BACKGROUND: Pain after Caesarean section is often treated with opioids with a risk of side effects. Wound infiltration with local anaesthetics is effective and has few side effects, but volume vs. dose concentration has not been examined.

METHODS: Ninety patients scheduled for elective Caesarean section included in a randomised, double-blinded, placebo-controlled trial receiving infiltration with 50 ml ropivacaine 0.5% or 125 ml ropivacaine 0.2% or 50 ml 0.9% saline (placebo) during surgery. Surgery was performed under lumbar spinal anaesthesia. Primary endpoint was post-operative pain. Secondary endpoints were rescue analgesic, post-operative nausea and vomiting, time spent in the postanesthesia care unit (PACU) and time to first mobilisation.

RESULTS: No difference in pain response between groups, but time until maximum pain score was prolonged in the ropivacaine 0.5% group compared with the placebo group (P = 0.0493). The administration of ketobemidone at 24 h post-operatively in the ropivacaine 0.5% group was reduced compared with the placebo group (P = 0.020), and between the ropivacaine 0.2% group and the ropivacaine 0.5% group (P = 0.044). No significant differences between groups were found concerning time spent in the PACU, to first mobilisation or in number of women with nausea/vomiting (P ≥ 0.05). No complications related to ropivacaine were observed.

CONCLUSIONS: Systematic infiltration with a high concentration, low volume compared with low concentration, high volume showed no significant effect on post-operative pain intensity. However, a statistically significant, but clinically limited opioid sparing effect was demonstrated compared with placebo in the high concentration, low volume group.