FKLG 312:

SU 6:

Blog 9

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

• myelinated fibres with unmyelinated fibres; and

Unmyelinated fibers and smaller myelinated fibers are blocked more efficiently by local anaesthetics than larger myelinated fibers. Thus, unmyelinated fibers are very sensitive to the effects of local anaesthetics.

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

The dorsal nerves, which lead impulses, are more sensitive to blockage/inhibition than pressure/touch nerves and will therefore be more easily inhibited.

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

Heart: Class 1 anti-arrhythmic agents, Lidocaic (Class 1 drug) that block Sodium Channels at heart. This causes the action to shorten potential and extend the re-shelf period. Local anaesthetics affects the cardiovascular system by causing cardiac depression.

CNS: It also affects the central nervous system by producing light-headedness, visual and auditory disturbances.

Skeletal muscle: Poor blocking effect, no clinical application.

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

Clinical use, the type of process that is being done, and the duration of time necessary for the numbing effect that is needed in that tissue.

• Why are LA solutions sometimes saturated with CO₂?

Because it will accelerate the onset of action of local anaesthetics. CO2 buffers the local anaesthetic.  This then reduces the pain of injection and a faster onset of local anaesthetics is achieved. This will also raise the effective concentration of the nonionized form of the local anaesthetic, for only the nonionized form can cross the plasma membrane to have an effect, and thus the onset time of the regional block will be shortened.

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

Oxybuprocaine, benzocaine and cocaine.