The technology for neonatal noninvasive monitoring is
usually developed for the adult population and adapted for use
in the newborn nursery. Thus, progress has been slow relative
to developments in the adult field.
Noninvasive monitoring of the
newborn is a primal biological phenomenon, and many species
within the animal kingdom monitor their offspring from birth.
In medicine, touching and feeling were the first methods used;
in more recent times, auscultation using a stethoscope and
documentation of temperature via thermometer have provided
important additional information. As medical knowledge has
progressed exponentially, so has noninvasive monitoring.
Progress in neonatal monitoring has been slow relative to
developments in adult monitoring, however. For most newborn
noninvasive monitoring modalities, the technology has been
developed for the wider adult population and is then adapted
for the newborn nursery. There are three main reasons for
this: neonatal medicine is a fairly new field, newborn
monitoring requires miniaturization of existing technology and
special designs because of the newborn’s unique physiology,
and some manufacturers have been reluctant to invest in
products that might produce a limited return.
Hospital and Home Monitors
One of the
most basic requirements for the well-being of the newborn is a
stable temperature. For premature and newborn infants, a
neutral thermal environment should be maintained, with
adequate warmth and humidity to minimize insensible heat and
water loss.1 Temperature monitoring allows the
caregiver to implement appropriate interventions to achieve
thermal stability in the neonate. The temperature probe may be
placed under the arm, on the infant’s abdomen, or in the
rectum. It can not only monitor the infant’s temperature, but
can connect to a radiant warmer bed and operate interactively
to regulate the amount of warming. When the infant is too
cool, the heat increases.
The first oximeters were expensive, cumbersome,
cart-mounted devices with fist-sized, C-shaped probes and
rubber ear covers. They failed to inspire confidence in
clinicians who used them. Today’s pulse oximeters are now so
ubiquitous, easy to use, and reliable that it is sometimes
necessary to remind oneself to question or challenge the
readings obtained from it. Although intended for adult use,
the smallest pulse oximeters currently available are little
larger than a clothespin, with both the electronics and
light-emitting–diode windows integrated into the probe itself.
Similar options for newborns cannot be far behind.
Neonatal pressure-cycled ventilators that provide minimal
information about lung function are being replaced by much
more sophisticated units that can be applied to adult,
pediatric, or neonatal care and can provide a much better look
at what the lungs are doing. Microprocessor technology built
into the new generation of ventilators provides detailed
monitoring parameters and alarm modes for patient spirometry,
measuring tidal volume, minute volume, flow, compliance,
airway resistance, and airway pressure. Liquid-crystal–display
video monitors can add real-time pressure, flow, volume, and
flow/volume loops. With pressure-regulated volume-control
ventilation mode, for example, users can rely on the
ventilator to adjust pressure automatically in response to
changing lung compliance. While ventilator-based monitors
could be considered invasive, no additional invasive
technology is required for their use because the patient has
already been intubated for ventilatory support.
Mainstream capnographs use a sampling window in the
ventilator circuit to provide continuous analysis and
recording of carbon dioxide levels in respiratory gases.
Sidestream analyzers aspirate the gas from the circuit or a
nasal catheter, and the analysis is performed within the
monitor.2 In either case, clinicians are provided
with important information about gas exchange. In addition,
transcutaneous monitoring of oxygen and carbon dioxide
provides estimates of Pao2 and Paco2.3
For many years, apnea monitors have brought noninvasive
monitoring of neonates into the home. Documented event
monitoring simultaneously monitors three channels of
information to provide monitor alarms or to verify the
presence or absence of episodes of central apnea, bradycardia,
and oxygen desaturation (events).5 Parents can care
for their infants at home while continually monitoring
chest-wall impedance, heart rate, and oxygen saturation.
Cardiac output can be
extrapolated noninvasively based on respiratory gas analysis
using a technique known as differential Fick partial
rebreathing. An airway sensor, consisting of a rebreathing
valve and a combined carbon dioxide/flow sensor, is placed in
the breathing circuit. A noninvasive cardiac-output
calculation is made based on the changes induced in carbon
dioxide elimination and end-tidal carbon dioxide (etco2) in
response to the rebreathing volume. The increase in etco2
reflects an increase in Paco2.
The Fick equation states that cardiac output is equal to
carbon dioxide elimination divided by the difference between
venous and arterial levels of carbon dioxide. The
partial-rebreathing method yields a differential form of the
Fick equation, eliminating the need to measure mixed venous
carbon dioxide, so a pulmonary arterial line is not required
as for the traditional (and highly invasive) thermodilution
method. This indirect Fick method is then corrected for
shunting, based on the Nunn isoshunt curve using oxygen
saturation (from pulse oximetry or arterial blood-gas
analysis) and a user-entered value for the fraction of
This important tool for assessing and treating hemodynamic
instability has not yet become the gold standard, and many
clinicians maintain a trust-but-verify approach to it.
