User:Wikimedstudent/Blue baby syndrome

Lead
Blue baby syndrome can refer to a number of conditions that decrease oxygen transportation in the blood, resulting in blueness of skin in babies-1. Historically, the term "blue baby syndrome" has referred to babies with one of two conditions:


 * 1) Cyanotic heart disease, which is a category of congenital heart defect that results in low levels of oxygen in the blood-2. This can be caused by either reduced blood flow to the lungs or mixing of oxygenated and deoxygenated blood.-3
 * 2) Methemoglobinemia, which is a disease defined by high levels of methemoglobin in the blood. Increased levels of methemoglobin prevent oxygen from being released into the tissues and result in hypoxemia.-4

Both of these conditions cause cyanosis, or a bluish discoloration of skin or mucous membranes.-5 Normally, oxygenated blood appears red and deoxygenated blood has more of a blue appearance.-6 In babies with low levels of oxygen or mixing of oxygenated and deoxygenated blood, the blood can have a blue or purple color, causing cyanosis.-7

Cyanotic heart disease
Specific types of congenital heart defects that cause blood to pass directly from the right side of the heart to the left side result in cyanosis. In these defects, some of the blood that is pumped to the body has not been oxygenated by the lungs and therefore will appear more blue. Infants with these types of heart defects may have a constant bluish tint to their skin, or they may have temporary episodes of cyanosis. The degree of cyanosis is dependent on how much deoxygenated blood is mixed with oxygenated blood before being pumped to the body.

The five most common cyanotic heart defects that may result in Blue Baby Syndrome include the following:

Methemoglobinemia
Blue baby syndrome can also be caused by methemoglobinemia, either due to a hereditary or acquired condition. Congenital methemoglobinemia is typically caused by an inherited deficiency in the enzyme NADH-cytochrome b5 reductase, which is responsible for reducing methemoglobin in the blood. Methemoglobinemia can be acquired in infancy from a number of exposures, including certain drugs or nitrates in drinking water. Nitrates from polluted drinking water form compounds in the body that change haemoglobin to methemoglobin, decreasing the ability of blood to carry oxygen. In infants, the condition can be fatal. The sources of nitrate can include fertilizers used in agricultural lands, waste dumps or pit latrines. For example, cases of blue baby syndrome have been reported in villages in Romania and Bulgaria, and were thought to be caused by groundwater polluted by nitrate leaching from pit latrines. Nitrate levels are subject to monitoring to comply with drinking water quality standards in the United States and other countries. The link between blue baby syndrome and nitrates in drinking water is widely accepted, but some studies indicate that other contaminants, or dietary nitrate sources, may also play a role in the syndrome.

Congenital methemoglobinemia is an autosomal recessive

mutatuon in the gene for cytochrome b5 reductase enzyme

Other causes
Other problems in neonates, such as respiratory distress syndrome, can also produce temporary cyanosis. Like methemoglobinemia, these are not structural lesions and are not regarded by most doctors as true "cyanotic lesions."

Mechanism
''Methemoglobinemia occurs when hemoglobin, found in red blood cells, is exposed to an oxidizing agent such as nitrite. Its exposure leads to the iron in hemoglobin to become Fe3+ instead of the normal Fe2+. ''

Nitrite is an oxidizing agent, absorbed through the intestines.

When bound to hemoglobin it becomes methemoglobin which

Diagnosis
In methemoglobinemia the pulse oximetry reading is remains falsely elevated