Field blocks require lower concentrations of local anesthetic than nerve blocks.

• A. Higher
• B. The same
• C. Not applicable
• D. Lower

Answer: (D)

The amount of local anesthetic needed depends on how the drug reaches the nerves. In a field block, the anesthetic is injected into tissue around the surgical area and then diffuses to nearby small nerve fibers over a broad area. Because the nerves are relatively close to the injection site and many fibers are affected, a lower concentration is enough when you can use a larger volume to bathe the field. The goal is adequate diffusion to block multiple nociceptive fibers across the area.

In a nerve block, the anesthetic is placed directly around a specific nerve or plexus and must penetrate the protective nerve coverings (like the perineurium) to reach the axons. That diffusion barrier means you typically need a higher concentration to achieve reliable blockade of all the fibers within the nerve.

So field blocks use lower concentrations than nerve blocks.