Epinephrine added to a solution of lignocaine for a peripheral nerve block will:

(Ref: K DT 6/e p354) Adrenaline and felypressin are the vasoconstrictors that are added to LA solution. By causing vasoconstriction, these drugs - decrease the systemic absorption resulting in less CNS adverse effects (decreased chances of seizures). Prolong the stay of drug at the site of action resulting in the increase in duration of action of LA.