Local anesthetics

Question 1

structure of local anesthetics

Answer 1

lipophilic (binds to membrane)

amide or ester (intermediate binding area)

hydrophilic

Question 2

characteristics of amides

Answer 2

stable in solution

enzymatic degradation (liver)

no p-Aminobenzoic acid metabolite

Question 3

characteristics of esters

Answer 3

unstable in solution

metabolized in plama (cholinesterase enzymes)

p-aminobenzoic acid metabolite (allergic reactions)

Question 4

commonly used amides and esters

Answer 4

• amides
  
  • lidocaine
  • bupivacaine
  • mepivacaine
  • ropivacaine
  • EMLA
• esters
  
  • cocaine
  • benzocaine
  • procaine
  • tetracaine

Question 5

onset of local anesthetics depends on:

Answer 5

lipophilicity

pKa

concentration

dose + volume

proximity to nerve

type of nerve

Question 6

duration of local anesthetics depends on:

Answer 6

vascular effect

tissue blood flow

vasoconstrictor (epi)

dose

affinity to Na+ receptor

Question 7

MOA of local anesthetics

Answer 7

• Na channel blocker
• acts on neuron axon
• affects depolarization
• decreases conduction
• sensory and motor

Question 8

factors affecting action of local anesthetics

Answer 8

pH/pKa

proximity

dose

volume

spread

Question 9

signs of neurologic toxicity of local anesthetics

Answer 9

tremor

nervousness

seizures

CC/CNS ratio (want it to be low!)

Question 10

signs of CV toxicity of local anesthetics

Answer 10

bradycardia

sinus arrest

fibrillation

bupivicaine

Question 11

topical local anesthetics

Answer 11

• larynx
  
  • intubation in cats
• splash block
  
  • mucous membranes
• EMLA

Question 12

infiltration of local anesthetics

Answer 12

• injection at the surgical site
• blockage of nociceptive input
• dose is higher
• can cause edema

Question 13

ring block

Answer 13

• 3 sites, or just a ring around the limb
• harder technique, but much better for surgery and animal

Question 14

regional blocks

Answer 14

• venous catheter or needle towards paw
• turniquet applied to slow blood flow in and out (esp venous outflow)
  
  • no more than an hour, then slowly relieve the pressure
• whole paw goes number for longer
• 4 mg/kg lidocaine, don’t want it to go systemic!

Question 15

epidural

Answer 15

• grey matter retention

Question 16

femoral compartment block

Answer 16

• substitute epidural
• psoas major
• L4-L5
• technique
• less invasive than epidural

Question 17

sciatic block

Answer 17

• substitute epidural
• relevant anatomy
• landmarks
• technique
• clinical use

Question 18

brachial plexus block

Answer 18

• block of innervations of front limb
• C6-T2 spinal nerves
• C6, radial artery, tip of shoulder
• technique
• decrease anesthetic: better post-op, ortho cases