EP003 Respiratory impact of local anaesthetic volume after an interscalene brachial plexus block with an extrafascial injection: a randomised controlled double-blinded trial

<h3>Background and Aims</h3> We have previously demonstrated that an extrafascial injection of 20 mL of local anaesthetic for interscalene brachial plexus block reduces the rate of hemidiaphragmatic paralysis by 70% compared with an intrafascial injection, with similar efficacy. In this double-blind trial, we tested the hypothesis that a local anaesthetic volume of 10 mL injected extrafascially would reduce the rate of hemidiaphragmatic paralysis versus a volume of 20 mL, while providing similar analgesia. <h3>Methods</h3> Sixty ASA I-III patients scheduled for elective shoulder surgery under general anaesthesia were randomised to receive ultrasound-guided extrafascial interscalene brachial plexus block using ropivacaine 0.75% 20 mL (control group) or 10 mL (low volume group) injected lateral to the brachial plexus sheath. The primary outcome was incidence of hemidiaphragmatic paralysis (diaphragmatic excursion reduction of &gt;75%), measured by M-mode ultrasonography, at 30 minutes after the procedure. Secondary outcomes included duration of analgesia and intravenous morphine consumption at 24 postoperative hours. <h3>Results</h3> The 30-minute hemidiaphragmatic paralysis rate was 80% (95% confidence interval [CI] 61–91%) in the control group and 19% (95% CI 8–40%) in the low volume group (p&lt;0.001). Patients in the low volume versus control group had a shorter duration of analgesia (550 vs. 873 min; p&lt;0.01) and higher intravenous morphine consumption (20 vs. 12 mg; p=0.03). <h3>Conclusions</h3> A low volume of local anaesthetic injected extrafascially reduced the rate of hemidiaphragmatic paralysis, but at the expense of a shorter duration of analgesia compared with standard dose extrafascial anaesthetic injection.