A comparative study of analgesic effects of ketamine, fentanyl and saline added to hyperbaric bupivacaine for central neuraxial blockade in total knee replacement surgery: A prospective, randomised, double-blind and placebo-controlled study

Background: Various adjuvants were combined with local anaesthetic agents, either intrathecally or epidurally, to prolong the duration of a denser neuraxial block and achieve adequate intraoperative conditions. Methods: In this prospective randomised double-blind placebo-controlled study, 90 patients were randomly allocated into three groups of 30 each depending upon the intrathecal adjuvant used. Standardised anaesthetic technique and monitoring for subarachnoid block (and epidural catheter placement) with 3 mL of 0.5% hyperbaric bupivacaine was followed. In addition, Group K (n = 30) received 0.3 mg/kg of preservative-free ketamine, Group F (n = 30) received 25 μg (0.5 mL) of fentanyl and Group C (control group, placebo, n = 30) received 0.5 mL normal saline. Time of onset and duration of sensory and motor block and duration of analgesia, haemodynamic parameters, sedation scores intra-operatively and post-operatively and side effects were recorded and analysed. Results: The mean time (sec) to onset of sensory (P = 0.04) and motor (P = 0.02) blockade was prolonged, and the duration (min) of sensory (P = 0.003) and motor (P = 0.009) block and the duration of analgesia (min) (P = 0.022) were shorter in the Group K compared to other two groups. Fentanyl showed shorter onset time, longer duration of sensory and motor block and duration of analgesia in contrast to ketamine and placebo. Conclusions: Fentanyl (25 μg) was superior to 0.3 mg/kg of ketamine and placebo as an intrathecal adjuvant with minimal side effects.