Case Presentation: Patient is a 23-year-old male with attention deficit hyperactivity disorder and depression who presented with a chief complaint of shortness of breath and bluish discoloration of his skin. Patient was at a friend’s house for dinner where he ate pork leg and returned home thereafter. One hour after dinner, he began to experience symptoms of tingling in his extremities, difficulty breathing, and severe headache. Soon after, he became lethargic and confused and his skin began to turn blue. Given his experience as a firefighter and emergency medical technician, he was concerned about methemoglobinemia and ultimately came to the hospital. In the waiting room, he was noted to be hypoxic to the sixties and immediately placed on a non-breather with improvement in oxygen saturation to eighties. He was subsequently escalated to high flow nasal cannula. Vital signs were notable for tachycardia and tachypnea. Labs were drawn immediately, and blood was noted to be brown in color. ABG noted a pH of 7.54, partial pressure of carbon dioxide (pCO2) 26, partial pressure of oxygen (PaO2) 425, and a bicarbonate of 22. Given concern for methemoglobinemia, toxicology was consulted, and the patient was immediately given methylene blue. Of note, complete blood count and comprehensive metabolic profile were within normal limits. Methemoglobin level was noted to be 53. With administration of methylene blue, patient’s oxygen saturation quickly improved, and he was weaned off supplemental oxygen and his cyanosis quickly resolved. Over the next 24 hours, the patient’s methemoglobin normalized, and he returned to his baseline clinical status.
Discussion: Methemoglobinemia is a potentially fatal disease in which ferrous hemoglobin is oxidized to the ferric state, called methemoglobin. Unlike hemoglobin, methemoglobin does not bind oxygen and therefore cannot deliver oxygen to the tissues leading to tissue hypoxia and cyanosis. There are a few genetic causes, but acquired forms are more common, in which formation of methemoglobin is induced by various exogenous substances. One of those exogenous substances includes nitrites, which is widely used to help cure meat products. Nitrites can oxidize hemoglobin to methemoglobin. To test for methemoglobin, you would need to obtain a serum methemoglobin level. The calculated oxygen saturation on ABG is falsely elevated in methemoglobinemia and pulse oximetry cannot detect methemoglobin. The failure of the oxygen saturation to improve with administration of supplemental oxygen is a clue that should raise the suspicion for methemoglobinemia. Cases in which methemoglobin levels are above 30% or lower if symptomatic from hypoxia, are considered medical emergencies. The treatment of choice is methylene blue, along with supplemental oxygen. Therefore, early identification and treatment are crucial to prevent potentially fatal outcomes of methemoglobinemia.
Conclusions: There are many acquired causes of methemoglobinemia, including meats cured with nitrites as in our case and it is a potentially fatal disease. Fortunately, it is easily treatable and reversible with methylene blue, and therefore prompt recognition of methemoglobinemia is vital.