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Entropy
3. Select the parameter ( RE or SE ).
NOTE
If the feature is not active, the alarm limits are greyed out.
Select Alarm On to set the alarms.
Stopping the Entropy measurement
1. Remove the Entropy sensor from the patient.
2. Disconnect the sensor from the sensor cable.
3. Discard the sensor.
Entropy measurement basics
Entropy measurement description
EEG signals reflect the underlying state of brain activity. As a person falls asleep or
is anesthetized, the brain function (activity) starts to decrease and becomes more
orderly and regular. EEG changes from irregular to more regular patterns when
anesthesia deepens. Similarly, frontal EMG quiets down as the deeper parts of the
brain are increasingly saturated with anesthetics.
Entropy measurement is based on processing of raw EEG and FEMG signals by
using the Entropy algorithm, a GE application of Spectral Entropy. The algorithm is
published: Viertiö-Oja H et al. Description of the Entropy algorithm as applied in the
Datex-Ohmeda S/5 Entropy Module. (Acta Anaesthesiologica Scandinavica 2004;
Volume 48: Issue 2:154-161, 2004).
Entropy measures irregularity of EEG and FEMG. The GE Entropy measurement devices
are responsible for EEG and FEMG signal acquisition, amplification, filtering and
digitization and electrode impedance measurement.
Entropy parameters
RE is a fast reacting parameter, which measures EEG and FEMG in the frequency
range 0.8 Hz to 47 Hz. Its reaction time is two seconds. It may give an indication
of the patient’s reaction to external stimuli, such as intubation and skin incision, if
neuromuscular blocking agents are not used.
SE is a more stable and robust parameter, which measures EEG in the frequency range
of 0.8 Hz to 32 Hz. Its reaction time is 15 seconds. SE may be used to assess the effect
of certain anesthetic drugs on the brain.
Entropy frequency and display ranges
Parameter
Display range Cortical EEG,
frequency range Facial EMG,
frequency range
RE 0 to 100 0 Hz to 32 Hz 32 Hz to 47 Hz
SE 0 to 91 0 Hz to 32 Hz no measurement
How to interpret the Entropy values
High values of Entropy indicate high irregularity of the signal, signifying that the
patient is awake. A more regular signal produces low Entropy values, which can be
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