Evaluation of efficacy and side effects of different doses of intrathecal Morphine for postoperative analgesia after anorectal surgery

Abstract EN

Background : Intrathecal opioids are frequently used in the management of postoperative pain, but may be associated with many adverse effects such as pruritus, nausea, vomiting, urinary retention, and respiratory depression, which may limit their use.

Aim of this study was to compare between six different doses of IT morphine (0.1 mg, 0.2 mg, 0.3 mg, 0.4 mg, 0.5 mg and 1 mg) as regarding postoperative analgesia and the side effects of IT morphine, and to determine the optimal dose of IT morphine that provides satisfactory analgesia to the patient with minimal side effects.

Methods : This study was conducted in Anesthesiology Department, Assiut university hospital, after approval of the local ethics committee.

Our study was performed on 95 patients of ASA physical status? And?? Aged from 20 to 40 scheduled for anorectal surgeries.

Spinal anesthesia was performed, with the patient in the sitting position, at L4, 5.

Each patient received 5 mg of hyperbaric bupivacaine with different doses of IT morphine in a total volume of 2 ml.

patients were kept in the sitting position for five minutes to get sacral block.

Intraoperative monitoring: Heart rate, O2 saturation, and non-invasive blood pressure were monitored.

Postoperative monitoring: Patients were evaluated for any pain or side effect of IT morphine (Pruritus, PONV, urinary retention, and respiratory depression) during the first 24 hours.

Supplemental analgesia in the form of I.V.

tenoxicam was available on patient request, and the doses needed for each patient were recorded.

Antipruritic and antiemetic therapy was available on patient request.

Results : Increasing the dose of IT morphine decreases the incidence of pain during the first 24 hours and subsequently decreases the need for supplemental analgesia.

The doses of 0.1 mg and 0.2 mg are comparable with each other as regard to pain relief.

100% of the patients receiving 0.1 mg and 75% of the patients receiving 0.2 mg of IT morphine experienced pain during the first 24 hours and subsequently required supplemental analgesia and even with 40 mg of I.V.

tenoxicam, some patient complained of postoperative pain.

The doses of 0.3 mg, 0.4 mg or 0.5 mg are comparable with each other.

Theses doses are enough to provide 24-hours analgesia in more than 50% of patients.

This percentage increases to 100% with the use of 20-40 mg of tenoxicam intravenously.

The dose of 1 mg provides 24-hours analgesia in 87% of patients.

Increasing the dose of IT morphine causes significant increase in the incidence and severity of pruritus.

Postoperative nausea and vomiting occurred in 30% of the patients in the control group.

There is a non-significant increase in both the incidence and severity of PONV by increasing the dose of IT morphine.

Urinary retention occurred in 20% of the patients in the control group.

Increasing the dose of IT morphine causes significant increase in the incidence of urinary retention.

Respiratory depression was not detected in any patient.

In conclusion : Our study clearly demonstrated that the use of IT morphine in a dose of 0.3 mg in adjuvant with intravenous tenoxicam in a dose of 20-40 mg provides excellent pain relief for 24 hours after anorectal surgeries with minimal side effects of IT morphine.