Prospective randomized trial of patient-controlled analgesia with ketamine and morphine or morphine alone after hysterectomy

BACKGROUND: previous studies have shown that adding ketamine to morphine for postsurgical pain can reduce the unwanted side effects of morphine. However, it is not known if the combination of ketamine and morphine reduces pain to a greater extent than morphine alone after hysterectomy. OBJETIVE: the primary objective was to determine whether the use of low-dose ketamine with morphine reduces pain to a greater extent than morphine alone. The secondary objective was to determine whether the use of low-dose ketamine with morphine was associated with fewer unwanted adverse effects. METHODS: thirty women scheduled for abdominal hysterectomy were randomly assigned to receive either ketamine and morphine or morphine alone. A double-blind procedure was used. Pharmacy staff prepared the syringes for patient-controlled analgesia, using a 1:1 ratio of 2 mg/mL solutions for the combination treatment and a solution with concentration 2 mg/mL for the morphine-only treatment. The Mann-Whitney U test was used to compare identified outcome measures for the 2 groups (nausea and vomiting, sedation, dizziness, hallucinations, nightmares, dreams, and amount of drug consumed). RESULTS: there were no significant differences between the 2 treatment groups for the primary outcome of pain after 24 h or for any of the secondary outcome measures. CONCLUSIONS: this study adds to the body of knowledge indicating that low-dose ketamine and morphine combined is no better than morphine alone in alleviating pain and that the combination offers no advantage in terms of unwanted side effects.