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Background and Aims Subarachnoid block has been extensively practiced for infraumbilical surgeries.Intrathecal adjuvants like Fentanyl, Midazolam are added to local anaesthetic Bupivacaine to improve the quality of neuraxial block and prolong the duration.To investigate the potentiation of analgesic effect by adding adjuvant Midazolam to local anesthetic Bupivacaine and adjuvant Fentanyl combination in subarachnoid block to the patients undergoing lower limb orthopedic surgery.

Methods Subjects were randomized to two groups according to the anaesthetic medication used. Group A received 2.8 ml of hyperbaric 0.5% Bupivacaine with 0.5 ml (25μg) of Fentanyl and 0.2 ml of Normal saline; Group B received 2.8 ml of hyperbaric 0.5% Bupivacaine with 0.5 ml (25μg) of Fentanyl and 0.2 ml (1 mg) of Midazolam. The onset and duration of sensory and motor blockade, duration of post-operative analgesia were recorded in a case record form. Statistical significance defined as p-value < 0.05 and confidence interval set at 95% level.

Results In this study, mean onset time of sensory block were 4.57±0.3 minutes and 4.29±0.1 minutes in group A and group B respectively. The mean onset times of motor block between two groups were 7.70±0.4 minutes and 7.35±0.3 minutes in group A and group B respectively. The mean (±SD) duration of analgesia was 307.3±11.3 minutes in group A and 364.9±16.6 minutes in group B. The comparison between outcome variables of two groups showed very highly significant (p<0.001) difference.

Conclusions Addition of intrathecal Midazolam to Bupivacaine and Fentanyl combination potentiates the analgesic effects in terms of prolonged duration of analgesia and sensory- motor block.