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What properties of local anesthetics determine the onset of action, potency, and duration of action?
- pKa determines the onset of action – the lower the pKa the more rapid the onset
- Lipid solubility determines the potency – permits anesthetic to penetrate the membrane more easily
- Protein binding is responsible for the duration of action. Duration also increased with vasoconstrictor which decreases blood flow and systemic absorption
- Amide LAs are metabolized in the Liver
What is the mechanism of action for local anesthetics?
Blockage of sodium channels by partitioning into 2 types, the charged acid (RNH+) and the uncharged basic form (RN), which penetrates the nerve membrane, ionizes and blocks the influx of sodium ions preventing depolarization (-70 mV → 40 mV)
What are some explanations for anesthetic failure?
- Hargreaves - 1) lower pH of inflamed tissue → reduces the amount of base form of anesthetic that penetrates the nerve membrane
- 2) Unsuccessful technique
- 3) Inflamed nerves have altered resting potentials and decreased excitability thresholds
- 4) TTX-R sodium channel which are resistant to LAs (increased expression in IP cases)
- 5) Apprehensive pts have decreased pain thresholds
- Fouad – 6 fold increase in TTX-resistant sodium channels in IP cases
Does accessory nerve innervation affect anesthesia?
- Frommer – mylohyoid nerve may supply accessory innervation
- Pogrel – cross innervation of Mand incisors
What are some supplemental anesthesia techniques and how do they work?
- PDL – IO anesthesia (Walton) – 92% effective
- Stabident / X-tip – IO anesthesia
- Intrapulpal – pressure anesthesia (Birchfield)
What are alternative injection techniques to the IAN block? Are they more successful?
- Gow-Gates & Vazirani-Akinosi
- Malmed – Gow-Gates is superior to IAN block
- Reader, Petrovic – failed to show either GG or V-A is better than IAN block
Compare the efficacy of different anesthetics?
Reader – NSD in 4% prilocaine, 3% mepivicaine & 2% lidocaine with IAN block
Is Articaine the solution?
- Reader – NSD between 4% articaine & 2% lidocaine with IAN block & IP
- Aritcaine did show increased success if given as a buccal infiltration injection following IAN block (88% vs 71% success rate)
- Haas – Articaine has a 5 fold higher incidence of paresthesias compared to lidocaine
Discuss Intraosseous anesthesia success and side effects?
- Reader – 67% had an increase in heart rate – ok with healthy pts; consider mepivicaine
- - Stabident with 2% lidocaine – 88% effective for IP
- - Stabident with 3% mepivicaine for IP– 80% successful x1 injection; 98% x2
What are the anesthetic and epinephrine concentrations in common anesthetics?
- 2% lidocaine w/ 1:100,000 epi = 36mg lido w/ .018mg epi
- 3% mepivacaine (Cabocaine, Polocaine) = 54mg mepivacaine
- 4% articaine w/ 1:100,000 epi = 72mg articaine w/ .018mg epi
- 0.5% bupivacaine (Marcaine) w/ 1:200,000 epi = 9mg bupivacaine w/ .009mg epi
What drug interactions are a concern with epinephrine?
- Tricyclic antidepressants – amitriptyline, doxepin
- Nonselective beta blockers – nadolol, propranolol
- Recreational drugs - cocaine
- Nonselective alpha adrenergic blockers – chropromazine, clozapine, haloperidol
- Digitalis - Digoxin
- Thyroid hormones – Levothyroxine
- MAO inhibitors
What is the max dosage of anesthetic?
- Moore – rule of 25 = 1 carp for every 25 pounds of pt weight
- Adults 4.4mg /kg
PDL injection reaches the pulpal nerve supply by entering the cancellous bone thru natural perforations in the socket wall and not by traveling down the length of the ligament à thus this method is a form of intraosseous anesthesia
Wu 2007 cold test and pulpal anesthesia?
cold test is reliable means for measuring pulpal anesthesia before access
Rosenberg, how does the pulp get anesthetized with intrapulpal anesthesia?
intrapulpal anesthesia works via pressure; can use saline and get same result
What did Walton say regarding the PDL injection?
PDL is IO injection and requires back-pressure; spreads thru cribiform plate; safe to periodontium & teeth; can’t be used to anesthetize single tooth, adjacent teeth are affected
What did Reader state regarding the PDL injection and Epi?
Epi better than no Epi; average pulp anesthesia is 20 min
What did Dr. Reader find out about the effects of IO injections?
Mean HR increase was 23-24 BPM, increase not significant in healthy patients; IANB only 25% effective in IP, IO w/ 3% mepivacaine is 80% effective, if use 2 carpules 3% mepivacaine then 98% success
What are the S/S initially of anesthetic overdose?
tinnitus, tremors, muscle twitching, convulsions, uticaria, erythema, intense itching, anaphylactic rxns, angioedema
What are the late findings of anesthetic overdose?
respiratory depression, lethargy, loss of consciousness
If a anesthetic has avasoconstrictor in it, it will have sulfites to perserve it, what kind of rxn can be seen with those who are allergic?
- Asthma-like rxns, tachypnea, wheezing,
- bronchospasm, dyspnea, tachycardia, palpitations, elevated BP, anxiety,
- nervousness, dizziness, weakness, severe flushing, tingling, rhinitis,
- conjunctivitis, nausea
What is the tx/managment for anesthetic overdose?
- (Little & Falace)
- Protect patient during convulsive phase,
- consider IV valium
- Monitor & record vitals
- Supportive therapy
- Supine position, O2, maintain BP, treat
- bradycardia w/ 0.4mg atropine IV, EMS
CPR if unconscious