The effect of intrathecal midazolam on the characteristics of bupivacaine spinal block and postoperative analgesia in gynaecological procedures

Objectives: The present study was undertaken to determine the onset of sensory block, the time to achieve the maximum level of sensory block and the analgesic efficacy of intrathecal midazolam when given in combination with bupivacaine, and also to observe any undesirable side-effects produced by the midazolam-bupivacaine combination. Setting and subjects: One hundred patients [American Society of Anesthesiologists (ASA) I and ASA II] aged 45-60 years and posted for elective gynaecological surgery, were randomly allocated to two groups of equal size. Group 1 (n = 50) received 12.5 mg of 0.5% hyperbaric bupivacaine with 0.4 ml of normal saline in the L3-L4 interspace, while Group 2 (n = 50) received 12.5 mg (2.5 ml) of 0.5% hyperbaric bupivacaine with 0.4 ml (2 mg) of preservative-free midazolam. Standard monitoring of haemodynamic parameters was recorded throughout the procedure. Outcome measures: The onset of sensory block, the time to achieve maximum sensory block and the level of block were also chronicled. The sedation scores were noted every two minutes for 20 minutes and then every 10 minutes until the end of surgery. Pain assessment was carried out according to the visual analogue scale (VAS) score. The duration of the painfree period up to rescue analgesia, or a VAS score greater than 40 mm, was documented. Unwanted side-effects were also recorded. Results: There was no significant difference in the demographic distribution of the patients. There was no statistically significant difference in the onset of the sensory block (p-value = 0.735) and time to achieve maximum level of sensory block in both groups (p-value = 0.45). The sedation score was comparable in both groups. There was a significantly higher duration of pain-free period in Group 2 (274.9 +/- 18.07 minutes) than in Group 1 (187.2 +/- 16.8 minutes) (p-value < 0.05). The number of rescue medications that were required was also significantly lower in the study group than in the controls. The number of patients who developed bradycardia and hypotension was comparable. Conclusion: The addition of midazolam to intrathecal bupivacaine prolonged the duration of postoperative analgesia in this study, without affecting the onset of block and without increasing the risk of side-effects.