Methemoglobinemia is a condition that is associated with impaired function of hemoglobin. It may affect virtually anyone, but it is particularly dangerous to infants, to whom it may be life-threatening.
Hemoglobin is a complex compound that is present in red blood cells (erythrocytes). Hemoglobin is composed of organic substance globin and inorganic component of heme. The hemoglobin molecule contains iron, which is able to bind oxygen and carbon dioxide. The main importance of hemoglobin is therefore the transport of breathing gases between lungs and other body tissues. Hemoglobin carries the oxygen from lungs to tissues where it is processed in local metabolism. The metabolism produces carbon dioxide, which is transferred back to lungs and exhaled.
The iron in hemoglobin molecules must have its oxidation number equal to II (Fe2+ ion). However, many substances in our body have the ability to oxidize iron to the oxidation number III (Fe3+ ion). Such oxidized iron is unable to bind oxygen and carbon dioxide and therefore it can not participate in exchange of breathing gases. The oxidizing of iron occurs constantly but our body has a loft of defensive enzymes that convert hemoglobin back to the oxidation number II, thus maintaining a kind of balance. Methemoglobinemia means an excessive amount of hemoglobin with oxidized iron in the blood (methemoglobin). This happens usually in case, that a substance with strong oxidizing effect enters our body.
The problem is worse in infants, because their body does not have sufficient capacity to change methemoglobin back to normal hemoglobin. If the infant receives a larger amount of a compound having oxidative effects, it can be life-threatening condition. Typically, this occurs when an infant receives higher levels of nitrates, developing the nitrate methemoglobinemia. Nitrates are substances that are found among others in the drinking water.
Note: There is also a form of congenital methemoglobinemia, when there is a significant concentration of methemoglobin present from birth. However, it is very rare.
Small concentrations of methemoglobin are present in everyone and have no symptoms. Higher concentration causes bluish discoloration of the skin, because methemoglobin shows through the skin in a different color than normal hemoglobin. High concentration of methemoglobin is related to inability of delivering oxygen to tissues. The organism reacts with accelerated cardiac and respiratory activity (rapid pulse and breathing rate). However, this effort is ineffective and the lack of oxygen may impair brain functions causing disorders of consciousness, confusion, disorientation and eventually coma and death.
Prevention is of great importance in infants. The threat of methemoglobinemia is the reason why specially prepared baby water containing only a small amount of nitrates may be used in preparation of infant formula.
In acute methemoglobinemia, it is necessary to administer a substance that helps to convert the methemoglobin back to hemoglobin such as compound known as methylene blue. As a support, it is possible to administer vitamin C and vitamin E that help to degrade the compound with oxidizing effect preventing further formation of methemoglobin.