LA: Intro to LA

Question 1

What is the individual axon bundled by?

Answer 1

Endoneurium

Question 2

What does the perineurium encase?

Answer 2

It bundles axons into fascicles

Question 3

What are the fascicles encased by?

Answer 3

Epineurium

Question 4

What is important to note about the histology of the axon fascicles in terms of solubility?

Answer 4

There are a lot of fat cells so the fat solubility of the anesthetic is important

Question 5

What type of neurons are A fibers?

Answer 5

Large and Myelinated

Question 6

How many subtypes of A fibers are there?

Answer 6

4: Alpha, Beta, Gamma, Delta

Question 7

Which A fiber type is afferent?

Answer 7

Delta

Question 8

What type of neuron in a B fiber?

Answer 8

Autonomic, Preganglionic

Question 9

What type of neuron is a C fiber?

Answer 9

Small, Unmyelinated
Autonomic post-ganglionic
Sensory for pain and temp

Question 10

Rank the A, B, and C fibers in order of sensitivity to LA

Answer 10

A > B > C

Question 11

What cell myelinates axons in the CNS?

Answer 11

Oligodendrocytes

Question 12

What cell myelinates axons in the PNS

Answer 12

Schwann

Question 13

During a nerve impulse propagation what is the first step?

Answer 13

Opening of the Sodium channels creating a depolarization

Question 14

After depolarization to +40 mV what is the next step of the nerve impulse?

Answer 14

Sodium channels close and the K permeability increases allowing K to flow out of cell down its gradient repolarizing the cell

Question 15

What is the special receptor theory of LA action?

Answer 15

LA acts by binding to receptor site within the sodium channel.

This prevents sodium influx and hence prevents nerve depolarization

Question 16

What are the three parts of the basic LA molecular structure?

Answer 16

Hydrophobic Aromatic Group
Intermediate chain (ESTER or AMIDE)
Hydrophilic Amino Group

Question 17

Which is the commonly used LA that is an ester?

Answer 17

Procaine (Novocaine)

Question 18

How does pH effect the molecular structure of the LA?

Answer 18

All LA exist in equilibrium between a neutral and ionized form, the ion is acidic.

The balance is dependent upon the molecule’s pKa and can be calculated using the HH equation

Question 19

Once the LA is injected how do its components work? (ACID VS BASE)

Answer 19

LA is injected as an acid, but it is the free base that is lipid soluble and does the actual work

Question 20

What is the most commonly used LA in the USA and UK?

Answer 20

Lidocaine

Lignospan, Octocaine, Xylocaine

Question 21

Is lidocaine and amide or ester?

Answer 21

Amide

Question 22

What is the max safe dose of Lidocaine?

Answer 22

4.4 mg/kg

300 mg MAX

Question 23

What is the max safe dose of Articaine?

Answer 23

7 mg/kg or 500 mg

Question 24

Why might articaine result in greater penetration into the nerve?

Answer 24

More lipid soluble

Question 25

Which LA has an extra ester linkage?

Answer 25

Articaine

Question 26

What nerve block should be used cautiously with Articaine?

Answer 26

IAN

Question 27

Why might Articaine have more neurotoxicity?

Answer 27

4% Solution

Question 28

How much solution does each cartridge of LA have?

Answer 28

1.8 ml

Question 29

Each 1% of LA is the equivalent of…?

Answer 29

10 mg/ml

Question 30

So how much in a 1%, 2%, 3%, 4% Carpule?

Answer 30

1%: 18 mg/cc
2%: 36 mg
3%: 54 mg
4%: 72 mg

Question 31

What does 1:100,000 mean

Answer 31

1 gram in 100,000 mL

Question 32

What is the max safe dose of epi for a normal adult?

Answer 32

.20 mg

Question 33

What is the max safe dose of epi for a cardiac patient?

Answer 33

40 micrograms

Question 34

What is important to balance with cardiac patients however?

Answer 34

Profound nerve block is key because too much pain could cause the patient to release endogenous epi.