These factors include hypoventilation, perfusion or ventilation differences in the lungs, and poor cardiac output of oxygenated blood, among others.

The blue baby syndrome or cyanosis occurs when absolute amount of deoxygenated hemoglobin > 3g/dL which is typically reflected with an O2 saturation of < 85 %.

Infants with these types of heart defects may have a constant bluish tint to their skin, or they may have temporary episodes of cyanosis.

[11] The five most common cyanotic heart defects that may result in Blue Baby Syndrome include the following: Methemoglobinemia can be acquired or congenital.

Infants younger than 4 months are at greater risk given that they drink more water per body weight, they have a lower NADH- cytochrome b5 reductase activity, and they have a higher level of fetal hemoglobin which converts more easily to methemoglobin.

[23] For example, nitrate levels are subject to monitoring to comply with drinking water quality standards in the United States and other countries.

[30] In addition, it is important to observe the infant for signs of respiratory distress, visualized as nasal flaring, subcostal retractions, etc.

[6] Additionally an arterial blood gas is useful, for example in the case of methemoglobinemia the PO2 can be expected to be normal even with a low oxygen saturation.

[29] Babies with cyanosis due to congenital heart disease usually present with symptoms hours to days after birth.

In addition to cyanosis, they often show signs of tachypnea (fast breathing), a heart murmur, and decreased peripheral pulses.

[32] In tetralogy of Fallot, episodes in which infants become cyanotic are called tet spells, typically occurring during feeding or crying.

[33] As of 22 May 2007, the United States Environmental Protection Agency has established a maximum contaminant level of 10 mg/L for nitrate and 1 mg/L for nitrite in drinking water due to the potential harmful effects in infants.

[36] Some babies born with cyanotic heart disease are treated with prostaglandin E1 after birth to keep the ductus arteriosus open and allow for more oxygenated blood to be pumped to the body.

[39] The first successful operation to treat blue baby syndrome caused by tetralogy of Fallot occurred at Johns Hopkins University in 1944.

Through a collaboration between pediatric cardiologist Helen Taussig, surgeon Alfred Blalock, and surgical technician Vivien Thomas, the Blalock-Thomas-Taussig shunt was created.

[40] The operation was published in the Journal of the American Medical Association in 1945 and impacted management of blue babies around the world.