Exam 1 Flashcards
Lidocaine composition that we use
2% lidocaine with 1:100,000 epinephrine
Halflife: 1.6
Short duration anesthetic we use
3% mepivicaine without vasoconstrictor
Halflife: 1.9
Intermediate duration anesthetic we use
4% articaine with 1:100,000 epinephrine
Halflife: 0.5
Long duration anesthetic we use
0.5% bupivacaine with 1:200,000 epinephrine
Halflife: 3.5
Antioxidant used in anesthetics
(with vasoconstrictors only)
sodium metabisulfite
Preservative used in anesthetics
(multidose vials only)
methylparaben
pH adjusting agents
HCl, NaOH
pH is usually acidic (4-6) especially with vasoconstrictors
What gylcoprotein has a higher protein binding affinity for lidocaine?
Alpha1-acid Glycoprotein (AGP, AAG)
What conditions increase alpha1-acid glycoprotein?
uremia, jaundice, pregnancy, or HIV infection
but might not have any clinical significance in binding of lidocaine
Unbound Drug Tissue Distribution
Rapid uptake by lungs (1 minute)
Brain, heart, liver, kidneys (5 minutes)
Muscle (15 minutes)
Fat (1-2 hours)
Ester-type anesthetics metabolism and excretion
circulating plasma pseudocholinesterase, renal excretion
Amide-type metabolism and excretion
AND EXCEPTIONS
hepatic metabolism, renal excretion
Exceptions:
-prilocaine has significant extrahepatic metabolism
-articaine is partly metabolized by pseudocholinesterase
Effects of lidocaine on CNS:
General Effects
Sedation
Disinhibition
-But low doses act like excitation
Effects of lidocaine on CNS:
Low doses
anticonvulsant activity
mild relaxation/sedation
generalized analgesia
Effects of lidocaine on CNS:
Moderate doses
euphoria lightheadedness dysphoria slurred speech drowsiness sensory changes (blurred, double vision) twitching
Effects of lidocaine on CNS:
Moderate to high doses
disorientation
tremor
unconsciousness
seizures
Effects of lidocaine on CNS:
high doses
Coma
Respiratory arrest
Effects on vasculature (LOCAL)
Vasodilation at local injection site
direct inhibition of vascular smooth muscle tone
bupivacaine > lidocaine > mepivacaine
Effects on vasculature (SYSTEMIC)
Low concentrations - mild increase in peripheral vascular resistance
Moderate concentrations - central effects predominate
decreased heart rate, cardiac output, PVR
Higher concentrations - systemic vasodilation and decreased resistance
Do more lipophillic drugs have a higher rxn with CV effects or CNS?
more lipophilic drugs have proportionally greater cardiovascular than CNS effects
Cardiac effects
Higher concentrations decrease: conduction velocity automaticity myocardial contractility cardiac output blood pressure
Are systemic effects of local anesthetics overshadowed by vasoconstrictor effects?
yes
Presynaptic Reuptake and metabolism
Leakage out of vesicles into cytoplasm – an active equilibrium
Degradation by MAO within the neuron
Hepatic degradation
by COMT
Now thought to be a relatively minor pathwa
alpha1 receptor
Area, Action, clinical effect
Vascular system (excitatory) Action: Vasoconstriction Clinical effect: increase BP
Beta1
Area, Action, clinical effect
– Heart (and small intestine)
Action: Increased heart rate and force of contraction
Clinical effect: increase heart rate
Beta2
Area, Action, clinical effect
– Vascular, pulmonary systems (inhibitory)
Action: Vasodilation in skeletal muscle
Clinical effect: Decrease BP
Alpha 2
Only action
Action: Inhibits release of norepinephrine
(presynaptic feedback inhibition)
Why do we use a vasoconstrictor?
3 reasons
- Improve local retention of anesthetic
- enhance local anesthetic effect
- prolong duration - Provide local hemostasis for surgery
- (Reduce systemic toxicity)
Effects of vasoconstrictor on Heart
Heart - increase contractility, rate, output
BUT net decrease in efficiency
If you take vasoconstrictor with:
Alpha blockers
Alpha1 - Blocked
B1 - Increased Heart Rate
B2 - Decreased Blood Pressure
Effect: Hypotension and Tachycardia
If you take vasoconstrictor with: Beta blockers (NON-SELECTIVE)
Alpha1 – Increased Blood Pressure
B1 – Blocked
B2 – Blocked
Effect: Hypertension & Bradycardia
If you take vasoconstrictor with: Beta blockers (SELECTIVE)
Alpha1 – Increased Blood Pressure
B1 – Blocked
B2 – Decreased BP
Effect: None
If you take vasoconstrictor with:
Tricyclic Antidepressants
Block reuptake of norepinephrine & epinephrine
Exogenous epinephrine may produce exaggerated effects
If you take vasoconstrictor with:
MAO inhibitor
Inhibit monoamine oxidase
But epinephrine is also metabolized by COMT
If you take VC with:
d-Amphetamine
Stimulates CNS adrenergic system
May be potentiated by epinephrine
Cocaine and Vasoconstrictors
Stimulates NE release Inhibits NE reuptake Causes tachycardia, hypertension Increased cardiac oxygen demand Decreased efficiency Leads to dysrhythmias, ischemia Sensitizes patient to epinephrine! Defer elective dental care 24 hours
What is “Special Care?”
