Dose–response relationship of local anaesthetic volume to hemidiaphragmatic paralysis following ultrasound-guided supraclavicular brachial plexus block: A randomised controlled trial

Background and Aims: Local anaesthetic (LA) volume is a recognized determinant of hemi diaphragmatic paralysis (HDP) following ultrasound-guided supraclavicular brachial plexus block (SCB). This randomised controlled trial aimed to evaluate the dose–response relationship between LA volume and the incidence and severity of HDP in patients undergoing upper limb orthopaedic surgery.Materials and Methods: In this prospective, randomised, parallel-group trial, 150 ASA physical status I/II patients aged 18–80 years with BMI 75% reduction or paradoxical movement) at the same intervals.Results: Baseline diaphragmatic excursions were comparable across groups (2.19 ± 0.26 cm, 2.14 ± 0.40 cm, 2.25 ± 0.45 cm; P = 0.125). At 15 and 30 minutes, diaphragmatic excursion was significantly more reduced in Groups 1 and 2 compared with Group 3 (P < 0.001). The incidence of partial HDP at 15 minutes was 65%, 100%, and 22% in Groups 1, 2, and 3, respectively (P < 0.001). At 30 minutes, partial HDP incidence was 66% (Group 1), 100% (Group 2), and 38% (Group 3) (P = 0.049). No patient developed complete HDP.Conclusions: A dose-dependent increase in diaphragmatic impairment was observed with higher LA volumes during US-guided supraclavicular block. Volumes ≥20 mL were associated with a significantly higher incidence of partial hemi diaphragmatic paralysis (HDP), whereas 15 mL reduced but did not eliminate HDP risk. These findings support the use of lower LA volumes when diaphragmatic sparing is clinically prioritized.