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38 Cards in this Set
- Front
- Back
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General structure of Local Anesthetic Agent
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1. Hydrophilic Amino group (one end)
2. Intermediate chain. Either Ester or Amide. 3. Lipophilic Aromatic group (hydrophilic) (one end). |
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General mechanism of action for local anesthetics
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1. Enter nerves in uncharged form.
2. Activation = Become charged (pH change) 3. Block Na channels of all fiber types by binding to receptor on inner part of Na-channel. - Preferentially bind to activated channels. - Blockage = Time & Voltage-dependent 4. Inc threshold of excitation & action potential generation. Most effective in rapidly firing neurons (stimulated pain fibers). |
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What needs to be altered and why when using local anesthesia in infected tissues.
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Dose must be increased.
Infected tissue is Acidic. Local Anesthetics are Bases. LAs are charged in infected tissue = decreased penetrance. Higher dosages of LAs need to be administered to achieve anesthesia in infected tissues. |
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Order of nerve fiber blockade with Local Anesthetic Agents.
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Small > Large & Myelinated > Un;
1. Small Myelinated Fibers 2. Small unmyelinated fibers 3. Large myelinated fibers 4. Large unmyelinated fibers |
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Order of sensation loss with Local Anesthetic Agents.
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(Autonomic fibers)
1. Pain 2. Temperature 3. Touch 4. Pressure 5. Proprioception 6. Motor |
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What is the action of most Local Anesthesia on vessels?
& what is the exception to this? |
Vasodilation.
Vasoconstrictors must be added to administered LAs to maintain local concentrations equivalent with effective anesthesia. Cocaine. natural vasoconstrictor. |
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Clinical uses of local anesthetics
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Topical anesthesia : mucousa, denuded skin
Infiltration anesthesia = direct injection Regional anesthesia: specific nerves & their fields Spinal Anesthesia = intrathecal injection/infusion - epidural or subdural |
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Disadvantages to Spinal Anesthesia.
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Potential for:
Hypotension Respiratory Arrest (2* to hypotension in cerebral vasculature) Neurological complications, especially Headaches. |
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pKa & onset of action in Local Anesthetics
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LA's typical pKa range = 8-9.
pKa close to physiologic pH (7.4) will have a more rapid onset of action. |
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Which local anesthetic is the most potent vasodilator?
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Procaine, an ester anesthetic agent.
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Which group of local anesthetic agents are more likely to cause allergic reactions?
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Ester anesthetics are more likly to cause allergic rxns due to PABA (end result of their metabolism)
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What local anesthetic is a vasoconstrictor? & why?
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Cocaine.
Inhibits NE reuptake thereby allowing NE to continue to work and constrict vasxulature. |
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What are the adverse effects of local anesthetics on CNS & what settings would potentiate those adversities?
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High Doses
Depress inhibitory neurons = appears as stimulation. - restlessness, tremor, convulsions May be followed by Depression = Death due to Respiratory Depression |
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What are the adverse effects of local anesthetics on CVS & what settings would potentiate those adversities?
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High systemic concentration
- Decreased myocardial excitability, conduction rate & force of contraction. - Arteriolar dilation |
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What does hypersensitivity to Local Anesthetia look like?
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Allergic dermatitis
Asthmatic attack especially seen in Ester anesthetics. |
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How do you treat local anesthetia toxicity?
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Supportive treatment mainly.
- maintain ventilation - Oxygen Convulsion Tx: - IV diazepam - IV midazolam |
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Cocaine
- Action - Use - C/I |
Local Ester Anesthetia
Blocks NE & Dopamine Reuptake - Vasoconstriction & Strong potential for abuse 2x procaine potency Medium duration of action Administration - Topical only! (ENT settings). C/I: Ophthalmic use = corneal damage. Avoid use due to strong addictive/abuse potential |
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Procaine
- Use - Pharmacodynamics - Adverse Effects |
(Novocaine)
Ester Anesthetic (1st Synthetic) Base-line potency Short Duration of Action Adverse Eff: - Hypersensitivity potential - Ineffective Topically in safe doses. |
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Tetracaine
- Pharmacodynamics - Use |
Ester Anesthetic
16 x potency of Procaine Long duration of action Slow onset (low pKa) Topically active Wide use in spinal anesthesia |
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Lidocaine
- Action - Pharmacodynamics - Adverse Effects |
Most used.
