Smartwatch Detection of Refractory Hypoxemia in Phenazopyridine-Induced Methemoglobinemia: A Case Report

Significant cases of methemoglobinemia will cause a signal interference in traditional dual-wavelength pulse oximetry leading to the classic finding of “refractory hypoxemia”. As smartwatches begin to incorporate pulse oximetry capabilities, it is unclear whether these devices will demonstrate the same type of interference in the presence of methemoglobinemia. This article reports a case where a patient’s Apple Watch© reported a hypoxemia alert in the setting of phenazopyridine induce methemoglobinemia. This is a case report of a 71-year-old female whose Apple Watch© reported a hypoxemia alarm in the setting of methemoglobinemia caused by phenazopyridine use. The patient’s smartwatch began signaling hypoxemia alerts the day before she noticed clinical cyanosis. 24 hours after the hypoxemia alerts began, she presented to the Emergency Department (ED) with shortness of breath and blue discoloration of skin. The Apple Watch© recorded oxygen saturation readings between 73% and 86%. Upon arrival to the ED, the patient’s SpO2 was 84% on traditional hospital-grade dual-wavelength pulse oximetry and her methemoglobin level was 19.8%. Her symptoms and methemoglobinemia resolved after administration of 1 mg/kg of IV methylene blue. Pulse oximetry used in smartwatch technology can trigger a hypoxemia alarm in the presence of drug-induced methemoglobinemia. If demonstrated to be a reproducible finding, smartwatch technology has the potential to be used as part of an early detection system for clinically significant methemoglobinemia.