Methemoglobin Information & Methemoglobin Links at HealthHaven.com

Methemoglobin (British English: Methaemoglobin) (pronounced "MET-hemoglobin") is a form of the oxygen-carrying protein hemoglobin (British English: haemoglobin), in which the iron in the heme group is in the Fe³⁺ state, not the Fe²⁺ of normal hemoglobin. Methemoglobin cannot carry oxygen. It is a bluish chocolate-brown in color. The NADH-dependent enzyme methemoglobin reductase (diaphorase I) is responsible for converting methemoglobin back to hemoglobin.

Normally one to two percent of people's hemoglobin is methemoglobin; a higher percentage than this can be genetic or caused by exposure to various chemicals and depending on the level can cause health problems known as Methemoglobinemia. A higher level of methemoglobin will tend to cause a pulse oximeter to read closer to 85% regardless of the true level of oxygen saturation.^[1]

[edit] Common causes

Reduced cellular defense mechanisms
- Children younger than 4 months exposed to various environmental agents
- Methemoglobin reductase deficiency
- G6PD deficiency
- Hemoglobin M disease
- Pyruvate kinase deficiency
Various pharmaceutical compounds
- Local anaesthetic agents, especially prilocaine as used in the Bier block
- Amyl nitrite, chloroquine, dapsone, nitrates, nitrites, nitroglycerin, nitroprusside, phenacetin, phenazopyridine, primaquine, quinones and sulfonamides
Environmental agents
- Aromatic amines (e.g. p-nitroaniline , patient case)
- Arsine
- Chlorobenzene
- Chromates
- Nitrates/nitrites
In cats
- Ingestion of acetaminophen (tylenol)

[edit] Therapeutic Uses

Amyl nitrite is administered to treat cyanide poisoning. It works by converting hemoglobin to methemoglobin, which allows for the binding of cyanide and the formation of non-toxic cyanomethemoglobin. ^[2]

[edit] Methemoglobin Saturation

Methemoglobin saturation is expressed as the percentage of hemoglobin in the methemoglobin state; That is MetHb as a proportion of Hb.

1-2% Normal
Less than 10% metHb - No symptoms
10-20% metHb - Skin discoloration only (most notably on mucus membranes)
20-30% metHb - Anxiety, headache, dyspnea on exertion
30-50% metHb - Fatigue, confusion, dizziness, tachypnea, palpitations
50-70% metHb - Coma, seizures, arrhythmias, acidosis
Greater than 70% metHb - Death

[edit] References

^ Denshaw-Burke, Mary (2006-11-07). "Methemoglobinema". http://www.emedicine.com/med/TOPIC1466.HTM. Retrieved 2008-03-31.
^ Vale, J. A. (2001). "Cyanide Antidotes: from Amyl Nitrite to Hydroxocobalamin - Which Antidote is Best?". Toxicology 168 (1): 37–38.

[edit] See also

blue baby syndrome

[edit] External links

[0] Denshaw-Burke, Mary (2006-11-07). "Methemoglobinema". http://www.emedicine.com/med/TOPIC1466.HTM. Retrieved 2008-03-31.

[1] Vale, J. A. (2001). "Cyanide Antidotes: from Amyl Nitrite to Hydroxocobalamin - Which Antidote is Best?". Toxicology 168 (1): 37–38.

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