Local Anesthesia

Question 1

What does an autonomic blockade block?

Answer 1

B and C fibers

Question 2

What does a somatic sensory blockade block?

Answer 2

A beta, A alpha, and A delta

Question 3

What are the different ways LAs are used?

Answer 3

1. infiltrated around a nerve
2. applied topically to skin or mucous membranes
3. injected into blood vessels (with the turniquit)
4. injected into subarachnoid and epidural space

Question 4

What causes the different nerve fibers to get blocked at different times in a differential blockade?

Answer 4

• the bigger the nerve, the less sensitive to the LA it is. This is because of where the bigger fibers are located in relation to the smaller ones.
• Smaller fibers are on the outside, so they feel the effects of the LA first
• Increased activity (the Na channels of the fiber opening) increases the strength and speed the LA will take effect.

Question 5

What is the mantle of the peripheral nerve?

Answer 5

the outer surface of the peripheral nerve

**usually serve more proximal structures

Question 6

What is the core of the peripheral nerve?

Answer 6

the inner surface of the peripheral nerve

**usually serve more distal structures

Question 7

What is the clinical sequence of an LA?

Answer 7

• 1st- sympathetic block (noted by vasodilation, warm skin_
• 2nd- loss of pain and temperature sensation
• 3rd- loss of proprioception
• 4th- loss of touch and pressure
• 5th- motor blockade

Question 8

What does an LA do to the Na channels that cause action potentials?

Answer 8

they block enough of the Na channels that the resting membrain potential never becomes less negative enough to reach threshold

Question 9

How does an LA block a Na channel?

Answer 9

1. the LA will access the channel while it is in the “activated-open” state.
2. It binds to the inside of the receptor in the “inactivated-closed” state
3. The more frequently the action potential cycles through, the more rapidly the block occurs
   
   1. a resting nerve is less sensitive to a block than a repetitively stimulated nerve

Question 10

What are the two chemical classification of LA’s?

How do you tell them apart?

Answer 10

• Aminoamides- has an “i” in the drug name before the caine part
• Aminoesters- does not have an “i” in the name before caine

Question 11

What are the different parts of an LA molecule?

Answer 11

1. lipophilic head
2. intermediate chain containing either an amide or an ester
3. hydrophilic tail