Use of a New Doppler Umbilical Cord Clamp to Measure
Heart Rate in Newborn Infants in the Delivery Room
Robert P. Lemke MD1, Michael Farrah BMET2, and Paul J. Byrne MBChB1
1Department of Pediatrics, University of Alberta, Edmonton, Alberta, Canada
2Department of Clinical Engineering, University of Alberta, Edmonton, Alberta, Canada
Address correspondence: Robert Lemke, MD
Stollery Children’s Hospital 3A3 Walter C Mackenzie HSC 8440 112 St NW
Edmonton, Alberta T6G 2B7
Email: rplemke@shaw.ca
Author Disclosure: All three authors have applied for a patent on the device described in this paper in multiple jurisdictions.
ABSTRACT
Objective: As an initial proof of concept, to determine whether a prototype umbilical cord clamp containing a Doppler ultrasound probe could quickly detect and accurately measure the heart rate of term newborns 5 min after birth.
Methods: Clinically stable, spontaneously breathing newborns in room air, ≥ 37 week’s gestation, had the prototype clamp applied to the base of their umbilical cord. We noted the time needed to detect a signal and then monitored the audible Doppler pulsations for approximately 1 minute while we simultaneously palpated the femoral pulse to confirm a 1:1 correlation.
Results: A total of 16 term infants (9 female, GA 39±2 weeks, BW 3265±425 grams, one minute Apgar 8±2, five minute Apgar 9±1) had the cord clamp applied. In all cases a Doppler signal was detected immediately after contact with the skin, and remained strong and correlated 1:1 with the palpated pulse for at least one minute. Movement and crying resulted in some noise but the Doppler heart rate signal was unaffected.
Conclusion: Under controlled conditions, a prototype umbilical cord clamp containing a Doppler ultrasound probe was able to detect and monitor the heart rate of 16 healthy newborns after birth. The technique has potential applications in guiding newborn resuscitation and requires further study.
Key words: newborn, Doppler, resuscitation, newborn heart rate monitor, delivery room
INTRODUCTION
The transition from fetus to an air-breathing
infant is a complex physiological process.1
Although most babies are successful in this regard, a significant number require some
emergent assistance during this transition,
2-4
and resuscitation interventions are not
themselves without risk.5-7 Fundamental to
the decision making protocol described in the Neonatal Resuscitation Program developed by the American Heart Association, is accurate real time knowledge of a newborn infant’s rapidly changing heart
rate.1,3,7 Continuous electronic monitoring of fetuses in utero, and of older infants in nurseries commonly occurs, and yet in the newborn during the critical first few minutes of life, heart rate measurement routinely
relies on simple palpation and auscultation.1
This critical information, used to initiate and guide resuscitation is typically only intermittently obtained, difficult to verify in retrospect, and when done under stressful
circumstances is subject to error.
1,6,8-10
Although more recently, electronic monitoring has been used in the delivery suite for neonates immediately after delivery
a number of problems remain.1,11 First, the
blood, mucus, amniotic fluid and vernix caseosa, which covers newborns must first be cleaned from the skin to ensure that adhesive probes stick and good contact
between the skin and probe is achieved.10
Even in experienced hands, application takes time and may paradoxically divert attention
away from the actual resuscitation.12
Second, the most investigated monitoring modality, pulse oximetry, depends on good tissue perfusion to ensure an error free
signal.12,13 Unfortunately perfusion is
poorest in those babies who are the most compromised. Finally, in all cases there is a time delay between the time the umbilical cord is cut and the baby is transferred to the overhead warmer before auscultation
and/or palpation can occur.3,7
We noted that Doppler ultrasound is an effective method to quickly detect pulsation that is unaffected by contamination of the skin with bodily fluids. Moreover we recognized that clamping a device to the umbilical cord can provide a robust mechanical method of fixation that is unaffected by the presence of bodily fluids. In fact the umbilical cord is an ideal site for such a monitoring device because it is centrally located on the body, universally
present, contains no pain receptors and is infrequently needed after birth. We therefore envisioned a new umbilical clamp, housing an integral wireless Doppler ultrasound probe, which is quick and simple to firmly attach to the baby’s cord immediately after birth. The heart rate data generated by the device could be transmitted wirelessly in real time to a monitor for audible and numeric display and data trending and storage.
METHODS
This pilot study was reviewed and approved by the Human Ethics and Research Board of the University of Alberta. Informed consent was obtained from the mother prior to birth for each patient enrolled.
