Methemoglobinemia

Aspect	Details
Condition	Methemoglobinemia (rare complication of isosorbide nitrate consumption)
Features	fatigue and brownish-colored blood
Cause	Nitrates oxidize hemoglobin (Fe²⁺) to methemoglobin (Fe³⁺)
Risk Factors	Higher in patients with coronary ischemia and anemia
Pulse Oximetry	Plateau of 80% to 85% irrespective of oxygen saturation
Diagnosis	Co-oximeters preferred to differentiate from carboxyhemoglobin, etc.
Treatment	Supportive care, cessation of isosorbide, methylene blue (1-2 mg/kg IV)

• Carboxy-hemoglobinemia - (carbon monoxide intoxication)

• Sideroblastic anemia - (ring sideroblasts, pyridoxine deficiency)

• Sulfhemoglobinemia - (irreversible, drug-induced - dapsone, sulfonamide)