Final answer:
The major complication of an interscalene block is diaphragmatic paralysis, which is a result of the local anesthetic affecting the phrenic nerve. This can lead to breathing difficulties, particularly in patients with underlying respiratory issues.
Step-by-step explanation:
The question asks about a complication associated with the interscalene block, which is a type of regional anesthesia technique used particularly for surgeries of the shoulder and upper arm. The most commonly reported major complication of this procedure is diaphragmatic paralysis. This occurs due to the local anesthetic spreading to the phrenic nerve, which innervates the diaphragm. Diaphragmatic paralysis can lead to compromised respiratory function, especially in patients with pre-existing lung conditions. Other potential complications of an interscalene block can include inadvertent epidural or spinal anesthesia, local anesthetic toxicity, nerve injury, and hematoma formation. It is crucial for practitioners to be aware of these complications and to monitor patients accordingly.