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JH Local - general

B Miller pg 123-131

QuestionAnswer
Local anesthetics exert their electrophysiologic effects by... blocking sodium ion conductance by decreasing the rate of depolarization, preventing achievement of threshold potential. (they do not alter resting transmembrane potential), (the influx of sodium ions through voltage-gated sodium ion channels is reduced).
The two major classes of local anesthetics are... Amino-esters (Procaine, Tetracaine, Chloroprocaine, Cocaine) and Amino-amides (Lidocaine, Mepivacaine, Prilocaine, Bupivacaine, Ropivacaine, Etidocaine)
The amide bond of amino-ester local anesthetics confers _____ and avoids ____ greater stability and avoids allergic reactions associated with ester anesthetics (which result from sensitivity to cleaved aromatic acid).
State the Henderson-Hasselbalch equation. pKa = pH - log [base]/[conjugate acid]
Why is the H-H equation important with regards to local anesthetics? The H-H equation expresses a compounds tendency to be chanrged or uncharged at a given pH. The lower the pKa, the greater percent of unionized fraction at a given pH.
Why is bicarb added to local anesthetics? Increases the pH which increases the unionized fraction (more lipid soluble) hastening the onset of anesthesia.
Rate Amino-ester local anesthetics in term of incresing potency. (lipid solubility generally correlates with local anesthetic potency and duration of action and inversely with onset of local anesthetic effect). Procaine (pKa 8.9, potency 1), Chloroprocaine (pKa 8.7, potency 2), Tetracaine (pKa 8.5, potency 8)
Rate Amino-amide local anesthetics in terms of potency. lidocaine (pKa 7.9, potency 1), Mepivacaine (pKa 7.6 potency 1), Prilocaine, (pKa 7.9, potency 2), Bupivacaine and Levobupivacaine (pKa 8.1, potency 17), Ropivacaine (pKa 8.1, potency 6)
One local anesthetic that only exists in uncharged for and is therefore not affected by pH is... Benzocaine
________ can be added to local anesthetic to decrease possibiliy of systemic toxicity and increase duration of action. epinephrine, usually 5 micrograms/mL
Epinephrine additions to local anesthetics should be avoided with _____ Peripheral nerve blocks in areas that lack collateral blood flow (digital blocks)
Systemic absorption of local anesthetic is greatest after injection of ________ and ______. Intercostal nerve block and caudal anesthesia. Intermediate is epidural anesthesia and least is brachial plexus blocks.
Max dose for infiltration of lidocaine and mepivacaine... 300 mg
Max dose for infiltration of bupivacaine 150 mg
Max dose for infiltration of Ropivacaine 200 mg
central nervous system toxicity of local anesthetic results in... tingling, vertigo, slurred speech, tonic-clonic seizures.
Cardiac toxicity is a result of _______ . ______ local anesthetic have increased cardiac toxicity. blocking cardiac sodium ion channels resulting in prolonged PR interval and widened QRS. Bupivacaine has greater cardiac toxicity.
Amino-ester local anesthetics produce metabolites related to _______, which is more likely to evoke allergic reactions when compared to amino-amides. PABA (para-aminobenzoic acid). Allergic reactions are rare.
Created by: anesthesia
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