When performing an interscalene block with a peripheral nerve stimulator you note diaphragmatic movement. You should now

When performing an interscalene block with a peripheral nerve stimulator you note diaphragmatic movement. You should now

• A. Inject the local anesthetic as the needle is in an appropriate location
• B. Redirect the needle in an anterior direction
• C. Redirect the needle in a more cephalad direction
• D. Redirect the needle in a posterior direction

Answer: (D)

Diaphragmatic movement during an interscalene block with a nerve stimulator means the phrenic nerve is being stimulated, because it lies on the anterior surface of the anterior scalene and can be reached if the needle is too anterior. To reduce this risk, redirect the needle toward the posterior aspect. A posterior shift moves away from the phrenic nerve and toward the posterior brachial plexus elements, allowing the block to be performed while minimizing phrenic nerve stimulation and potential diaphragmatic paralysis. Injecting further in an already anterior position would keep hitting the phrenic nerve; redirecting more cephalad doesn’t specifically address the phrenic nerve location, and going anterior would worsen it.

Diaphragmatic movement during an interscalene block with a nerve stimulator means the phrenic nerve is being stimulated, because it lies on the anterior surface of the anterior scalene and can be reached if the needle is too anterior. To reduce this risk, redirect the needle toward the posterior aspect. A posterior shift moves away from the phrenic nerve and toward the posterior brachial plexus elements, allowing the block to be performed while minimizing phrenic nerve stimulation and potential diaphragmatic paralysis. Injecting further in an already anterior position would keep hitting the phrenic nerve; redirecting more cephalad doesn’t specifically address the phrenic nerve location, and going anterior would worsen it.