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

## TL;DR

Injecting saline before a brachial plexus block reduces diaphragm paralysis without affecting pain relief, potentially making the procedure safer for patients with breathing issues.

## Contribution

A novel pre-injection technique using saline to reduce hemidiaphragmatic paralysis during brachial plexus blocks is introduced and validated.

## Key findings

- ASM group had significantly lower hemidiaphragmatic paralysis incidence compared to controls at 30 minutes post-block.
- Saline pre-injection reduced hypoxemia and hoarseness without compromising analgesic outcomes.
- Cadaveric dissections confirmed saline blocked anesthetic spread toward the phrenic nerve.

## Abstract

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).

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.

At 30 min, the ASM group had significantly lower HDP incidence than controls (rest breathing: 16.6% vs. 76.7%, p < 0.001; forced breathing: 10% vs. 70%, p < 0.001). DE reduction was also milder in the ASM group (p < 0.001). No statistically significant differences were found between the ASM and control groups at post-operation (95% CI:−11.8 to 22.3; P = 0.551). Fewer ASM patients experienced hypoxemia (3.3% vs. 26.6%, p = 0.027) or hoarseness (0% vs. 20.2%, p = 0.024), with equivalent analgesia (p > 0.05). Cadaveric studies confirmed that saline blocked anesthetic spread toward the phrenic nerve.

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.