Combined sciatic-femoral nerve block with 0.75% ropivacaine: effects of adding a systemically inactive dose of fentanyl.

To evaluate the effects of adding low-dose fentanyl to 0.75% ropivacaine during peripheral nerve blocks, 30 ASA physical status I-II patients undergoing hallux valgus repair under combined sciatic-femoral nerve block were randomly allocated in a double-blind fashion to receive nerve block placement with 30 mL of either 0.75% ropivacaine alone (group: ropivacaine, n = 15) or 0.75% ropivacaine plus fentanyl 1 microg kg(-1) (group: ropivacaine-fentanyl, n = 15). A blinded observer recorded haemodynamic variables and sedation, as well as the time required to achieve surgical block and the first request for analgesia. Readiness to surgery required 10 min (5-20 min) with 0.75% ropivacaine and 10 min (3-20 min) with the ropivacaine-fentanyl mixture. No differences in the degree of sedation, peripheral oxygen saturation, and haemodynamic variables were observed between the two groups. The degree of pain measured at first analgesic request, and the consumption of postoperative analgesics, was similar in the two groups, while the mean time from block placement to the first request for pain medication was 13.7 h (25-75th percentiles: 11.8-14.5 h) in the ropivacaine group and 13.9 h (25-75th percentiles: 10.5-14.5 h) in the ropivacaine-fentanyl group (P = not significant). We conclude that adding fentanyl 1 microg kg(-1) to 0.75% ropivacaine did not provide clinically relevant advantages in terms of onset time, quality and duration of combined sciatic-femoral nerve block in patients undergoing elective hallux valgus repair.