[False decrease in pulse oximetry readings due to patent blue in a patient with breast cancer].

Abstract

A 61-year-old woman with breast cancer was scheduled for breast preserving therapy under general anesthesia. After the tracheal intubation, 4 ml of 2% patent blue was injected into the skin to determine sentinel lymph node. Thirty seconds after injection, the pulse oximetry reading (SpO2) decreased from 100% to 60% and recovered to 90% over the next 5 minutes. At the time when SpO2 was 88%, arterial blood gas analysis showed PaO2 184.4 mmHg (FIO2 0.45) and all other vital signs were normal. About 120 minutes later, SpO2 rose to 99%. The operation was completed uneventfully and the patient recovered from anesthesia smoothly. After extubation, arterial blood gas analysis was performed again and it showed PaO2 of 82.5 mmHg (FIO2 0.21). We conclude that patent blue injection caused this decrease in SpO2 and recommend to evaluate the oxygen status not only by pulse oximetry but also by blood gas analysis when patent blue is used.