Postoperative analgesia with epidural bupivacaine and low-dose fentanyl--a comparison of two concentrations.

BACKGROUND

The purpose of the study was to compare the analgesic and side effects of two epidurally administered mixtures of bupivacaine and fentanyl with the same drug ratios.

METHODS

One hundred patients scheduled for colorectal surgery were randomized to receive a thoracic epidural infusion of either bupivacaine 0.12% with fentanyl 2 micrograms/ml or bupivacaine 0.24% with fentanyl 4 micrograms/ml during 48 h postoperatively. The pumps were adjusted to keep the visual analogue scale (VAS) pain score at 3 or less (on a scale of 0-10) with a minimum of adverse effects.

RESULTS

There were no statistically significantly differences between the two groups in VAS pain scores. The average VAS pain score resting varied between 0.5 and 1, and coughing between 1.9 and 3.4. One case of respiratory depression with breathing frequency 7 occurred in each group, but none of the patients required naloxone. One patient in the low concentration group developed partial motor weakness in both legs 36 h postoperatively. Equal drug amounts--bupivacaine 10.8-11 mg/h and fentanyl 18-18.4 micrograms/h--were given in both groups throughout the study.

CONCLUSIONS

Both groups had low pain scores with few and comparable adverse effects. It thus seems that the volume is not important when mixtures of bupivacaine and fentanyl in the studies concentrations are infused epidurally at a low thoracic level. Practical reasons favour the higher concentration mixture.