The effect of motor activity on the onset and progression of brachial plexus block with bupivacaine: a randomized prospective study in patients undergoing arthroscopic shoulder surgery.

BACKGROUND: A decreased latency of onset of neural blockade has been noted when muscular exercise of the hand was performed after supraclavicular brachial plexus block using lidocaine. In this observational study, we examined the effect of repetitive muscle contraction of the hand on the speed of onset of interscalene brachial plexus block (ISB) using bupivacaine.

METHODS: Forty patients were enrolled, all of whom received an ISB as one component of their anesthetic management for elective arthroscopic shoulder surgery. Patients were asked either to rest their arms after the performance of the ISB (nonexercise group) or to perform a repetitive hand exercise for 5 min (exercise group). Bilateral hand grip strength and tolerance to transcutaneous electrical stimulation were used to quantify the degree of motor and sensory blockade.

RESULTS: Patients in the exercise group had a statistically significant lower tolerance to transcutaneous electrical stimulation 20 min after completion of the block (P < 0.05).

CONCLUSIONS: Our results imply that attempting to use a frequency-dependent conduction block with repetitive motor activity as a clinical adjuvant to brachial plexus block with bupivacaine is without merit.