Pulse oximetry from the right upper limb (pre-ductal) and lower limbs (post-ductal) can identify a right-to-left shunt through the ductus arteriosus.
In a right-to-left shunt, the post-ductal circulation contains mixed blood from the right-side (pre-lung) and the left-side (post-lung) and hence the post-ductal O2 saturations are lower than the pre-ductal, if there is no transposition.
A difference of ≥10% is significant, although some sources quote lower differences.
Granelli, A. D. W., Wennergren, M., Sandberg, K., Mellander, M., Bejlum, C., Inganäs, L., … & Östman-Smith, I. (2009). Impact of pulse oximetry screening on the detection of duct dependent congenital heart disease: a Swedish prospective screening study in 39 821 newborns. BMJ; 338:a3037 doi:10.1136/bmj.a3037
Previously published: 23/05/14, 14/05/15