Epidural fentanyl decreases the minimum local analgesic concentration of epidural lidocaine.

BACKGROUND

Epidural lidocaine can be used when regional anesthesia needs to be established quickly, but the effect of co-administering epidural fentanyl on the minimum local analgesic concentration (MLAC) of lidocaine is not known. We compared the MLAC of epidural lidocaine in combination with different doses of fentanyl for epidural anesthesia in adults.

METHODS

One hundred and twenty patients requiring epidural analgesia were randomly allocated to receive 20 ml of one of four solutions: lidocaine, or lidocaine plus fentanyl 1 µg/ml, 2 µg/ml, or 3 µg/ml. The first patient in each group was administered 1% lidocaine weight by volume; subsequent patients received a concentration determined by the response of the previous patient to a higher or lower concentration according to up and down sequential allocation in 0.1% increments. Efficacy was assessed using a visual analog pain scale, and accepted if this was = 10 mm on a 100 mm scale within 30 minutes. The extent of motor block and of nausea and vomiting were recorded at 30 minutes after administration of the epidural solution and two hours after surgery, respectively.

RESULTS

The MLAC of lidocaine in those receiving lidocaine alone was 0.785% (95%CI 0.738 - 0.864). A significant dose-dependent reduction was observed with the addition of fentanyl: the MLAC of lidocaine with fentanyl at 2 µg/ml was 0.596% (95%CI 0.537 - 0.660) and 0.387% with fentanyl at 3 µg/ml (95%CI 0.329 - 0.446, P < 0.001).

CONCLUSION

Epidural fentanyl significantly reduces the dose of lidocaine required for effective epidural analgesia in adults without causing adverse side effects.