Preoperative adjuvant epidural tramadol: the effect of different doses on postoperative analgesia and pain processing

Background: Tramadol is an analgesic with combined opioid agonist and monoamine reuptake blocker properties, which may be useful as a perioperative analgesic and antinociceptive adjuvant.
Methods: The dose-dependent effects of adjuvant preoperative epidural tramadol on postoperative analgesia (pain scores and patient-controlled analgesia (PCA) use) and pain processing (heat pain thresholds) were prospectively studied in a double-blind, randomised, placebo-controlled 5-day trial. Forty patients undergoing knee or hip surgery received anaesthesia with epidural lidocaine and epidural tramadol 20, 50 or 100 mg or placebo as a preoperative adjuvant. Postoperative analgesia was by intravenous PCA tramadol in all patients.
Results: Postoperative pain scores were similar in all groups. The time to first PCA use was shorter, the total dose and duration of PCA use greater, and side-effects more common with 20 mg tramadol than with 100 mg or placebo ( P <0.05). There were no differences in PCA doses required or side-effects between the tramadol 100 mg and placebo treatment groups. Heat pain tolerance thresholds were increased with 100 mg tramadol at 48 h postoperatively compared to baseline and placebo ( P = 0.01).
Conclusions: Preoperative adjuvant epidural tramadol does not improve postoperative analgesia after lidocaine epidural anaesthesia compared to placebo. Tramadol 20 mg results in anti-analgesia and increased side-effects. While tramadol 100 mg depresses postoperative pain-processing, as measured by heat pain tolerance thresholds, this is not reflected in improved clinical pain measures.