Comparison of Intravenous Dexmedetomidine with Midazolam in Prolonging Spinal Anaesthesia with Ropivacaine.

INTRODUCTION: Midazolam and dexmedetomidine both being sedatives, but the latter with additional analgesic properties is expected to prolong the duration of sensory and motor block obtained with spinal anaesthesia.

AIM: To compare intravenous dexmedetomidine with midazolam and placebo with respect to sensory and motor block duration, analgesia, and sedation in patients undergoing lower limb and lower abdominal surgeries with intrathecal ropivacaine anaesthesia.

MATERIALS AND METHODS: In this single blind placebo controlled trial, 60 patients, classified as American Society of Anaesthesiologists' (ASA) physical status I-II, were randomized into three groups (n=20 per group). All patients were administered ropivacaine (15 mg) for spinal anaesthesia. Intravenous dexmedetomidine was administered in Group D (1 μg/kg loading dose over 10 minutes, followed by a continuous infusion (0.5 μg/kg/hr), intravenous midazolam was administered in Group M (0.05 mg/kg) loading dose, followed by a continuous infusion (0.02 mg/kg/hr) and normal saline was infused in Group C. Intraoperative haemodynamic changes, onset, level and duration of sensory block, onset and duration of motor block, level of sedation, postoperative analgesia and side effects were recorded.

RESULTS: Heart rate was seen to fall significantly in Group D patients for the first 15 minutes. Measurements of mean blood pressure revealed significant decrease in Group D after 40 minutes, whereas the fall in Group C occurred after 15 minutes. Duration of sensory block was significantly longer in Group D patients (208±19.358 mins) as compared to Group M and C where the duration was (177±15.252 mins) and (177±17.800 mins) respectively. Higher levels of sedation were achieved in Group D and M where sedation score was 3 (fully asleep but arousable), 90% cases in Group D and 100% cases in Group M. The time at which first analgesic was given to patients (VAS score 4) was (271.50±21.831) in Group D and (202±25.047) in M and (218.50±38.013) in Group C. Dexmedetomidine significantly prolongs duration of analgesia providing pain relief in intraoperative and postoperative period. Injection of diclofenac sodium 75 mg intramuscular was used as rescue analgesic. The VAS score reached a value of 4 earlier in the midazolam and saline group than dexmedetomidine group.

CONCLUSION: Intravenous dexmedetomidine prolonged spinal anaesthesia, though midazolam did not. It also provided sedation and additional analgesia. Therefore, dexmedetomidine is appropriate during spinal anaesthesia, although heart rate needs to be monitored cautiously.