Role of Pulse Oximetry as a Screening Tool for the Detection of Congenital Heart Disease in Newborn Babies

Abstract

Background:

Congenital heart disease (CHD) is one of the commonly seen malformations, with incidence varying from 7 to 8/1000 live birth. Causes are multifactorial. Routine examination of neonates may miss more than 50% of cases. Pulse oximetry is a simple, noninvasive, bedside test which estimates the percentage of oxygen bound to hemoglobin (oxygen saturation [SpO₂]). Detection of critical CHD (CCHD) has been possible with SpO₂ screening. Many countries included SpO₂ as part of newborn screening due to this. As a primary approach, both pre- and post-ductal extremity SpO₂ is measured after 24 h of life. Echocardiography (ECHO) will be done on neonates with SpO₂ readings <95%. Neonates born in high-altitude regions, studies have suggest to use adjusted threshold values. In India, there are limited studies.

Aims:

The aim of this study was to determine the usefulness of pulse oximetry as a screening tool for early detection of CHD in otherwise asymptomatic newborns. To determine, the accuracy of SpO₂ for detecting clinically unrecognized CCHD in newborns.

Materials and Methods:

This is a prospective observational study done in the department of pediatrics in a tertiary hospital. The study was conducted over 12 months. During the study period, all neonates born who fulfilled the inclusion criteria were included in the study. After 24 h of life, neonates were examined clinically and the pre- and post-ductal SpO₂ was measured. Neonates with SpO₂ <90% in room air were excluded from the study. If the SpO₂ was between 90% and 94%, clinical examination was repeated, if suspicious of CHD, they were referred for ECHO. If there was no suspicion of CHD, SpO₂ was repeated after 6 h and ECHO was done if SpO₂ ≤95. The difference of SpO₂ >3% between the right upper limb and right lower limb was considered positive. Positive neonates were evaluated with two-dimensional echocardiograph. Inclusion criteria - All hemodynamically stable neonates were born during the study period. Exclusion criteria (1) Antenatally diagnosed cardiac anomalies, (2) Outborn neonates, (3) Parents/guardians are not willing to participate in the study and/or further investigation, (4) Sick neonates and those with SpO₂ <90% at birth.

Results:

1117 (83.7%) were eligible for the study out of 1333 neonates born. 669 (59.9%) were born by cesarean section and 448 (40.1%) by vaginal delivery. 996 (89.2%) were born at term (≥37 weeks of gestation) and 121 (10.8%) were preterm (<37 weeks of gestation). The male-to-female ratio was 1.03:1. The mean birth weight of the neonates was 2.91 ± 0.46 kg (mean ± standard deviation). The mean SPO₂ in the right upper limb was 96.62 ± 1.73, in the right lower limb was 96.87 ± 1.76, in the left upper limb was 96.59 ± 1.90, and in the left lower limb was 97.06 ± 1.74. The average SPO₂ difference between the right upper limb and right lower limb was 1.04 ± 1.07. Based on SpO_2, 858 (76.8%) cases were not suspected of having CHD and 259 (23.3%) were suspected of having CHD and were evaluated with ECHO. Six (0.5%) neonates had CHD in whom echo was done. In our study, for detecting CCHD, SPO₂ cutoff value of ≤90% showed 90% sensitivity, 99.94% specificity, 75% positive predictive value, and 99.98% negative predictive value.

Conclusions:

This study emphasizes noninvasive SPO₂ as reliable and feasible, with good negative predictive value screening for CHD in neonates.

