Methemoglobinemia

Heme in Ferric state instead of Ferrous.

O2 content: Decreased
PaO2: Normal
SaO2: Decreased (Ferric state cannot bind O2)

Left shifts O2 Dissociation curve

Causes:
---> Heme oxidized by nitro/sulfa drugs: Dapsone, Primaquine, Nitroglycerin, Quinine, Trimethoprim/Sulfamethoxazole, Nitrofurantoin.
---> Person coming from Rocky Mountains - Have high Nitro compounds in such area
---> Common in HIV - Bcoz they are Rx with Trimethoprim/Sulfamethoxazole for P.Carinii

S/S:
Cyanotic
Blood: Chocolate colored -> cause increased Deoxy-Hb

Rx:
IV Methylene Blue: Gold standard -> activates methemoglobin reductase system which is normally not operative
Ascorbic Acid: Reducing agent, ancillary therapy.