The Dose-response Relationship Of Three Local Anesthetics After Intrathecal Injection For Elderly Patients

With the improvement of living standards and health care system, the average life expectancy in China has been much longer than before, the ratio of the elderly people has increased obviously, and the amount of elderly patients undergoing surgery has become larger and larger in most of the hospitals. This phenomenon has excited the attention of many anesthesiologists. How to ensure the safety and efficacy of anesthesia is especially important.Levobupivacaine and ropivacaine, two new long-acting local anesthetics, have been developed as an alternative to bupivacaine, after the evidence of its severe toxicity. Both of these agents are pure left-isomers and, due to their three-dimensional structure, seem to have less toxic effects on the central nervous system and on the cardiovascular system. A large number of studies confirmed that intrathecal or epidural injection of levobupivacaine or ropivacaine are safe and effective. We can expect that levobupicacaine and ropivacaine using in spinal anesthesia or analgesia will have broad application prospects.As we all know, being bedridden is one of the important factors of deep vein thrombosis , early motor resumption can shorten the time of patients stay in bed and to avoid the complication of deep vein thrombosis. Spinal block will always lead to sensory and motor block. The aim of this study was how to select the appropriate local anesthetic, and the appropriate dose of local anesthetic in order to not only make an excellent effects of sensory block, but also to avoid unexpected deep motor block. Therefore this study compared the sensory and motor block potencies of intrathecal bupivacaine, levobupivacaine and ropivacaine for elderly patients, and accordingly compared the sensory-motor separation trend, provide a reference for clinical application.Part oneThe Median Effective Dose of Levobupivacaine, Ropivacaine, and Bupivacaine After Intrathecal Injection for Elderly Patients Undergoing TURPObjectiveTo determine the median effective dose (ED₅₀) and the relative potencies of intrathecal levobubivacaine, ropivacaine, and bupivacaine for elderly patients undergoing TURP.MethodsIn this study ED₅₀ was determined by up-and-down sequential allocation. Ninety ASA I^III elderly patients aged 69⁸2 years with body mass index less than 30kg/mundergoing TURP under combined spinal-epidural anesthesia were randomized into 3 groups receiving intrathecal 0.5% levobupivacine , ropivacaine , and bubivacaine respectively . The initial dose was 10 mg and the testing interval was set at 1mg , Subsequent does in each group were determined by the outcome in the previous patient using success or failure of the spinal anesthesia as the primary end point. A success was determined if a bilateral sensory block to the T₁₀ dermatome was attained within 20 min after intrathecal injection, and surgery was complete, or proceded until at least 60 min after the intrathecal injection. If a failure was recorded, the dose of the study drug for the next patient was increased by 1 mg in that group. The ED₅₀ was calculated using the methord of Dixon and Massey, and also tested by using the methord of Probit Regression Analysis. ResultsThe ED₅₀s were 7.114 mg 95%CI: 6.869 7.359 mg for levobupivacine, 9.194mg 95%CI: 8.889 9.499 mg for ropivacaine , and 5.773 mg 95%CI:5.487 6.059 mg for bupivacaine . the relative motor block potency ratios were levobupivacaine / bupivacaine 0.81, ropivacaine / bupivacaine 0.63, and ropivacaine/ levobupivacaine 0.77.ConclusionsThis study suggested that in intrathecal anesthesia for elderly patients undergoing TURP, There is a clinical profile of potency : low, intermediate, and high for ropivacaine, levobupivacaine, and bupivacaine respectively.Part twoThe Relative Potencies for Motor Block After Intrathecal Levobupivacaine, Ropivacaine, and Bupivacaine for Elderly PatientsObjectiveTo determine the median effective dose (ED₅₀) for motor block after intrathecal levobubivacaine, ropivacaine, and bupivacaine and to define their relative motor- blocking potencies ratios for elderly patients.MethodsIn this study ED₅₀ was determined by up-and-down sequential allocation. Ninety ASAⅠ^Ⅲelderly patients aged 66⁸1 years with body mass index less than 30kg/mundergoing elective TURP under combined spinal-epidural anesthesia were randomized into 3 groups receiving intrathecal 0.5% levobupivacine , ropivacaine , and bubivacaine respectively . The initial dose was 5mg and the testing interval was set at 1mg , Subsequent does in each group were determined by the outcome in the previous patient using success or failure of the spinal anesthesia as the primary end point. A success was determined by the occurrence of any motor block in either lower limb(modified Bromage scale 1) within 20 min after the spinal injection. If a failure was recorded, the dose of the study drug for the next patient was increased by 1 mg in that group. The ED₅₀ was calculated using the methord of Dixon and Massey, and also tested by using the methord of Probit Regression Analysis.ResultsIntrathecal ED₅₀s for motor block was 5.483 mg 95%CI: 5.236 5.741 mg for levobupivacine, 7.516 mg 95%CI: 7.211 7.834 mg for ropivacaine , and 4.277 mg 95%CI: 4.074 4.498 mg for bupivacaine . the relative motor block potency ratios were levobupivacaine / bupivacaine 0.78, ropivacaine / bupivacaine 0.57, and ropivacaine/ levobupivacaine 0.73.ConclusionsThe motor-blocking potencies of levobupivacaine and roivacaine are lower than that of bupivacaine in elderly patients. There is a clinical profile of potency for motor block when administered spinally: low, intermediate, and high for ropivacaine, levobupivacaine, and bupivacaine respectively.