The Effect of Continuous Interscalene Brachial Plexus Block With 0.125% Bupivacaine Versus 0.2% Ropivacaine on Diaphragmatic Motility and Ventilatory Function

INTRODUCTION

Shoulder surgery is associated with severe postoperative pain and continuous interscalene brachial plexus blocks can control this pain. Compared to single-shot injections, continuous interscalene blocks can increase patient satisfaction, decrease narcotic requirements, which then decreases postoperative nausea and vomiting , improve quality of sleep and decrease hospital length of stay .

The concept of continuous peripheral nerve blocks at home (CPNBH) with disposable pumps began in 1998 in Sweden. The authors chose 0.125% bupivacaine for interscalene catheters and their choice was not based on any evidence in the literature, but rather "because this concentration was already available at the institution for epidural infusions" (personal communication, Dr. Narinder Rawal, January 2013). Two years later, as ropivacaine became more widely available, others chose to evaluate the safety and efficacy of 0.2% ropivacaine for continuous interscalene infusions. Again, the choice of this specific concentration was not evidence-based, but rather "because the company made it in this concentration" (personal communication, Dr. Stephen Klein, January 2013). To date, published reviews show that most studies use either of those formulations, yet there have been no studies comparing the effects of these two drugs and concentrations, particularly on pain relief and on major side effects of CPNBH.

One of those major side effects is ipsilateral phrenic nerve paresis. This is because blockade of the brachial plexus at the interscalene groove with a single large-volume injection causes diaphragmatic hemiparesis in 100% of patients. This incidence is decreased to 20% with a continuous infusion of a dilute solution11, where 9% of patients have a subjective feeling of shortness of breath. An ideal infusate in CPNBH would control postoperative pain and have minimal effects on the phrenic nerve.

Ropivacaine has been shown to have blockade properties that differ from bupivacaine; specifically, ropivacaine seems to preferentially block sensory nerve fibers, while weakly blocking motor fibers. It is not known whether this translates into a more attenuated block of the phrenic nerve with ropivacaine. Therefore, the purpose of this study was to evaluate the effects of continuous interscalene peripheral nerve blocks with 0.125% bupivacaine versus 0.2% ropivacaine, comparing their effect on pain relief and respiratory function. The primary hypothesis is that respiratory function is more affected by bupivacaine than ropivacaine, with equal effects on pain relief.