Introduction

One of the most prevalent groups of multifactorial malformations is congenital heart disease (CHD). There are 7–8 cases/1000 live births. More than 50% of newborns may not be diagnosed during routine cardiac examination.^[1] Malformation-related infant deaths account for 20%–40% of all infant deaths, and 25% of CHDs are fatal.^[2],[3] The gold standard for diagnosing CHD is echocardiography (ECHO) but is not readily available as a standard screening tool in developing nations, and requires a trained expert.^[4] The proportion of oxygen-saturated hemoglobin to total hemoglobin (unsaturated plus saturated) in the blood is known as oxygen saturation (SpO₂). In other words, SpO₂ is the ratio of oxygenated blood carrying to its maximum carrying capacity. A simple, noninvasive method for estimating SpO₂ is pulse oximetry. Multiple studies demonstrate that routine pulse oximetry screening has made it possible to improve the detection of critical CHD (CCHD). In most nations, pulse oximetry has been included as a part of mandatory newborn screening. Pre- and postductal extremity SpO₂ measured after 24 h of life is done as a primary approach. When a baby's pulse oximetry SpO₂ reading is <95%, ECHO is done. Some researchers suggest adjusting the threshold values for babies born in high-altitude regions.^[5] To screen for CHD, the pulse oximetry SpO₂ was measured after 24 h of life.^[6] In India, there are limited studies.

Aims

• To determine the usefulness of pulse oximetry as a screening tool for early detection of CHD in otherwise asymptomatic newborns

• To determine the accuracy of SpO₂ for detecting clinically unrecognized CCHD in newborns.

Materials and Methods

This is a prospective observational study conducted in a tertiary care hospital. After getting approval from the institute ethics committee, this study was conducted for 1 year from February 1^st, 2019 to January 31^st, 2020. All neonates born during the study period who fulfilled the inclusion criteria were included in the study. Informed consent was obtained from parents.

The measurements of SpO₂ were performed using a G.E multipara monitor model CARESCAPE V100 serial number SH616230374SA with a neonatal Reusable Nellcor SpO₂ sensor OXI-A/N probe.

The pre- and post-ductal SpO₂ was measured by pulse oximetry on all the neonates after 24 h of life. The SpO₂ readings of <90% at room air the neonates were excluded from the study. If the SpO₂ was between 90% and 94%, a clinical examination was performed. ECHO was done in neonates suspected to have CHD. If there was no suspicion of CHD, then saturation was repeated after 6 h and ECHO was done if SpO₂ ≤95. The difference of SpO₂ >3% between the right upper limb and the right lower limb was considered positive. The two-dimensional ECHO was performed on positive newborns. Neonates were cared for as per the preset protocol.

CCHD, which can be ruled out with pulse oximetry screening is the total anomalous pulmonary venous return, tricuspid atresia, pulmonary atresia, transposition of great arteries, truncus arteriosus, and Fallot's tetralogy (TOF) all these being cyanotic and left-sided obstructive lesions, including critical aortic stenosis, coarctation of the aorta, interrupted aortic arch, and hypoplastic left heart syndrome.

Inclusion criteria

All neonates who were born during the study period and were stable hemodynamically.

Exclusion criteria

• Antenatally diagnosed cardiac anomalies

• Out born neonates

• Parents/guardians not willing to participate in the study and/or not willing for further investigation

• Sick neonates and those with SpO₂ <90% at birth.

Statistical analysis

All relevant data were entered into Microsoft Excel sheet and were analyzed using SPSS 22 (IBM SPSS for windows, Armonk, NY:IBM Corp). Categorical data were represented in the form of frequencies and proportions. Continuous data were represented as mean and standard deviation (SD). The diagnostic accuracy, sensitivity, specificity, positive predictive values, and negative predictive values of pulse oximetry were estimated for detecting the CCHD.

Results

There were 1333 births total during the study period, of which 1117 (83.7%) were eligible for the study. There were 216 cases excluded from the study or 16.2%; 202 (15.15%) did not meet the study's eligibility criteria, and 14 (0.10%) did not give consent.

669 (59.9%) babies were delivered through cesarean section, whereas 448 (40.1%) babies were delivered vaginally. 996 (89.2%) babies were born at term (≥37 weeks of gestation), whereas 121 (10.8%) babies were born premature (<37 weeks of gestation). There were 567 (50.8%) male and 550 (49.2%) female neonates, with a ratio of 1.03:1. The newborns' mean (SD) birth weight was 2.91 ± 0.46 kg.

