• Christian Steen-Hansen, Mikkel H Madsen, LangeKai H WKHWDepartment of Anaesthesiology, Nordsjaellands Hospital, University of Copenhagen, Copenhagen, Denmark.Department of Clinical Medicine, University of Copenhagen, Copenhagen, Denmark., Lars H Lundstrøm, and Christian Rothe.
• Department of Anaesthesiology, Nordsjaellands Hospital, University of Copenhagen, Copenhagen, Denmark.
• Acta Anaesthesiol Scand. 2023 Jan 1; 67 (1): 104111104-111.

BackgroundA shoulder block without lung affection is desirable. In this study, we compared a low versus a high volume of a modified supraclavicular brachial plexus block. We hypothesised that a low volume of local anaesthetic would provide non-inferior block success rate with better preserved lung function.MethodsHealthy volunteers were randomised to receive ultrasound guided 5 or 20 ml ropivacaine 0.5% at the departure of the suprascapular nerve from the brachial plexus. Primary outcome was successful shoulder block-defined as cutaneous sensory affection of the axillary nerve and motor affection of the suprascapular nerve (>50% reduction in external rotation force measured with dynamometry). We used a non-inferiority margin of 20%. Secondary outcome was change in lung function measured with spirometry.ResultsThirteen of 16 (81.3%; 95% confidence interval [CI] 57.0% to 93.4%) in the 5 ml group and 15 of 16 (93.8%; 95% CI 71.7% to 98.9%) in the 20 ml group had successful shoulder block (p = .6). The ratio of the event rates of the 20 ml (standard) and 5 ml (intervention) groups was (15/16)/(13/16) = 0.937/0.813 = 1.15 (95% CI 0.88 to 1.51). All mean reductions in lung function parameters were non-significantly lower in the 5 ml group compared with the 20 ml group.ConclusionFor our primary outcome, the 95% CI of the difference of event ratio included the non-inferiority margin. We are therefore unable to conclude that 5 ml LA is non-inferior to 20 ml LA with respect to block success rate.© 2022 Acta Anaesthesiologica Scandinavica Foundation.

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