Comparative Study on the Effect of Low Dose Dexmedetomidine and Clonidine as Adjuvant on the Quality of Subarachnoid Block by 0.5% Heavy Bupivacaine

Abstract

Background: Spinal anaesthesia is a well-established anaesthetic technique due to its quick onset and reliable sensory-motor inhibition. However, limited postoperative analgesia remains a major drawback of bupivacaine-based subarachnoid block. The addition of intrathecal adjuvants has been explored to improve block quality and extend analgesic duration. Among these, α₂-adrenergic agonists such as dexmedetomidine and clonidine have demonstrated favourable effects on anaesthetic performance. Owing to its greater α₂-receptor selectivity, dexmedetomidine may offer advantages over clonidine in enhancing spinal anaesthesia outcomes. Objective: To compare the efficacy and safety of dexmedetomidine and clonidine as intrathecal adjuvants to hyperbaric bupivacaine in spinal anaesthesia. Methods: This study was designed as a prospective randomized comparative trial at Combined Military Hospital, Dhaka, between December 2019 and December 2020. Study population consisted of adult patients (n = 120) undergoing elective infraumbilical surgery with spinal anaesthesia. were registered and randomly split into two groups equally. Group A received 10 mg of 0.5% hyperbaric bupivacaine combined with dexmedetomidine 5 µg, whereas Group B received the same dose of bupivacaine with clonidine 30 µg. Outcomes assessed included onset and duration of sensory and motor blockade, duration of postoperative analgesia, haemodynamic variables, and treatment-related adverse events. Results: Patients receiving dexmedetomidine exhibited a significantly shorter time to peak sensory blockade compared with those receiving clonidine (2.13±0.54 vs 3.52±0.34 minutes; p<0.001). Similarly, complete motor blockade was achieved earlier in the dexmedetomidine group (2.93±0.43 vs 4.42±0.34 minutes; p<0.001). Dexmedetomidine was also associated with significantly prolonged sensory regression time, delayed motor recovery, and extended postoperative analgesia (all p<0.001). The mean duration before rescue analgesia was required was 544.5±17.6 minutes in Group A and 423.5±16.6 minutes in Group B. Haemodynamic measurements remained stable in both groups, and the incidence of adverse effects was comparable, with no episodes of clinically significant respiratory depression or excessive sedation. Conclusion: Low-dose intrathecal dexmedetomidine provided superior block characteristics and longer postoperative analgesia than clonidine while maintaining stable hemodynamic and safety profiles. It appears to be an effective adjuvant to hyperbaric bupivacaine with a comparable safety profile in subarachnoid anesthesia.