- stress reduction
- limit epinephrine use
- limited treatment
How to treat people with Stable vs Unstable Angina:
Stable: cautious with stress and epinephrine
Unstable: monitored setting
How to treat people with Myocardial Infarction:
- recent
- 6 months ago
- recent: cautious with stress and epinephrine
- 6 months ago (6-8 weeks in recent studies):
controlled: low risk
uncontrolled: cautious with stress and epi
How to treat people with Coronary Artery Bypass Surgery
- Recent
- > 3 months ago
Recent: caution with stress, epinephrine
More than 3 months ago: Variable, similar to MI
How to treat people with Arrthymia
SUPER DIFFICULT TO ASSESS: Need PCP/Cardiologist consultation
- Controlled: caution with epinephrine
- Refractory/Uncontrolled: treat in monitored setting
How to treat people with hypertension:
- controlled
- uncontrollable
- Controlled:
Consider drug interactions, monitor pressure
may need to reduce epinephrine use - Severe, untreated, uncontrollable
limit epinephrine use
consider monitored setting
How to treat people with Congestive Heart Failure
- controlled
- uncontrolled
- Controlled
Low risk - Uncontrolled, untreated
stress, time in chair are major issues
How to treat people with strokes
- variable presentation
May be low risk; watch BP
2.Variable risk for recurrence
monitor pressure
may need to reduce epinephrine
How to treat people with diabetes
- controlled
- uncontrolled
controlled: you’re good
uncontrolled: monitor for other diseases
How to treat people with hyperthyroidism
- controlled
- uncontrolled
Controlled: no problem Uncontrolled Hyperthyroidism: Recognize (see text), defer treatment avoid stress, epinephrine
Pheochromocytoma
rare tumor in medulla of adrenal gland that secretes cathecholamines and such: defer treatment, avoid stress and epinephrine
How to treat people with Coagulopathy
congenital or acquired
alter technique to avoid deep blocks
How to treat people with Methemoglobinemia:
no oxyhemoglobin cuz Fe3+ instead of Fe2+
avoid prilocaine
lidocaine may be a trigger but is lowest risk anesthetic
How to treat people with asthma:
no treatment necessary
How to treat people with COPD (Chronic Obstructive Pulmonary Disease )
Time in chair may be issue
How to treat people with liver disease:
unlikely to cause issue
How to treat people with renal disease
Unlikely to be an issue unless they have dialysis in which case treat the day after
How to treat people with pregnancy
limit care generally
local anesthetics are ok
Conditions that beckon you use amide esters:
Malignant Hyperthermia
no problem with amide anesthetics
Atypical Plasma Pseudocholinesterase
delayed metabolism of esters
amide anesthetics are not a problem
Issues with tricyclic antidepressants or MAO inhibitors?
No just monitor blood pressure
Issues with Beta Blockers
selective:
little concern
nonselective:
monitor pressure with epinephrine use
Possible allergies to local anesthetics : 1. Amide 2. Esters Preservatives/stabilizing agents 3. Parabens 4. Sulfites
Amide – very rare but possible
Esters – possible, but we aren’t injecting them any more
Preservatives/stabilizing agents
Parabens – we don’t use
Sulfites – possible (in epi.-containing anesthetics)
ADA criteria for dental Syringe (FOUR)
1- Should provide effective aspiration
2- Durable and withstand repeated sterilization
3- Inexpensive, light weight and simple to use
4- permit the use of wide variety of cartilages and needles of different manufacturers
1- Infiltration
1- Infiltration - local area where treatment will be
2- Field block
2- Field block - Local anesthetic is deposited toward larger nerve terminal branches
Treatment is done away from the site of local anesthetic injection
Maxillary injections administered above the apex of the tooth to be treated are properly referred to as field blocks not local infiltrations
- nerve block
3- Nerve block -Local anesthetic is deposited close to a main nerve trunk, usually at a site removed from the area of treatment (PSA, IANB, NPB)
A nerve fibers
A: Large, myelinated alpha (Aα), beta (Aβ), gamma (Aγ) motor, proprioception delta (A) sensory
B and C nerve fibers
B: Preganglionic autonomic (otherwise like A)
C: Small, unmyelinated
sensory, postganglionic autonomic
Sodium channel (how to activate and gates)
Gating
activation (m) gate
inactivation (h) gate
Initial depolarization opens activation gate
Rapid depolarization closes inactivation gate
Refractory Period of Na+ Channel
Channel must “reset” before reopening
determined by the time needed for the axon to repolarize
What is responsible for repolarization of axons?
Na+ channel inactivation is responsible for repolarization
Do K+ channels play a large role in conduction along axon?
K+ channels in between nodes play a very small role in conduction but is more important in unmyelinated
Where are Na+channels concentrated?
at nodes of Ranvier
Specific Receptor Theory
anesthetic agent receptor in channel
accessed from intracellular side
charged agents not effective unless nerve is stimulated (=phasic block)
uncharged agents not stimulation dependent
Membrane Interaction Theory
agent molecules associate with hydrophobic membrane
membrane is “disordered”
channel conformational changes are prevented
Anesthetic structure:
Aromatic (hydrophobic) group
Intermediate chain (ester or amide)
Amino (hydrophilic) group
Organic:Aqueous Distribution Constant: Q
reflects ability to penetrate hydrophobic tissue
correlates with duration (protein binding?)
Dissociation Constant: pKa
Proportion of ionized to un-ionized molecules
correlates with onset
In order of last to go and first to come back:
Sensations of anesthetics
dull pain warmth cold sharp pain touch pressure proprioception