The study investigated whether preinjection of saline into the anterior scalene muscle reduces hemidiaphragmatic paralysis (paralysis of the diaphragm) after interscalene brachial plexus block. Sixty patients scheduled for upper extremity surgery were divided into two groups - one received 10 ml of physiological solution before the blockade, and the other only the blockade itself. Diaphragmatic motility measurements by ultrasonography were performed at baseline and subsequently 10, 20, and 30 minutes after the block. After 30 minutes, the saline pre-injection group had a significantly lower incidence of hemidiaphragmatic paralysis – 16.6% in quiet breathing compared to 76.7% in the control group and 10% in forced breathing compared to 70%. Fewer patients in the preinjection group experienced hypoxemia (3.3% vs. 26.6%) and hoarseness (0% vs. 20.2%), while the analgesic effect was similar in both groups. Cadaveric dissections confirmed that saline blocked the spread of anesthetic towards the phrenic nerve. The authors conclude that this technique may expand the use of interscalene blockade in patients with respiratory problems.