Impact of the addition of sufentanil 5 microg or clonidine 75 microg on the minimum local analgesic concentration of ropivacaine for epidural analgesia in labour: a randomized comparison.

BACKGROUND

Addition of lipophilic opioids or alpha2-agonists to local anaesthetic solutions reduces local anaesthetic requirements and side effects. While the efficacy and side effects of these adjuvants are dose-related, information about their relative analgesic potencies is lacking, making it difficult to draw meaningful clinical conclusions. The aim of the present study was to assess the relative sparing of ropivacaine by clinically relevant doses of sufentanil and clonidine using the minimum local analgesic concentration (MLAC) model.

METHODS

In this prospective, double-blind study, the sparing effect of sufentanil 5 microg and clonidine 75 microg on the MLAC of ropivacaine administered for labour epidural analgesia was compared in 78 women at <5 cm cervical dilatation. Women were randomly allocated to one of three groups: plain ropivacaine, ropivacaine with sufentanil 5 microg and ropivacaine with clonidine 75 microg.

RESULTS

The MLAC of plain ropivacaine was 0.099% wt/vol (95%CI: 0.090 to 0.109) and was reduced to 0.036% wt/vol (95% CI: 0.024 to 0.049) when combined with sufentanil 5 microg and to 0.036% wt/vol (95% CI: 0.027 to 0.046) with clonidine 75 microg (P < 0.001). The wt/wt local anesthetic sparing potency ratio of sufentanil to clonidine was 15.1 (95% CI: 10.3 to 23.4).

CONCLUSIONS

Sufentanil 5 microg and clonidine 75 microg produce similar reductions in the MLAC of ropivacaine. This finding will make feasible the assessment of the side effects of these adjuvants administered at equipotent doses in further studies.