Background Anorectal surgery can lead to significant postoperative pain. One common approach involves the addition of neuraxial opioids to local anesthetics, which has shown promise for improving patient pain outcomes. However, this method may be associated with adverse effects, such as urinary retention, nausea, and vomiting. This study primarily aimed to compare the incidence of postoperative urinary retention in patients undergoing anorectal surgery using morphine and nalbuphine. Methods A total of 150 patients undergoing anorectal surgery were randomized into three groups. Groups B, N, and M received intrathecal 0.5% hyperbaric bupivacaine (5–10 mg) alone, or with 0.2 mg nalbuphine or 0.15 mg morphine, respectively. The primary outcome was the incidence of postoperative urinary retention, defined as the inability to void spontaneously within 7 h after surgery. The secondary outcomes included postoperative pain scores, nausea and vomiting scores, pruritus scores, sedation scores, use of rescue medications, and the volume of catheterized urine. Results The incidence of postoperative urinary retention was 8% (4/50) in both Group N and Group B ( P = 1.00), and 60% (30/50) in Group M. Group N reported significantly lower postoperative pain scores at 12 h compared to Group B. Group M exhibited significantly lower pain scores at 6 and 12 h, but demonstrated a significantly higher incidence of urinary retention, nausea, vomiting, and pruritus compared to both groups N and B ( P = 1.00). Conclusions Intrathecal 0.2 mg nalbuphine as an adjuvant to bupivacaine effectively reduces postoperative pain without increasing the risk of urinary retention. In contrast, while intrathecal morphine provides slightly better analgesia, it is associated with significantly higher incidences of urinary retention and other opioid-related side effects. Trial registration Thai Clinical Trials Registry identifier: TCTR No.20240328010
Thepsoparn et al. (Fri,) studied this question.