Local Anesthesia Flashcards
what percentage of adults fear the dentist
21%
what percentage of the US population avoid dental care due to fear
10%
what are the top 10 fear evoking dental situations
- dentist laying out instruments
- sitting in the waiting room
- dentist squirts air into a cavity
- dentist laughs as he looks at your mouth
- dentist places a probe in a cavity
- dentist is giving you a shot
- dentist hold needle in front of you
- dentist tells you your teeth are bad
- dentist is drilling your tooth
- dentist is pulling your tooth
what are the desirable properties for local anesthesia
- no irritation to tissue
- no permanent alteration
- low systemic toxicity
- effective if injected into tissue or mucous membranes
- short onset
- long enough duration of action for procedure
- potent yet not harmfully concentrated
- not elicit allergic reaction
- readily undergo biotransformation
- sterile or capable of being sterilized by heat without deterioration
what are the ways to control pain and anxiety in dentistry
- local anesthesia
- oral sedation
- I.M. sedation
- NO sedation
- I.V. sedation
- general anesthesia
what does local anesthesia do
prevent generation and/or conduction of a nerve impulse
- decrease permeability of ion channels to Na
- nerve block by local anesthesia is a non depolarizing block
what is pain threshold
the least experience of pain which a subject can recognize
what is pain tolerance
the greatest level of pain which a subject is prepared to tolerate
what is a sensory neuron made of
- CNS
- trigeminal ganglion
- foramen
- nerve fiber
- pain receptors
what is the charge of ECF
more positively charged
what is the charge of the axoplasm
more negatively charged
describe nerve impulse transmission
- nerve axon membrane channel closed
- fiber stimulated, channel opens sodium enters
- cell depolarized and channel closes
- potassium exits down concentration and electrical gradients
- fiber repolarized, Na/K pump restores balance
where do local anesthetics work
nerve membrane
what is the specific receptor theory
local anesthesia bind to specific receptor on the Na channel
what are the different theories that try to explain how local anesthetics work
-acetylcholine theory
- calcium dependent
- surface charge
- membrane expansion but failed
what is the conduction rate of C fibers vs Alpha and delta fibers
C fiber is 1.2 m/sec
alpha and delta is 120 m/sec
what channel is in the node of ranvier
sodium channel
what is the basic structure of local anesthetics
- lipophilic group and hydrophilic group attached by amide or ester link
which fiber type is myelinated
alpha and delta fibers
to ensure effective anesthesia:
-2-3 nodes need to be blocked
- 8-10 mm length needed
what does myelin sheath do
insulates axons electrically and pharmacologically
what are the majority of active forms of local anesthetics
tertiary amine except prilocaine and hexylcaine
all local anesthetics are ____ except ____
amphipathic; benzocaine
which anesthetics have weak local anesthetic properties
antihistamine and anticholinergic
what are the two types of local anesthetics and describe both
-amide: resist hydrolysis , excrete unchanged in urine
-ester: readily hydrolyzed in aqueous solution
what are the ester anesthetics
-procaine
- propoxycaine
- tetracaine
- cocaine
- benzocaine
- dyclonine
what are the amide anesthetics
- lidocaine
- etidocaine
- mepivacaine
- bupicacaine
- prilocaine
- articaine
why is benzocaine a topical and not an injector
it doesnt have a hydrophilic group
how does local anesthesia dissociate
- they are weak basic compounds
- combine with acids to from local anesthetic salt (HCl)
what is the chemical formula for dissociation of local
RNH+ -> RN + H+
where RNH+ is cation and RN is uncharged molecule (free base)
what does the relative proportion of ionic form depend on
pKa
what is the henderson- hasselbalch equation
log base/acid = pH - pKa
when pH of a solution = pKa you have:
50/50 RN/RNH+
what are the two factors involved in the action of local anesthesia
-diffusion through nerve sheath
- binding at receptor site
what is the normal tissue pH of etidocaine and how much acid and base is there
7.4
- 25% free base (RN), 75% cation (RNH+)
if theres 1000 molecules available of etidocaine how many will diffuse through the membrane
250 lipophilic RN
once at intracellular level etidocaine will re- equilibrate into
70 RN and 180 RNH+
high pKa will translate to ____ because
slow onset because few base molecules available to diffuse
why is inflamed or infected tissue much more difficult to get adequate anesthesia to
because of lower pH or high H+
what does low pH equate to in local anesthesia
longer shelf life
what is the optimum pH for most anesthesia
5.5 to 7
what is sodium bisulfite added with
vasoconstrictor
what difference does adding a vasoconstrictor make
slower onset
most topical anesthesia is prepared in _______ compared to injectable local anesthesia
more concentraated
why is topical anesthesia more concentrated compared to injectable
poor buffering capacity of mucous membrane
what is the order of layers the anesthesia crosses in the nerve
endoneurium -> perineurium -> epineurium
which layer of the nerve is the greatest barrier of diffusion for the anesthesia and why
perineurium because it is thickest
where do mantle fibers innervate
proximal region of molars
what does the core fiber innervate
distal points such as incisors
what does complete conduction blockade require
volume and concentration
what happens to injected local anesthesia
- absorbed by nonneural tissue
- diluted by interstitial fluid
- removed by capillaries and lymphatic system
- for ester type: immediate enzymatic hydrolysis
how does lower pKa affect onset of action
faster
how does lipid solubility relate to potency
greater potency if more lipids
how does protein binding affect duration of anesthetic
increased protein binding increases duration
nerve membrane is ____ lipid
90%
nerve membrane is ____ protein
10%
how does the tissue recover from nerve block
- reverse of anesthetic induction pattern
- intraneural concentration exceeds extraneural concentration
what is meant by recurrence of immediate profound anesthesia
- reduced concentration at mantle fibers
- residual local + newly deposited supply = immediate profound anesthesia
when is it difficult to reestablish profound anesthesia
- surgical procedure outlasts effectiveness of med
- tachyphylaxis
what is tachyphylaxis
increased tolerance to frug after repeated administration
what are the factors that affect tachyphylaxis
- edema
- localized hemorrhage
- clot formation
- transudation
- hypernatremia
- decreased pH of the tissue
what are the 3 main physiochemical properties of local anesthetics
- lipid solubility
- pKa
- protein binding
when is pain tolerance the highest? lowest?
- highest: 8 am
- lowest: 4 pm
what does lipid solubility influence
potency
what does pKa influence
onset
what does protein binding influence
duration
