A cadaver study to determine the minimum volume of methylene blue or black naphthol required to completely color the nerves relevant for anesthesia during breast surgery.

Regional anesthesia for breast surgery may require a large amount of local anesthetic solution to provide an adequate blockade of all relevant structures. The purpose of this study was to determine the minimal volume of fluid required to anesthetize all nerves to adequately provide anesthesia for breast surgery. This is an open randomized study. Cadavers were embalmed using Thiel's technique and were injected with different volumes of 0.2% methylene blue or 0.2% black naphthol for a superficial cervical plexus block (2, 5, 10, or 15 mL), an interscalene block (5, 10, 15, or 20 mL), paravertebral blocks from C(8) to T(6), and intercostal nerve blocks at 8 cm from the midline (2 or 3 mL) under ultrasound-guided or assisted techniques. The following minimal volumes of fluid were required for complete coloration of the nerves: 2 mL for the supraclavicular nerves; 20 mL for the nerve roots from C(5) to C(7), inclusive, if intraneural injection was avoided; 3 mL per root for the nerve roots from C(8) to T(6), inclusive, for a paravertebral block; and 2 mL per nerve for intercostal nerve blocks at T(4) and lower. With 20 mL of solution at the interscalene level, the roots of C(3) and C(4) were also colored; therefore, a separate injection for the supraclavicular nerves was unnecessary. We conclude that regional anesthesia for complex breast surgery can be achieved with a volume of local anesthetic as low as 41 mL.