Pulse oximetry is commonly used in clinical practice as an indirect monitor of blood oxygen saturation. There are many factors, however, that can interfere with accurate readings. We present a case of a woman with metastatic thyroid cancer that had a sudden drop in her pulse oximetry during bronchoscopy and that eventually was found to have an uncommon cause for a misleading persistently low oxygen saturation.
Keywords: Hypoxemia, methemoglobin, acidosis, methylene blue, methemoglobinemia
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