The Blue Baby Syndromes
Did environment or infection cause a blood disorder in newborns?
Science can be a powerful tool for discovery and problem solving, but it can also be a messy, nonlinear process that does not provide all the answers. In such cases, people are forced to make the best decisions possible based on the available information, often erring on the side of caution—especially where public health is concerned. Whether or not those decisions are too conservative will often be the topic of long debate. One such example, involving drinking water standards and the health of newborns, has continued for more than half a century.
In 1987, the Journal of the American Medical Association reprinted, as part of its Landmark series, a case study originally published in 1945, accompanied by a commentary and a report of a new and fatal instance. The author of the original paper, Hunter Comly, was a pediatric resident in Iowa City when he described two examples of a previously unrecognized blood condition in infants. Called infantile methemoglobinemia, the affliction had as its main symptom cyanosis, or turning blue (thus the condition was also sometimes called blue baby syndrome). Cyanosis can also be a symptom of a congenital heart disease, so Comly felt that the two conditions might be confused.
In the congenital condition, called tetralogy of Fallot, a complicated structural defect allows blood returning from the body to the heart to be pumped out again without going to the lungs to be resupplied with oxygen. The hemoglobin in red blood cells turns red when iron in the molecule binds to oxygen; it turns bluish-purple when the oxygen is unloaded, which is why veins are bluish. With too much deoxygenated blood in the arteries, the skin turns from pink to blue (cyanosis comes from the Greek kyanos, meaning dark blue).
Alternatively, some chemicals can oxidize the iron in hemoglobin. The altered form, called methemoglobin, loses the ability to bind oxygen, and the pigment now changes to greenish brown or almost black. The human body contains enzymes to reverse methemoglobinemia, but only up to certain levels. After blood levels reach 15 percent, adults become visibly cyanotic. If more than half of the hemoglobin is converted, oxygen transport, particularly to the brain, is severely hampered, respiratory distress is likely, and death is possible.
In congenital heart disease the cyanosis is apt to improve if treated with oxygen, and if a sample of shed blood is shaken in air, it often becomes lighter and redder in color. Since methemoglobin does not bind oxygen, infants with that condition do not “pink up” on oxygen, and samples of shed blood exposed to air undergo little or no change in color.
The two conditions also look a little different. During the influenza epidemic of 1918, the word “heliotrope” was used to describe the color of the cyanosis of hypoxia, whereas the cyanosis of methemoglobinemia is often described as slate-gray. Simple laboratory tests are available to identify and quantify methemoglobin in blood, and infants with high levels of it respond rapidly to intravenous methylene blue—this blue dye turns the blue baby pink. When cyanosis develops post-partum, it is usually noticed first in the lips, spreading gradually to the nail beds of the fingers and toes, the face and then the whole body. Both congenital heart disease and methemoglobinemia tend to result in hypoxia and peripheral vasodilation, which may intensify the cyanosis.