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
In normal tissue, which property of drug has greatest effect on speed of onset?
b. Protein binding
c. Intrinsic vasoconstrictor activity
Which of the following is responsible for duration of action of LA?
c. Molecular Weight (MW)
d. Tissue protein binding
e. Volume injected
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
Which has longest elimination half-time?
Para-aminobenzoic acid (PABA) is a metabolite of?
Which local anesthetic undergoes least hepatic clearance?
Benzocaine has all of following properties except
a. Weak alkaline
b. Used only topically
c. Metabolized by esterase in blood
d. Formation of methemoglobin
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
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
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
Plasma concentration of equal doses of LA highest at site of admin at
a. Axillary brachial plexus
d. Lumbar epidural
Refractory cardiac arrest most likely after rapid unintentional injection of which of following?
ASRA guidelines for treatment of LAST and cardiac arrhythmias include use of intralipid and avoidance of all of the following drugs except:
b. Beta blockers
c. Calcium channel blockers
d. Low dose epi (<= 1mcg/kg)
Which of following is sign of lidocaine toxicity from a high blood level?
d. Tonic clonic seizures
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
TNS after spinal anesthesia associated w/ each of following except:
b. Lithotomy position
c. Ambulatory anesthesia
d. Concentration of local anesthetic injected
TNS most commonly seen after spinal injection of which local anesthetic?
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