A comparison of epidural tramadol and epidural morphine for postoperative analgesia

The present study compared epidural tramadol with epidural morphine for postoperative analgesia in 20 patients undergoing major abdominal surgery. Intraoperatively, the patients were anaesthetized by a balanced technique of general anaesthesia combined with lumbar epidural lidocaine. In ten of the patients 100 mg tramadol diluted in 10 ml normal saline was also injected epidurally, while 4 mg epidural morphine was used in the other ten patients. In all patients, the visual analogue pain score, PaO₂, PaCO₂ and respiratory rate were monitored every hour for the first 24 hr postoperatively. In both the tramadol and morphine groups, the mean hourly pain scores ranged from 0.2 ± 0.6 to 1.4 ± 2.5 throughout the period of observations. However, the mean PaO₂ was decreased postoperatively in the epidural morphine group, while no change was observed in the epidural tramadol group. The maximal decrease of PaO₂ in the epidural morphine group was observed at the tenth hour postoperatively, when it decreased to 72.8 ± 10.3 mm Hg. This was not associated with any increase in PaCO₂ or a decrease of respiratory rate, suggesting that hypoxaemia rather than hypercarbia or decreased respiratory rate may be an earlier indicator of respiratory depression in patients breathing room air without oxygen supplementation. The absence of clinically relevant respiratory depression following epidural tramadol compared with epidural morphine may be attributed to the different mechanisms of their analgesic action. The results suggest that epidural tramadol can be used to provide prolonged postoperative analgesia without serious side effects.