Development of Doppler ultrasound for measuring the neonatal heart rate at birth.

The heart rate of a newborn baby is a very important measure of its health and is routinely required to be documented at every birth. The imprecise measurement and lack of real-time documentation of the neonatal heart rate at birth has been recognised for many years but auscultation still remains the recommended method in routine births. The heart rate of the fetus is measured and documented during pregnancy and labour by Doppler ultrasound but immediately after birth the heart rate is measured by auscultation. Auscultation is well recognised to be inaccurate and undocumented in real-time.to obtain the beats per minute heart rate. The contrast with determining and documenting the fetal heart rate with the neonatal heart rate is remarkable. Recently a new ECG device has been developed in an attempt to provide more continuous monitoring and documentation of the neonatal heart rate has been developed. There has also been investigation of the use of a hand-held foetal Doppler recently to determine the neonatal heart rate immediately after birth. It was found to be very effective but has not been seriously considered by the International Liaison Committee On Resuscitation. One reason may be the fact that, unlike the ECG, but similar to a stethoscope, the Doppler is not hands-free, as it requires one member of the resuscitation team to keep the transducer on the neonatal chest. Experience of over 50 years shows that even the slowest and weakest fetal hearts can be detected by Doppler ultrasound. This research was to develop and test a hands-free version of a hand-held fetal Doppler device and to test this device for accuracy and functionality on adults and neonates. The initial study was carried out on healthy adult volunteers using a standard hand-held fetal Doppler device. The Doppler heart rate was compared with the ECG heart rate and found to have good correlation. The Bland Altman Plot of Doppler vs ECG showed all but two measurements were within the 95% confidence intervals. A problem with documentation and the need for a hands-free transducer was highlighted. This initial study fuelled the drive to construct a modified Doppler device to be hands-free and document electronically the heart rate results in real time. The problem of precise documentation of both the Doppler heart rate and the ECG heart rate was explored. A further modification was required and the final device tested in a second adult study. This showed much improved ease of use during the investigation, excellent correlation and that the Doppler usually determined the heart rate consistently before the ECG. The final part of the study involved using the modified hands free Doppler device on neonates at the Children’s Hospital Sleep Unit and comparing the Doppler heart rate with that of the hospital ECG. This demonstrated that the modified Doppler device was truly hands-free and, in the opinion of the parents, highly acceptable for use on their neonate.