Pulmonary Function and Interscalene Block

The objective of our study is to compare the degree of phrenic nerve blockade after interscalene block using 0.1% ropivacaine or 0.2% ropivacaine. Our hypothesis is that using a lower concentration of local anesthetic will result in lesser degree of phrenic nerve block. 40 patients will be enrolled. Half will receive the block with 0.1% ropivacaine and half with 0.2% ropivacaine. Phrenic nerve and diaphragm function will be assessed by bedside spirometry and ultrasound visualization.