Respiratory therapists may be seeking and developing
evidence-based physician support. Studies are under way to
document that, in real-world settings, calculating cardiac
output noninvasively can reduce arterial blood-gas sampling,
assist in optimizing ventilator parameters, assess weaning
progress, and provide a reliable evaluation of the
mechanically ventilated newborn.
On the Horizon
Today’s research and
development teams are unveiling noninvasive monitoring
techniques that no one would have been likely to imagine a
decade ago. For example, a bilirubinometer that is effective
in diagnosing and tracking jaundice using color-science
technology has received clearance from the US Food and Drug
Administration for commercial marketing. Soon, repeatedly
drawing blood samples to assess bilirubin levels may become a
practice from the dark ages of newborn care.6,7
Noninvasive monitoring for hemoglobin (hematocrit) using
wavelength technology combined with a pressurizing site cuff
is also in development.
Hospital personnel are constantly challenged by the
ventilator tubing, intravenous lines, and monitor wires
connected to critically ill patients. Parents may also be
disturbed at the sight of their newborns tethered to so many
devices. The challenge of noninvasive monitoring is compounded
in the newborn nursery because of the tiny size of the
patients. Clearly, it would be better to eliminate monitor
wires without losing the important information that the
monitors provide. An oximetry sensor, for example, could be
powered by a miniature battery or solar cell and could
transmit its information to a monitor mounted above the
patient, to the nursing station, or to a handheld device
carried by the RT.
Why settle for monitoring one or two parameters from a
patch or probe? Why not incorporate many or all of the
parameters to be monitored into one or two patches, or an
elastic chest band, and eliminate most or all of the wires and
cables? Research and development in the noninvasive-monitoring
field are now focusing on incorporating wireless technology
into current modalities and bringing diverse elements together
in a cohesive package. When that becomes reality, it will be
possible to monitor infants from any location, and the
information generated will become part of the electronic
medical record with no manual notation required.
This idea is currently in development throughout the
industry, with devices built to measure several parameters not
far behind. In Finland, for example, emergency medical
technicians are reportedly using a monitor blanket that
measures multiple parameters simultaneously. Although it is
not available for use in the United States, and is not used
for neonates, the concept is clearly far beyond the
imagination stage. Refinement and implementation of similar
technology can not be far away. As with most developments in
newborn monitoring, breakthroughs are usually developed for
the adult market and the technology is adapted for neonatal
For about $100, bicyclists can purchase a wristwatch that
monitors the rider’s current and maximum heart rate, exercise
time, and information transmitted wirelessly from a sensor on
the bicycle’s front fork, which is then used to calculate
current, average, and maximum speed; distance traveled; and
other trip data. The information can be downloaded to the
cyclist’s computer wirelessly, as well. This device makes it
obvious that most of the technology needed to integrate
newborn monitors with life-support systems is already
available to developers. Developments in artificial
intelligence will also make it possible to evaluate and
organize the data in a meaningful way. Clinicians could not
only be warned of threatening conditions, for example, but
specific plans of action could be suggested (and automatically
enacted, if desired). A temperature probe is already trusted
to adjust the heat lamp in a newborn's bed. It is conceivable
that clinicians will also come to trust other noninvasive
monitors to interact with more sophisticated life-support
systems, such as ventilators, to adjust settings within preset
guidelines in reaction to changing patient conditions. The
emerging field of microelectromechanical systems has important
implications for the noninvasive monitoring and management of
newborns, who will benefit from better monitoring, better
life-support management, and more time with parents.
John A. Wolfe, RRT, CPFT, is a contributing writer for
RT and a member of RT’s editorial advisory board.
1. Fink JB, Hess DR.
Humidity and aerosol therapy. In: Hess DR, MacIntyre NR,
Mishoe SC, Galvin WF, Adams A, Saposnick AB, eds. Respiratory
Care: Principles and Practices. Philadelphia: WB Saunders;
2. AARC Clinical Practice Guideline.
Capnography/Capnometry During Mechanical Ventilation—2003
Revision & Update. Respir Care. 2003;48:534-537.
AARC Clinical Practice Guideline. Transcutaneous blood gas
monitoring for neonatal and pediatric patients. Respir Care.
4. Estrem B. Infant apnea monitoring.
In: Hess DR, MacIntyre NR, Mishoe SC, Galvin WF, Adams A,
Saposnick AB, eds. Respiratory Care: Principles and Practices.
Philadelphia: WB Saunders; 2002:550-564.
Cardiopulmonary Management System User’s Manual. Wallingford,
Conn: Respironics Novametrix; 2003.
6. US Food and Drug
Administration Briefing Document for June 11 Open Session of
the Pediatric Advisory Committee on Hyperbilirubinemia and
Drug Development in the Term and Near–Term Newborn Infant.
From: Division of Pediatric Drug Development; To: Pediatric
Subcommittee of the Anti-Infective Drugs Advisory Committee.
Rockville, Md: FDA; 2003.
7. Bertini G, Rubaltelli F.
Non-invasive bilirubinometry in neonatal jaundice. Semin