L5: Regional Blocks (Garcia)

Question 1

pH effect on local anesthetic efficacy

Answer 1

Lower pH (more acidic) –> works less, but has more in ionized form

Question 2

Toxic effects of local anesthetics like lidocaine

Answer 2

Neurotoxic effects (seizure, twitching, agitation, etc.) followed by CV effects (bradycardia, sinus arrest, fibrillation)

Question 3

Lipid rescue for cardiac toxicity due to local anesthetic overdose

Answer 3

“Intralipid”
-give bolus IV
(-adverse effects: cyanosis, hyperlipemia, hepatomegaly, dyspnea, sepsis, etc.)

Question 4

MOA of bupivacaine

Answer 4

Binds to Na channels

• hard to reverse
• can still reverse w/ intralipid

Question 5

Ring block for paw

Answer 5

Dorsal: block radial n.
Ventral: block median and ulnar nn.

Block just above carpal pad (this is where bulk of nerves are before they branch)

Question 6

Bier block

Answer 6

• Vascular block
• can only use lidocaine bc this local anesthetic has least CV effects
• insert catheter close to carpus pointing down leg
• squeeze blood away from the limb, then place tourniquet to minimize dilution of drug
• should see vasculature blow up when you inject
• should numb whole paw

Question 7

Local anesthetics more effective if administered at a healthy spot

Answer 7

Can’t effectively locally block a heavily infected site

Question 8

Chars. Of amides

Answer 8

• stable in solution
• enzymatic degradation (liver)
• No p-aminobenzic acid metabolite

Question 9

Chars. Of esters

Answer 9

• unstable in solution
• metabolized in plasma (cholinesterase enzymes)
• p-Aminobenzoic acid metabolite (causes allergic rxns)

Question 10

Common amide drugs

Answer 10

Lidocaine
Bupivacaine
Mepivacaine
Ropivacaine
EMLA

Question 11

Commonly used ester drugs

Answer 11

Cocaine
Benzocaine
Procaine
Tetracaine

Question 12

Onset of local anesthetics dependent on:

Answer 12

-lipophilicity
-pKa
-concentration
-dose
-volume
Proximity to nerve
-type of nerve

Question 13

Duration of local anesthetic dependent on:

Answer 13

• vascular effect
• tissue blood flow
• vasoconstrictor
• dose
• affinity to Na receptor
• lipophilicity

Question 14

MOA of local anesthetics

Answer 14

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

Question 15

Factors affecting action of local anesthetics

Answer 15

• pH/pKa
• proximity
• dose
• volume
• spread

Question 16

Alpha nerve fibers

Answer 16

• efferent to muscles

- motor

Question 17

Beta nerve fibers

Answer 17

• afferent from skin and joints

- tactile, proprioception

Question 18

Gamma nerve fibers

Answer 18

• efferent to muscle spindles
• fx: muscle tone
• very susceptible to local anesthetic block

Question 19

Delta nerve fibers

Answer 19

• afferent sensory nerves
• fx: pain, cold, touch
• goo susceptibility to local block

Question 20

Toxic effects of local anesthetics

Answer 20

Neurologic: tremor, nervousness, seizure, CC/CNS ratio

CV: brady, sinus arrest, fibrillation

bupivacaine assoc. with more CV effects

Question 21

Can only use which anesthetic with Bier block?

Answer 21

Lidocaine (least CV toxic)

Question 22

Infraorbital block

Answer 22

Inject halfway between medial canthus and canine tooth

Question 23

Lumbosacral plexus location

Answer 23

L3-S3 (relevant anatomy/sciatic n. At L6-S2)

Question 24

Where does sciatic nerve run?

Answer 24

B/w greater trochanter and ischiatic tuberosity (cranial third space)

Question 25

Sciatic nerve contains which 2 nerves?

Answer 25

Common peroneal

Tibial

Question 26

Location of femoral n. Block

Answer 26

• Just lateral to femoral a. -inject cranially and superficially into the skin
• nerve located cranial to a.

Question 27

Location of brachial plexus

Answer 27

C5-T2

• cranial to first rib
• inject medial to arm, lateral to first rib
• avoid vessels