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| REVIEW ARTICLE |
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| Year : 2017 | Volume
: 6
| Issue : 4 | Page : 1-7 |
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Pulse oximetry screening of neonates for congenital heart disease
NB Mathur1, Surendra Bahadur Mathur2
1 Department of Neonatology, Maulana Azad Medical College, New Delhi, India
2 Department of Pediatrics, Lady Hardinge Medical College, New Delhi, India
| Date of Web Publication | 22-Jan-2018 |
Correspondence Address:
Prof. N B Mathur
Department of Neonatology, Maulana Azad Medical College, New Delhi - 110 002
India
 Source of Support: None, Conflict of Interest: None
DOI: 10.4103/rcm.rcm_31_17
We tried to discuss the impact of early diagnosis on outcome of critical congenital heart diseases (CCHDs), current options, and their limitations in timely diagnosis, utility of pulse oximetry screening (POS), current recommendations for screening and challenges in resource constrained countries and to suggest further avenues to cover existing gaps. Evidence acquisition process was performed on the PubMed database and Google scholar for every available article in peer reviewed journals. Prevalence of congenital heart disease (CHD) at birth is estimated to be 8/1,000 live births. About 25% of CHDs are life threatening CCHDs. The current guidelines for POS recommend that all neonates in well newborn nurseries should preferably be screened after 24 h of life. A screen is taken to be positive, “out of range” or a fail if oxygen saturation is (i) <90%, (ii) <95% in right hand and one foot after three measurements (each taken 1 h apart), or iii) difference of >3% in preductal and postductal saturations after three measurements (each separated by 1 h). POS has a specificity of 99.9% for the detection of CCHDs. It has a false positive rate of 0.05% for the same. It is estimated that POS may be able to detect nearly 50%–70% of infants born with undiagnosed CCHDss. Opportunity and feasibility for POS is higher in the sick nursery even in the resource constrained setting where most of the well nurseries may not have availability of pulse oximeter, echocardiography and neonatal cardiothoracic surgery services. CCHDs can be detected early using POS which is a convenient, noninvasive and cost effective method. All necessary criteria required for inclusion to universal newborn screening panel are fulfilled by POS. The current POS guidelines are for asymptomatic newborns in well newborn nurseries. Evidence based guidelines are still lacking for screening infants in neonatal intensive care settings. We also propose here a protocol for POS in the neonatal Intensive Care Unit.
Keywords: Critical congenital heart disease, neonatal Intensive Care Units, oxygen saturation, pulse oximetry screening, strategies
How to cite this article:
Mathur N B, Mathur SB. Pulse oximetry screening of neonates for congenital heart disease. Res Cardiovasc Med 2017;6:1-7 |
| Introduction | |  |
Ten important criteria have been described for consideration before a disease should be included for universal screening.[1] These are (i) The condition must be an important public health problem, (ii) There should be an accepted treatment for the condition, (iii) Facilities for diagnosis and treatment of the condition should be available, (iv) There should be a recognizable early symptomatic stage of the condition, (v) There should be a suitable test for screening the disease, (vi) The screening test should be acceptable to the population, (vii) The natural history of the disease should be adequately understood, (viii) There should be an agreed policy on which affected individuals should be treated, (ix) The cost of case finding should be balanced in relation to the expenditure on medical care, (x) Case finding by the screening should be a continuing process and not a single time project.