The right upper limb had a mean SPO₂ of 96.62 ± 1.73, the right lower limb had a mean SPO₂ of 96.87 ± 1.76, the left upper limb SPO₂ had a mean of 96.59 ± 1.90, and the left lower limb SPO₂ had a mean of 97.06 ± 1.74. The right upper and right lower limbs had an average minimum SPO₂ of 96.22–1.67, and the right upper and right lower limbs SPO₂ had an average difference of 1.04–1.07.

Based on SpO_2, 858 (76.8%) cases were not suspected of having CHD and 259 (23.3%) got ECHO done as they were suspected of having CHD. Among neonates, who got ECHO done, 6 (0.5%) cases were diagnosed to have CHD. There was no statistical association between SPO₂ suspected and complications during pregnancy (P = 0.531). In our study, for detecting CCHD, a pulse oximetry cutoff value of ≤90% had 90% sensitivity, 99.94% specificity, 75% positive predictive value, and 99.98% negative predictive value.

Discussion

CHDs account for 10% of infant mortality and 50% of malformation-related death.^[1] Although ECHO is the gold standard for CHD diagnosis, it is not feasible or readily available as a standard screening tool in developing nations.^[4] In addition, it requires the expertise of a trained expert to perform and provide accurate interpretation. Screening newborns with the noninvasive measurement of SpO₂ is the accepted method for detecting CHDs.^[6] Out of 1117 newborns, six are diagnosed with CHD in our study. In their study, Koppel et al. found that pulse oximetry screening for CHD was effective in 60% of asymptomatic newborns; specificity: 99.95%; value as a predictor: 75%; value as a negative predictor: 99.98%; and 99.97% accuracy.^[7] In their study of 4027 newborns, Fernanda et al. found 9 (0.23%) cases of CHD.^[8] In a study done by Mathur et al. found that out of 950 screened cases, 72 (7.57%) cases had CHD.^[9] This is primarily attributable to the utilization of ECHO for the detection of cardiac lesions during the screening of suspicious infants.

According to Ainsworth et al., only 44% of newborn cardiac malformations are found during the neonatal examination. They also came to the conclusion that there is a 54% chance of an underlying cardiac malformation if a murmur is heard.^[10] With a combined sensitivity of 77% and specificity of 99.7%, Bakr and Habib found 46% CHD with clinical examination and 31% with pulse oximetry.^[11] In 41,445 births, Riede et al. reported foot pulse oximetry with a sensitivity of 77.8% and a false positive rate (FPR) of 0.1%.^[12]

Using a simple, noninvasive bedside pulse oximetry estimation of SpO₂ with 90% sensitivity, 99.94% specificity, 75% positive predictive value, and 99.98% negative predictive value, we were able to rule out CHD in 858 (or 76.8%) of newborns in our study.

Pulse oximetry SPO₂ is a useful, noninvasive, and inexpensive method for detecting CHDs. These newborns' outcomes have improved as a result of prompt detection and treatment. However, clinical examination's limitations in the early detection of CCHD in infants have been highlighted in studies. The challenges in the clinical examination of neonates with CHDs include the lack of specificity of neonatal heart murmurs, the absence of any cardiac findings, including murmur, in nearly half of all infants with CCHD, and the limited experience of pediatricians in distinguishing innocent murmurs from pathological murmurs.^[13]

Therefore, in the screening for CHDs, pulse oximetry SPO₂ will be used in addition to the clinical evaluation, particularly in developing nations.^[3] When a problem is found during the screening, ECHO is needed.

This study reaffirms the importance of pulse oximetry SPO₂ screening as an easy, simple, noninvasive method for the early detection of CHD in clinically normal newborns.

Conclusions

This study emphasizes noninvasive SpO₂ as reliable and feasible, with good negative predictive value screening for CHD in neonates.