In order to prove our concept, we developed a simple prototype cord clamp (Figure 1) which consisted of a milled polyethylene plastic housing through which the umbilical cord passed and positioned a pencil Doppler ultrasound probe with its tip covered in gel (Koven Technologies, St Louis, Missouri) against the infant’s abdominal wall at the base of the cord. We hypothesized that this umbilical clamp, would detect a pulsation in the intra-abdominal arteries within 5 seconds of application to the skin and do so for at least 1 minute within the first 5 minutes after birth. Moreover, this pulsation would correlate 1:1 with the heartbeat as determined by concurrent palpation of the femoral pulse. The intended pilot study population were clinically stable, spontaneously breathing newborns in room
air, ≥ 37 weeks gestation, who did not
require resuscitation beyond simple stimulation. Any infant with a suspected congenital anomaly, or who was requiring oxygen or ventilatory support, or a gestational age < 37 weeks was excluded.
The application of the Doppler cord clamp in the delivery suite was straightforward. At birth, the obstetrician was asked to clamp a hemostat to the cord in such a way as to provide at least 10 cm of cord for us to apply our device. After delivery, the infant was first handed to the resuscitation team for assessment and appropriate care. At 4 minutes, if the baby was deemed stable, we attached the device to the base of the cord, applying mild traction to the cord through the housing using a Hollister disposable cord clamp (Hollister Incorporated, Libertyville, Illinois) to minimize movement. We noted the time needed to detect an audible signal and then monitored the audible Doppler
pulsations for at least 1 minute while we simultaneously palpated the femoral pulse to confirm a 1:1 correlation. Once the monitoring period was completed, the Doppler cord clamp assembly was removed by unclipping the housing from the cord. We then applied a second Hollister cord clamp at the base of the cord, and trimmed the excess cord before returning the baby to the parents.
We planned to use the prototype clamp on a total of 10 to 20 newborns to assess i). the process of clamp application, ii). the clamp’s ability to detect pulsation and iii). its ability to measure heart rate. This sample size was arbitrary but based on our belief that it constituted a reasonable sample to reveal any needed modifications of the device
and/or process of application for
further development. We completed successful clamp application, pulse detection and heart rate measurements in 16 newborns. In 8 infants, a 10 MHz probe, applied 15 degrees from midline, and
directed 45o cephalad from vertical, was
used to target an umbilical artery as it passed caudad in the abdominal wall. In the remaining 8 babies, a 5 MHz probe was
applied midline, directed 45o cephalad from
vertical, to target deeper arteries in the pelvis. Data collection consisted of standard demographic data (i.e. gender, birth weight and Apgar scores) and observations regarding the application of the device, signal acquisition and strength, and correlation with palpated pulse.
RESULTS
A total of 16 term infants (9 female, GA 39±2 weeks, BW 3265±425 grams, one minute Apgar 8±2, five minute Apgar 9±1 [mean ± standard deviation]) had the cord clamp applied by one of the authors within 5 minutes of birth at the Caseroom of
the Grey Nuns Community Hospital in Edmonton, Alberta, Canada. In 8 infants the umbilical artery was the target and in the remaining 8 deeper pelvic arteries were insonated. In all cases an audible Doppler signal was detected immediately after contact with the skin and remained clear and strong and correlated 1:1 with the palpated femoral pulse for at least 1 minute. The average heart rate measured immediately after application of the clamp was 145±27 bpm (mean ± standard deviation) for an umbilical artery target and 150±20 bpm for the deeper signal target. There was no subjective difference noted in signal strength or ease of acquisition between the two targets. Eleven infants were crying during the use of the Doppler cord clamp and the remaining five were quiet. Movement and crying resulted in some noise but the Doppler heart rate signal was unaffected. As anticipated, the presence of bodily fluids on the cord and infant skin did not interfere with signal detection. Overall the clamp was well tolerated by all the infants.
DISCUSSION
In this proof of concept study, we successfully used a prototype Doppler cord clamp to detect and monitor the heart rate of 16 healthy term infants in the delivery room of a community hospital. Under these very controlled circumstances, the clamp pro-vided rapid and accurate heart rate data using two different potential Doppler signal sources.
The use of Doppler ultrasound to measure heart rate immediately after birth has not been previously described. Because of concerns regarding the inaccuracy of clinically assessed heart rate measurements, a number of studies have explored the use of ECG and/or pulse oximetry in newborn
resuscitation.10,11 However, concerns remain
for a number of reasons. Data are not available for up to 90 seconds because of delays associated with skin cleaning, probe
application and signal acquisition.12,13
Moreover, in low skin perfusion states, pulse
oximetry can be inaccurate.11,13 Despite
these limitations, the use of pulse oximetry is encouraged to provide some form of
objective heart rate data.1,3,7 There are a
number of theoretical factors which could result in attenuation and/or interference with the Doppler signal and thereby limit the usefulness of the cord clamp in resuscitation. First, in the case of the umbilical arteries, vasospasm and clotting are physiologic processes which ultimately obliterate these vessels as a source for heart rate data. While there are no published data available to document the speed with which the umbilical arteries be-come nonpulsatile after the cord is clamped and cut, in our pilot study we had no difficulty detecting a pulse signal up to 5 minutes of age suggesting that it may take some time to lose the umbilical arterial signal completely. Second, the presence of bowel gas is well known to attenuate ultrasound signal strength. However, at birth the bowel is fluid filled and it takes time for swallowed gas to travel distally. We were able to easily detect a deeper pelvic Doppler signal in our study patients, many of who were crying and presumably swallowing air, suggesting that this would not be an important concern in newborns soon after birth. Finally, movement can introduce noise in the Doppler signal, which if of sufficient intensity, could interfere with or obliterate the pulse waveform and result in signal loss. Again, this was not an issue in the patients we studied. Moreover, we suggest that this is of minimal practical importance in the Doppler cord clamp’s appli-cation because it is in the quiet or
unresponsive infant that resuscitation concerns arise, not the vigorous, crying neonate.
