Influence of the addition of potassium to 0.5% prilocaine solution during I.V. regional anaesthesia.

Six volunteers underwent i.v. regional anaesthesia on two occasions using 0.5% prilocaine 40 ml with potassium 0 or 4 mmol litre-1. Addition of potassium produced more rapid sensory blockade to pinprick at five of the six sites tested, although this was statistically significant at only one site (P less than 0.05) and more rapid sensory blockade to pinch with Allis forceps at four of the six sites (n.s.). Recovery of sensory blockade was rapid and only one site showed any significant effect, pinprick blockade being prolonged by potassium (P less than 0.05), although there was no overall effect. It is suggested that the addition of physiological (extracellular) concentrations of potassium to prilocaine for i.v. regional anaesthesia confers no clinical advantage, but that further study of other agents and sites of blockade is required.