Chapter 29: Local Anesthetics

Question 1

Describe the physiologic manner by which local anesthetics work.

Answer 1

Local anesthetics block sodium channels in nerve axons, preventing sodium influx and stopping nerve impulse conduction, thus suppressing pain without causing CNS depression.

Question 2

Differentiate between ester and amide types of local anesthetics in terms of mechanism of action, elimination, and allergic reactions.

Answer 2

Both esters and amides block sodium channels.

Esters are metabolized by plasma esterases and have a higher risk of allergic reactions.

Amides are metabolized by liver enzymes and have a very low risk of allergic reactions.

Question 3

Describe ways to prevent systemic toxicity from topical administration of local anesthetics.

Answer 3

Use the smallest effective dose, avoid large areas and broken skin, and prevent conditions that raise skin temperature (e.g., exercise, heat, wrapping).

Question 4

State reasons and rationales for including a vasoconstrictor (e.g., epinephrine) in a parenteral formulation of local anesthetic.

Answer 4

Epinephrine prolongs anesthesia by slowing absorption, reduces systemic toxicity, and increases anesthetic intensity. It should be avoided in end-artery areas to prevent gangrene.