As evidence mounts for the use of pulse-ox screening to detect congenital heart defects a few key points have arisen. The evidence comes from many publications but one of the best which summarizes the body of evidence is the systematic review by Thangaratinam S which included over 200000 asymptomatic newborns. The key here is to note that as this is a screening test if there are symptoms of congenital heart disease one should be referring to a specialist to rule out a significant CHD rather than spending time with such screening tests. The four points to highlight though are:
- Comparing preductal to postductal saturations enhances sensitivity
- Performing such testing after 24 hours decreases false positive results from conditions leading to desaturation that are not CHD such as TTN.
- The false positive rate is 0.14% if the first two criteria are applied using the cutoffs of < 95% in any limb or > 3% difference between pre and post ductal locations.
- Pulse-ox screening does not detect ALL CHD but rather the ones that are deemed critical or immediately life threatening if not identified in the newborn period.
|Examples of CCHD Lesions Detectable with Pulse Oximetry Screening|
|Most consistently cyanotic||May be cyanotic|
|Hypoplastic left heart syndrome (HLHS)
Pulmonary atresia with intact septum (PA IVS)
Total anomalous pulmonary venous return (TAPVR)
Tetralogy of Fallot (TOF)
Transposition of the great arteries (TGA)
|Coarctation of the aorta (COA)
Double outlet right ventricle (DORV)
Interrupted aortic arch (IAA)
Is there a danger in screening too early?
As you screen closer to birth the risk of detecting conditions leading to desaturation which are not CHD rises. Common conditions such as TTN or mild pulmonary hypertension may mimic CHD and lead to a false positive finding. Thinking of the hospital environment, how many patients are sent to triage beds on a daily basis with tachypnea and mild desaturation?
This month the first real assessment of screening in the home environment was completed by Cawsey MJ entitled Feasibility of pulse oximetry screening for critical congenital heart defects in homebirths. This study describes in a retrospective fashion the results of applying a pulse-ox screening protocol in the UK to 90 babies screened at 2 hours of age. This study is important as the typical early discharge of patients from birth centres or could potentially benefit as well by having the results of such work available. Out of the 90 patients screened 4 had abnormal results and after rescreening two were normal but 2 were persistently abnormal and required admission for further workup. Neither of the two had CHD but were diagnosed with congenital pneumonia.
This yields a false positive rate of 2% or about 16 times as high as screening after 24 hours.
How do we apply the results?
As the saying goes “something is better than nothing”. In the home or birthing centre environment, waiting until after 24 hours to perform the screen may not be possible either due to the midwife leaving after the delivery or in the case of a birth centre the couple leaving before 6 hours as is the case in our local centre. As I see it all is not lost in doing screening in such circumstances early as one may detect TTN, pneumonia or another vascular condition such as PPHN before it becomes symptomatic. Intervening earlier in the course of the illness may actually result in better outcomes for the infant. We have to be careful though when looking at the ability of this screen to detect CHD. The truth is there are not enough patients screened in this study to really draw any conclusions. With an incidence of about 1:100 births a sample of 90 patients would be lucky to find one patient so the absence of any detected patients is not surprising.
The study though does draw attention to a couple important points. First as mentioned above, the midwife has the opportunity by screening early to detect ANY cause of desaturation and then plan for further management. Secondly, it does raise the question with a 2% false positive rate whether screening programs regardless of home or birth centre should include follow-up by a midwife after 24 hours to do testing. My vote would be a resounding yes. If applied to a population there would certainly be kids detected with CHD over time and reducing the false positive rate is important in terms of the downstream consequences of overwhelming our Cardiology colleagues who would ultimately need to see such patients to rule in or out significant CHD.
I am not a midwife, nor do I attend home or birthing centre deliveries but I would ask that the consideration of such screening programs consider the timing of testing as sending 2 per 100 deliveries vs 1 in 1000 deliveries for further assessment to rule out CHD is something that our overwhelmed health care systems need to consider strongly.