Intrathecal morphine for postoperative analgesia; comparison between three small doses in anorectal surgery

Intrathecal morphine [ITM] has a magic role in postoperative pain relief. The use of less than the optimal dose of ITM to avoid its side effects results in inadequate analgesia. To obtain the dose of intrathecal morphine which provides the best balance between analgesic efficacy and side effects in patients subjected to anorectal surgery. This control random blind study included 48 patients ASA I and II physical status scheduled for anorectal surgery under spinal anesthesia. The patients were allocated into four equal groups, all received 1 ml of 0.5% hyperbaric bupivacaine intrathecally to which is added 1 ml of 0.9% saline in the control group, 0.1 mg morphine in 1 ml of 0.9% saline in group 7, 0.2 mg morphine in 1 ml 0.9% saline in group 17 and 0.3 mg morphine in 1 ml 0.9% saline in group III. Postoperatively the patients were evaluated for any pain during the first 24 hours, rescue analgesia in the form of I.V. tenoxicam was administered on patient request. The amount of requested analgesics was recorded. The patients were followed for the incidence of pruritis and whether it requires treatment or not, postoperative nausea and vomiting [PONV], urinary retention and respiratory depression. The incidence of pain and requested analgesia was significantly less only in group III in comparison to the control group and group I. Although there was no significance difference in the dose of rescue analgesia between the 4 groups, the number of patients experienced pain after the maximal dose of tenoxicam decreased nonsignificantly from the control group [8 patients] to 4 patients in group I and significantly to 2 and 0 patients in groups II, III respectively. The incidence of pruritus was more significant only in groups II and III in comparison to the control group and group I. Pruritus required treatment only in one patient in each of group II and III with no significant difference between the four groups. There was no significant difference in the incidence of PONV and urinary retention between the four groups. There was no evidence of respiratory depression in the four groups. 0.3 mg ITM in conjunction with 20-40 mg tenoxicam provides excellent analgesia for 24 hours in anorectal surgery with minimal side effects