Abstract: Objective To investigate the effects of intravenous dexmedetomidine on block duration of subarachnoid bupivacaine in patients undergoing cesarean section. Methods 50 parturients of ASA ⅠorⅡscheduled for caesarean section were randomly allocated to two groups: dexmedetomidine group (DEX group) and normal saline group (NS group). All parturients received 0.5% hyperbaric bupivacaine 8 mg intrathecally. 10 mins after delivery, DEX group received dexmedetomidine 1μg/kg bolus infusion for 10mins followed by 0.5 μg/(kg?h) continuous infusion until end of surgery, whereas NS group were infused equivalent amount of volume. The onset time, sensory and motor block duration of subarachnoid bupivacaine, Ramsay score, MAP and HR of timepoint of before delivery (T0), 10 mins after delivery (T1), 10 mins(T2), 20 mins(T3) and 30 mins(T4) after study drug infusion were recorded respectively. The incidence of drug adverse effect and Apgar score were also recorded. Results The sensory and motor block duration of DEX group were significantly prolonged compared with NS group (p<0.05). Ramsay score of DEX group was higher than NS group (p<0.05), and the HR of T2 of DEX group was lower than that of NS group (p<0.05). 6 patients (24%) in DEX group experienced bradycardia. Conclusions Intravenous dexmedetomidine could significantly prolong the sensory and motor block duration of subarachnoid bupivacaine in patients undergoing cesarean section, and in the meantime provide satisfactory sedation without any obvious influence on parturient hemodynamics and neonate Apgar score. The primary adverse effect observed is bradycardia.

Key words: dexmedetomidine, bupivacaine, spinal anesthesia, cesarean section