Can Pulse Oximetry help Heart Babies?

Summary

Tiny Tickers believes that Pulse Oximetry (PO) is a useful tool to screen a newborn baby before it goes home from hospital.

However, care must be taken as PO cannot detect all forms of congenital heart disease (CHD) - as explained below.

There is still a vital need for accurate antenatal detection using ultrasound at the routine "20 week" scan.

What is Pulse Oximetry (PO)?

Pulse Oximetry (PO), is a method of measuring the amount of oxygen in the blood using a sensor on the skin.

With skill and experience, this can be performed relatively quickly and the information can tell us a lot about a baby's health.

PO can detect some, but not all, types of congenital heart disease (CHD) in new born babies.

In a recent study in the West Midlands (1), published in August 2011, PO detected 5/5 cases of Transposition (TGA), but only 2/9 (22%) cases of Coarctation of the Aorta (CoA) - which is similar to a previous study in Sweden, where 3/9 (33%) cases of CoA were detected. (2)

Therefore, it is important to understand what type of CHD can be detected by PO and what cannot.  This is explained in more detail, below.

What is Simple Transpostion of the Great Arteries (Transposition or TGA) ?

Transposition (TGA) is a serious type of heart disease, where the two major vessels that supply blood to the body (the Aorta) and return blood to the lungs (the Pulmonary Artery) are switched.  As soon as a baby is born, this has to be corrected.  Fortunately, surgery can switch these two vessels back. 

Note:  Simple Transposition is the name given to Transposition when there are no other complications.

What is Coarctation of the Aorta (Coartctation or CoA) ?

Coarctation (CoA) is a life-threatening type of heart disease, where there is a narrowing or obstruction in the arch of the Aorta (Ao), the main artery from the heart that delivers oxygenated blood to the body.

Before birth, there is an extra path (the arterial duct), which bypasses the coarctation, so that blood can still flow. 
Click on the heart diagram on the right for a larger diagram where you can see the arch and duct >>

When a baby is born, the arterial duct may remain open up to 3 weeks after birth, providing enough blood flow for a baby with CoA to survive.  As soon as the arterial duct closes, a baby can collapse.  At this point, a baby needs to have a rapid diagnosis, to get the right treatment. 

Think HEART

Babies with Coartation can sometimes seem pale and waxy, due to poor heart function (low cardiac output) and this can be misinterpreted as having an infection.

One way to help diagnose babies with CoA rapidly, is for health visitors, GPs and new parents to remember Think HEART©, a mnemonic to look for signs of congenital heart disease after birth (Heart rate, Energy levels & eating, Arterial saturations, Respiratory rate, Temperature in hands & feet). (4).

If a baby has collapsed at home and is tested again using Pulse Oximetry - it should be possible to detect low oxygen levels.

More details of the PO study

The study describes the role of Pulse Oximetry (PO) in improving postnatal detection of congenital heart disease (CHD) in 20,000 babies born in 6 West Midlands maternity hospitals over 1 year period(1).

It was conducted in the setting of the NHS in England and Wales where, unlike a previous larger Swedish study(2), we already have an established antenatal screening programme to detect fetal abnormality, including CHD.

• In this study, Pulse Oximetry (PO) is good for picking up certain types of CHD, such as "simple" Transposition of the Great Arteries (TGA), which means TGA without other complications:
  • ONLY 1/5 (20%) "simple" TGA was detected antenatally, but PO picked up 5/5 (100%).
  • NOTE: Babies with TGA are usually “blue babies” – although studies show that “blueness” (low oxygen) may be missed in a multi-ethnic population.
  • CCAD (Central Cardiac Audit Database, set up after Bristol Inquiry), shows West Midlands antenatal detection to be 25-30%, which is slightly lower than the national average for England & Wales, excluding Scotland where antenatal detection remains patchy (3). 
• In this study ONLY 1 of the 9 (11%) cases of isolated CoA was detected at antenatal screening and ONLY 2 of the remaining cases were detected by Pulse Oximetry. Hence 6 out of 9 were missed by both methods. This highlights the importance of appropriately trained maternity units which can detect the majority of cases of CoA at antenatal screening.
  • Pulse Oximetry is unable to detect most cases of important, life-threatening "aortic arch" CHD, particularly isolated Coarctation of the Aorta, CoA (a narrowing of main body artery) as has been shown in other studies, such as one in Sweden in 2009 (2).
  • The explanation is that at birth, the circulation changes, and the arterial duct usually closes shortly after birth – however, it can stay open for upto 3 weeks after birth, in CHD.  So for PO to be truly effective in the detection of life-threatening disease, it needs to be performed in the community at the first suspicion of circulatory illness in babies.

References

1. "Pulse oximetry screening for congenital heart defects in newborn infants (PulseOx): a test accuracy study". 
Ewer AK et al., The Lancet, 5th August 2011 (online:  http://press.thelancet.com/pulseox.pdf)

2. De Wahl Granelli et al., 2009, BMJ

3. CCAD, http://www.ccad.org.uk/002/congenital.nsf/vwContent/Antenatal%20Diagnosis?Opendocument

4. Think HEART©