[A case of prolonged reduction in arterial oxygen saturation measured by pulse oxymetry after administering patent blue in an elderly patient].

A 93-year-old woman with a vulvar cancer was scheduled for resection of the tumor and sentinel lymph node biopsy under general anesthesia. At the beginning of the operation, a total of 20 ml of 2.5% patent blue was injected into the tumor and the surroundings to identify sentinel lymph node. After the injection, arterial oxygen saturation measured by pulse oximetry gradually dropped to 80%. The oxygen saturation recovered to the original level at 300 min post-injection, but blue pigmentation distributed throughout her body persisted until the following day. Her perioperative course was uneventful. In case of desaturation after dye injection, it is important to rule out true hypoxemia immediately by performing arterial blood gas analysis. Conversely, CO-oximetry is not necessarily useful for accurate diagnosis.