In 2011, the United States Secretary of Health recommended that pulse oximetry screening (POS) before discharge from the newborn nursery should be included in the universal newborn screening panel for timely detection of critical congenital heart disease (CCHD) in all infants.[2] CCHD is defined as congenital heart disease (CHD) requiring a catheter intervention or surgery within the first 12 months of life. CCHDs accounts for approximately 25% of all children with CHD. The goal of the above mentioned recommendation was to identify structural heart defects associated with hypoxia which consequent to closure of the ductus arteriosus could have significant morbidity or mortality in the early life. The US Health and Human Services Secretary's Advisory Committee on Heritable Disorders in Newborns and Children (SACHDNC) considered seven lesions as primary targets for screening. These were: (i) hypoplastic left heart syndrome, (ii) pulmonary atresia, (iii) tetralogy of Fallot, (iv) total anomalous pulmonary venous return, (v) transposition of the great arteries, (vi) tricuspid atresia and (vii) truncus arteriosus. This group of lesions excludes those usually not associated with hypoxia (e.g., aortic valve stenosis).[3]
Secondary targets include (i) Anomalies of proximal aortic arch (like interrupted aortic arch or aortic atresia), (ii) coarctation of the aorta with patent ductus arteriosus, (iii) Ebstein's anomaly, (iv) double outlet right ventricle and (v) single ventricle lesions.[4] Pulse oximetry monitoring also has the ability to detect noncardiac secondary targets like persistent pulmonary hypertension. Lesions which are “possibly screenable” with the same protocol include (i) aortic stenosis with a patent ductus arteriosus, (ii) severe pulmonary stenosis, and (ii) complete common atrioventricular canal. Cardiac lesions “not screenable” include left-sided obstructive lesions such as coarctation of the aorta without patent ductus arteriosus and aortic stenosis without a patent ductus arteriosus, Ebstein's anomaly without inter atrial right-to-left shunt, all other lesions causing left-to-right shunting and valve anomalies not included in the previous groups.[5]
Pulse oximetry measures the percentage of hemoglobin saturated with oxygen. It provides a continuous transcutaneous, noninvasive estimate of arterial saturation of oxygen and displays a plethysmographic waveform with a heart rate. The monitoring of hemoglobin saturation is possible by pulse oximetry because of the transparency of tissue to light in the near-infrared spectrum and the distinct absorption spectra of the chromophores such as oxyhemoglobin and deoxyhemoglobin.
The objective of this review is to discuss the extent of problem, effect of early diagnosis by POS on the impact of CHDs, current options for early diagnosis of CHDs, the limitation of these options in timely diagnosis of CHDs, utility of POS in early detection of CHDs, current recommendations for screening, challenges in resource constrained countries and to suggest further avenues to cover existing gaps.
| Evidence Acquisition | | |
Evidence was acquired on PubMed (www.ncbi.nlm.nih.gov/pubmed) database and Google scholar (http://scholar.google.com) by searching for every available article in peer reviewed journals. Search terms included “pulse oximeter, screening, strategies, oxygen saturation, CHD, neonatal Intensive Care Unit (NICU).” We focused on the articles that were completely or partially relevant.
| Results | | |
Epidemiology of congenital heart disease and critical congenital heart disease
Prevalence of CHD at birth is estimated to be 8/1000 live births. Worldwide, approximately 1.35 million newborns every year are born with CHDs. CHDs account for 6%–10% of all infant deaths. They also contribute to 20%–40% of all the infant mortality from congenital malformations.[6] About 25% of CHDs manifest before the first routine clinical examination and are life threatening CCHDs.[6] An estimated prevalence CCHD of 2.2 infants/1000 births was published in a large population based study in 2008.[7] Thus CCHD is an important health-care problem.
Various factors such as increase in maternal age, illnesses during pregnancy, increased exposure to drugs such as anticonvulsants, steroids, and alcohol during pregnancy and environmental exposure to chemicals such as organic solvent, dichlorodiphenyltrichloroethane have attributed to the true increase in the prevalence of CHDs.[8]
Limitations of current options
Prior to the introduction of POS, prenatal screening and physical examination after birth have been primarily relied upon for the detection of CCHD. The first opportunity for a postnatal diagnosis of a CCHD is when the healthcare providers examine the neonate after birth. The importance of history and clinical examination in early detection of infants with CCHD needs to be highlighted as it can sometimes detect a CCHD before desaturation occurs. Clinical examination may have some limitations in detecting CCHDs as heart murmurs in newborns have low specificity, nearly half of all the infants with CCHDs have absence of any cardiac findings including murmurs and physicians have limited experience in discriminating innocent murmurs from pathological murmurs in newborns. In addition, visual assessment of cyanosis is also considered suboptimal.[9],[10] Skin thickness, skin color, perfusion, hemoglobin concentration and environmental factors such as ambient light can also influence the newborn's color.
In a well nursery study from India, significant predictors of CHD, on multivariate analysis, were murmur, central cyanosis, abnormal precordial pulsations and abnormal pulse oximetry. Combination of pulse oximetry and clinical evaluation had a sensitivity of 19% for all CHDs and 20% for major CHDs. The specificity for the same was 88%.[11]
In a study at a sick nursery from India, significant predictors of cyanotic heart disease were murmur, central cyanosis, male gender, consanguinity in the family, family history of smoking and history of pregnancy induced hypertension in the mother.[12] Clinical examination is contributory in detecting acyanotic CHDs.
In the absence of POS, up to 30%–50% of all cases with CCHD are discharged undiagnosed from the hospitals.[3],[13] This diagnostic gap may be even higher in countries with limited resources.
