Philips Avalon FM20, Инструкция по эксплуатации

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10 Monitoring FHR and FMP Using Ultrasound
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It is strongly recommended that the maternal pulse oximeter or maternal ECG be employed to make
use of the monitor’s Cross-Channel Verification (CCV) feature, especially during the second stage of
labor or when the maternal pulse is elevated over 100 bpm. The Philips Avalon fetal monitor offers
maternal pulse oximetry (SpO
2
) and maternal ECG for maternal pulse detection and the creation of a
maternal heart rate pattern plotted on the same recorder as the FHR pattern. When either of these
parameters is utilized, the monitor will automatically and continuously perform a CCV of the maternal
heart rate pattern against the FHR pattern displayed on the monitor. If the patterns and rates are
similar, the CCV provides an alert that both rates are likely to be from the same source (i.e., they both
represent the maternal heart rate pattern and the fetus is not being monitored). Repositioning the
ultrasound transducer will usually correct this, but it may be necessary to apply a fetal scalp electrode.
Advising the mother to temporarily cease pushing during contractions may help to more rapidly
resolve any uncertainty in this situation.
Doubling: The autocorrelation algorithm can display a doubled fetal or maternal heart rate if the
duration of diastole and of systole are similar to each other and if the heart rate is below 120 bpm.
Doubling, usually brief, is accompanied by an abrupt switch of the trace to double the baseline value.
Halving: With fetal tachycardia (above 180 bpm) and some interference from breathing or maternal
arteries the autocorrelation algorithm may only recognize every second beat resulting in a halved rate
for a limited time. If the actual FHR is above the maximum limit of the monitor (240 bpm), the
algorithm will also half-count. Halving is accompanied by an abrupt switch of the trace to exactly half
the prior baseline value. This switch may simulate a FHR deceleration and be referred to by clinicians
as a “false deceleration.”
Switching to maternal heart rate (also referred to as "Maternal Insertion"): The fetal heart can
move partly or fully out of the ultrasound beam and the autocorrelation algorithm may then pick up
and display the maternal heart rate. Depending on the signal mix in the ultrasound signal, switching to
the maternal heart rate may mimic several conditions with the potential for erroneous interpretation
and response as follows:
♦
The switch to the maternal heart rate may simulate a FHR deceleration (i.e., a decrease of
the fetal heart rate, and be referred to by clinicians as a “false deceleration”).
♦
The maternal heart rate may simulate a normal fetal heart rate pattern (i.e., it may mask a
FHR deceleration or fetal demise).
Especially during pushing with contractions in the second stage of labor, the maternal heart rate may
increase to the point where it may equal or exceed the fetal rate. Here the maternal trace may mimic a
normal fetal trace while the fetus may be having decelerations or fetal demise has occurred. This
change from fetal to maternal heart rate pattern may not be at all obvious unless CCV is used and
represents the most dangerous pitfall of all the artifacts because fetal distress may go unrecognized.
♦
The maternal heart rate may simulate a FHR acceleration , which is an increase of the fetal
heart rate.
During expulsive efforts, the maternal heart rate normally accelerates and may be at or above the
normal FHR range.
♦
The FHR may display gradual appearing decelerations . Generally, the “false decelerations”
described above are abrupt. Rarely, combinations of “noisy/erratic signal” associated with changes
in maternal and/or fetal rate or movement will produce more gradual appearing “false
decelerations” but these are usually short-lived with an
abrupt return to an obviously stable FHR
baseline.