False low oximetry reading caused by patent blue vital dye during breast surgery

Patent blue vital (patent blue V; Laboratoire Guerbet, France) is used to identify the sentinel node during surgery for invasive breast cancer. Detecting the sentinel node that first drains the primary tumor reduces the need for total breast and wide axillary node removal, with the problems that such radical surgery involves. Like other dyes, patent blue V can interfere with accurate pulse oximeter reading, leading to underestimation of real values. We report the case of a 31-year-old woman who underwent lumpectomy and removal of the sentinel node. After intradermal injection of patent blue V dye into the left breast (100 mg administered because the sentinel node was difficult to locate) a drop in peripheral oxyhemoglobin saturation from 99% to 93% was detected by the pulse oximeter. When arterial blood gas analysis showed normal values and other causes were ruled out, the diagnosis was false low oximetry reading due to patent blue V dye.