Abstract: Objective To study the minimal dose and safty of bupivacaine spinal anesthesia in caesarean section.Methods Ninety patients ready for caesarean section were recruited and randomly divided into three groups(groups A,B and C with 30 cases for each group) and received combined spinal-epidural anesthesia(CSEA).Patients were injected intrathecally with 0.5% iso-proportional bupivacaine 5 mg(group A),6 mg(group B) and 7 mg(group C).Additional 2% lidocaine were added if necessary.If the systolic pressure was less than 90 mmHg or the diastolic pressure was 20% less than standard values,10 mg ephedrine would be used to correct it.After these steps,all medical indexes were abserved as follows: I-D time(interval skin incision to delivery),U-D time(interval from uterine incision to delivery) and anesthesia & operation time were recorded;meanwhile the level of anesthesia,bromage scores,blockade effectiveness,and the effectivness of additional epidural lidocaine were recorded.As well as patients'heart rate,blood pressure,and blood oxygen saturation at each postanesthetic time interval.Apgar scores of the neonate,side effects such as panting,nausea,vomiting and traction reflex of the gravide were also observed.Results Statistical analyses were performed by SPSS 10.0.ANOVA(analysis of variance) and Chi-square tests were used.The standard level of significance used to justify a claim of a statistically significant effect was 0.05.Major results were listed as follows.Anesthesia and operation times of groups B and C were(43.30±11.50)min and(43.50±10.90)min respectively, which were shorter than group A(51.20±12.8)min(P<0.05),but there was no difference about I-D timeand U-D time in three groups(P<0.05).Levels of anesthesia in groups A,B,C were T7.75±1.71、T6.27±1.85 and T6.21±1.42,respectively.Group B and group C were higher than group A(P<0.01).Bromage scores of groups A,B,C were(2.07±0.77)、(2.41±0.63) and(2.81±0.49),respectively.Group C were superior to group A(P<0.05).Blockade effect of group B(1.24±0.44) and group C(1.15±0.37) were superior to group A(2.11±0.69)(P<0.01);additional use of epidural 2% lidocaine occured more often in group A(67.9%) than in group B(24.1%)and group C(11.5%)(P<0.01).Systolic and diastolic blood pressures at postanesthetic 5th minute in group C(100.2±24.0 mmHg,(62.3±16.6)mmHg correspondingly were lower than group A(110.2±12.2)mmHg,(70.7±10.3)mmHg respectively(P<0.05),but there was no difference at other times among three groups(P>0.05).Also there were no difference in terms of heart rate,SPO₂ and Apgar scores of the neonate among three groups(P>0.05).Nausea and panting in group C(38.5%,57.7%) were more often than in group A(14.3%、7.1%) and group B(13.8%、6.9%)(P<0.05,P<0.01 respectively).Conclusion The dosage of bupivacaine is substantially related to its side effects and toxicity.0.5% bupivacaine 6 mg is the minimal and reliable effective-dose to be used in caesarean section with lumbar anesthesia,and is highly recommended.

Key words: bupivacaine, lumbar anesthesia, caesarean section, minimal effective-dose