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					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
1
    Department of Pediatrics, University of Alberta, Edmonton, Alberta, Canada
2
    Department 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                  themselves without risk.5-7 Fundamental to
infant is a complex physiological process.1                    the decision making protocol described in
Although most babies are successful in this                    the Neonatal Resuscitation Program
regard, a significant number require some                      developed by the American Heart
emergent assistance during this transition,2-                  Association, is accurate real time knowledge
4
  and resuscitation interventions are not                      of a newborn infant’s rapidly changing heart


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New Doppler Umbilical Cord Clamp                                                       Lemke et al


rate.1,3,7 Continuous electronic monitoring of       present, contains no pain receptors and is
fetuses in utero, and of older infants               infrequently needed after birth. We therefore
in nurseries commonly occurs, and yet in the         envisioned a new umbilical clamp, housing
newborn during the critical first few minutes        an integral wireless Doppler ultrasound
of life, heart rate measurement routinely            probe, which is quick and simple to firmly
relies on simple palpation and auscultation.1        attach to the baby’s cord immediately after
This critical information, used to initiate and      birth. The heart rate data generated by the
guide       resuscitation   is typically only        device could be transmitted wirelessly in
intermittently obtained, difficult to verify in      real time to a monitor for audible and
retrospect, and when done under stressful            numeric display and data trending and
circumstances is subject to error.1,6,8-             storage.
10
   Although more recently, electronic
monitoring has been used in the delivery             METHODS
suite for neonates immediately after delivery
a number of problems remain.1,11 First, the          This pilot study was reviewed and approved
blood, mucus, amniotic fluid and vernix              by the Human Ethics and Research Board of
caseosa, which covers newborns must first            the University of Alberta. Informed consent
be cleaned from the skin to ensure that              was obtained from the mother prior to birth
adhesive probes stick and good contact               for each patient enrolled.
between the skin and probe is achieved.10
Even in experienced hands, application takes         In order to prove our concept, we developed
time and may paradoxically divert attention          a simple prototype cord clamp (Figure 1)
away from the actual resuscitation.12                which consisted of a milled polyethylene
Second, the most investigated monitoring             plastic housing through which the umbilical
modality, pulse oximetry, depends on good            cord passed and positioned a pencil Doppler
tissue perfusion to ensure an error free             ultrasound probe with its tip covered in gel
signal.12,13 Unfortunately       perfusion    is     (Koven Technologies, St Louis, Missouri)
poorest in those babies who are the most             against the infant’s abdominal wall at the
compromised. Finally, in all cases there is a        base of the cord. We hypothesized that
time delay between the time the umbilical            this umbilical clamp, would detect a
cord is cut and the baby is transferred to the       pulsation in the intra-abdominal arteries
overhead warmer before auscultation                  within 5 seconds of application to the skin
and/or palpation can occur.3,7                       and do so for at least 1 minute within the
                                                     first 5 minutes after birth. Moreover, this
We noted that Doppler ultrasound is an               pulsation would correlate 1:1 with the
effective method to quickly detect pulsation         heartbeat as determined by concurrent
that is unaffected by contamination of the           palpation of the femoral pulse. The intended
skin with bodily fluids. Moreover we                 pilot study population were clinically stable,
recognized that clamping a device to the             spontaneously breathing newborns in room
umbilical cord can provide a robust                  air, ≥ 37 weeks gestation, who did not
mechanical method of fixation that is                require resuscitation    beyond        simple
unaffected by the presence of bodily fluids.         stimulation. Any infant with a suspected
In fact the umbilical cord is an ideal site for      congenital anomaly, or who was requiring
such a monitoring device because it is               oxygen or ventilatory support, or a
centrally located on the body, universally           gestational age < 37 weeks was excluded.


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New Doppler Umbilical Cord Clamp                                                         Lemke et al


                                                    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
The application of the Doppler cord clamp
                                                    applied midline, directed 45o cephalad from
in the delivery suite was straightforward. At
                                                    vertical, to target deeper arteries in the
birth, the obstetrician was asked to clamp a
                                                    pelvis. Data collection consisted of standard
hemostat to the cord in such a way as to
                                                    demographic data (i.e. gender, birth weight
provide at least 10 cm of cord for us to apply
                                                    and Apgar scores) and observations
our device. After delivery, the infant was
                                                    regarding the application of the device,
first handed to the resuscitation team for
                                                    signal     acquisition    and strength,      and
assessment and appropriate care. At 4
                                                    correlation with palpated pulse.
minutes, if the baby was deemed stable, we
attached the device to the base of the cord,        RESULTS
applying mild traction to the cord through
the housing using a Hollister disposable cord       A total of 16 term infants (9 female, GA
clamp (Hollister Incorporated, Libertyville,        39±2 weeks, BW 3265±425 grams,
Illinois) to minimize movement. We noted            one minute Apgar 8±2, five minute Apgar
the time needed to detect an audible signal         9±1 [mean ± standard deviation]) had
and then monitored the audible Doppler              the cord clamp applied by one of the authors
                                                    within 5 minutes of birth at the Caseroom of


