Pulse oximetry for diagnosis of critical congenital heart defects

Review question

We reviewed evidence on the accuracy of pulse oximetry for detection of critical congenital heart defects (CCHDs) in asymptomatic newborn infants.

Background

CCHDs occur in around two in 1000 newborn infants and are a leading cause of infant death. Timely diagnosis is crucial for best outcomes for these babies, but current screening methods may miss up to 50% of affected newborn infants before birth, and those sent home before diagnosis frequently die or endure major morbidity. However, babies with CCHD often have low blood oxygen levels, which can be detected quickly and non-invasively by pulse oximetry, using a sensor placed on the newborn infant’s hand or foot. A pulse oximeter is a machine that can measure, non-invasively, the amount of oxygen carried around the body by red blood cells. Oxygen from the lungs is bound to hemoglobin in red blood cells, forming oxyhemoglobin. If oxygen is not bound, de-oxyhemoglobin is formed. In health, almost all hemoglobin is oxyhemoglobin, and so oxygen saturation (ie, the percentage of hemoglobin that has bound oxygen) is close to 100%. The pulse oximeter measures this by passing light through peripheral blood vessels (eg, a fingertip in an adult, in a hand or foot in a baby). Oxyhemoglobin and de-oxyhemoglobin absorb this light in different ways, and the proportion of light absorbed can be analyzed by software within the oximeter, which then calculates the percentage of hemoglobin saturated with oxygen.

Study characteristics

We searched until March 2017 for evidence on use of pulse oximetry to detect CCHD in newborn infants and found 21 studies. These studies used different thresholds to define a pulse oximetry test as positive. We combined all studies using a threshold around 95% (19 studies with 436,758 newborn infants).

Key results

This review found that for every 10,000 apparently healthy newborn infants screened, around six of them will have CCHD. The pulse oximetry test will correctly identify five of these newborn infants with CCHD (but will miss one case). Newborn infants who are missed could die or experience major morbidity.

For every 10,000 apparently healthy newborn infants screened, 9994 will not have CCHD. The pulse oximetry test will correctly identify 9980 of them (but 14 newborn infants will be investigated for suspected CCHD). Some of these infants may be exposed to unnecessary additional tests and a prolonged hospital stay, but a proportion will have a potentially serious non-cardiac illness.

The number of newborn infants incorrectly investigated for CCHD decreases when pulse oximetry is performed longer than 24 hours after birth.

Certainty of evidence

We judged the included studies to be mainly at low or unclear risk of bias for several of the certainty domains assessed. Some studies used less robust methods to verify negative results. We considered the overall certainty of the evidence as moderate.

Authors' conclusions: 

Pulse oximetry is a highly specific and moderately sensitive test for detection of CCHD with very low false-positive rates. Current evidence supports the introduction of routine screening for CCHD in asymptomatic newborns before discharge from the well-baby nursery.

Read the full abstract...
Background: 

Health outcomes are improved when newborn babies with critical congenital heart defects (CCHDs) are detected before acute cardiovascular collapse. The main screening tests used to identify these babies include prenatal ultrasonography and postnatal clinical examination; however, even though both of these methods are available, a significant proportion of babies are still missed. Routine pulse oximetry has been reported as an additional screening test that can potentially improve detection of CCHD.

Objectives: 

• To determine the diagnostic accuracy of pulse oximetry as a screening method for detection of CCHD in asymptomatic newborn infants

• To assess potential sources of heterogeneity, including:

○ characteristics of the population: inclusion or exclusion of antenatally detected congenital heart defects;

○ timing of testing: < 24 hours versus ≥ 24 hours after birth;

○ site of testing: right hand and foot (pre-ductal and post-ductal) versus foot only (post-ductal);

○ oxygen saturation: functional versus fractional;

study design: retrospective versus prospective design, consecutive versus non-consecutive series; and

risk of bias for the "flow and timing" domain of QUADAS-2.

Search strategy: 

We searched the Cochrane Central Register of Controlled Trials (CENTRAL; 2017, Issue 2) in the Cochrane Library and the following databases: MEDLINE, Embase, the Cumulative Index to Nursing and Allied Health Literature (CINAHL), and Health Services Research Projects in Progress (HSRProj), up to March 2017. We searched the reference lists of all included articles and relevant systematic reviews to identify additional studies not found through the electronic search. We applied no language restrictions.

Selection criteria: 

We selected studies that met predefined criteria for design, population, tests, and outcomes. We included cross-sectional and cohort studies assessing the diagnostic accuracy of pulse oximetry screening for diagnosis of CCHD in term and late preterm asymptomatic newborn infants. We considered all protocols of pulse oximetry screening (eg, different saturation thresholds to define abnormality, post-ductal only or pre-ductal and post-ductal measurements, test timing less than or greater than 24 hours). Reference standards were diagnostic echocardiography (echocardiogram) and clinical follow-up, including postmortem findings, mortality, and congenital anomaly databases.

Data collection and analysis: 

We extracted accuracy data for the threshold used in primary studies. We explored between-study variability and correlation between indices visually through use of forest and receiver operating characteristic (ROC) plots. We assessed risk of bias in included studies using the QUADAS-2 tool. We used the bivariate model to calculate random-effects pooled sensitivity and specificity values. We investigated sources of heterogeneity using subgroup analyses and meta-regression.

Main results: 

Twenty-one studies met our inclusion criteria (N = 457,202 participants). Nineteen studies provided data for the primary analysis (oxygen saturation threshold < 95% or ≤ 95%; N = 436,758 participants). The overall sensitivity of pulse oximetry for detection of CCHD was 76.3% (95% confidence interval [CI] 69.5 to 82.0) (low certainty of the evidence). Specificity was 99.9% (95% CI 99.7 to 99.9), with a false-positive rate of 0.14% (95% CI 0.07 to 0.22) (high certainty of the evidence). Summary positive and negative likelihood ratios were 535.6 (95% CI 280.3 to 1023.4) and 0.24 (95% CI 0.18 to 0.31), respectively. These results showed that out of 10,000 apparently healthy late preterm or full-term newborn infants, six will have CCHD (median prevalence in our review). Screening by pulse oximetry will detect five of these infants as having CCHD and will miss one case. In addition, screening by pulse oximetry will falsely identify another 14 infants out of the 10,000 as having suspected CCHD when they do not have it.

The false-positive rate for detection of CCHD was lower when newborn pulse oximetry was performed longer than 24 hours after birth than when it was performed within 24 hours (0.06%, 95% CI 0.03 to 0.13, vs 0.42%, 95% CI 0.20 to 0.89; P = 0.027).

Forest and ROC plots showed greater variability in estimated sensitivity than specificity across studies. We explored heterogeneity by conducting subgroup analyses and meta-regression of inclusion or exclusion of antenatally detected congenital heart defects, timing of testing, and risk of bias for the "flow and timing" domain of QUADAS-2, and we did not find an explanation for the heterogeneity in sensitivity.

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