Given the extent of disagreement among observers regarding the color of infants observed under identical conditions (i.e., via video recording), the study authors concluded that real-world visual assessment of newborn color is unreliable. Moreover, the lack of correlation between perceived color and SpO2 suggests that visual assessment is an unreliable method for evaluating oxygenation.14
Pulse oximetry. Pulse oximetry is a noninvasive and painless test that measures the percentage of hemoglobin in blood that is saturated with oxygen. Pulse oximetry has been evaluated as a screening tool for CCHD based on the rationale that most defects involve a degree of hypoxemia that may not necessarily produce visible cyanosis.17
Pulse oximetry can reliably detect mild hypoxemia, a feature of many subtypes of CCHD that is difficult to recognize by physical examination.14 As an adjunct to the standard newborn examination, therefore, pulse oximetry can identify cases of CCHD that escape routine clinical detection.
In several clinical trials, pulse oximetry has been shown to be a simple, safe, feasible, and cost-effective screening tool that adds value to the routine physical evaluation of newborns.18-20 In 2012, Thangaratinam and colleagues presented findings from a meta-analysis of studies that assessed the performance of screening for CCHD using pulse oximetry in a total of 229,421 asymptomatic newborns.17
In this study, pulse oximetry was highly specific (99.9%) and moderately sensitive (76.5%) for the detection of CCHD, meeting standard thresholds for universal screening. The overall false-positive rate was 0.14%, but fell to 0.05%, without any compromise in sensitivity, when pulse oximetry was performed after 24 hours from birth. Although the goal of screening is to detect CCHD, other life-threatening disorders of noncardiac origin, including group B streptococcal pneumonia and pulmonary hypertension, may be detected.
Although the rationale and evidence supporting the use of pulse oximetry as a screening tool are firmly established, the implementation of CCHD screening involves practical issues that remain under evaluation. For instance, the false-positive rate and positive predictive values are dependent on both the timing of the oximetry and whether or not a repeat measurement of abnormal values had been performed in the at-risk patient.
In most studies, a postductal saturation between 94% and 96% has been used as the cutoff point for “normal.”21 Selecting the threshold for a positive pulse-oximetry monitoring result is challenging, because it must trade off the harm of missing CCHD against the harm of false-positive screen results.22 Screening performed either primarily after 24 hours or repeated after 24 hours will provide the lowest false-positive rate and the highest positive predictive value.5,9
Earlier screening can lead to false-positive results because of the transition from fetal to neonatal circulation and stabilization of systemic oxygen saturation levels, and later screening can miss an opportunity for intervention before closing of the ductus arteriosus.22 Therefore, most publications recommend the use of CCHD screening at or after 24 hours of life.17,23
CCHD screening and the ”diagnostic gap”
Riede and colleagues recently described the “diagnostic gap” in CCHD, where cardiac defects are not recognized despite standard assessment with prenatal ultrasound and newborn physical examination.5
In a prospective multicenter study, the investigators examined the potential role of pulse oximetry to close the diagnostic gap in real-world clinical practice.5 Among 48,348 newborns, 90 cases of CCHD were ultimately diagnosed. Neonatal screening and clinical observation during the first 24 hours of life, however, detected only 80% of these cases, leaving a diagnostic gap of 20%.
All newborns also underwent screening at the age of 24 to 72 hours of life. 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 screening protocol closed the CCHD diagnostic gap to 4.4% (Figure 2).5
Several other trials have also demonstrated improved detection rates when pulse oximetry is added to existing diagnostic mechanisms.9,24 Studies in Sweden and the United Kingdom (UK) found that performing a typical physical examination alone for CCHD led to almost 10 times more false-positive results compared with using CCHD screening protocols.9,25 Overall, CCHD screening after 24 hours of life improves early in-hospital detection of CCHD and may reduce the number missed and diagnosed after discharge.26 Even with evidence of improved detection, however, investigators emphasize the importance of using pulse oximetry as an adjunct to the standard newborn physical examination.22,27,28
Current status of CCHD screening
Despite growing evidence supporting the implementation of CCHD screening, uptake has been a slow process. In a 2011 survey of hospitals across the UK, only 7% routinely used CCHD screening to supplement the standard newborn physical examination.29 Moreover, there was wide variability among screening protocols, with different screening schedules, different SpO2 values used to trigger further investigation, and different follow-up procedures. These findings reinforce the importance of standardized guidelines for screening procedures, including saturation measurements and follow-up investigations.