Here's the situation, with prenatal ultrasound and a good physical exam while in the hospital, we were still missing a large number of babies who had critical congenital heart diseases. Some researchers in Europe, England, and Sweden to be exact had the idea to use a pulse oximeter and find more of these babies before they became sick. The idea is this, babies who have critical congenital heart diseases, generally have problems with the formation of their hearts, such that they cannot keep oxygenated and unoxygenated blood separate. Remember, that in babies and adults, this is a crucial feature of the anatomy and function of the heart. That is oxygenated and unoxygenated blood represented by red and blue in this diagram, do not mix. A pulse oximeter is a small machine that can assess the amount of oxygen in a patient's bloodstream by measuring light absorption. Blood cells carrying oxygen will absorb more of the light than blood cells without oxygen. The machine will send light out from one probe, pass it through a body part, and measure the light at the other side. In an adult, the probes are placed on a finger. Because they are so much smaller, we can use other body parts in the baby. The pulse oximeter gives a reading as a percentage, this indicates the percentage of red blood cells that are carrying oxygen. Normally, more than 95 percent of the red blood cells should carry oxygen. Remember a few minutes ago when I mentioned that the first few blood vessels that branch off the aorta are those that feed the heart, the brain, and the right arm? That means if we put the pulse oximeter on the right arm, or hand, we will get a reading that indicates the best oxygen level in the baby, the same amount of oxygen that is being delivered to the heart muscle and the brain. If the heart is put together correctly, the reading will be greater than 95 percent. If the heart is malformed, and the oxygenated and unoxygenated blood are mixing, the pulse oximetry reading will be lower. To illustrate this complicated idea, let's consider a congenital heart lesion known as single ventricle, in this case, the wall that separates the lower chambers of the heart is missing. That means that oxygenated blood coming back from the lungs and an oxygenated blood from the rest of the body, will end up combining in a single chamber. When the heart contracts, this mixed blood will be pushed out through the main arteries; the aorta, and the pulmonary artery. When you measure the blood in the right-hand with a pulse oximeter, it will be mixed blood, and therefore, will have a lower oxygen level. No matter how much oxygen you add to the lungs, it will always get mixed again in the single ventricle, and it will be impossible to obtain high levels of oxygen in the aorta. Other critical congenital heart diseases are not as obvious, but have the same problem. The oxygenated and unoxygenated blood cannot be kept separate. There is one type of critical congenital heart disease that does not cause mixing of oxygenated and unoxygenated blood, it is called coarctation of the aorta. The aorta is the large blood vessel leaving the left ventricle of the heart, carrying blood with high oxygen content. Coarctation means narrowing. So the aorta is narrowed, usually at a point beyond the branches which go to the heart muscle, the brain, and the right arm. As you might imagine, this means that the blood flow to the branches of the aorta, beyond the coarctation will be decreased, and the oxygen that is carried will be less than that of the right-hand. So if we put a pulse oximetry probe on the right-hand and another on a foot, we will see a normal value in the right arm, of greater than 95 percent and a lower value in the foot. In 2011, the United States Department of Health and Human Services recommended that all babies be screened with pulse oximetry to look for critical congenital heart disease. It took a few years for all the states to adopt this recommendation, but in January of 2018, Wyoming became the final state to institute this practice. Now, nearly all newborns in our country are screened. Here's a diagram of the recommendations. It's not important to memorize the details now. The general idea is this, after 24 hours of age, place a pulse oximetry probe on the right-hand and check the percentage of oxygen in the blood, then place the probe on one of the feet, and check the oxygen percentage there. In order to pass the test, at least one of the two readings has to be more than 95 percent, and there should not be more than three points difference between the hand and the foot. If a baby passes in this manner, you can reassure the parents that it is highly unlikely that the baby has a critical congenital heart disease. If the baby does not meet these criteria but looks well, the recommendation is to repeat the test two more times over the next few hours. If a baby continues to fail, there is a possibility that she does have critical congenital heart disease. If a baby continues to have low oxygen, there are few things to think about. First, was the equipment working properly? It's always important to be sure that you can trust the results. Next, consider other causes of low oxygen. Respiratory diseases are much more common than the cardiac diseases in this age group. Listen to the lungs, consider a chest X-ray, try giving baby oxygen. If she gets better with oxygen, lung disease is more likely than heart disease. Another possibility for failing is that the baby is taking a bit longer than usual to get through the transition period, that is to switch from foetal circulation to newborn circulation. The shunts that are so useful in a foetus can be a problem if they don't close soon after birth. They should be closed by 24 hours of life. When you've considered all of these possibilities, and you are convinced that the results are true, and that baby does not have respiratory disease, you must come to the conclusion that she might have critical congenital heart disease. The next step is to perform an echocardiogram, an ultrasound of the heart. This is inexpensive test, and requires a cardiologist or a heart specialist to evaluate it. Remember though, that the diagnosis of CCHD early, can save a child's life. At this time, pediatric cardiac surgeons can correct or improve nearly all malformations of the heart, even those considered critical. Babies will benefit most if the lesion is discovered early in life, before they are discharged from the birth center. In this manner, the surgeons will be operating on a child who though, she has heart disease, is otherwise healthy. Pulse oximetry is a modality that is used for many reasons on both children and adults. They are affordable and portable units available. Little training is required to use a pulse oximetry effectively. With the use of this simple device, it is possible to screen all newborns for critical congenital heart disease. I would recommend this practice for all providers who care for newborn babies.
