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 questionable. An adjunct analgesic approach is needed to maximize the benefits of low-dose spinal ropivacaine for PELD.

PURPOSE: This study aimed to explore the effectiveness and safety of 100 µg intrathecal morphine (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 multiple 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 µg 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.

CONCLUSION

The addition of 100 µg ITM to low-dose ropivacaine appears to be effective in analgesia without compromised motor function for PELD; however, ITM increased the risk of pruritus and clinicians should be vigilant about its potential risk of respiratory depression.