A randomised controlled trial comparing the effect of adjuvant intrathecal 2MG midazolam to 20-micrograms fentanyl on post-operative pain for patients undergoing lower limb orthopaedic surgery under spinal anaesthesia

Background: Intrathecal adjuvants are added to local anaesthetics to improve the quality of neuraxial blockade and prolong the duration of analgesia during spinal anaesthesia. As an intrathecal adjuvant, fentanyl improves the onset and quality of spinal blockade as compared to plain bupivacaine and confers a short duration of postoperative analgesia. However, its use is associated with several adverse effects that range from pruritus to life threatening respiratory depression. Intrathecal midazolam as an adjuvant has been used and shown to improve the quality of spinal anaesthesia and prolong the duration of postoperative analgesia. No studies have been done comparing intrathecal fentanyl with bupivacaine and intrathecal 2mg midazolam with bupivacaine. Objective: To compare the effect of intrathecal 2mg midazolam to intrathecal 20 micrograms fentanyl when added to 2.6 ml of 0.5% hyperbaric bupivacaine, on post-operative pain, in patients undergoing lower limb orthopaedic surgery under spinal anaesthesia. Study design: Single blinded Randomized Controlled Trial Methods: A total of 40 patients undergoing lower limb orthopaedic surgery under spinal anaesthesia were randomized to two groups Group 1; 2.6mls 0.5% hyperbaric bupivacaine with 0.4mls (20micrograms) fentanyl Group 2; 2.6mls of 0.5% hyperbaric bupivacaine with 0.4mls (2mg) midazolam Results: The duration of effective analgesia was longer in the midazolam group 384.05min as compared to the fentanyl group 342.6min. There was no significant difference (‘P’ 0.4047). The time to onset was significantly longer in midazolam group 17.1min as compared to the fentanyl group 13.2min (‘P 0.023’). The visual analogue score at rescue was significantly lower in the midazolam group 5.55 as compared to the fentanyl group 6.35 (‘P - 0.043’). Conclusion: On the basis of the results of this study, there was no significant difference in the duration of effective analgesia between adjuvant intrathecal 2mg midazolam as compared to intrathecal 20micrograms fentanyl for patients undergoing lower limb orthopaedic surgery