FCEM2-0802

A 35 year old man presents to the emergency department complaining of worsening difficulty breathing that has been developing over the last 2 days. His partner mentioned that he looked pale. He informs you that he usually doesn’t take any medications but started taking chloroquine for malaria prevention 5 days ago as he is planning to travel to Kenya next week. His oxygen saturation is 89% on room air and you observe that he appears bluish in color. Upon obtaining a blood gas, you notice that his blood has a chocolate-like hue. What is the probable diagnosis?