Analgesia was assessed quantitatively at various dermatomes (C7, T8, T10, T12, L1, L3, S1) for the first 30 min after subarachnoid administration of 0.5bupivacaine 3.5 ml. stimulation with 10 needles and laser stimulation could avoke pain in dermatomes with adequate analgesia was assessed by thresholds (sensory and pain) and by pain related brain potentials (amplitude and latency) to laser stimulation. Little analgfesia was found at T10, but it increased gradually towards caudal segments. The dermatome related to the side of the injection (L3) was not blocked to a greater extent than the surrounding dermatomed. Conduction time (the latency of the evoked brain potential) was increased relatively more than from the S1 dermatome compared with L1.
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