Which of the following nerve fibres are most susceptible to action of local anesthetic?
Local anesthetics depress transmission in the group C fibers before they affect group A touch fibers. Conversely, pressure on a nerve can cause loss of conduction in large-diameter motor, touch, and pressure fibers while pain sensation remains relatively intact. Patterns of this type are sometimes seen in individuals who sleep with their arms under their heads for long periods, causing compression of the nerves in the arms. Because of the association of deep sleep with alcoholic intoxication, the syndrome is most common on weekends and has acquired the interesting name Saturday night or Sunday morning paralysis.
Key concept 
Local anesthetics depress transmission in the group C fibers before they affect group A (touch) fibers.
Reference: Ganong’s Review of Medical Physiology T W E N T Y - F I F T H   E D I T I O N page no 95
A fibres
B fibres
C fibres
D fibres