[Patent blue V : inert dye or potent allergen].

Patent blue V is widely used as a food dye. Clinically, patent blue V dye has been increasingly used in oncological surgery to identify the sentinel lymph nodes in breast cancer and other malignancies. The case of a patient who developed severe anaphylactic shock to subcutaneous injection of patent blue V during breast surgery is presented. The clinical course and the anesthesiological management are presented, and the pitfalls that may delay the correct diagnosis are highlighted.