Current guidelines
The evidence on the use of POS for early detection of CCHD was reviewed by a work group formed by the SACHDNC in collaboration with the American Academy of Pediatrics (AAP), American Heart Association (AHA), and the American College of Cardiology Foundation (ACCF). The work group recommendations published in 2011were endorsed by AAP, ACCF and the AHA Council on Cardiovascular Disease in the Young.[14]
These guidelines recommend that POS should be performed preferably after 24 h of life on all infants in well newborn nurseries. Early screening may lead to high false positives as a result of transition from fetal to neonatal circulation and stabilization of systemic oxygen saturation levels. A late timing for the screen may miss the chance for interventions before the closure of the ductus arteriosus. Thus, the screening may be delayed as late as possible if an early discharge is planned. However, it should be completed on day two of life. Screening should be performed by measuring oxygen saturation in the right hand (preductal saturation) and either foot (postductal saturation) concurrently or in immediate succession. The measurement of pulse oximetry is considered to be complete once the plethysmograph waveform on the pulse oximeter is stable. Other indications of appropriate tracking of the infant's pulse rate may also be used for the same. An oxygen saturation of >95% in the right hand or either foot and <3% difference of oxygen saturation between the right hand and either foot is considered negative, “in range” or a pass. Before discharge, this group requires no further evaluations.[14]
A screen is considered positive, “out of range” or a fail if oxygen saturation is measured to be (i) <90%, (ii) <95% in both extremities after 3 measurements (each separated by an interval of one hour), or (iii) a difference of >3% between preductal and postductal oxygen saturations after 3 measurements (each separated by one hour). Diagnostic echocardiogram and evaluation by a physician/pediatric cardiologist should be provided to all infants with a failed screening. All infants with a positive screen may not have CCHD. Positive screen may also be seen in infants with other conditions associated with hypoxemia such as certain hemoglobinopathies and persistent pulmonary hypertension.[14]
Challenges of pulse oximetry screening and future avenues
The prerequisite for effective POS and subsequent management of the screened neonates to be effective include availability of pulse oximeter, echocardiography by pediatric cardiologist and state of the art cardiothoracic intervention services capable of neonatal cardiothoracic surgery. Even though the utility of POS in detecting CCHD is evident, the implementation of POS has been slow.
Challenges in managing CHDs in resource constrained countries are delay in diagnosis, transportation of sick newborns to tertiary care centres for echocardiography or surgical intervention, and limited availability of pediatric cardiac centres providing intervention services.[15],[16] This may be associated with significant parental anxiety and transportation distances may be very large particularly in rural areas.
Left sided obstructive lesions may not cause hypoxemia, but if not detected early enough, may still lead to end organ damage. The detection of coarctation of the aorta by POS is only 53% (95% confidence interval [CI]; 30%–75%).[17] One of the most promising additional diagnostic strategy clinically available for such lesions is the peripheral perfusion index, which is displayed on some new generation pulse oximeters. Its assessment is based on the ratio of the pulsatile and nonpulsatile components of the pulse oximetry signal. It thus detects the relative changes in the arterial perfusion.[5],[18] It may be useful in detecting decreased perfusion in settings of left heart obstructive lesions like aortic stenosis, coarctation of aorta and hypoplastic left heart syndrome. However, the distribution of peripheral perfusion index values in normal population is highly skewed and it is also sensitive to skin temperature. The reference cut off values in newborns for possibly impaired peripheral perfusion and for definite hypoperfusion are <0.70 and <0.50 respectively.[19] Further studies are required to incorporate peripheral perfusion index in screening process for CCHD.
Cost effectiveness
It is unlikely that POS will place significant burden on the existing manpower and resources. Studies conducted in the US and Europe shown that POS is a cost effective intervention.[20],[21],[22],[23],[24] The hospital cost for POS was estimated to be $13.50 per newborn in a study. This included costs of labor and equipment which were estimated to be $6.68 and $6.82 per new born screened, respectively.[21] Analysis for cost effectiveness in different countries will vary depending on the diagnostic gap in that population. This will be dependent on the access to prenatal care, rates of prenatal detection of CCHDs, quality of postnatal care, and local costs for equipment, labor and health care. In low resource countries where a high diagnostic gap is expected, POS will be likely to be more cost effective.
Insufficient data is available about the burden due to the increase in the number of echocardiograms required, resulting from failed POS, on the health care system.
