The effects of intrathecal midazolam on the duration of analgesia in patients undergoing knee arthroscopy

Background: Spinal anaesthesia is a common anaesthetic technique for lower limb surgery. Many adjuvants have been tried to prolong the duration of analgesia provided by local anaesthetics when administered intrathecally. Midazolam has been shown to prolong the duration of analgesia when used as an adjuvant, providing the added advantages of mild sedation and amnesia, while being devoid of neurotoxicity, and the adverse effects of opioids. This study was designed to evaluate the effect of 2 mg preservative-free intrathecal midazolam added to spinal bupivacaine during postoperative analgesia, and the incidence of adverse effects, if any, in patients undergoing knee arthroscopies. Method: Fifty consenting American Society of Anesthesiologists (ASA) physical status I or II patients of either gender (men = 19, women = 31), aged between 18-56 years, were randomly allocated to two groups (25 each). Group M received 0.5% hyperbaric bupivacaine with preservative-free midazolam 2 mg intrathecally, and Group S received 0.5% hyperbaric bupivacaine with saline intrathecally. Peak sensory level, total duration of analgesia, duration of motor blockade, pain score using the Visual Analogue Scale, and sedation score using the Observer Assessment Score of Sedation were assessed, along with vital parameters, namely heart rate and systolic, diastolic and mean blood pressure. Results: The total duration of analgesia observed was significantly higher in Group M (399 ± 88.11 minutes) vs. Group S (301.60 ± 110.14 minutes), and the pain score was lower in Group M (33.6 ± 4.68 mm) vs. Group S (56.6 ± 8.64 mm). Conclusion: The addition of preservative-free midazolam 2 mg to intrathecal 0.5% hyperbaric bupivacaine prolongs the duration of analgesia without any observed adverse effects in patients undergoing knee arthroscopies.