Use of high-flow nasal cannula in a pregnant patient with methemoglobinemia: A case report

Pregnancy complicated by methemoglobinemia is a rare clinical condition, primarily characterized by cyanosis and desaturation. The effectiveness of conventional oxygen therapy is often limited, and the optimal respiratory support has not been determined. A 31-year-old Chinese woman at 29 weeks of gestation presented with intermittent chest tightness, cyanosis, and a methemoglobin (MetHb) level of 16.6% on arterial blood gas analysis (ABG). Although conventional oxygen therapy via nasal cannula or face mask maintained her pulse oxygen saturation (SpO 2 ) at 93–95%, it failed to relieve her chest tightness. Her clinical condition subsequently worsened, with the development of respiratory alkalosis and activity-induced oxygen desaturation. High-flow nasal cannula (HFNC) therapy was initiated at a flow rate of 30 L/min, with an inspired oxygen fraction (FiO 2 ) of 40% and a temperature of 34°C, resulting in rapid resolution of chest tightness within 2 hours. The patient underwent an uncomplicated cesarean section, with favorable maternal and fetal outcomes. This case demonstrates that HFNC may have improved respiratory comfort and reduced the work of breathing while definitive medical therapy addressed the underlying methemoglobinemia. Therefore, it may represent a valuable non-invasive respiratory support modality.