Local Anesthetics Flashcards
Rank the sensitivity of each nerve fiber type to the physiologic effects of local anesthetics: A alpha fibers, A delta fibers, B fibers, C fibers
- B fibers
- C fibers
- A delta (smaller diameter)
- A alpha (larger diameter)
The primary mechanism of action for local anesthetic blockade is:
voltage-gated sodium channels
What subunit of the voltage-gated sodium channels do local anesthetics reversibly bind to?
Alpha subunit
Saltatory conduction does NOT occur in:
C fibers (they lack myelination)
What part of a local anesthetic determines allergic potential?
Intermediate chain
What part of a local anesthetic determines lipophilicity?
Benzene ring (determines class- amide or ester)
What part of a local anesthetic makes it a weak base?
Tertiary amine
Local anesthetic potency best correlates with:
lipid solubility
Local anesthetic onset of action best correlates with:
pKa
Local anesthetic duration of action best correlates with:
protein binding
What is the definition of pKa?
the pH where 50% of a drug exists as the uncharged base (unionized) and 50% of the drug exists as the conjugate acid (ionized)
Rank the following local anesthetics according to their degrees of ionization at physiologic pH: lidocaine, tetracaine, bupivicaine, chloroprocaine
- Chloroprocaine (most ionized)
- Tetracaine
- Bupivicaine
- Lidocaine (least ionized)
What is the pKa of Lidocaine?
7.8
What is the pKa of Bupivicaine?
8.1
What is the pKa of Tetracaine?
8.4
What is the pKa of Chloroprocaine?
8.7-9.1
Which local anesthetic is unionized at physiologic pH?
Benzocaine (pKa 3.5); for all other LA, the charged species is required to produce the anesthetic effect
Local anesthetics are ___ that are ___ at physiologic pH. (with the exception of benzocaine)
weak bases, ionized (charged)
What is a side effect of benzocaine administration?
Metheglobinemia
What is subarachnoid chloroprocaine negatively associated with?
Neurotoxicity (Chloro is not used for spinals- its preservative bisulfite might be the cause of the toxicity)
Which local anesthetic is least protein bound in the plasma?
Chloroprocaine
Rank the speed of local anesthetic uptake after injection for the following sites: intercostal, caudal, epidural, interpleural, brachial plexus, subcutaneous, sciatic, femoral
- Interpleural
- Intercostal
- Caudal
- Epidural
- Brachial plexus
- Femoral
- Sciatic
- Subcutaneous
What is the initial bolus dose of 20% lipid emulsion therapy for a patient suffering from LAST?
1.5 mL/kg (lean body mass) over 1 minute followed by an infusion of 0.25 mL/kg/min.
What factors increase the the risk of local anesthetic toxicity?
hypercarbia/acidosis, local anesthetic potency, hyperkalemia
What metabolite of ester-type local anesthetics is MOST likely to cause a type-1 hypersensitivity reaction?
Para-aminobenzoic acid
What is the makeup of 5% EMLA cream?
50/50 combo of 2.5% Lidocaine and 2.5% Prilocaine
How long does is take for EMLA cream to produce analgesia?
1 hr; achieves max effect in 2-3 hrs
