Local Anesthetics

Question 1

Benzocaine

Procaine

Answer 1

Cat: Short acting ester LA (benzocaine = topical, procaine = infiltrate, epidural)
MOA: Blocks activated/inactivated Na channels
Adverse: allergy to PABA, anxiety, convulsions (GABA block - tx w/diazepam), CV collapse

Question 2

Cocaine

Answer 2

Cat: short acting ester for nose/throat
MOA: block activated/inactivated Na channels, use dependent
SE: PABA allergy, anxiety, convulsions (GABA block - tx w/ diazepam), inc HR/contraction, VFib, hypertension
Beware of drug abuse

Question 3

Lidocaine

Ropivacaine

Answer 3

Cat: long acting amide LA
MOA: block activated and inactivated Na channels, use dependent
SE: anxiety, convulsions d/t GABA, CV collapse (bradycardia, hypotension)

Question 4

Which LA has reduced affinity for cardiac sodium channels and is therefore associated with less cardiac toxicity?

Answer 4

S-isomer of ropivacaine

Question 5

Locations of use of lidocaine vs ropivacaine

Answer 5

Lidocaine: infiltration, Bier block, peripheral, epidural, spinal
Ropivacaine: peripheral

Question 6

Epinephrine

Answer 6

Reduces systemic absorp of local anesthetics via vasoconstriction via alpha 1 adrenergic activation
SE: localized tissue necrosis
Increases LA action by 50%

Question 7

Clonidine

Answer 7

Used with LAs for epidural and spinal admin to further reduce pain transmission
MOA: prevents NT release at C and Ad fibers via presynaptic alpha 2

Question 8

Diazepam

Answer 8

Treat convulsions d/t systemic absorption of LA into CNS by activating GABA receptors in CNS

Question 9

3 characteristics that determine level of lipophilic

Answer 9

1. # of hydrocarbon chains and length
2. Length of intermediate connecting chain
3. # /length of aromatic ring hydrocarbons

Question 10

A delta fibers

Answer 10

Fast pain
Glutamate to NMDA
Neospinthalmic neurons
Myelinated

Question 11

C fibers

Answer 11

Second pain
Substance P to P receptors
Paleospinothalmic neurons

Question 12

Esters

Answer 12

One “i”
Short duration of action
Metab by plasma/live pseudocholinesterases
Allergies: PABA derivatives

Question 13

Amides

Answer 13

Two Is
Longer duration of action
Metab: liver p450

Question 14

Why don’t local anesthetics work well in infected tissue?

Answer 14

Lower pH means that the LA is more charged, leaving it unable to cross the cell membrane leading to decreased potency and longer onset time

Question 15

Fiber types most susceptible to LA

Answer 15

Small diameter
Myelinated
Firing a lot
Exterior fibers

Question 16

Topical anesthesia

Answer 16

ENT procedures - directly to surface

Ex. Benzocaine or cocaine

Question 17

Infiltration anesthesia

Answer 17

Injection into skin, subcut, or mucous membrane

Ex. Procaine or lidocaine

Question 18

Bier block

Answer 18

Regional anesthesia via injection and impeding of venous flow with a tourniquet < 1 hr
Ex. Lidocaine

Question 19

Peripheral nerve block

Answer 19

Around nerve or plexus for regional anesthesia

Ex. Lidocaine or ropivacaine

Question 20

Epidural and spinal anesthesia

Answer 20

Epidural doesn’t puncture dura
Spinal does puncture dura
Procaine and lidocaine

Question 21

Greatest risk for system toxicity

Answer 21

Areas of high vascularization
Intercostal > caudal > epidural

Low: brachial plexus, sciatic nerve

Question 22

Low systemic absorption of LA effects

Answer 22

Disruption of sensory perception

Question 23

High systemic absorption of LA effects

Answer 23

Brain: confusion, tremor, convulsions
CV: dec contractility, bradycardia, vasodilation, hypotension

Question 24

Direct injection of LA into vasculature causes…

Answer 24

Temporary blindness
Aphasia
Hemiparesis
Convulsions
Coma
Cardiac arrest

Question 25

What can help reduce cardiac and neurotoxicities from direct injection

Answer 25

IV lipid emulsions