Abstract: ObjectiveTo compare the safety and effectiveness of different doses of hypobaric bupivacaine for spinal anesthesia for hip surgery in elderly patients, in order to screen the best clinical safety dose. 
MethodsSixty elderly patients with hip fracture of American Society of Anesthesiologists(ASA) Ⅱ-Ⅲ were scheduled for elective hip surgery. According to the random number table method, the patients were divided into low dose group(group L),medium dose group(group M) and high dose group(group H), with 20 cases in each group. The affected side was kept in the upper lateral supine position, and subarachnoid block anesthesia was performed in the L3-4 in tervertebral space. After successful puncture, 0.375% bupivacaine(0.75% bupivacaine + sterilized water for injection) was injected into the subarachnoid space, and the doses were calculated according to unit height of 0.033 mg/cm,0.05 mg/cm, and 0.08 mg/cm, respectively. Changes of mean arterial pressure(MAP) and heart rate(HR) at entry(T0) and at each time point(T1-T5) after administration in the three groups were recorded. Intraoperative use of vasoactive drugs, the onset time of anesthesia, fixation time of the anesthesia plane, the number of anesthesia block segments on the affected side, and the duration of anesthesia block, and the occurrence of complications during and after operation were recorded and compared among the three groups. 
ResultsThe frequency of vasoactive drugs in group H was higher than that in groups L and M, and the difference was statistically significant(P＜0.05). After injection, MAP in the three groups showed a trend of initial decrease and subsequent increase, with the greatest fluctuation in MAP and HR in group H, and there were statistically significant differences in the interaction among groups, time points, and time points among groups(P＜0.05). The onset time of anesthesia and the fixation time of anesthesia plane in group H were shorter than those in groups L and M,and shorter in group M than in group L(P＜0.05); The duration of anesthesia and analgesia was longer than groups L and M(P＜0.05). The Bromage score of group H was higher than that of groups L and M at 1 d after operation(P＜0.05). The MMSE scores of the three groups showed a trend of initial decrease and subsequent increase, with the greatest fluctuation in group H, and there were statistically significant differences in the interaction among groups, time points, and time points among groups(P＜0.05). The incidence rate of intraoperative hypotension and sinus bradycardia in group H was higher than that in groups L and M, and the differences were statistically significant(P＜0.05). 
ConclusionLow-dose(0.033 mg/cm) light specific gravity lumbar anesthesia with bupivacaine can be safely and effectively used in hip surgery in elderly patients which is the recommended dose for clinical safety.

Key words: hip fractures, anesthesia, spinal, bupivacaine, elderly, 80 and over