• How does the sensitivity for blockade by a LA compare regarding the following types of fibers:

1. Myelinated fibres with unmyelinated fibres:

Smaller myelinated fibers are blocked much easier in comparison to the larger unmyelinated fibers, which are much less sensitive to blockade by the local anaesthetics.

2. Pressure/touch nerves with the dorsal nerves that transmit pain impulses:

Activated pain fibers fire rapidly, therefore pain sensation may be selectively blocked by local anaesthetics. Fibers that are located in outside of the thick nerve bundles are blocked sooner than the fibers located in the middle of thick nerve bundles. This is because they are exposed too higher concentrations of the anaesthetic much earlier.

• Make a list of the effects of LA on other tissues.

Heart:

• LA have Class I anti-arrhythmic drug effects.
• Sodium channels in heart tissue is blocked.
• Resulting in cardiac depression.

Skeletal muscle:

• Weak blocking effects
• No clinical application.

• What is the basis for the selection of a LA?

A local anaesthetic is chosen due to the following factors:

• The type of procedure that is being done
• The type of tissue that the local anaesthetic should be used on
• The duration of the numbing effect that is needed

• Why are LA solutions sometimes saturated with CO₂?

The carbon dioxide acts as a buffer to the local anaesthetic. This will potentiate the effects of the local anaesthetic.

• Which of the LA are typically used for surface anaesthesia?
  • Benzocaine
  • Cocaine
  • Oxybuprocaine

These drugs move through gums and reach nerves.

Reference list:

Brand, L.Prof.  2021.  Study Unit 6: Local Anaesthesia.  Unpublished lecture notes on efundi, FKLG 312.  Potchefstroom: NWU.  [PowerPoint presentation].