Pre-injection of saline on the anterior scalene muscle reduced brachial plexus nerve block-induced hemidiaphragmatic paralysis.

Objective: This study aimed to evaluate the effect of pre-injecting normal saline over the anterior scalene muscle (ASM) on the incidence of hemidiaphragmatic paralysis (HDP) following an interscalene brachial plexus block (ISB). Methods: In this randomized controlled trial, 60 patients selected to upper extremity surgery were divided into two groups: the ASM group (10 ml saline pre-injection followed by 10 ml 0.25% ropivacaine ISB) and the control group (ISB alone). Diaphragmatic excursion (DE) was measured via ultrasonography at baseline and 10, 20, and 30 min post-block during rest and forced breathing. HDP was defined as follows: partial HDP was defined as a ≥ 25% reduction, and complete HDP as a ≥ 75% reduction, in DE from the baseline measurement. Additional Cadaveric dissections assessed anesthetic spread. Results: At 30 min, the ASM group had significantly lower HDP incidence than controls (rest breathing: 16.6% vs. 76.7%, Conclusion: ASM saline pre-injection significantly reduces HDP after ISB without compromising analgesia. This technique may broaden ISB use in patients with respiratory limitations by minimizing diaphragmatic dysfunction.