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

Area of Science:

• Anesthesiology
• Thoracic Surgery
• Pulmonary Medicine

Background:

• Interscalene blocks are associated with ipsilateral hemidiaphragmatic paresis when large local anesthetic volumes (>34 ml) are used.
• Previous studies indicated a high incidence of diaphragmatic dysfunction following interscalene blocks.

Purpose of the Study:

• To determine if a reduced local anesthetic volume (20 ml) could spare diaphragmatic function during interscalene brachial plexus blocks.
• To assess the impact of reduced anesthetic volume on pulmonary function and sensory/motor block characteristics.

Main Methods:

• Twenty patients undergoing interscalene brachial plexus block were randomized to receive either 45 ml or 20 ml of 1.5% mepivacaine with epinephrine and bicarbonate.
• Diaphragmatic excursion during maximal sniff, pulmonary function tests, sensory anesthesia extent, and motor function were measured before and for 30 minutes after injection.

Main Results:

• No significant differences were observed between the 45 ml and 20 ml groups in any measured variable.
• All patients experienced significant reductions in pulmonary function tests within 2 minutes post-injection.
• At 30 minutes, forced vital capacity (FVC) decreased by approximately 40.9% in the 45 ml group and 32.0% in the 20 ml group.

Conclusions:

• Reducing local anesthetic volume to 20 ml did not prevent diaphragmatic paresis during interscalene blocks.
• Smaller anesthetic volumes did not significantly lessen the compromise in pulmonary function compared to larger volumes.