Background noise in the delivery room may further interfere with the audible heart sounds-especially with the low-level heart sounds of a compromised or preterm neonate. Inevitably, this method has limited accuracy, and is undocumented for later review and audit. Auscultation is intermittent, and heard by only one clinician, who has to count the number of heartbeats over a fixed time period. However, thereafter, methods for getting an accurate heart rate are unsatisfactory. It takes no significant amount of time to place the stethoscope on the neonate’s chest. Accuracy and Time Taken to Obtain the Heart RateĪuscultation is the recommended mode to determine the initial heart rate in newborns by ILCOR.
In one study, the authors found that the Doppler ultrasound did not function well with crying and moving babies. The time taken after application of the Doppler probe for a digital heart rate display was quite variable between the studies, but was less than or equivalent to the time taken for the ECG to display a heart rate.
All studies showed a satisfactory correlation of the displayed heart rate between Doppler and the gold standard. The gold standard for the heart rate in the studies was the electrocardiogram (ECG), and in addition, pulse oximetry was measured in one study. All were handheld transducers placed over the neonatal precordium with a sound output and a digital heart rate display. The foetal Doppler machines used in the studies were either 2 or 3 MHz transducers. These studies were not included in the data analysis, but are included in the Discussion, for the reasons explained. Of the two animal studies, one was in healthy newborn piglets, while the other was in asphyxiated piglets. included a range of both healthy and asphyxiated neonates at term or preterm. Recently, the possibility of this well-established technology used for the foetal heart rate has been explored for use in determining the neonatal heart rate, and the use of Doppler ultrasound forms the basis of this systematic review.Īgrawal et al. The safety of Doppler ultrasound is fully established, with its use in millions of pregnancies over the last 50 years. The heart rate can be determined through an electronic algorithm, or by the clinical assessment of counting over a measured time. The strength of the sound is correlated with the speed of the tissue movement. Foetal heart sounds are familiar to all midwives and obstetricians. Heart valve movements are rapid, and result in the major Doppler effects. Ultrasound readily passes through the maternal tissues, and the frequency of the reflected sound is altered by the movements of the heart. Doppler ultrasound is the routine method for monitoring the foetal heart rate. Both of these technologies can readily record and document the heart rate for later review.Ī more satisfactory method for routine use to determine the neonatal heart rate at birth is required. Both of these technologies take time to apply, and may be difficult after the neonate is placed in a polythene bag-routine care in preterm neonates to reduce the risk of hypothermia. ECG technology is also widespread, and increasingly reliable and low-cost.
It is the standard for determining the health of neonates. Oximetry technology is widespread, reliable, and low-cost. Furthermore, the heart rate is undocumented in real time, and there is no opportunity to review the result.įor these reasons, other approaches to determine the heart rate have been sought. In healthy neonates, auscultation provides a satisfactory estimate of the heart rate as determined by an ECG, but in a compromised neonate, in a noisy birth room and with weak heart sounds, this may not be the case. The interval needs to be short-6 s or 10 s is recommended-so as to quickly obtain the estimated rate in beats per minute. ĭetermining the heart rate by auscultation requires the number of heartbeats heard to be counted over a known interval of time. Auscultation is recommended for routine measurement of the heart rate, which needs to be determined quickly and accurately, since there are specific thresholds for intervention defined by the neonatal heart rate.
Heart rate determines the level of care required and any interventions. The neonatal branch of the International Liaison Committee on Resuscitation recommends that the heart rate of the newborn baby be determined within the first minute after birth. After birth, when the newborn baby can be observed, heart rate is still a major measure of health-especially in a compromised neonate who is not breathing, crying, or moving. During labour, the main parameter for determining the health of the foetus is heart rate (HR).
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