Methemoglobinemia in Babies
According to the National Institutes of Health, methemoglobinemia occurs when an abnormal amount of hemoglobin, part of red blood cells, builds up in the blood. This blood disorder may be due to either a genetic disorder where it runs in families, or it may be acquired due to environmental factors such as drugs, chemicals or even certain foods such as beets or food additives.
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Inherited Forms
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Methemoglobinemia that is genetic has two forms. The first form is due to a problem with a certain enzyme, cytochrome b5 reductase. In this form, both parents carry the gene for the disorder but typically neither has the disorder themselves.
In the first form there are two types, Type I and Type II. In Type I, also known as erythrocyte reductase deficiency, red blood cells lack the cytochrome b5 reductase enzyme. In Type II, also known as generalized reductase deficiency, the problem is that the enzyme is unable to work anywhere in the body, and is not limited to the red blood cells.
The second form of inherited methemoglobinemia is also called hemoglobin M disease and requires only one parent to be a carrier. This is caused by defects in the hemoglobin molecule.
Acquired Forms
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Acquired methemoglobinemia is more common than the inherited forms and occurs after exposure to certain chemicals and drugs. It is more likely to occur in premature infants and babies younger than four months of age.
It can be caused by anesthetics such as benzocaine and Xylocaine, the chemical benzene, antibiotics such as dapsone and chloroquine and nitrates, which are used in meats as a preservative but also found in water near farms.
Seriously ill infants and infants who are fed too many nitrate rich vegetables such as beets can also acquire the disorder. However, according to the Centers for Disease Control and Prevention, most acquired cases of methemoglobinemia are attributed to drinking water contaminated with nitrates typically from run-off from farm fertilizers.
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Symptoms
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Genetic forms of methemoglobinemia are asymptomatic other than cyanosis, or bluish coloration of the skin. However, if undetected and untreated, symptoms in the type II form or generalized reductase deficiency eventually can include failure to thrive, developmental delays, seizures and mental impairments. Symptoms of the acquired form are usually mild but can include cyanosis, lethargy, dizziness, headache and impaired mental function.
Diagnosis
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Diagnosis of methemoglobinemia in a baby will occur due to cyanosis. However, arterial blood gases and pulse oximetry, or the measurement of oxygen saturation measured non-invasively with a sensor, will be normal. A blood test for methemoglobin levels will reveal numbers in the 40 to 50 percent range, while a level around 1 percent is normal.
Treatment and Prognosis
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Treatment for inherited forms of methemoglobinemia is with the drug methylene blue, typically as a 1 percent IV solution delivered over five minutes then repeated an hour later if levels are at 30 percent or higher. This treatment is not done if the patient has G-6-PD deficiency, a blood disease, as the medicine is dangerous for such individuals. Ascorbic acid (vitamin C) is also helpful for treating methemoglobinemia, usually as a daily supplement of 200 to 500 mg. Other alternative treatments include hyperbaric oxygen therapy and exchange transfusions, where the patient's blood is slowly removed and replaced with donor blood or plasma.
Those with mild acquired methemoglobinemia often require no treatment other than avoiding the agent that precipitated the condition. Severe cases however may require blood transfusion.
The prognosis for methemoglobinemia is good for most cases of Type I and hemoglobin M disease. Those with acquired methemoglobinemia typically do well once the cause is avoided. Those with Type II have a more dire prognosis often only surviving a few years.
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