Congenital heart disease (CHD) is a potentially devastating diagnosis that accounts for 24% of infant deaths due to congenital malformations.1 Early diagnosis and follow-up are essential first steps in preventing infant morbidity and mortality associated with cardiac defects. Timely care is particularly important for critical CHD (CCHD), a heterogenous group of disorders affecting 1.2 infants per 1,000 live births in the United States in which surgical or catheter-based therapy within the first year of life is mandatory for survival. Despite the urgency of diagnosis, however, CCHD is missed in one in three affected newborns, increasing the risk of unrecognized hypoxemia, clinical deterioration, and life-threatening complications.
This second article of the educational activity, CCHD Screening Guidelines, is designed to provide guidance on the use of screening for CCHD using pulse oximetry to improve early detection in newborns across a range of care settings. The first article discussed the burden of CCHD and introduced the role of pulse oximetry as a simple, safe, and effective screening tool that improves the detection of CCHD when added to physical examination. Here, the second article in the series provides an in-depth examination of current guideline recommendations for universal CCHD screening with pulse oximetry, including strategies for implementing screening recommendations and establishing a medical home for infants who are found to have CCHD.
Rationale for CCHD screening using pulse oximetry
Several subtypes of CCHD lesions are ductal-dependent (Table 1). As a result, the affected neonate may not be symptomatic during the birth hospitalization because the ductus arteriosus has not closed prior to discharge. Closure of a patent ductus arteriosus can precipitate rapid clinical deterioration with potentially life-threatening consequences (i.e., severe metabolic acidosis, seizures, cardiogenic shock, cardiac arrest, or end-organ injury).2
In parts of the United States, hospital stays of 12 to 24 hours for uncomplicated vaginal births, and 48 to 72 hours for uncomplicated caesarean births, had become standard by the mid-1990s.3 One reason why CCHD may be missed in newborns, but certainly not the only reason, focuses on possible adverse outcomes of early discharge.
Such concerns led the U.S. Congress to pass legislation in 1996 mandating that private insurers cover postnatal stays of at least 48 hours after a vaginal birth and 96 hours after a caesarean section. However, four years later, the majority of newborn term infants were still being discharged “early.”4,5
Therefore, the newborn physical examination can miss CCHD, particularly in infants with subtle clinical signs.6 Half of all newborns with CCHD, particularly those with ductal-dependent defects, have no distinctive murmur.7 In many cases, symptoms of CCHD do not present until after hospital discharge.8 Indeed, one in three infants with a potentially life-threatening cardiac defect is discharged from the hospital nursery undiagnosed.9
Current estimates indicate that the diagnosis of CCHD is missed or delayed in 1 in 3,500 to 1 in 25,000 live births, depending on the type of defect.6,9-11 Diagnostic delays can prevent newborns with cardiac defects from receiving timely treatment, which in turn increases the risk of complications and poor outcomes.7 Postponing treatment until newborns with CCHD are critically ill increases surgical mortality, prolongs hospital stays, and increases the risk of such serious adverse effects as neurological dysfunction.7 The goal of screening for CCHD using pulse oximetry is to increase the rate of detection prior to clinical deterioration in affected newborns.
Hypoxemia is a common feature of CCHD that results from the mixing of systemic and venous circulations or other circulatory defects (Table 1).8 Approximately 4 g to 5 g of deoxygenated hemoglobin is needed to produce visible hypoxemia, independent of the hemoglobin concentration.7 For the typical newborn with a hemoglobin concentration of 17.5 g/dL, cyanosis will become visible only when arterial oxygen saturation falls below 83%.12 For those with low hemoglobin concentration (eg, 13.5 g/dL), oxygen saturation must be <78% to produce visible cyanosis.12
Given these parameters, mild hypoxemia is often missed with visual assessment alone. Such factors as skin thickness, skin color, and perfusion can influence color, while such environmental factors as ambient light conditions can influence color perception.13 Indeed, a major limitation of the newborn physical examination is the inability for the human eye to detect important degrees of cyanosis.12
Even when clinicians agreed that infants turned pink, the SpO2 (arterial oxyhemoglobin saturation as measured noninvasively by pulse oximetry) at which individual infants were perceived to become pink varied from 10% to 100%. The gap between normal oxygen saturation and visible cyanosis, approximately 95% to 80%, has been described as the cyanotic blind spot.14
Following delivery, newborns transition from fetal to neonatal circulation. During this time there is fluctuation in oxygen saturation levels. Oxygen saturation levels typically stabilize within 24 hours.8 The median value measured at 24 hours at the lower extremity is 97.3%,15 or slightly lower at higher altitudes.16
Screening with pulse oximetry bridges the diagnostic gap in CCHD, where cardiac defects are not recognized despite prenatal ultrasound and newborn physical examination.17 In a prospective multicenter study of 48,348 newborns, 90 were diagnosed with CCHD. After the first physical examination and clinical observation during the first 24 hours of life, i.e., before pulse-oximetry screening, 80% of all CCHD had been diagnosed, leaving a diagnostic gap of 20%. In this study, all newborns also underwent screening at the age of 24 to 72 hours.
Any newborn with an SpO2 of ≤95% measured on the lower extremities and confirmed after one hour underwent complete clinical examination and echocardiography. Adding pulse oximetry to the standardized screening protocol closed the CCHD diagnostic gap to 4.4%.17 Pulse oximetry is best used as an adjunct to the newborn physical examination, and is not meant to replace standard clinical judgment and physical assessment.18-21
Current screening recommendations
The U.S. Department of Health and Human Services (HHS) Secretary’s Advisory Committee on Heritable Disorders in Newborns and Children (SACHDNC) provides guidance to the Secretary of HHS about which conditions should be included in the recommended uniform screening panel (RUSP), and how to implement screening programs and follow-up care. Historically, screening has been limited to dried blood spot analysis to detect various endocrine, hematologic, and metabolic conditions. More recently, newborn hearing screening has been added.20
The current approach to universal CCHD screening reflects the efforts of multiple agencies and collaborative groups, with several important milestones (Table 2). In 2009, the American Academy of Pediatrics (AAP) and the American Heart Association (AHA) published a joint scientific statement describing the compelling reasons for utilizing pulse oximetry as part of the newborn clinical evaluation for CCHD.8 Based on the evidence at the time, however, the AAP/AHA statement stopped short of recommending universal screening.
Instead, the AAP/AHA called for additional data on key issues that required further clarification, such as variability in arterial oxygen saturation during the first hours of life, appropriate thresholds for “normal” oxygen saturation, the influence of sensor placement and altitude on test performance, as well as appropriate implementation at the community hospital level.
In 2010, the SACHDNC recommended that CCHD be added to the RUSP, with the goal of identifying newborns with cardiac defects that may cause significant early morbidity and mortality associated with closing of the ductus arteriosus or other adverse physiologic changes.20