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

Myelinated fibres with unmyelinated fibres: the smaller, myelinated fibres have a higher chance and susceptibility for blockade than unmyelinated fibres.

Pressure/touch nerves with the dorsal nerves that transmit pain impulses: activated pain fibres flare much quicker, and pain sensation can be selectively blocked by LA. Fibres in the centre of the large nerve bundle are more slowly blocked than those on the outside of the bundle.

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

Cardiac tissue:

• Class 1 anti-arrhythmic drugs block Na channels in the cardiac tissues with the purpose of shortening the action potential and to prolong the refractory period.

Skeletal muscle tissue:

• Weak blocking/inhibiting effects, no clinical application

Cocaine:

• “Improves” the state of mind, influences central catecholamine-mediated neurotransmission – thus inhibits NA reuptake.

What is the basis for the selection of a LA?

The selection of the appropriate LA could be based on the clinical indication for the drug, meaning what it is going to be used for. The clinical indication could be one of the following:

• Minor surgical procedures
• Spinal anaesthesia
• Autonomic blockade in ischaemic conditions
• Post-operative analgesia

The selection could also be based on for how long the LA is going to be used for, and also depends on the duration of action of the LA.

Why are LA solutions sometimes saturated with CO2?

Carbon dioxide potentiates the effects of local anaesthetics, meaning it could increase the rate of the LA action.

Which of the LA are typically used for surface anaesthesia?

• Cocaine
• Benzocaine
• Oxybuprocaine