Utility of pulse oximetry screening in early detection of critical congenital heart disease
It is increasingly being recognized that adverse neurodevelopmental outcomes are associated with a significant proportion of neonates and infants requiring cardiac surgery.[25],[26] It is possible that the early detection and treatment of CCHDs will provide a more stable perioperative status and thus decrease neurological injury in the infants. A timely diagnosis of life threatening forms of CCHDs is associated with improved survival and reduced morbidity.
In 2009, the AAP and the AHA had reviewed the evidence to consider for recommendations on universal POS.[3] A total of 123,846 infants enrolled in ten studies were included in the analysis. This meta analysis reported a false positive rate of 0.87%. A false positive rate of 0.035% was observed if the screening was done after 24 h of life. A false positive rate of 0.035% can easily be understood as approximately 3–4 infants out of every 10,000 infants screened will have a false positive screen.
Following this, several prospective studies were reported from Europe and Asia.[11],[12],[20],[27],[28],[29] Although, there were some differences in the study design and the definitions of CCHD in these studies, all evaluated the role of POS in early identification of CCHD. Due to its inability to detect acyanotic left heart obstructive lesions such as coarctation of aorta, POS had low sensitivity in these studies. Detection of pulmonary duct dependent lesions and transposition of great arteries had a sensitivity of almost 100%. Early age at screening was probably the cause of the high false positive rate in some of these studies. The abnormal pulse oximetry values could however be explained in nearly 50% of all the infants with a false positive screen by some other underlying medical condition.
Thangaratinam et al. completed a meta analysis in 2012 which included 13 studies and nearly 230,000 infants.[30] The included studies were conducted in a variety of newborn care settings. Number of pulse oximetry readings varied from single to multiple. Over half of included studies used the foot alone (postductal) to measure oxygen saturation while other studies used both right hand and foot (preductal and postductal). Reference standards used to verify the test results included echocardiography for positive results and use of congenital anomaly registers, mortality data and clinical follow-up for negative results. Definitions of congenital heart defects varied and several cardiac lesions were reported. Studies were considered to be good if they demonstrated prospective consecutive recruitment; adequate description of the population, test and reference standard; blinding of test and reference standard; full verification of the test with the reference standard; and with more than 90% follow-up. Most studies scored well on the above criteria considered to represent good quality, with the exception of blinding of the index test which was carried out in only one study. POS was reported to have a specificity of 99.9%. A false positive rate of 0.05% (5 false positive cases per 10,000 screened infants) was also reported. On the basis of the findings of this meta analysis, it was estimated that the diagnostic gap can be reduced from 30% to 5% with the use of POS. It is estimated that POS can detect nearly 50%–70% of infants born with undiagnosed CCHD.
Threshold for positive pulse oximetry screening result
Receiver operator characteristic curves for the cut off for POS are lacking. Bakr et al. chose the cut off value of oxygen saturation of <94%,[31] Reich et al. chose the value <94%,[32] Ewer et al., Meberg et al., de-Wahl Granelli et al., Arlettaz et al. and Richmond et al. chose a value of <95%,[20],[29],[33],[34],[35] and Riede et al., Rosati et al. and Koppel et al. chose the value <95% as a positive screening result.[36],[37],[38] Ewer et al. considered a difference of >2% in the oxygen saturation between the limbs as a positive screening result,[29] while de-Wahl Granelli et al. adopted the difference of >3% in the oxygen saturation between the limbs as a positive screening result.[20]
The threshold for a positive POS should be lower at high altitude areas. If POS for CCHD has to be carried out in the high altitude areas, the normal values of arterial saturation for oxygen should be established first.
Pulse oximetry screening in sick nursery/neonatal Intensive Care Unit
Although pulse oximetry is available in the sick nursery even in resource constrained settings, studies on POS in the NICU are scanty and its implementation including observation of pre- and post-ductal saturations is poor.[12],[39],[40],[41],[42],[43] Opportunity and feasibility for POS is higher in the sick nursery even in the resource constrained setting where most of the well nurseries may not have availability of pulse oximeter, echocardiography and neonatal cardiothoracic surgery services.
