methemoglobinemia


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Related to methemoglobinemia: Blue baby syndrome

Methemoglobinemia

 

Definition

When excessive hemoglobin in the blood is converted to another chemical that cannot deliver oxygen to tissues, called methemoglobin.

Description

The molecule hemoglobin in the blood is responsible for binding oxygen to give to the body. When hemoglobin is oxidized to methemoglobin its structure changes and it is no longer able to bind oxygen. Hemoglobin is constantly under oxidizing stresses: however, normally less than 1% of a person's hemoglobin is in the methemoglobin state. This is due to the body's systems that reduce methemoglobin back to hemoglobin. Infants have a higher risk of acquiring methemoglobinemia because infant hemoglobin is more prone to be oxidized to methemoglobin.

Causes and symptoms

Methemoglobinemia can either be congenital or acquired.
There are two causes of the congenital form. One cause is a defect in the body's systems to reduce methemoglobin to hemoglobin. The other cause is a mutant form of hemoglobin called hemoglobin M that cannot bind to oxygen. Both of these forms are typically benign.
Acquired methemoglobinemia is caused by an external source, usually a drug or medication. Some of these medications include benzocaine, lidocaine and prilocaine. These medications can inhibit the body's systems of reducing methemoglobin to hemoglobin resulting in methemoglobinemia.
With a methemoglobin level of 3-15% skin can turn to a pale gray or blue (cyanosis). With levels above 25% the following symptoms may be present:
  • Cyanosis unaffected by oxygen administration
  • Blood that is dark or chocolate in color that will not change to red in the presence of oxygen
  • Headache
  • Weakness
  • Confusion
  • Chest pain
When methemoglobin levels are above 70% death may result if not treated immediately.

Diagnosis

Diagnosis is based on the symptoms and history. If these are indicative of methemoglobinemia blood tests are performed to confirm the presence and level of methemoglobin.

Treatment

For acquired methemoglobinemia the typical treatment is with methylene blue. This is administered with an IV over a five-minute period and results are typically seen within 20 minutes. Methylene blue reduces methemoglobin back to hemoglobin.
Though congenital methemoglobinemia is usually benign, the form due to a defective reducing system can be treated with ascorbic acid (vitamin C) taken daily. The other congenital form due to hemoglobin M has no treatment as of late.

Alternative treatment

There are not any known alternative treatments for methemoglobinemia. Methylene blue, or a similar treatment, is needed to reduce methemoglobin to hemoglobin.

Prognosis

If found early, acquired methemoglobinemia can be easily treated with no side effects. After treatment with methylene blue the patient can expect a full recovery.
Congenital methemoglobinemia is typically benign and should be observed. If methemoglobinemia symptoms occur the person should be taken to the hospital for treatment.

Prevention

If a person gets methemoglobinemia from a certain medication that medication should be avoided at all costs in the future. For people with congenital methemoglobinemia medications or other things that are known to oxidize hemoglobin should be avoided.

Resources

Books

Beutler, Ernest. "Methemoglobinemia and Other Causes of Cyanois." In Williams Hematology. 6th ed. New York: McGraw-Hill, 2001, pp. 611-17.

Periodicals

Wilburn-Goo, Dawn, and Lloyd. "When Patients Become Cyanotic: Acquired Methemoglobinemia." Journal of the American Dental Association June 1999: 826-31.
Wright, Lewander, and Woolf. "Methemoglobinemia: Etiology, Pharmacology, and Clinical Management." Annals of Emergency Medicine November 1999: 646-56.

Other

eMedicine. Website. 2001. http://www.emedicine.com.

Key terms

Cyanosis — When the body does not receive enough oxygen.
Oxidation — When a chemical element or compound loses an electron.
Reduction — When a chemical element or compound gains an electron.

methemoglobinemia

 [met-he″mo-glo″bĭ-ne´me-ah]
the presence of excessive methemoglobin in the blood, resulting in cyanosis and headache, dizziness, fatigue, ataxia, dyspnea, tachycardia, nausea, vomiting, and drowsiness, which can progress to stupor, coma, and occasionally death. It may be either chemical- or drug-induced (acquired or toxic methemoglobinemia) or hereditary (congenital or hereditary methemoglobinemia).

met·he·mo·glo·bi·ne·mi·a

(met-hē'mō-glō'bi-nē'mē-ă),
The presence of methemoglobin in the circulating blood; when severe, there is inadequate oxygenation of the tissues. Methemoglobin causes the blood to have a brownish color, which may be mistaken for cyanosis.
[methemoglobin + G. haima, blood]

methemoglobinemia

(mĕt′hē-mə-glō′bə-nē′mē-ə)
n.
The presence of methemoglobin in the blood.

methemoglobinemia

(mĕt′hē-mə-glō′bə-nē′mē-ə)
n.
The presence of methemoglobin in the blood.

methemoglobinemia

Hematology A condition characterized by excess–> 3%–methemoglobin in the circulation Clinical Cyanosis, headache, dyspnea, fatigue, drowsiness, ataxia, stupor. See Acquired methemoglobinemia, Methemoglobin.

met·he·mo·glo·bi·ne·mi·a

(met-hē'mŏ-glō-bi-nē'mē-ă)
The presence of methemoglobin in the circulating blood.
Synonym(s): hemiglobinemia, methaemoglobinaemia.
[methemoglobin + G. haima, blood]

met·he·mo·glo·bi·ne·mi·a

(met-hē'mŏ-glō-bi-nē'mē-ă)
The presence of methemoglobin in the circulating blood.
Synonym(s): methaemoglobinaemia.
[methemoglobin + G. haima, blood]
References in periodicals archive ?
Methemoglobinemia may be due to either acquired or congenital causes.
Infant methemoglobinemia: the role of dietary nitrate, in food and water, Pediatrics.
Survey of literature related to infant methemoglobinemia due to nitrate contaminated water.
Chocolate brown blood may indicate methemoglobinemia; watery not coagulable blood and bleeding from the venepuncture site suggest anticoagulant rodenticides (Patterino et al., 2004).
Methemoglobinemia leads to a diminished oxygen supply resulting in a "saturation gap" between the oxygen saturations on a pulse oximetry and the arterial blood gas.
Since fetal hemoglobin is more apt to ferric state compared to adult hemoglobin (Hb A2), newborn infants have a greater tendency to methemoglobinemia. In addition, the fact that the activity of cytochrome b5 reductase enzyme is transiently deficient in the first 3-4 months of life leads to a tendency towards methemoglobinemia in newborns and infants (5).
FDA officials say that the use of benzocaine gels and liquids to relieve gum and mouth pain can lead to a rare bur potentially deadly condition called methemoglobinemia, in which the amount of oxygen carried through the bloodstream is greatly reduced.
Excessive concentrations of nitrates in drinking water cause the blood disorder methemoglobinemia and may also contribute to the risk of thyroid problems, adverse birth outcomes, and cancer.
Fifteen minutes after ingestion, the men became cyanotic and subsequently were treated for refractory methemoglobinemia and hemolytic anemia.
Acquired methemoglobinemia: a retrospective series of 138 cases at 2 teaching hospitals.