Ropivacaine 0.2% vs 0.4% for US-Guided Interscalene CPNB

Study Summary

The study looked at 65 adult patients undergoing total shoulder replacement or rotator cuff repair (arthroscopic or open). One of two experienced operators placed a perineural catheter under ultrasound guidance next to the C5-6 nerve roots in the interscalene region. An initial bolus of 30ml of 0.5% ropivacaine was administered preoperatively, and the patients subsequently also received a general anesthetic. Postoperatively, the patients were started on a continuous perineural infusion of ropivacaine at 2ml/h with patient-controlled boluses of 5ml. They were randomized to receive either a 0.2% or 0.4% concentration of ropivacaine. All patients also received round-the clock acetaminophen and diclofenac.

There was no difference between the groups for all indices of postoperative analgesia (pain scores at rest and movement on postoperative days 1 and 2, supplemental opioid, ropivacaine boluses, night awakenings). There were, however, significantly fewer episodes of an insensate arm (0 vs 5) in the 0.2% ropivacaine group, as well as greater patient satisfaction (95% CI 8.6-9.6 vs 6.8-8.7).

The specifics of the technique used in this study should be noted when attempting to generalize the results to one's clinical practice. In particular, experienced operators performed all the blocks, and the catheter tip was placed adjacent to the C5-6 nerve roots using ultrasound-guidance. This may account for the effectiveness of an infusion at only 2 ml/h.

Other studies of varying local anaesthetic concentration in continuous interscalene (1) and infraclavicular block (2) have also found that 0.2% ropivacaine solution at 8ml/h provides better postoperative analgesia than 0.4% ropivacaine at 4ml/h. As the authors of this paper point out, these findings indicate that volume, rather than concentration, may be the important factor in determining analgesic efficacy of continuous peripheral nerve blockade of the upper limb.

References

1. Le LT et al. Effects of local anesthetic concentration and dose on continous interscalene nerve blocks: a dual-center, randomized, observed-masked, controlled study. Reg Anesth Pain Med 2008;33:518-25.
2. Ilfeld BM et al. The effects of local anesthetic concentration and dose on continuous infraclavicular nerve blocks: a multicenter, randomized, observer-masked, controlled study. Anesth Analg 2009;108:345-50.