Background: Treatment with analgesics before surgery may be effective in reducing post-operative pain. This approach is defined as "pre-emptive analgesia" and recent reviews show conflicting results.
Objectives: The aim of this study was to investigate the efficacy of pre-emptive analgesia with sublingual morphine sulphate, compared with sublingual midazolam in patients undergoing elective abdominal surgery.
Methods: Prior to surgery, 29 patients were randomized and premedicated with sublingual morphine sulphate 0.5 mg/kg (Group A; n = 15) or with sublingual midazolam 0.03 mg/kg (Group B; n = 14). General anaesthesia was maintained with sevoflurane and fentanyl. Post-operatively, intravenous (IV) acetaminophen 0.02 mg/kg was given to all patients and a bolus of IV morphine 0.1 mg/kg was given to Group B patients. Post-operative pain was controlled by IV morphine via a patient-controlled analgesia (PCA) device. IV acetaminophen 0.02 mg/kg was also administered four times daily. Efficacy was assessed using static Visual Analogue Scale (sVAS) scores, dynamic VAS (dVAS) scores, number of PCA doses administered and number of failed doses registered from the PCA device at 4, 6, 24 and 48 hours after surgery. Results were statistically analysed using the Student t-test; a value of p < 0.05 was considered significant.
Results: Significantly lower sVAS and dVAS scores were observed in Group A patients than in Group B at all assessment periods (p < 0.05 for all time points). There were less PCA administered and failed doses in Group A, compared with Group B (all time points p < 0.05). There was no difference in the occurrence of common side effects between the two treatments.
Conclusions: In patients undergoing elective abdominal surgery, premedication with sublingual morphine sulphate results in a better control of post-operative pain, compared to premedication with sublingual midazolam. The beneficial effect of pre-operative sublingual morphine sulphate was apparent in the immediate post-operative period and was sustained over the 48-hour assessment period.