that toxicity of 1mL of drug “A” is equivalent to 1mL of drug “B”
for two drugs that reach the same therapeutic effect per volume, a drug in 1mg/mL is more/less potent than a drug in 2mg/mL
more
___ is the most potent local anesthetic packaged for dentistry, and ___ and ___ are the least potent
- bupivacaine
- prilocaine and articaine
what is the primary rationale for adding vasoconstrictors to local anesthetics?
increase duration of effect
what are the secondary rationales for adding vasoconstrictors to local anesthetics?
reduce systemic toxicity by decreasing the rate of systemic absorption of a given dose of LA and reduce bleeding by decreasing blood flow into the operative area
what are the drug interactions for local anesthetics and antidepressants?
- increased sensitivity to epinephrine
- antidepressants = tricyclic (amytriptyline, elavil) and newer atypical drugs (duloxetine, cymbalta)
what are the drug interactions for local anesthetics and nonspecific beta blockers?
- enhance peripheral alpha 1 adrenergic effects with beta 2 blockade (unopposed alpha)
- blockade decreases heart rate
- epinephrine increases blood pressure
- the net result is likely to be an increase in blood pressure without tachycardia
- nonspecific beta blockers = propranolol, inderal
in a normal, healthy patient, what is the maximum dose of epinephrine? what about for patients with cardiovascular compromise or pts taking tricyclic or atypical antidepressants or nonselective beta blockers?
- 200ug for the healthy pt
- limit to 40ug per appointment for compromised pts
what are the pregnancy class C drugs (increased risk)?
articaine, bupivacaine, mepivacaine, epinephrine
what are the pregnancy class B drugs (no risk)?
lidocaine, prilocaine
what is the safest local anesthetic for use in children if the safety is based on the number of mL that may be administered to a pediatric patient of a given size?
2% lidocaine w/1:100,000 epi
which local anesthetic is contraindicated in children?
bupivacaine (not approved for use in children under 12 years)
what is the pKa and max recommended dose of articaine 4%?
pKa 7.7, MRD 7mg/kg
what is the pKa and max total dose of bupivacaine 0.5%?
pKa 8.1, MTD 90mg
what is the pKa and max recommended dose of lidocaine 2%?
pKa 7.7, MRD 7mg/kg
what is the pKa and max recommended dose of mepivacaine 2%, 3%?
pKa 7.6, MRD 6.6mg/kg
what is the pKa and max recommended dose of prilocaine 4%?
pKa 7.8, MRD 8mg/kg
short needles average ___mm and long needles average ___mm
20mm, 32mm
what are the outside diameters of the most common gauged needles?
30 gauge averages 0.3mm
27 gauge averages 0.4mm
25 gauge averages 0.5mm
positive aspiration is directly correlated to ___
needle gauge
T or F:
larger gauge needles deflect more often
false
about 97% of needle breaks involved breakage of which gauge needle?
- 30 gauge
- larger gauge needles do not break as often
can patients tell the difference in feel between 25, 27, and 30 gauge needles?
no
what is the area of anesthesia for the posterior superior alveolar (PSA) nerve block?
from the maxillary third molar anteriorly to the maxillary first molar with the possible exception of the mesiobuccal aspect of the maxillary first molar
describe the technique (needle position) of the PSA block
- position the needle distal to the malar process
- at 45 degrees to the mesiodistal plane
- at 45 degrees to the buccolingual plane
- 15-16mm depth of penetration
- deposit 1mL of local anesthetic slowly after aspiration
what is the area of anesthesia for a true anterior superior alveolar (ASA) nerve block?
- from the midline of the maxilla to the mesiobuccal aspect of the maxillary first molar
- anesthetizes the ASA, MSA, inferior palpebral, lateral nasal, and superior labial nerves
describe the technique of the true ASA nerve block
- needle penetration is over the maxillary first premolar in the long axis of the tooth
- 15mm deep and lateral to or at the height of the buccal vestibule
- needle touches bone as an endpoint
- after aspiration, 0.9mL is injected slowly
- pressure is applied for 2 minutes
- first 4 steps describe the infraorbital nerve block (does not guarantee tooth anesthesia); the last step makes it a true ASA nerve block
what is the area of anesthesia for the greater palatine block?
on the palate from the canine distally to the posterior aspect of the hard palate and from the gingival margin to the midline
the greater palatine foramen is generally located where?
roughly halfway between the gingival margin and midline of the palate and approximately 5mm anterior to the junction of hard and soft palate
what is the technique for the greater palatine nerve block?
