Bupivacaine Versus Ropivacaine on Diaphragmatic Motility and Ventilatory Function

Background: Outpatient continuous interscalene brachial plexus blocks are used to control pain after shoulder surgery, with infusions of 0.125% bupivacaine or 0.2% ropivacaine. There have been no studies comparing the effects of these two formulations. The major concern is hemidiaphragmatic paresis, and since ropivacaine preferentially blocks sensory fibers, it may cause less blockade of the phrenic nerve. This study was to evaluate the effects of continuous interscalene brachial plexus infusions, with the hypothesis that respiratory function is more affected by 0.125% bupivacaine than 0.2% ropivacaine, with equal effects on pain relief. Methods: All patients underwent baseline spirometry and ultrasound evaluation of diaphragmatic excursion, followed by interscalene catheter placement for their surgery, then randomized to receive a pump containing 0.2% ropivacaine or 0.125% bupivacaine. Patients returned to the hospital the following day for spirometry, ultrasound reevaluation, and evaluation of their pain level since discharge.