Local Anesthetics

Question 1

Name the ester local anesthetics.

Answer 1

Cocaine, procaine, benzocaine

Question 2

Name the amide local anesthetics.

Answer 2

Lidocaine, mepivicaine, bupivicaine, etidocaine, prilocaine, ropivicaine, dibucaine
names all have 2+ i’s in them

Question 3

What is the mechanism of action of both the ester and amide local anesthetics?

Answer 3

• Nonionized form crosses axonal membrane

- Ionized form (active form) blocks intracellular portion of inactive (refractory) voltage-gated sodium channel

Question 4

What are some side effects of the local anesthetics?

Answer 4

• Local: transient neurologic symptoms (basically, really bad pain) and neuronal injury
• Systemic: methemoglobinemia (more with benzocaine and prilocaine)

Question 5

Where are the amide local anesthetics metabolized and how are they cleared?

Answer 5

metabolized-liver (hepatic amidases)

cleared-kidney

Question 6

Which class is more likely to cause an allergic reaction and why?

Answer 6

• the ester local anesthetics because they contain PABA derivatives (Cocaine, procaine, benzocaine)
• *Used less frequently and have shorter duration of effect**

Question 7

What enzymes metabolize the ester local anesthetics? (Cocaine, procaine, benzocaine)

Answer 7

plasma esterases

Question 8

What are the “ideal properties” of the local anesthetics?

Answer 8

• fast onset
• minimal absorption
• minimal distribution
• predictable and reversible action
• large margin of safety

Question 9

<p>

| How does pKa play into the effects of local anesthetics?</p>

Answer 9

<p>

| the higher the pKa, less is available to diffuse across membranes and therefore onset is slower</p>

Question 10

What does the onset of the block depend on?

Answer 10

• degree of myelination (myelinated>unmyelinated)
• firing frequency (only blocks in refractory)
• size of nerve fiber (smaller> bigger)

Question 11

What determines the absorption of local anesthetics?

Answer 11

• site of injection
• presence of vasoconstrictors (delays absorption–>longer duration of action)
• local anesthetic agent

Question 12

What are the 4 ways to administer a local anesthetic?

Answer 12

topical
infiltration
regional
spinal/epidural

Question 13

What is infiltration?

Answer 13

injection of local anesthetic directly into tissue without consideration of course of cutaneous nerves

Question 14

What is regional use of local anesthetic?

Answer 14

injection of local anesthetic around individual nerves or nerve plexus
can also block somatic motor nerves

Question 15

What is a spinal?

Answer 15

injection of lower dose of local anesthetic under the dura with a faster onset than epidural

Question 16

What is an epidural?

Answer 16

injection of a bigger dose of local anesthetic, above the dura with a slow controlled onset

Question 17

What is an intravenous regional anesthesia block (biers block)?

Answer 17

uses vasculature to bring the local anesthetic to nerve trunks and endings