• neonatology
• cardiology
• pulse oximetry
• newborn screening
• congenital heart defect

Routine pulse oximetry screening (POS) of newborn babies before discharge from hospital has been shown to identifying cases of critical congenital heart disease (CCHD) with consistent test accuracy1 and to reduce mortality from these conditions by one-third.2

There is increasing uptake of POS in high-income and middle-income countries1–4; in July 2018, after several years of state-by-state introduction, POS became mandatory across the USA2 which means that almost 4 million babies a year will undergo the test in that country alone.

POS reduces the ‘diagnostic gap’ for CCHD, that is, it identifies additional cases which are missed by other screening methods such as antenatal ultrasound and postnatal examination.1 The size of this gap varies depending on local circumstances, but the addition of POS consistently reduces it to less than 10%.4

However, as described in this recent Archimedes article,5 POS is not a perfect test. Some babies (particularly those with defects that obstruct left ventricular outflow such as coarctation of the aorta [CoA] and interrupted aortic arch [IAA]) are missed by POS and other routine screening tests4 and Searle and colleagues quite rightly ask if an additional screening tool—perfusion index (PI)—could have identified such defects earlier.5

As Searle et al describe, PI is an assessment of pulse strength—measured at the same time as oxygen saturations by a pulse oximeter which calculates the ratio of pulsatile to non-pulsatile blood. Lower PI values represent reduced perfusion.5

Given that critical obstruction …