Our group’s research goal is to investigate the use of pulse oximetry screening to detect congenital heart disease. This research is important because some babies with significant heart defects will appear to be perfectly well for the first few days after they are born, only to become critically ill within days of going home from the hospital. The use of pulse oximetry screening may help to identify these babies before they get into trouble.
Although there may be no outward signs of a heart problem, such as a heart murmur, breathing difficulties, or abnormal skin color, nearly all of these babies will have an abnormally low amount of oxygen in their blood. Unfortunately, the human eye can only detect very low oxygen saturations and even trained observers cannot detect the type of low oxygen saturations present in these babies. This “cyanotic blind spot” where abnormally low oxygen saturations cannot be visibly detected can be closed by measuring the oxygen concentration in a baby’s blood.
Over the last several years, a number of studies have been performed to determine if measuring the oxygen saturation with a pulse oximeter in seemingly healthy babies would identify those with significant congenital heart disease. Pulse oximeters measure the amount of oxygen in the blood by looking at the wavelengths of light which are absorbed as a red light passes through the skin. The measurement is painless and harmless.
As more studies have been performed, the technique has been refined. In general, if the oxygen saturation measurement is done too early, many children with normal hearts will fail the screening tests (false positive tests). The more false positive tests there are, the less useful the testing. Most studies have shown that if the pulse oximetry study is performed after 24 hours of age, the number of false positives is very low.
In most of these babies, the pulse oximetry measurements in the feet will be abnormal, and may be significantly lower than the pulse oximetry measurement in the right hand. In some studies, measurements are taken only in one of the feet, but in others, measurements are taken in the right hand as well as one of the feet. There are some types of important heart disease that may be harder to detect if only a foot measurement is taken, but the additional measurement in the hand requires more time to perform. As there are more data measurements, there may be a greater chance of a false positive result when both the hand and foot measurements are taken.
In these studies, when a child fails the screening test, an echocardiogram is performed to determine if a critical congenital heart defect is present. Echocardiography is an excellent way of evaluating a baby’s heart, but requires an expensive piece of medical equipment, a highly trained technician to perform the study, and someone familiar with congenital heart disease to interpret the study (typically a pediatric cardiologist). One of the criticisms of these types of screening program is that the three components needed for the echocardiogram many not be available in all settings where babies are delivered. If they are not available, the baby may need to be transferred to a facility where an echocardiogram can be performed. Understandably, the stress of transferring a baby is justified if a life threatening heart defect is present. Concerns remain about the effects of false positive tests, particularly when a baby has to be transported to another facility for an echocardiogram.
Pulse oximetry screening to detect congenital heart disease is not an easy concept to study. As a missed diagnosis of congenital heart diseases only occurs in one in every fourteen to twenty five thousand babies, even studies of several thousand babies may not be large enough to fully evaluate the effectiveness of pulse oximetry screening.
As with many types of medical research, the different published studies can be difficult to compare. The type of screening performed (foot alone or both hand and foot measurements), the timing of the screening, and the way in which health care is delivered varies between the available studies.
With any medical screening test, there must be a balance between the effort involved to perform the screening, the reliability of the screening test, and the consequences if the disease in question is missed.
Pulse Oximetry Screening at Meriter Hospital in Madison, Wisconsin
In the summer of 2007, pulse oximetry as a screening tool for critical congenital heart disease was implemented at Meriter hospital. Since then, more than 12,000 babies have been screened for critical congenital heart disease.
In the Meriter screening program, a pulse oximetry measurement is taken in the foot of each healthy term (>37 weeks gestation) and late preterm (35-37 weeks gestation) baby after 24 hours of age. If the initial saturation measurement is > 94%, no further action is taken. If the initial saturation is between 90 and 94%, the measurement is repeated in two hours. If the initial saturation measurement is less than 90%, the neonatology team is contacted for immediate evaluation.
If the repeat saturation measurement is > 94%, no further action is taken. If the repeat saturation is between 90 and 94%, an echocardiogram is performed. If the repeat saturation measurement is less than 90%, the neonatology team is contacted for immediate evaluation.
The preliminary results of this screening were presented at the American Academy of Pediatrics (AAP) National Conference and Exhibition in October 2008. A more complete study of this screening is currently being prepared for the 2011 AAP meetings.
Additional Research Activities
This research group focuses on the problem of unrecognized critical congenital heart disease in newborns. The current research projects address the current screening programs at Meriter Hospital and the resources which are available should pulse oximetry screening implemented in the State of Wisconsin.
- Boelke, Kristi (Neonatology Fellow) & Goetz, Elizabeth, Screening for Unrecognized Congenital Heart Disease at Meriter Hospital with Pulse Oximetry and Blood Pressure Measurement 2008 to 2011. In this project we will review the current screening process for congenital heart disease at Meriter in over 10,000 newborns. This screening involves the measurement of pre- and post-ductal blood pressures as well as post-ductal pulse oximetry. (Approved by Meriter IRB 1-19-11)
- Beissel, Dan (Pediatric Resident) & Goetz, Elizabeth, Neonatal Readiness in Wisconsin. In this project, we will survey the hospitals and birthing centers in Wisconsin to determine their readiness for neonatal emergencies, with an emphasis on the ability to implement additional screening for congenital heart disease. (Approved by the UW IRB 2-7-11)