Circadian Effects on Neural Blockade of Intrathecal Hyperbaric Bupivacaine

BACKGROUND Circadian variations in the absorption, distribution, protein binding, elimination and metabolism of drugs account for many of the administration-time-dependent differences in their pharmacokinetics. The aim of this study is to determine whether the time of intrathecal injection influences spinal anesthesia. METHODS Ninety patients scheduled for orthopedic surgery were randomly assigned to three groups. Each group received spinal anesthesia with 0.5% bupivacaine 10 mg at different times; group AM (8 am to 12:00), group Noon (12:00 to 4:00 pm) and group PM (4:00 pm to 8:00 pm). Sensory and motor blockade were assessed by pinprick and a four-point modified Bromage scale. Time to first postoperative analgesic requirement and side effects such as hypotension, bradycardia, nausea, and shivering were recorded. RESULTS No significant differences were found among the three groups in peak sensory blockade, duration of motor block to Bromage 1 or side effects, but time to first postoperative analgesic requirement (P = 0.008), and recovery time of S1 sensation to pinprick were significantly prolonged in group Noon compared with the other groups (P = 0.03). CONCLUSIONS The tine of administration of spinal local anesthetics influences the duration of local anesthesia.