- topical anesthesia
- pressure anesthesia for at least 20 seconds
- angulation of the needle insertion is immaterial
- depth of penetration is to bone (about 5mm)
- inject 0.5mL after aspiration
what is the area of anesthesia for the nasopalatine nerve block?
palatal soft tissue from canine to canine, bilaterally (premaxilla)
what is the technique for the nasopalatine nerve block?
- topical anesthesia
- pressure anesthesia for at least 20 seconds
- needle tip at 45 degree angle to the palatal soft tissue; penetration is at the junction of the palate and incisive papilla
- endpoint is bone
- inject 0.5mL after aspiration
what is the area of anesthesia for the mental nerve block?
soft tissue on the buccal of the premolars anteriorly to the midline lip, chin, periosteum, and bone in the affected area
what is the technique for the mental/incisive nerve block?
- topical anesthesia
- insert needle in the depth of the buccal vestibule opposite the mandibular premolars
- 5mm depth of insertion
- deposit 0.9mL local anesthetic
- pressure for 2 minutes
- steps 1-4 are for the mental block, which is soft tissue only. the last step makes it an incisive nerve block and anesthetizes the teeth
what is the area of anesthesia for the inferior alveolar nerve block?
pulps and buccal soft tissues of the mandibular teeth (except the area innervated by the buccal nerve), lip, chin, periosteum, and bone in the affected area
what is the anatomic target for the traditional (halstead) IA block?
- approach from contralateral premolars
- 1cm above the mandibular occlusal plane and parallel to it
- with a needle endpoint 50% of the mesiodistal length of the ramus, distally
what is the anatomic target for the higher mandibular block?
- approach from the contralateral premolars
- 1.5cm above the mandibular occlusal plane and parallel to it
- with a needle endpoint of 60% of the mesiodistal length of the ramus, distally
what is the technique for the IA nerve block (works for either traditional or higher targets)?
- advance a 25 gauge log needle until you hit bone (required), withdraw 1mm and aspirate
- inject 1.5mL of LA over 2 minutes
- withdraw the needle halfway (approx 10-15mm) and aspirate
- slowly inject the lingual nerve
- save a few drops of anesthetic for the long buccal nerve if needed
what nerves does the vazirani akinosi technique block?
inferior alveolar, lingual, long buccal
the vazirani akinosi technique is useful for treating which patients?
uncooperative children and patients with trismus
what is the technique for the vazirani akinosi block?
- long needle is inserted parallel to the maxillary occlusal plane at the level of the maxillary buccal vestibule
- depth of penetration is approx 1/2 the mesiodistal length of the ramus (about 25mm in adults, less in children)
- this endpoint is just superior to the lingula
- the injection is performed blindly because no bony endpoint exists
- in adult patients, a rule of thumb is that at the depth of needle penetration, the hub of the needle should be between the maxillary first and second molars
the original gow gates technique involved only ___ landmarks
extraoral
what nerves does the gow gates block anesthetize?
IA, lingual, auriculotemporal, mylohyoid, and long buccal (75% of the time)
what is the technique for the gow gates block?
- beginning from the contralateral canine, the needle is positioned so that a puncture point is made approx at the location of the distobuccal cusp of the maxillary second molar
- needle is inserted to a depth of 25-30mm until bone is contacted (required), then withdraw slightly and inject entire cartridge after aspiration
what is the pre-insertion technique for the gow gates block?
- have the patient open their mouth as widely as possible to rotate and translate the condyle forward
- the condyle is palpated with the fingers of the nondominant hand while the cheek is retracted with the thumb
which injection is unique among intraoral injections because the operator does not attempt to get as close as possible to the nerve to be anesthetized?
- gow gates
- the needle tip should be approximately 1cm directly superior to the nerve, in the superior aspect of the pterygomandibular space