A pilot study including 950 neonates was conducted in a tertiary referral NICU in India and evaluated POS for detection of congenital cyanotic heart disease.[12] Pulse oximetry was considered abnormal if the oxygen saturation at room air or on oxygen measured <90% or a >3% difference between right hand and foot was present. 3 observations each at an interval of at least 1 h were taken in all neonates with abnormal pulse oximetry. POS positive was considered only if the abnormal pulse oximetry continued to be present till the last reading [Table 1]. The objective of using a lower threshold of <90% saturation was used to reduce referrals for echocardiography. All congenital cyanotic heart diseases (except one case of tetralogy of Fallot with SaO2 between 90 and <95%) were detected using POS. Detection of CCHD by POS had sensitivity, specificity, positive predictive value, negative predictive value of 95.2%, 52.4%, 9.5%, 99.5% respectively. It was also found to have a positive likelihood ratio, negative likelihood ratio and odds ratio (95% CI) of 2.0, 0.1 and 22 (5.3–91.4) respectively. Detection of CCHD and persistent pulmonary hypertension by POS had sensitivity and negative predictive value of 97.5% (39/40) and 99.5% (209/210) respectively. A cut off value of <95% persistent oxygen saturation for positive POS would have lead to only one more true positive (tetralogy of Fallot with mild pulmonary stenosis and large left to right shunt which would not require urgent surgical intervention) but 120 additional referrals of false positives for echocardiography [Table 2]. As POS was additionally positive in cases of respiratory diseases, acyanotic heart diseases with congestive heart failure, shock and persistent pulmonary hypertension, it had a low specificity. These conditions are common in intensive care settings for newborns. False positivity is thus higher in NICU as compared to well baby nursery. However, false positives also help in timely diagnosis and management of respiratory infection and persistent pulmonary hypertension. | Table 1: Proposed criteria for positive pulse oximetry screening in neonatal Intensive Care Unit/sick nursery
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 | Table 2: Pulse oximetry screening positivity (number of cases) with different thresholds of pulse oximetry screening
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Plan after pulse oximetry screening
The final interpretation of a screening result is based on the primary analysis (clinical evaluation) and second tier testing (pulse oximetry) followed by confirmatory testing (echocardiography). Possible causes of positive pulse oximetry like respiratory diseases, acyanotic CHDs with congestive heart failure or respiratory infection, persistent pulmonary hypertension and shock besides CCHD need to be evaluated by primary care provider as soon as possible. This facilitates in the next step towards confirmation and management of the disorders. Category based customized fact sheets and confirmatory algorithms should be available with the primary care provider. If the suspected disorder (respiratory infection, shock, congestive cardiac failure) improves promptly with specific therapy, further POS can be done and need for echocardiography evaluated [Figure 1]. POS in NICU should be done in all neonates on room air. In those requiring oxygen, pre- and pos-tductal saturations should be seen and POS should be repeated after weaning to room air. All cases with prolonged unexplained requirement of oxygen should be subjected to echocardiography. A proposed protocol for POS in the NICU is given in [Figure 2]. These recommendations for POS in the NICU are empirical and not evidence based. We suggest that these need critical evaluation by further prospective studies. | Figure 2: The proposed pulse oximetry monitoring protocol based on results from the right hand and either foot in neonatal Intensive Care Unit. Neonates pulse oximetry screening positive on room air or after weaning from oxygen therapy, those with significant difference in pre and postductal saturations on oxygen and those requiring unexplained prolonged oxygen therapy should be subjected to echocardiography. RH: Right hand, F: Foot
Click here to view |
Gaps in knowledge
The current screening guidelines are for well newborn nurseries and are supposed to be followed for asymptomatic newborns. For the screening of infants in neonatal intensive care settings, evidence based guidelines are still lacking. These recommendations for POS in the NICU are empirical, not evidence based and need critical evaluation by further prospective studies. Although there is insufficient data available on the burden of the increase in echocardiograms required due to failed POS on the health care system, a recent study in India suggested that a cut off of <90% oxygen saturation would lead to reduced referrals for echocardiography.[12] There is also lack of consensus on appropriate oxygen saturation cutoffs for use at higher altitudes because baseline oxygen saturations in healthy infants born at high altitude are lower.
| Conclusions | | |
In conclusion, POS for early identification of CCHD fulfills the required necessary criteria for inclusion to universal newborn screening panel. It is a simple, noninvasive and cost effective test. Significant decrease in morbidity and mortality in infants with CCHD can be observed by a wider acceptance and adoption of POS. This reduction in morbidity and mortality is likely to be more pronounced in infants who are born without a prenatal diagnosis especially those in low resource settings. In resource limited countries, a cut off of 90% oxygen saturation would lead to reduced referrals for echocardiography and needs further evaluation.
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conflicts of interest.
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| 43. | Iyengar H, Kumar P, Kumar P. Pulse-oximetry screening to detect critical congenital heart disease in the neonatal Intensive Care Unit. Pediatr Cardiol 2014;35:406-10. |
[Figure 1], [Figure 2]
[Table 1], [Table 2]
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