Amide Anesthetic Anti-arrythmic (shortens refractory period & prevents re-entry arrythmias) Significant Vasodilation (add epinephrine) 4x potent to procaine Medium duration of action rapid onset (low pKa) Adverse Effects: - Cardiac effects (CoDeath) - Drowsy, Headache, Sedation |
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Mepivacaine
- use - Pharmacodynamics |
Amide Anesthetic
2x potency of Procaine Medium duration of action (Quick onset) |
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Prilocaine
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Amide Anesthetic
3x potency of Procaine Medium duration of action available without vasoconstrictor (use when conscern about epi cardio effects) Adv Eff: - May cause methemoglobinemia, esp in peds (due to metabolite, orthotoluidine) |
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Bupivacaine
- Uses - Pharmacodynamics |
Amide Anesthetic
Local Anesthesia --> Analgesia 16x potent than Procaine (4x than Lidocaine) Long duration of action - Advantage for long procedures |
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Articaine
- Use - Advantage |
Amide & Ester Anesthetic
Better able to diffuse therough soft tissue and bone. |
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Proparacaine
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Local anesthetic reserved for Ophthalmic use
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Pramoxine
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Local anesthetic reserved for anesthetizing skin & less-delicate mucous membranes (hemorrhoids, endoscopy, intubation, cystoscopy.
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Dyclonine
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Local anesthetic reserved for anesthetizing skin & less-delicate mucous membranes (hemorrhoids, endoscopy, intubation, cystoscopy.
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Benzocaine
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Local anesthetic with low water solubility. Can be applied directly to an open wouldn w/ producing high circulating levels.
Uses: Sunburn, Poison ivy, hemorrhoids |
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Eutectic Mixture of Local Anesthetics (EMLA)
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1:1 combo of Lidocaine & Prilocaine, in free base form (oil)
Apply topically 45-60 min before painful procedures: Bone marrow aspiration, IV catheter insertion, lumbar punctures, renal biopsies. |
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Why add Epinephrine to Local Anesthesia preps?
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Vasoconstriction.
- Decreases rate of absorption of anesthetic. - localizes anesthetic and action longer. - reduces systemic toxicity - reduces the blood loss and obscurence of the field for better visualization. |
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What disadvantages are there to vasoconstrictor additives in Local anesthesia preps?
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- Reduces bleeding, if you "knick" something you won't know till the vasoconstrictor wears off (when you've closed)
- Increased Cardiac Effects - Ischemia/Necrosis - NEVER use epi in areas of poor/limited blood supply (digits) |
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What is Sodium Bisulfite's role in Local Anesthetic preps?
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Sodium Bisulfite stabilizes/preserves epinephrine in the LA prep.
May be a source of allergy - Ask pt how they tolerate Red Wine to avoid this. |
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What drugs &/or drug classes will interact with a typical Local Anesthetic preparation?
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Alpha Adrenergic Antagonist
Tricyclic antidepressants Cimetidine Sulphonamides. |
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Interaction:
- Lidocaine + Epi - Alpha adrenergic antagonist |
Epi + A1 antagonist =
Potential Hypotensive reaction Epi unable to bind a1 will bind B-receptor = vasodilation |
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Interaction:
- Lidocaine + Epi - Tricyclic Antidepressants |
increased effects on the heart.
Arrhythmias Sudden death from ventricular fib |
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Name 5 Alpha Adrenergic Antagonists
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Prazosin
Tamsulosin Labetalol Carvedilol Phentolamine |
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Interaction:
- Lidocaine + Epi - Cimetidine |
Cimetidine (H2 blocker) inhibits drug metabolizing enzymes.
= Increased plasma concentration & likelihood of toxicity. |
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Interaction:
- Local Anesthetic + Epi - Sulphonamides |
PABA (metabolite of Ester Anesthetic) decreased antimicrobial effects of sulphonamides.
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