Untangling a rare case of hypoxia

ABSTRACT

Introduction: Hypoxia is a very common symptom during this COVID-19 pandemic. Detailed history, clinical examination and relevant investigations are important in distinguishing rare causes from commonest. Case Report 52-year-old lady presented to emergency room with sudden onset breathlessness. She was recently diagnosed with Idiopathic Thrombocytopenic Purpura (ITP). She was found to be hypoxic with a room air saturation of 82% in pulse oximeter. She was started on high flow oxygen. But her saturation didn't improve. Chest X-ray showed normal lung fields and bedside echocardiography revealed normal cardiac status. Point of care blood gas analysis (ABG) revealed a normal partial pressure of oxygen (Pao2-100). The discrepancy between oxygen saturation recorded in pulse oximetry and PaO2 in blood gas analysis tempted us to relook the ABG. It was found that the methaemoglobin level in ABG was 10.7%. When we analysed her drug history, we found that there was dapsone intake for the treatment of ITP which strongly supported us to reach the diagnosis of methemoglobinemia. She was then treated with intravenous methylene blue in the emergency room. She responded well and her repeated ABG revealed normalized level of methaemoglobin. Her hypoxia also resolved. Dapsone was later removed from her regular medications. Conclusion: Methemoglobinemia is an extremely rare cause for hypoxia. Though rare its potentially life threatening if not identified on time. Refractory hypoxia with a discrepancy in spo2 and PaO2 should raise the suspicion of methemoglobinemia. IV methylene blue is the recommended treatment for methemoglobinemia.