• How does the sensitivity for blockade by a LA compare regarding the following types of fibres:
  1. Myelinated fibres with Unmyelinated fibres; and

Smaller fibres are blocked more easily than larger fibres

Myelinated fibres are blocked more easily than unmyelinated fibres.

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

Pressure/ Touch- Has heavy Myelination

Pain- Dorsal root with  No Myelination

• • Activated pain fibres fire rapidly; thus, pain sensation appears to be selectively blocked by local anaesthetics. Fibres located in the periphery of a thick nerve bundle are blocked sooner than those in the core because they are exposed earlier to higher concentrations of the anaesthetic.
  • Pain sensation selectively is blocked by local anaesthetics.

• Make a list of the effects of LA on other tissues.
  • Skeletal muscles: weak blocking action
  • Heart: class 1 anti-arrhythmic drug

• Peripheral Nervous System And Central Nervous System

As local anaesthetics are absorbed from the injection site, their concentration in the bloodstream rises and the peripheral nervous system and central nervous system (CNS) are depressed in a dose-dependent manner.

• Cardiovascular System

Low serum concentrations are used clinically for suppressing cardiac arrhythmias and status seizures, but ironically, higher concentrations induce seizure activity. Convulsive seizures are the initial life-threatening consequence of local anaesthetic overdose. Presumably, this is due to selective depression of central inhibitory tracts, which allow excitatory tracts to run amuck.

• Respiratory System

As serum concentrations continue to rise further, all pathways are inhibited, resulting in coma, respiratory arrest, and eventually cardiovascular collapse.

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

The basis of selection of the local anaesthetic is for:

• • small surgical procedures,
  • spinal anaesthesia or
  • post-operative analgesia.

• Why are LA solutions sometimes saturated with CO₂?

To potentiate the effects of local anaesthetics. 

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