Effect of high thoracic epidural sympathetic block on cerebral vasospasm after subarachnoid hemorrhage in rabbits

Objective To evaluate the effect of high thoracic epidural sympathetic block(HTESB)on cerebral vasospasm(CVS)after subarachnoid hemorrhage(SAH)in rabbits.Methods Twenty-four Japanese long-ear white rabbits of both sexes weighing 2.0-2.6 kg were randomly divided into 3 groups(n=8 each):group Ⅰ control;group Ⅱ SAH and group Ⅲ SAH + HTESB.The ammals.were anesthetized with iv 3% pentobarbital 30 mg/kg.An catheter was inserted into epidural space at T3-4 interspace and advanced 1.5 cm cephalad with the tip directed at T2 vertebral body and fixed.Cerebral vasospasm(CVS)model was produced by injecting 1 ml/kg non-coagulated autologous arterial blood into cistema magna twice at 48 h interval.In control group normal saline (NS)was injected into cisterna magna twice instead of non-coagulated autologous arterial blood,In group Ⅲ 0.5% lidocaine 0.5 ml was injected through the epidural catheter every 2 h and T1-5 sympathetic nerves were blocked.Blood flow velocity of common carotid artery was detected by transcranial Doppler(TCD)ultrasonography at 15 min after epidural lidocaine before(T0)and at day 7 after operation(T1).Mean velocity(Vm),peak blood flow velocity at systole(Vs),end-diastolic velocity(Vd)were measured and pulsation index(PI)and resistance index(RI)were calculated.ECG,MAP and HR were continuously monitored.Food intake and delayed ischemic neurological deficit(DIND)were evaluated every day.Results The food intake was siguificantly decreased and DIND increased after SAH in group Ⅱ.High thoracic epidural block significantly attenuated the changes in food intake and DIND induced by SAH and there was no significant difference in food intake and DINL,after operation between control group and SAH + HTESP group.Vm,Vs and Vd were significantly increased and PI and RI decreased after operation at T1 as compared with the baseline values at T0 in SAH group and control group.High thoracic epidural block significantly attenuated the changes in Vm,Vs,Vd and PI and RI induced by SAH.Conclusion High thoracic epidural sympathetic nerve block with 0.5% lidocaine can significantly improve food intake and attenuate DIND after SAH and decrease carotid artery blood flow velocity and HR,suggesting that overactivity of sympathetic nervous system may be involved in the pathogenesis of CVS induced by SAH. Key words: Anesthesia,epidural; Vasospasm,intracranial; Subarachnoid hemorrhage; Autonomic nerve block