I found that 2.6ml of 0.5% levobupivacaine had similar clinical characteristics as the same volume of 0.5% bupivacaine in spinal anaesthesia. Both were effective for spinal anaesthesia in urological surgery, when a sensory block up to at least T10 dermatome was required. In comparing the use of levobupivacaine alone and levobupivacaine with fentanyl, there were no significant differences in haemodynamic changes and quality of sensory and motor block, when 2.6ml of levobupivacaine alone or 2.3ml of levobupivacaine with fentanyl 15mcg (0.3ml) were used in spinal anaesthesia. Both were effective for spinal anaesthesia in urological surgery. In comparing the use of ropivacaine 10mg and bupivacaine 10mg, both with fentanyl 15mcg in spinal anaesthesia for urological surgery, all the patients achieved adequate level of sensory block up to T10 dermatome or higher. The two drugs were similar in the onset time of motor block, the characteristics of sensory block and haemodynamic changes; however, the duration of motor block was shorter with ropivacaine. I concluded that both studied solutions, ropivacaine-fentanyl and bupivacaine-fentanyl, were effective for spinal anaesthesia in urological surgery and the duration of motor block was shorter with the ropivacaine-fentanyl solution. The dose-response relationship of ropivacaine in spinal anaesthesia for lower limb surgery requiring a sensory block up to at least the T12 dermatome was defined. Anaesthesia was successful in 0, 0, 42, 83 and 100% when ropivacaine at doses of 2, 4, 7, 10 and 14mg respectively were given. The derived values for ED50 and ED95 were 7.6mg and 11.4mg respectively. The cephalic level of sensory block and the degree of motor block increased with larger doses of ropivacaine. Finally, the median effective dose (ED50) of bupivacaine, levobupivacaine and ropivacaine in spinal anaesthesia for lower limb surgery were defined as 5.50mg (95% CI: 4.90--6.10mg), 5.68mg (95% CI: 4.92--6.44mg), and 8.41mg (95% CI: 7.15--9.67mg) respectively. The relative potency ratios were 0.97 (95% CI: 0.81--1.17) for levobupivacaine/bupivacaine, 0.65 (95% CI: 0.54--0.80) for ropivacaine/bupivacaine and 0.68 (95% CI: 0.55--0.84) for ropivacainellevobupivacaine. / In this series of studies, I have shown that levobupivacaine and ropivacaine are effective local anaesthetic agents for spinal anaesthesia in lower limb and urological surgery. This proved my hypothesis. Both are suitable alternatives to bupivacaine for spinal anaesthesia. Furthermore, these studies showed that ropivacaine is less potent than levobupivacaine and bupivacaine and the potency is similar between levobupivacaine and bupivacaine at median effective dose. / Levobupivacaine and ropivacaine are two relatively new local anaesthetics which were developed in view of their potential for less cardiotoxicity in comparison with bupivacaine, the most common local anaesthetic used in spinal anaesthesia for many years. Both are produced in pure S(-) enantiomer form in contrast to bupivacaine which is a racemic mixture. They have been shown to be effective in peripheral nerve blocks, and epidural analgesia and anaesthesia; nevertheless, experience of their use in spinal anaesthesia is limited. The objective of this thesis was to evaluate their use in spinal anaesthesia for surgery in non-obstetric patients. My hypothesis was that levobupivacaine and ropivacaine are effective local anaesthetic agents for spinal anaesthesia in lower limb and urological surgery. In order to test this hypothesis, I conducted five clinical studies on 269 patients who had urological surgery or lower limb surgery under spinal or combined spinal-epidural anaesthesia. First, I investigated the efficacy and clinical characteristics of levobupivacaine and the mixture of levobupivacaine with fentanyl in spinal anaesthesia. Next, I compared the use of ropivacaine-fentanyl with bupivacaine-fentanyl in spinal anaesthesia. Finally, I defined the dose-response relationship of ropivacaine in spinal anaesthesia using traditional dose-response methodology and defined the relative potency among levobupivacaine, ropivacaine and bupivacaine by comparing the defined ED50 in spinal anaesthesia using up-down sequential allocation method. / Lee, Ying Yin. / Source: Dissertation Abstracts International, Volume: 73-06, Section: B, page: . / Thesis (M.D.)--Chinese University of Hong Kong, 2011. / Includes bibliographical references (leaves 133-150). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [201-] System requirements: Adobe Acrobat Reader. Available via World Wide Web.