 The primary objective of this double blind randomized study is to determine the effect of dexmedetomidine on onset and duration of the sensory and motor block and on the influence on bladder function after spinal anesthesia with chloroprocaine. Our primary hypothesis is that sensory block will significantly be prolonged by dexmedetomidine administered by both the spinal and the intravenous route. The investigators do not expect a significant difference in motor block duration between intravenous or spinal administration. Secondary outcomes are micturition problems, duration of analgesia and the occurrence of side effects such as sedation and hypotension. 