Inject only as much anesthetic as is needed to create this “donut” appearance. With experience, we have found that the three forearm nerves can be adequately blocked with a total of 10 mL of anesthetic agent (much lower than the maximum dosing guidelines). Withdraw the needle and apply a dressing to the skin site.

Duration and toxicity of anesthetic agents. Table 2 shows the duration and maximum dosages of the most commonly used anesthetic agents.

Complications

Ultrasound-guided nerve blocks are a useful technique to supply anesthesia to the hand, but like all procedures, may have associated complications.

Inadvertent vascular puncture and intraneural injections (two feared but uncommon complications) can be avoided by selecting an injection site where the nerve and artery are sufficiently separate and by visualizing the needle tip during the procedure. Inadvertent vascular puncture can also be avoided by drawing back on the syringe before injection, and ensuring that anechoic fluid is visualized on the ultrasound screen when anesthetic is deposited. To avoid intraneural injections, infuse anesthetic under low pressures. If the patient experiences any pain or paresthesias during the injection, stop injecting and pull back the needle until it is clear that the needle tip is not within the nerve bundle.

References

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