Diagram showing normal blood circulation (above) and the blood circulation on a heart suffering from ToF
The most common cause of blue baby syndrome, and the one which was the subject of the classic "blue baby operation" developed at Johns Hopkins in the 1940s, is tetralogy of Fallot. In the normal heart, there are four separate chambers; the two top chambers, or atria, pump blood simultaneously into the two bottom chambers, or ventricles. Blood first enters the heart at the right atrium, which then empties blood into the right ventricle, which pumps the blood into the lungs through the pulmonary artery to get oxygen. From the lungs, the blood enters the left atrium through the pulmonary vein; the left atrium empties into the left ventricle, which pumps the blood into the aorta and from there reaches the rest of the body. Because the left ventricle is responsible for getting blood to the entire body through the aorta, it is usually the biggest and strongest chamber of the heart.
The following is a depiction of normal blood flow through the body. Valves keep the blood from flowing backwards. Capital letters indicate oxygenated blood:
After the body uses up the oxygen delivered by the blood flowing through the arteries, then arterioles, then capillaries, the unoxygenated blood returns to the heart by the capillaries, then venules, then veins.
The blue baby syndrome known as tetralogy of Fallot consists of an incomplete wall between the ventricles (known as a ventricular septal defect or VSD); an aorta that sits over this defect so that its blood comes from both ventricles instead of just from the left (overriding aorta); a defective right ventricular outflow tract near the pulmonary valve that prevents full flow of blood to the lungs; and a muscular right ventricle necessary to accomplish the extra work required to overcome that defect (right ventricular hypertrophy).
The following is a depiction of blood flow in tetralogy of Fallot. Mixed capital letters indicate partially oxygenated blood.
veins → superior or inferior vena cava → right atrium ——tricuspid valve→
rIgHt vEnTrIcLe ——VSD→ LeFt VeNtRiClE or
——pulmonary valve→ pulmonary artery → LUNGS → PULMONARY VEIN →
LEFT ATRIUM ——mitral valve→
LeFt VeNtRiClE <—————————————————————————————————————————rIgHt vEnTrIcLe
——aortic valve→ aOrTa → aRtErIeS
Unoxygenated blood from the right ventricle flows into the aorta preferentially because of the obstructed outflow tract into the lungs. This means less blood has the opportunity to be oxygenated in the lungs. Blood mixes abnormally between the left and right ventricles and into the aorta. Oxygen gives blood its reddish color; cyanosis describes the "blueness" in the baby which results from the pumping of mixed oxygenated and unoxygenated blood throughout the body.
A sort of "blue baby syndrome" can also be caused by methemoglobinemia. It is believed to be caused by nitrate contamination in groundwater resulting in decreased oxygen carrying capacity of hemoglobin in babies leading to death. The groundwater can be contaminated by leaching of nitrate generated from fertilizer used in agricultural lands, waste dumps or pit latrines. Cases of blue baby syndrome have for example been reported in villages in Romania and Bulgaria where the groundwater has been polluted with nitrate leaching from pit latrines.
Other insults in neonates, such as respiratory distress syndrome, can also produce a "blue baby syndrome". Like methemoglobinemia, these are not structural lesions and are not regarded by most doctors as true "cyanotic lesions."
On November 29, 1944, the first successful operation for tetralogy of Fallot was performed at the Johns Hopkins Hospital. In 1943, the syndrome had been brought to the attention of surgeon Alfred Blalock by pediatric cardiologist Helen B. Taussig. Taussig was trying to figure out a way to treat the hundreds of babies and children who had congenital blue baby syndrome. Blalock's surgical technician, Vivien Thomas, had earlier developed for another purpose a procedure involving the anastomosis, or joining, of the subclavian artery to the pulmonary artery. Adapting this procedure for patients with tetralogy of Fallot gave the blood another chance to become oxygenated. The surgery, which became known as a Blalock-Taussig shunt, rapidly spread worldwide as the treatment of choice for Tetralogy of Fallot. Thomas was later recognized as the true developer of the procedure, which is sometimes called the Blalock-Thomas-Taussig shunt. In 1976, Johns Hopkins University presented Thomas with an honorary doctorate.