Pulmonary function changes during interscalene brachial plexus block: effects of decreasing local anesthetic injection volume.

BACKGROUND AND OBJECTIVES: During interscalene block, ipsilateral hemidiaphragmatic paresis occurred in all patients who received > 34 ml of local anesthetic in the authors' previous studies. This study was done to determine whether diaphragmatic function could be spared by a smaller local anesthetic volume.
METHODS: Twenty patients were randomly assigned to receive either a 45 ml or 20 ml interscalene brachial plexus block. For all blocks, 1.5% mepivacaine with added epinephrine and bicarbonate was used. Baseline serial measurements and those over a 30-minute test period before surgery were analyzed for significant differences between groups in onset or final change in any of the following measured variables: cephalad dermatomal extent of sensory anesthesia, clinically assessed upper extremity motor function, ipsilateral hemidiaphragmatic excursion during maximal sniff (inspiratory), and pulmonary function.
RESULTS: There were no clinically significant differences between groups in any of the measured variables. Large reductions in routine pulmonary function tests were measured in all patients in both groups at 2 minutes after injection. At 30 minutes, baseline forced vital capacity (FVC) had diminished by 40.9 +/- 11.7% in the 45 ml group and 32.0 +/- 8.9% in the 20 ml group. One patient with pre-existing chronic obstructive pulmonary disease had a decrease in FVC from 1.83 l to 0.59 l, a 68% decrement from the baseline measurement, both measured in the supine position.
CONCLUSION: Reducing the volume of local anesthetic to 20 ml did not prevent the 100% incidence of diaphragmatic paresis or significantly lessen the compromise in pulmonary function that had been reported to occur during interscalene brachial plexus anesthesia.

RCT Entities:   Population Interventions Outcomes