Effectiveness and safety of intrathecal morphine for percutaneous endoscopic lumbar discectomy under low-dose ropivacaine: a prospective, randomized, double-blind clinical trial

BACKGROUND CONTEXT: Percutaneous endoscopic lumbar discectomy (PELD) is a surgical setting that requires minimal motor impairment. Low-dose spinal ropivacaine induces little motor blockade and could be ideal for maintaining safety of PELD, but its analgesic efficacy is question-able. An adjunct analgesic approach is needed to maximize the benefits of low-dose spinal ropiva-caine for PELD.PURPOSE: This study aimed to explore the effectiveness and safety of 100 mg intrathecal mor-phine (ITM) as an adjuvant analgesic method for PELD under low-dose spinal ropivacaine.STUDY DESIGN: A double-blind, randomized, placebo-controlled trial. Trial registration: ChiCTR2000039842 (www.chictr.org.cn). SAMPLE: Ninety patients scheduled for elective single-level PELD under low-dose spinal ropivacaine.OUTCOME MEASURES: The primary outcome was the overall intraoperative visual analogue scale (VAS) score for pain. Secondary outcomes were intraoperative VAS scores assessed at multi-ple timepoints; intraoperative rescue analgesic requirement; postoperative VAS scores; disability scale; patients' satisfaction with anesthesia; adverse events; and radiographic outcomes.METHODS: Patients were randomized to receive low-dose ropivacaine spinal anesthesia with (ITM group, n=45) or without (control group, n=45) 100 mg ITM.RESULTS: The overall intraoperative VAS score in the ITM group was significantly lower than that in the control group (0 [0, 1] vs 2 [1, 3], p<.001). During operation, the VAS scores at cannula insertion, 30 minutes after insertion, 60 minutes after insertion, and 120 minutes after insertion were all significantly lower in the ITM group (all p<.05). Less patients in the ITM group required rescue analgesia during operation compared with those in the control group (14% vs 42%, p= .003). The VAS score for back pain in the ITM group was lower than that in the control group at 1 hour, 12 hours, and 24 hours postoperatively. Besides, the satisfaction score in the ITM group was significantly higher than that in the control group (p=.017). For adverse events, 8/43 of ITM and 1/44 of control participants experienced pruritus (p=.014), with a relative risk (95% confidence interval) of 8.37 (1.09-64.16). The incidence of other adverse events was similar between the two groups. Of note, respiratory depression occurred in one ITM-treated patient.