Dose-Response Relationships for Hemidiaphragmatic Paresis Following Ultrasound-Guided Supraclavicular Block

"M-mode tracings of right diaphragm motion will be made and recorded by a skilled anesthesiologist. Patients will be examined in the supine position and scanned from a low intercostal or subcostal approach using the liver as an acoustic window. Patients will be asked to perform a voluntary sniff (VS) test, for which they will be asked to forcefully inhale through the nose in a sniffing position. The above measurement will be performed immediately preceding the brachial plexus blockade, and then at 15 minute and 30 minutes after block."

The patient will be positioned supine with the head turned to the contralateral side. The ultrasound will be placed in the supraclavicular fossa, and the skin and subcutaneous tissues will be infiltrated lateral to the probe with 2% lidocaine. The anesthesiologist can redirect the needle and perform additional injections for complete coverage of the brachial plexus. The local anesthetic will be a 2:1 mix of 1.5% mepivacaine and 0.5% bupivacaine.

A bedside negative inspiratory force (NIF) meter will be used to measure negative inspiratory force prior to the block and 30 minutes after the block.