Philips Avalon FM20 Instructions For Use Manual page 105

"Noisy/Erratic" signals: With mixed or weak signals the tracing may reveal very brief episodes of
erratic recorded traces. These represent the autocorrelation algorithm finding brief sequences of
apparent and persistent heartbeats amidst a mixed or weak signal. These erratic recorded traces are
commonplace, especially in association with fetal or maternal movement. During prolonged periods
of such noisy/erratic signals, the fetus is not being adequately monitored.
Drop out: With mixed or weak signals there may be no heart rate tracing at all. These episodes reflect
that if the algorithm does not find an apparent and persistent heartbeat amidst a mixed or weak signal,
it will not print a heart rate on the tracing. Brief episodes of drop out are commonplace, especially in
association with fetal or maternal movement. During prolonged periods of drop out, the fetus is
not being adequately monitored.
Multiple Fetuses
With multiple fetuses, the potential to experience these artifacts is increased. Positioning of the
transducer is even more critical. Ultrasound scanning should be used to help with positioning of
individual transducers.
Obtaining a Good Heart Signal
To successfully position the ultrasound transducer, first determine the fetal position using palpation.
Position the transducer over the strongest audible fetal heart sound from the monitor's speaker and
wait at least six seconds after each transducer adjustment to verify a good signal quality displayed
on the Signal Quality Indicator and a consistent FHR numeric display. Having determined the position
that provides a strong fetal signal, fix the transducer on the abdomen with the belt.
If the quality of the signal or the appearance of the heart rate trace from the ultrasound transducer is
questionable, the transducer should be repositioned as described above. Alternatively, the use of an
ultrasound scanner will greatly facilitate the determination of the optimal site for the ultrasound heart
rate transducer. Factors during the second stage of labor that may influence the quality of the FHR
tracing obtained with ultrasound include:
♦ Uterine contractions
♦ Changing contour of the maternal abdomen
♦
Maternal body movement - positioning
♦
Maternal expulsive efforts - pushing
♦
Maternal tachycardia/accelerations with contractions
♦
Fetal decelerations, Fetal tachycardia
♦ Delayed return of the fetal heart rate from a deceleration
♦
Descent of the fetus in the birth canal
♦
Rotation of the fetus in the birth canal
In some cases during the second stage of labor, a good and reliable ultrasound FHR signal may not be
obtainable, and the use of a fetal scalp electrode must be considered (fetal ECG).
10 Monitoring FHR and FMP Using Ultrasound
105