ORAL SURGERY Local Anesthesia Flashcards
(61 cards)
___ 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
