Episode 180: Keywords part 12 with Gillian Isaac: Local Anesthetics

In this 180th episode I welcome back Dr. Gillian Isaac for another ABA keyword episode. We review local anesthetics.

Also check out Episode 41 for an in-depth episode on local anesthetics

CORRECTION: At 28:58 I state that hyperventilation increases the seizure threshold. This is incorrect, it DECREASES the seizure threshold.

Reference: Barash Clinical Anesthesia 8th edition: Chapter on Local Anesthetics
Outline by Brian Park, MD

Local anesthetics block nerve conduction by?
a. Closing calcium channels
b. Decreasing intracellular sodium concentration
c. Decreasing K conductance
d. Causing extrusion of intracellular K
e. Inhibiting cellular influx of sodium

Discussion (4:44)

In normal tissue, which property of drug has greatest effect on speed of onset?
a. Amide
b. Protein binding
c. Intrinsic vasoconstrictor activity
d. pKa
e. potency

Discussion (5:50)

Which of the following is responsible for duration of action of LA?
a. Concentration
b. Metabolism
c. Molecular Weight (MW)
d. Tissue protein binding
e. Volume injected

Discussion (7:29)

Which of following characteristics associated w/ longer duration of action?
a. High degree of lipid solubility
b. High degree of protein binding
c. High MW
d. High pKa
e. Presence of ester linkage

Discussion (8:07)

Which has longest elimination half-time?
a. Bupivacaine
b. Lidocaine
c. Mepivacaine
d. Ropivacaine

Discussion (8:55)

Para-aminobenzoic acid (PABA) is a metabolite of?
a. Mepivacaine
b. Ropivacaine
c. Bupivacaine
d. Procaine

Discussion (8:54)

Which local anesthetic undergoes least hepatic clearance?
a. Chloroprocaine
b. Bupivacaine
c. Ropivacaine
d. Lidocaine

Discussion (11:27)

Benzocaine has all of following properties except
a. Weak alkaline
b. Used only topically
c. Metabolized by esterase in blood
d. Formation of methemoglobin

Discussion (12:52)

Which of following statement concerning PK is true:
a. ↓ MW ~ ↓ incidence of allergic reaction
b. ↓ protein bind ~ ↓ systemic toxicity
c. ↑ ionization ~ ↑ placental transfer
d. ↓ lipid sol ~ faster onset
e. Presence of ester linkage ~ ↑ duration of action

Discussion (14:41)

70 kg pt c/o pain of thigh abscess, which has been infiltrated w/ 30 mL of 1% lidocaine and 1:200,000 epi. Effect of LA ineffective most likely bc:
a. Acidosis at site of injection
b. Epi-induced limitation of duration
c. Insufficient dose
d. Low ionization of lidocaine
e. Protein binding ligand

Discussion (17:38)

Which of following statements concerning intercostal blocks and postop pain is true?
a. Block at mid-axillary line provides analgesia to anterior and lateral ab walls
b. Blood levels of LA higher than axillary block
c. Intervascular injection unlikely
d. Loss of resistance insures proper needle placement
e. Paravertebral spread prevented by adding epi to solution

Discussion (20:43)

Plasma concentration of equal doses of LA highest at site of admin at
a. Axillary brachial plexus
b. Caudal
c. Intercostal
d. Lumbar epidural
e. Subcutaneous

Discussion (21:36)

Refractory cardiac arrest most likely after rapid unintentional injection of which of following?
a. Lidocaine
b. Bupivacaine
c. Ropivacaine
d. Chloroprocaine

Discussion (22:41)

ASRA guidelines for treatment of LAST and cardiac arrhythmias include use of intralipid and avoidance of all of the following drugs except:
a. Vasopressin
b. Beta blockers
c. Calcium channel blockers
d. Low dose epi (<= 1mcg/kg)

Discussion (23:29)

Which of following is sign of lidocaine toxicity from a high blood level?
a. Shivering
b. Nystagmus
c. Lightheadedness
d. Tonic clonic seizures

Discussion (26:40)

18 M has seizures during placement of interscalene brachial plexus block using 0.5% bupivacaine. Anesthesiologist begins to hyperventilate w/ 100% O2. Rationale for this therapy include all of following except?
a. Therapy helps prevent hypoxia
b. Hyperventilation decrease blood flow and delivery of LA to brain
c. Hyperventilation elevates seizure threshold
d. Hyperventilation induce LA to ionized form

Discussion (28:11)

TNS after spinal anesthesia associated w/ each of following except:
a. Lidocaine
b. Lithotomy position
c. Ambulatory anesthesia
d. Concentration of local anesthetic injected

Discussion (30:28)

TNS most commonly seen after spinal injection of which local anesthetic?
a. Lidocaine
b. Bupivacaine
c. Prilocaine
d. Tetracaine

Discussion (31:09)

Prilocaine not rec for OB anesthesia because:
a. Cause met-Hb
b. Very short DOA
c. Not metabolized by newborn
d. Most toxic of local amides
e. Produce longer motor than sensory block

Discussion (32:32)


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