Introduction: Transurethral resection of prostrate (Turp) and transurethral resection bladder tumour (Turbt) are major operations, subarachnoid block is a well accepted and popular technique for Turp and Turbt. Materials and method: This randomized prospective double blind study conducted at MIOT hospitals, Chennai, from October 2014 – December 2015, evaluated the effective dose of clonidine with 10mg of 0.5% heavy bupivacaine in 80 patients posted for these surgeries and also to find the effect of various doses of clonidine on various subarachnoid block characteristics. Results: The level of peak sensory block (mean ± SD) was thoracic vertebral level T9.4 ± 0.68 in group BN T8.95 ± 0.94 In group BC 15, T8.3 ± 1.41 in group BC 25 and T7.5 ±
1.19 in group BC 35. There were significant differences in the peak sensory level between the groups. The 2 segment regression time (mean ± SD) defined as the time taken for the peak sensory level to regress 2 segments was compared between the 4 groups. It was 53.65 ± 5.81 min in group BN compared to 56.15 ± 7.23 min in groupBC15, 63.60 ± 8.66 min in group BC 25 and min 65.25 ± 6.87 in group BC 35. The difference in 2 segment regression was significant between the groups. The time to first requirement of analgesia was compared the
4 groups. It was 85.95 ± 6.21 min in group BN, 89.25 ± 6.37 min in group BC 15, 95.90 ± 8.59 min in group BC 25, 99.50 ± 5.72 min in group BC 35 . The difference was significant between the groups. Conclusion: Addition of 35mcg of clonidine to bupivacaine when compared to 25mcg/15mcg clonidine significantly prolongs the duration of analgesia without affecting the onset and maximum level achieved of sensory block.