Epidemiology

---

Etiology

---

• nitrites

Pathophysiology

---

• Methemoglobin is created when reduced ferrous iron (Fe2+) bound to oxyhemoglobin is oxidized to ferric iron (Fe3+).
• Ferric iron in methemoglobin cannot bind oxygen→ ↓ total blood oxygen content and ↓ blood oxygen saturation → tissue hypoxia

Tip

The ferric iron in methemoglobin has a high affinity for cyanide, thus, amyl nitrite-induced methemoglobin is used as a competitive inhibitor in the treatment of cyanide poisoning.

Clinical features

---

• Cyanosis (brownish-blue or gray skin and membranes)

Diagnostics

---

Treatment

---

• Methylene blue is the first-line treatment for acquired methemoglobinemia.
  • Acts as a cofactor to reduce methemoglobin to hemoglobin