Question | Answer |
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. |