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New Doppler Umbilical Cord Clamp                                                        Lemke et al


the Grey Nuns Community Hospital in                 for a number of reasons. Data are not
Edmonton, Alberta, Canada. In 8 infants the         available for up to 90 seconds because of
umbilical artery was the target and in the          delays associated with skin cleaning, probe
remaining 8 deeper pelvic arteries were             application      and signal    acquisition.12,13
insonated. In all cases an audible Doppler          Moreover, in low skin perfusion states, pulse
signal was detected immediately after               oximetry can be inaccurate.11,13 Despite
contact with the skin and remained clear and        these limitations, the use of pulse oximetry
strong and correlated 1:1 with the palpated         is encouraged to provide some form of
femoral pulse for at least 1 minute. The            objective heart rate data.1,3,7 There are a
average heart rate measured immediately             number of theoretical factors which could
after application of the clamp was 145±27           result in attenuation and/or interference with
bpm (mean ± standard deviation) for an              the Doppler signal and thereby limit the
umbilical artery target and 150±20 bpm for          usefulness      of    the cord      clamp     in
the deeper signal target. There was no
                                                    resuscitation. First, in the case of the
subjective difference noted in signal strength
                                                    umbilical arteries, vasospasm and clotting
or ease of acquisition between the two
                                                    are physiologic processes which ultimately
targets. Eleven infants were crying during
                                                    obliterate these vessels as a source for heart
the use of the Doppler cord clamp and the
remaining five were quiet. Movement                 rate data. While there are no published
and crying resulted in some noise but the           data available to document the speed with
Doppler heart rate signal was unaffected.           which      the      umbilical    arteries   be-
As anticipated, the presence of bodily fluids       come nonpulsatile after the cord is clamped
on the cord and infant skin did not interfere       and cut, in our pilot study we had no
with signal detection. Overall the clamp was        difficulty detecting a pulse signal up to 5
well tolerated by all the infants.                  minutes of age suggesting that it may take
                                                    some time to lose the umbilical arterial
DISCUSSION                                          signal completely. Second, the presence
                                                    of bowel gas is well known to attenuate
In this proof of concept study, we                  ultrasound signal strength. However, at
successfully used a prototype Doppler cord          birth the bowel is fluid filled and it takes
clamp to detect and monitor the heart rate of       time for swallowed gas to travel distally.
16 healthy term infants in the delivery room        We were able to easily detect a deeper
of a community hospital. Under these very           pelvic Doppler signal in our study
controlled circumstances, the clamp pro-            patients, many of who were crying and
vided rapid and accurate heart rate data            presumably swallowing air, suggesting that
using two different potential Doppler signal        this would not be an important concern in
sources.                                            newborns           soon       after       birth.
                                                    Finally, movement can introduce noise in
The use of Doppler ultrasound to measure            the Doppler signal, which if of sufficient
heart rate immediately after birth has not          intensity, could interfere with or obliterate
been previously described. Because of               the pulse waveform and result in signal
concerns regarding the inaccuracy of                loss. Again, this was not an issue in the
clinically assessed heart rate measurements,        patients we studied. Moreover, we suggest
a number of studies have explored the use of        that this is of minimal practical importance
ECG and/or pulse oximetry in newborn                in the Doppler cord clamp’s appli-
resuscitation.10,11 However, concerns remain        cation because it is in the quiet or


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New Doppler Umbilical Cord Clamp                                                                   Lemke et al


unresponsive infant that resuscitation                     designed the prototype clamp to engage the
concerns arise, not the vigorous, crying                   cord 3 cm above the infant’s abdomen, and
neonate.                                                   to be easily removed thereby ensuring an
                                                           adequate length of cord if subsequent
In this study we targeted pulsations from                  umbilical line insertion was needed.
deep and superficial arteries using com-
mercially available pencil Doppler probes of               The application of a prototype umbilical
5 and 10 MHz respectively. Although it is                  Doppler clamp in this pilot study detected
clear that the superficial vessel signal source            accurate heart rate in newborns after birth.
should be the umbilical artery, the identity               Our ultimate goal is to have the clamp
of the specific arteries, which provided the               applied to the infants cord while at the
deeper pulse signal, is not clear from this                mother’s perineum. This would document
study. Likely target arteries include the                  heart rate immediately after birth,
aorta, iliac or the abdominal umbilical                    information which is currently not readily
artery. All of these vessels are large and                 available. Such objective heart rate data
would be expected to provide an accurate                   could then be used to both signal the need
signal      even      in      the      severely            for and guide neonatal resuscitation. The
hemodynamically        compromised        new-             potential clinical application of this device
born. One potential practical problem with                 in both sick and well infants is apparent.
                                                           However, the device is in a very early
the attachment of a monitoring system to the
                                                           prototype development and there is still
umbilical cord is its possible interference
                                                           considerable work to be done before it could
with the insertion of umbilical lines should
                                                           see clinical use.
the need arise. To overcome this issue we


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