In this study we targeted pulsations from deep and superficial arteries using com-mercially available pencil Doppler probes of 5 and 10 MHz respectively. Although it is clear that the superficial vessel signal source should be the umbilical artery, the identity of the specific arteries, which provided the deeper pulse signal, is not clear from this study. Likely target arteries include the aorta, iliac or the abdominal umbilical artery. All of these vessels are large and would be expected to provide an accurate signal even in the severely
hemodynamically compromised
new-born. One potential practical problem with the attachment of a monitoring system to the umbilical cord is its possible interference with the insertion of umbilical lines should the need arise. To overcome this issue we
designed the prototype clamp to engage the cord 3 cm above the infant’s abdomen, and to be easily removed thereby ensuring an adequate length of cord if subsequent umbilical line insertion was needed.
The application of a prototype umbilical Doppler clamp in this pilot study detected accurate heart rate in newborns after birth. Our ultimate goal is to have the clamp applied to the infants cord while at the mother’s perineum. This would document heart rate immediately after birth, information which is currently not readily available. Such objective heart rate data could then be used to both signal the need for and guide neonatal resuscitation. The potential clinical application of this device in both sick and well infants is apparent. However, the device is in a very early prototype development and there is still considerable work to be done before it could see clinical use.
REFERENCES
1. American Academy of Pediatrics and American Heart Association. Textbook of Neonatal Resuscitation. 5th ed. Elk Grove Village (IL): American Academy of Pediatrics; Dallas (TX): American Heart Association; 2006.
2. Leone TA, Rich W, Finer NN. A survey of delivery room resuscitation practices in the United States. Pediatrics. 2006; 117(2):e164-75.
3. Perlman JM, Wyllie J, Kattwinkel J, Atkins DL, Chameides L, Goldsmith JP, et al. on behalf of the Neonatal Resuscitation Chapter Collaborators. Part II: neonatal resuscitation: 2010 International Consensus on Cardio-pulmonary Resuscitation and Emergency Cardiovascular Care Science With
Treatment Recommendations. Circulation
2010; 122 (suppl 2):S516–S538.
4. Rajani AK, Chitkara R, Halamek LP. Delivery room management of the newborn.
Pediatr Clin N Am 2009; 56:515-535. 5. Perlman JM, Kattwinkel J. Delivery room
resuscitation past, present, and the future.
Clin Perinatol 2006; 33:1-9.
6. O’Donnell CPF, Kamlin COF, Davis PG, Morley CJ. Endotracheal intubation attempts during neonatal resuscitation: Success rate, duration, and adverse effects. Pediatrics
2006; 117: e16-e21.
7. Kattwinkel J, Perlman JM, Aziz K, Colby C, Fairchild K, Gallagher J, et al. Part 15: neonatal resuscitation: 2010 American Heart Association Guidelines for Cardiopulm-onary Resuscitation and
Emer-gency Cardiovascular Care. Circulation. 2010; 122:S909–S919.
8. Kattwinkel J. Evaluating resuscitation practices on the basis of evidence: the findings at first glance may seem illogical. J Pediatr 2003; 142:221–2.
9. Carbine DN. Finer NN. Knodel E. Rich W. Video recording as a means of evaluating neonatal resuscitation performance.
Pediatrics. 2000; 106(4): 654-8.
10. Kamlin CO, O'Donnell CP, Everest NJ, Davis PG, Morley CJ. Accuracy of clinical assessment of infant heart rate in the delivery room. Resuscitation 2006; 71(3):319-21.
11. Dawson JA, Davis PG, O’Donnell CPF, Kamlin COF, Morley CJ. Pulse oximetry for monitoring infants in the delivery room: a review. Arch Dis Child Fetal Neonatal Ed
2007; 92:F4-F7.
12. Finer N, Rich W. Neonatal resuscitation for the preterm infant: evidence versus practice.
J Perinatol 2010; 30:S57-S66.
13. Kamlin CO. Dawson JA. O'Donnell CP. Morley CJ. Donath SM. Sekhon J.et al. Accuracy of pulse oximetry measurement of heart rate of newborn infants in the delivery room. J Pediatr 2008; 152(6):756-60.
