→ cannot participate in oxygen transport. → Excess __ can cause tissue hypoxia– because of incapable binding to oxygen. Treatment:

Methemoglobinemia - ferrous hemoglobin iron oxidized → ferric ion Treatment: →high flow oxygen (conc. greater than 30%) to symptomatic patients with methemoglobinemia to maximize oxygen saturation on the residual normal ferrous hemoglobin → concentrations greater than 30%, methylthioninium chloride (Methylene Blue) 2 mg/kg − intravenously over 5–10 minutes as a 1% solution.