Variation in spinal analgesia with plain bupivacaine 0.5% when repeated in the same patient

The study was done to see if it was possible to predict the level of analgesia in repeated spinal blocks with our routine technique where the patient is seated during injection of plain 0.5% bupivacaine 3.5 ml at the L3-L4 interspace and placed in the lithotomy position after 0.5 min. Thirty patients with tumour of the bladder had two spinal blocks during a 13-month period. The segmental spread of sensory loss was tested with the pin-prick technique. A wide range of height of blocks was found, increasing with age. Regression analysis on maximum cephalad spread of the second spinal analgesia against the first had a slope of 0.48 (P less than 0.01 for the hypothesis that the slope is zero). A significant correlation between the time for maximal cephalad spread was found, while the correlation between duration of thoracal analgesia was non-significant.