Background: The primary goal of ambulatory anaesthesia is rapid recovery leading to early patient discharge with minimal side effects. Ropivacaine, due to its property of sensory-motor dissociation, may be a potentially useful agent when an equivalent spinal anaesthesia and quicker recovery of motor function is desirable. The main objective of our study was to compare 0.75% intrathecal isobaric ropivacaine (15mg) and 0.5% intrathecal isobaric bupivacaine (10mg) to assess the efficacy of anaesthesia, analgesia, postoperative recovery profile and readiness for discharge in patients undergoing arthroscopic knee surgery.

Materials and methods: 90 adult ASA grade 1 and 2 patients were randomized into two groups to receive 2 ml plain solution of either 0.5% bupivacaine (Group B) or 0.75 % ropivacaine (Group R). In the intraoperative period, onset, efficacy, duration and regression of sensory and motor block were noted in both the groups at regular intervals. Postoperatively, the groups were compared for pain score using the visual analog scale (VAS), recovery profile using post anaesthetic discharge scoring system (PADSS), analgesic requirement and complications.

Results:  The mean time of onset of sensory block at L1 was significantly less (p=0.025) and duration of sensory (284.64 vs 257.57 mins) and motor block (250.07 vs 222.11 mins) was significantly more (p=0.001) with bupivacaine as compared to ropivacaine. Maximum upper level of sensory block was at T8 in both the groups, and the number of patients who attained this block was significantly more with bupivacaine (37.4% vs 22%, p=0.017). The number of patients who required 2 analgesic doses on the first postoperative day (33.3% vs 11.1%, p=0.011) and incidence of delayed voiding of urine (13.33% vs 0; p = 0.022) was significantly more with ropivacaine. There was no difference in postoperative recovery profile and discharge times between the groups.

Conclusions: Isobaric bupivacaine provides a shorter onset and longer duration of sensory block, decreased postoperative analgesic requirement and lesser complication rate as compared with isobaric ropivacaine. Though, isobaric ropivacaine is associated with a shorter duration of motor block, postoperative recovery profile and discharge time between the groups was similar. Therefore, isobaric bupivacaine should be preferred over isobaric ropivacaine for day care knee arthroscopy, especially in cases with anticipated longer duration of surgery.