Blog #9 (SU 6.3)

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

1. myelinated fibres with unmyelinated fibres; and

Myelinated fibres are blocked easier than unmyelinated fibres and thus myelinated fibres are more sensitive for blockade by local anaesthetics.

 

2. pressure/touch nerves with the dorsal nerves that transmit pain impulses?

Activated pain fibres fire faster so pain sensation can be selectively blocked by local anaesthetics. Fibres that are outside the thick nerve bundles are blocked before fibres that are in the middle of thick nerve bundles which are blocked slower. This is because fibres on the outside of nerve bundles are exposed too higher concentrations of the anaesthetic earlier than the fibres at the middle of the fibre bundle.

 

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

Effects of local anaesthetics on the heart:

• • Local anaesthetics have a class I antiarrhythmic drug effect.
  • Sodium channels in the heart muscle tissue is blocked.
  • This can cause toxicity and lead to cardiac depression.

Effects of local anaesthetics on the skeletal muscle:

• • Has weak blocking effects.
  • Has no clinical application.

 

• What is the basis for the selection of a LA?
  • Type of procedure being done.
  • The duration of the procedure and duration the drug needs to have an effect.
  • The type of tissue the drug needs to be administered in to.

 

• Why are LA solutions sometimes saturated with CO₂?

CO₂ potentiates the effect of the local anaesthetic thus acting as a buffer.

 

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

 

Reference list.

Brand, L. 2021. SU 6 Local Anaesthetics. https://efundi.nwu.ac.za/access/lessonbuilder/item/5726323/group/dd46f2da-d3be-402e-9ba7-2c5955cedd9d/English%20power%20point/English%20PP%202021/SU%206.pdf Date of access: 30 Mar. 2021. [PowerPoint presentation]

Katzung, B.G.  2018.  Basic & Clinical Pharmacology.  14^th ed.  California, San Francisco: McGraw-Hill Companies, Inc.