Blocks of the brachial plexus above the clavicle — interscalene, superior trunk and, to a lesser degree, supraclavicular — commonly spread to the phrenic nerve and weaken the ipsilateral hemidiaphragm. A healthy patient tolerates this; a patient with severe COPD, obesity hypoventilation, contralateral phrenic palsy or limited reserve may not. Ask about breathlessness and home oxygen, check the other hemidiaphragm on a chest film if in doubt, and choose a more distal or diaphragm-sparing approach, or a lower volume, when reserve is poor. Warn every patient they may feel short of breath.
- Ask about breathlessness, home oxygen and sleep-disordered breathing before an interscalene or superior trunk block.
- Avoid proximal blocks in patients with contralateral diaphragm palsy.
- Consider a more distal block, lower volume or alternative analgesia when respiratory reserve is poor.
- Warn patients they may feel breathless after the block, and that it usually resolves as the block wears off.
Why it matters
Today's lead study shows significant diaphragm weakness is the norm after these blocks, not a rare complication.
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