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pharmacology of local anesthesia (amide based (lidocaine (2% plain =…
pharmacology of local anesthesia
onset of anesthesia
dependent upon anesthetic agent
concentration
diffusion to site
dependent on overall diameter of nerve bundle; amount of myelin present
central core theory: central fibers anesthetized last
critical length = 3 nodes minimum
lipid solubility
protein binding to receptor site
technique
block
longer duration, slower onset
IA = 1 cartridge or more; 2/3 for kids
infiltration
slower duration, faster onset
works well on children
good hemostasis
disadvantages: multiple injections for multiple teeth
1/2 - 3/4 cartridge; 1/3 for kids
vasoconstrictor presence (not concentration)
amide based
lidocaine
2% plain = pulpal anesthesia for 5-10 min; soft tissue for 1-2 hours
2% with 1:100,000 or 1:50,000 epi: pulpal anesthesia for 1-2 hours; soft tissue for 3-5 hours
mepivacaine
3% plain: pulpal anesthesia for 20-40 min; soft tissue for 2-3 hours
2% with 1:20,000 levonordefrin: pulpal for 1-1.5 hours; soft tissue for 3-5 hours
prilocaine
4% plain: pulpal 40-60 min if block; soft tissue for 2-3 hours
4% with 1:200,000 epi: pulpal for 1-1.5 hours; soft tissue for 3-8 hours
difficult to anesthetize patients
articaine
4% with 1:100,000 or 1:200,000 epi: pulp for 1-1.5 hours; soft tissue for 2-4 hours
difficult to anesthetize patients
bupivacaine
0.5% with 1:200,000 epi; long acting by block injection only; pulpal for 1.5-4 hours; soft tissue for 5-12 hours
long procedures (more than 2 hours)
true allergy = rare
inject BH+ as active form (water soluble)
dissociation to basic, unionized form B
diffuses across nerve membrane (hydrophobic)
re-association with H+
binds to nerve receptors
reasons for anesthetic failures
anatomical/physiological variations
technical errors of administration
patient anxiety
inflammation and infection
increased tissue acidity
less buffering
less anesthetic solution can enter into the nerve due to change in dissociation equilibrium
give block away from site of any local inflammation or infection
articaine works well in infected environment
defective/expired solutions
ester based
high incidence of allergic reaction
frequent cross-reactivity
no longer available in US in dental cartridges
adverse reactions
psychogenic reactions
syncope
76% of medical emergencies in dental offices related to stress/axiety
to avoid syncope, give injections with patients lying supine, then slow sit the patient upright
allergic reactions
get full history
most common reason for allergy = sodium or potassium metabisulfite as preserving agent in anesthesia with vasoconstrictors
4% solutions should not be used for blocks due to risks of paresthesia
theories of causes of paresthesia
direct contact of needle with nerve
injury of direct contact of anesthetic solution with nerve
combination of higher doses and mechanical insult
dosage: dependent on weight and max dose depending on the type of anesthetic
max dosage for children = 2.0 mg/lb for all anesthetics
half life = potential toxicity; not related to anesthetic duration
small amounts given over time provide better duration and are safer than large amounts given quickly
absolute contraindications of vasoconstrictors: unstable angina, myocardial infarction within 6 months, refractory arrhythmias, untreated or uncontrolled hypertension, untreated or uncontrolled congestive heart disease, uncontrolled diabetes
metabolism
amide agents primarily biotransformed in liver by P-450 cytochrome enzymes
articaine begins biotransformation in bloodstream so good for patients with impaired liver function
3 strikes rule: 3 attempts, then stop