Similar to cyanide it impairs oxygen utilization and induces lactic acidosis via anaerobic metabolism. The gas is a byproduct of the decomposition of organic materials and occurs in caves, volcanoes, sulfur springs, sewers, swamps, petroleum processing, paper production, and leather finishing and manufacturing. Treatment is supportive. Hyperbaric oxygen and induction of methemoglobin via amyl or sodium nitrate are controversial but may be helpful.
Source
Irwin & Rippe's Intensive Care Medicine, 5th ed.