| Background:The primary aim of this study was to determine the median effective dose (ED50) for motor block of intrathecally-administered plain bupivacaine in adults (18-83 years), and to assess the effect of age on ED50 required for motor block. The another aim of this study was determined the median effective dose (ED50) for motor block of intrathecally administered different concentration of bupivacaine in younger patients and in older patients.Methods:This study was performed in 233 adult patients undergoing transurethral, urological or lower limb surgery under combined spinal and epidural anesthesia. This study was divided three parts:Part I:Patients who were enrolled 129 were stratified according to age:20-30,31-40,41-50,51-60,61-70, and 71-80 years; Part ?:patients who were enrolled 40 were randomly classified into two groups according to concentration (0.75% bupivacaine and 0.375% bupivacaine). Part ?:patients who were enrolled 64 were assigned randomly into three groups to receive intrathecal 0.75%,0.375% or 0.25%bupivacaine. The spinal component of the anesthetic was established by bolus administration of up-and-down doses of 0.75% plain bupivacaine, determined by Dixon's method. These up-and-down doses were determined by Dixon's up-and-down method. The first patient of each group was given 7.5 mg bupivacaine and the testing interval was set at 0.75 mg. The dose was up or down 0.75 mg increments according to the failure or success of the preceding patient's motor block. The initial concentration was choose 0.75% bupivacaine, and added one time or two times the same volume as the diluent of 0.9% saline to obtain 0.375% or 0.25% bupivacaine. The degree of motor block after intrathecal administration bubivacaine was evaluated by the modified Bromage and Hip motor function score. A score= 0 within 5 min means that the dose was ineffective and score> 0 within 5 min, means that the dose was effective. The ED50 were estimated from the up-and-down sequences using the method of Dixon and Massey and logistic regression. Other endpoints were included on the basis of sensory block level, duration of motor blockade, hypotension, and vasopressor requirements.Results:Part I:ED50 for motor block using intrathecal bupivacaine was 10.22 mg (95%CI:9.96-10.49 mg) in 20-30,9.52 mg (95%CI:9.02-10.07 mg) in 31-40, 8.37 mg (95% CI:7.56-9.26 mg) in 41-50,7.30 mg (95% CI:6.84-7.79 mg) in 51-60, 6.55 mg (95%CI:6.01-7.13 mg) in 61-70, and 5.78 mg (95% CI:5.01-6.67 mg) in 71-80 years old patients. The maximum cephalic analgesic level was L1-L2 level at 5 minutes, and T10-L1 at 10 minutes after administration of intrathecal plain bupivacaine in the six age groups. There was significant difference in the duration of motor blockade among groups(P< 0.05). Part ?:The ED50 for motor block of intrathecal bupivacaine was 9.998mg in 0.75% bupivacaine and 8.890 mg in 0.375% bupivacaine. Part ?:The ED50 for motor block of bupivacaine was 6.10 mg (95% CI: 5.68,6.55 mg) in 0.75% bupivacaine group,6.04 mg (95% CI:5.76,6.33 mg) in 0.375% bupivacaine group, and 5.43 mg (95% CI:5.16,5.71 mg) in 0.25% bupivacaine group.Conclusion:ED50 for motor block of intrathecally-administered plain bupivacaine decreased steeply with advancing age. The effect of concentration of bupivacaine on the ED50 for motor block was similar in different age group, which the ED50 for motor block decreased steeply with the bupivacaine concentration decreased in younger group and in older groups. |
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