Administration of an interscalene block is associated virtually 100% of the time with which?

Administration of an interscalene block is associated virtually 100% of the time with which?

• A. Hoarseness
• B. Ulnar nerve blockade
• C. Ipsilateral Horner's syndrome
• D. Diaphragmatic hemiparalysis

Answer: (D)

Interscalene blocks target the upper brachial plexus (near the C5–C7 roots) but lie very close to the phrenic nerve, which runs along the anterior scalene muscle. The local anesthetic often spreads to or around the phrenic nerve, causing ipsilateral diaphragmatic paralysis (hemiparalysis) in virtually all cases with typical volumes. This proximity makes diaphragmatic dysfunction the most consistent and expected accompanying effect of this block. Hoarseness can occur if spread affects the recurrent laryngeal nerve, and Horner’s syndrome can occur with sympathetic involvement, but these are not universal. Ulnar nerve blockade would require spread to parts of the lower trunk or medial cord and is not a common or consistent finding with an interscalene approach.

Interscalene blocks target the upper brachial plexus (near the C5–C7 roots) but lie very close to the phrenic nerve, which runs along the anterior scalene muscle. The local anesthetic often spreads to or around the phrenic nerve, causing ipsilateral diaphragmatic paralysis (hemiparalysis) in virtually all cases with typical volumes. This proximity makes diaphragmatic dysfunction the most consistent and expected accompanying effect of this block.

Hoarseness can occur if spread affects the recurrent laryngeal nerve, and Horner’s syndrome can occur with sympathetic involvement, but these are not universal. Ulnar nerve blockade would require spread to parts of the lower trunk or medial cord and is not a common or consistent finding with an interscalene approach.