A Case of Acquired Methemoglobinemia Following Sentinel Lymph Node Dye With Patent Blue V.

Methemoglobinemia is a rare but potentially life-threatening condition in which hemoglobin is oxidized, impairing the oxygen-carrying capacity. While congenital forms exist, acquired methemoglobinemia can occur in perioperative settings, especially following exposure to oxidizing agents such as dyes used in sentinel lymph node biopsy (SLNB). Patent Blue V, a synthetic aniline dye commonly used for SLNB, has been associated with rare but serious adverse effects, including methemoglobinemia. We report a case of acquired methemoglobinemia in a 68-year-old female undergoing bilateral modified radical mastectomy with SLNB for breast carcinoma. The patient experienced a sudden and progressive decline in oxygen saturation (SpO2) following administration of 6 ml of 2.5% Patent Blue V. Despite supplemental oxygen therapy, hypoxia persisted, prompting arterial blood gas (ABG) analysis, which confirmed methemoglobinemia (9.2%). Immediate treatment with methylene blue (1 mg/kg) resulted in rapid clinical improvement, with the methemoglobin levels normalizing within eight hours. This case highlights the importance of early recognition and treatment of acquired methemoglobinemia, particularly in a perioperative setting. Patent Blue V is associated with both hypersensitivity reactions and methemoglobinemia, and its interference with pulse oximetry readings can complicate intraoperative monitoring. Prompt administration of methylene blue remains the standard treatment, leading to favorable outcomes. Clinicians should be vigilant regarding the possibility of methemoglobinemia when using dyes such as Patent Blue V during surgical procedures. Diagnostic tools, such as ABG or co-oximetry, are essential for accurate diagnosis, and early treatment with methylene blue can prevent serious complications.