Philips Fetal Monitor User manual

Philips Fetal Monitors

P

Fetal Monitoring Technology

Application Note

This application note explains how Philips fetal
monitoring technology supports safe and accurate
fetal and maternal monitoring. Four technological
aspects are collected together here:

• Precision Signal Track and Hold

• Cross-Channel Verification

• Fetal Heart Rate Baseline Offset

•Fetal Movement Profile

Precision Signal Track and Hold

This technology allows the monitor to track the fetal
heart rate signal very closely to ensure an accurate
fetal heart rate measurement with almost no gaps.

The signal is monitored with two ultrasound
receiver channels so that two overlapping time
windows can be monitored (ultrasound travelling
time=depth). When the signal is strong in both
windows the optimal monitoring depth is found.
The measurement window stays in this position
while the control window is moved in both
directions to check the strength of the signal at
different depths. When the control window registers
a change in the signal position (due to movement of
the fetus or mother) the measurement window is
moved to the new optimal position. This adaptation
to changing depth happens with each heart beat and
so virtually eliminates gaps in the trace due to lost
signals.

As the signal is so well tracked, the measurement
window around the heart can be made as small as

possible thus reducing the ultrasound energy that
mother and fetus are exposed to.

Ultrasound Crystal Placement for Optimal Geometry

The crystals in the Ultrasound transducer are located
six around the circumference and one in the center.
In this configuration, all lines between crystals are
equidistant. If a line were drawn from crystal to
crystal, a series of equilateral triangles would be
created. This allows the coverage area to be
homogenous, or of equal signal strength throughout.

crystals

A homogenous signal eliminates any "dark spots" in
the beam, which will reduce the number of times the
clinician will need to reposition the transducer. If
there are more than 7 crystals within a transducer
there are no longer equidistant lines between the
crystals and the triangles created are isosceles
triangles. This configuration is unlikely to provide a
homogenous signal, but rather "dark spots" within
the beam.

AD

Correlation to Directly Measured FHR

The signal tracking and the homogenous ultrasound
signal from the 7-crystal transducer both contribute
to a fetal heart rate measured by ultrasound which
correlates very highly to the directly measured fetal

heart rate. The degree of smoothing caused by
autocorrelation signal processing is reduced to a
minimum as seen in the following comparison of
traces.

fetal trace from ultrasound

Cross-Channel Verification

Cross-Channel Verification indicates when the same
heart rate is being recorded by different transducers.

When the maternal heart rate and fetal heart rate are
being monitored, Cross-Channel Verification will
alert you when the values are the same. This may be
an indication that the fetus is deceased and the
transducer is picking up a signal from the maternal
heart or a large blood vessel.

Cross-Channel Verification can compare all fetal and
maternal heart rates and indicates when multiple
channels are picking up the same signal. This means
when monitoring multiples and maternal heart rate
simultaneously Cross-Channel Verification will
compare the values from all fetuses and each of these
values with the maternal heart rate.

This technology helps reduce potential legal liability
associated with continuing to monitor an incorrect
heart rate.

When signal “cross-over” occurs, you are alerted
within approximately 60 seconds to check the traces
and potentially reposition the transducers.

Note: Be aware that

a maternal heart rate trace can

exhibit features that are very similar to those of a
fetal heart rate trace, even including

accelerations

and decelerations. Do not rely solely on trace pattern
features to identify a fetal source.

original DECG trace

Figure 1 CCV symbol prints on the trace when two

channels are recording the same heart beat

Cross-Channel Verification Plus (CCV+) indicator

(Series 50 XMO, not available in the USA and Japan)

To warn you if you accidentally record maternal
SpO

instead of fetal SpO2, (because the sensor is

2

facing the uterine wall instead of the fetus) the
monitor compares the heartrate it derives from
DECG on the Cardio 1/Combi channel, (or from
US on the Cardio 2 channel if DECG is not in use)
with the pulse rate it derives from FSpO

. The

2

CCV+ indicator illuminates and is printed on
the trace if the monitor records a pulse rate from
FSpO

and a heart rate from DECG or ultrasound

2

that do not match for more than one minute.

FHR Baseline Offset

Fetal Movement Profile

When the baselines of multiple FHR traces are very
similar, independent trend interpretation can be
difficult. To alleviate this, you can offset a baseline
by 20 bpm. You can deactivate the offset feature and
return the FHR trace to its original baseline anytime
you wish.

A section of a twins’ tracing is shown above. It shows
the FHR 1 trace before (Line a) and after (Line b)
the baseline offset feature is activated. To indicate
the recording is in the offset mode, a +20 symbol is
repetitively printed at the top of the trace.

Study finds Philips’ FMP saves clinicians’ and patients’

time, costs, and undue concern

Fetal movement is recognized as an important
indication of fetal condition. Consequently,
recordings of fetal movement are increasingly being
obtained as part of routine antepartum screenings in
obstetricians’ offices, clinics and hospitals.

In use in Europe, the United States and Japan since
1991, Philips Fetal Monitors simultaneously assess
fetal heart rate (FHR), fetal gross body movement
via the Fetal Movement Profile (FMP) parameter,
and uterine activity.

Benefits of the FHR-FMP assessment range from:

• helping clinicians determine the baseline heart
rate - especially in difficult-to-interpret traces, to

• predicting and supervising high risk pregnancies
which involve a number of fetal disorders,
including fetal growth retardation (IUGR).

One of the most important benefits of Philips’ FMP
monitoring is its efficiency and cost effectiveness as
an early screening tool.

Clinical trials confirm that the use of Philips Fetal
Monitors in routine antepartum screenings reduces
the number of patients with “suspicious” FHR test
results, thus eliminating their need for additional
expensive, second-level testing at the hospital. For
the patient, this represents significant savings in
time, cost and concern. It also means cost savings for
the health care system.

Fetal Movement and Fetal Heart Rate

The classic evaluation of fetal movement employs
the mother’s own perception. Clinical trials show
that the Philips Fetal Monitors detect on average 40
percent more movement than perceived by the
mother. Not only can they assure both mother and
clinicians of a more accurate level of fetal movement
detection, but the FMP, recorded simultaneously
with the heart rate, helps in the interpretation of the
FHR trace.

Physicians know that heart rate is directly influenced
by the physical activity of the fetus and they can
assign the baseline heart rate more efficiently with
the Fetal Movement Profile recording.

Furthermore, studies confirm that reduced or lack of
fetal gross body movement often precedes the
change in FHR pattern associated with intrauterine
growth retardation (IUGR)