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

(a) myelinated fibres with unmyelinated fibres; and 

(b) pressure/touch nerves with the dorsal nerves that transmit pain impulses?

a) Smaller and myelinated fibres are easier blocked than large unmyelinated fibers.

b) Activated pain fibers fire faster, pain sensation selectively blocked by LA. Fibers in a thick bundle blocked slower than those at the outside of the bundle.

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

• Heart: Class I anti-arryhthmic drug
• Skeletal muscle: Weak blocking action, no clinical application.

What is the basis for the selection of a LA?

Type of procedure necessary;

• Smaller surgical procedures
• Spinal anaesthesia
• Autonomic blockade in ischemic conditions
• Postoperative analgesia

Why are LA solutions sometimes saturated with CO₂?

It is used as a buffer. The pH of the tissue should not influence the reaction.

Which of the LA are typically used for surface anaesthesia?

• Benzocaine
• Cocaine
• Oxybuprocaine