The effects of adjuvant intrathecal fentanyl on postoperative pain and rebound pain for anorectal surgery under saddle anesthesia

BACKGROUND: Intrathecal opioid has been known to enhance the quality and prolong the duration of spinal anesthesia, as well as to reduce postoperative pain. The purpose of this study was to evaluate postoperative analgesic characteristics of intrathecal fentanyl for the first 48 hours after anorectal surgery under saddle anesthesia. METHODS: Eighty patients were recruited in our study. Forty patients were randomly allocated to group B that received 0.5% bupivacaine 5 mg with 0.3 ml normal saline. The other 40 patients were assigned to group BF which was given 0.5% bupivacaine 5 mg with fentanyl 15 μg. The primary outcome variable was a numeric rating scale (NRS) at six hours postoperatively. Secondary outcomes included changes in the NRS score between one and 48 hours postoperatively, consumption of rescue analgesics, and the frequency of rebound pain. RESULTS: Group BF exhibited a lower mean NRS score at postoperative six hours compared to group B (P < 0.001). However, the mean NRS score was not different after postoperative six hours between the two groups. The median consumption of rescue analgesics in group BF was less than that of group B (P = 0.028) and the frequency of rebound pain decreased in group BF when compared to group B (P = 0.021). The levels of sensory block were S1 dermatome and motor block scores were 0 for both groups. There was no significant difference in adverse effects between the groups. CONCLUSIONS: Intrathecal fentanyl 15 μg for anorectal surgery under saddle anesthesia led to an improved pain score for the first six hours after surgery and decreased postoperative analgesic use. Rebound pain diminished with intrathecal fentanyl and adverse effects did not increase.