Completing the Adequacy of
Adequate anesthesia results from a balance
of many components, and needs to be
assessed with more than one parameter.
When the Surgical Pleth Index is used
together with other monitored parameters,
such as hemodynamics, NMT, and Entropy,
you can get a complete picture of the
patient’s status combined on one screen.
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Entropy is a trademark of GE Healthcare Finland Oy.
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features shown herein, or discontinue the product described at any time without
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SPI may not be available in all markets. Please check with your local representative.
Consult the monitor User’s Guide or SPI User Manual Addendum for
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Surgical Pleth Index
For monitoring the patient’s
hemodynamic responses to surgical
stimuli and analgesic medication
under general anesthesia
What is the Surgical Pleth Index?
Clinical use of the SPI
SPI monitoring is based on the acquisition of the
readily available plethysmographic pulse wave, which
is processed with a unique algorithm. The calculation
analyzes the photoplethysmographic amplitude and
the photoplethysmographic pulse interval, and then
combines these two parameters to create a single
digit, the Surgical Pleth Index.
At the beginning of measurement, and as needed,
the SPI’s algorithm starts learning and processing the
signals. The digit will be grey in color, and a “learning”
message is shown. Learning is marked in the trends
as a dashed, vertical line. When the measurement
is started, it will take about three minutes for the
learning process to take place.
The details of the SPI algorithm have been published
in an article in the British Journal of Anaesthesia
titled, “Assessment of surgical stress during general
Things to remember when using SPI
The Surgical Pleth Index, or SPI, is a digit that may be
used to monitor the patient’s hemodynamic responses
to surgical stimuli and analgesic medications
during general anesthesia. SPI reflects the patient’s
responses, which result from increased sympathetic
activity as a reaction to painful (nociceptive) stimuli.
SPI learning at
the beginning of
The number is
displayed in grey.
SPI can be used to help assess both acute nociceptive
events, as well as long-term state reactions during
general anesthesia. In general, when the SPI goes
up, the patient is responding to the events. When the
index goes down, the level of surgical responsiveness
SPI is a parameter for adults (over 18 years old)
undergoing general anesthesia. The use of SPI
is contraindicated in pacemaker patients and
during the use of atropine. Factors which effect the
hemodynamic stability of the anesthetized patient
may effect SPI, as well.
SPI is an optional software licence that has certain
requirements for the monitor used. Also it needs GE
Ohmeda SpO2 technology and compatible sensors.
Please contact your GE Healthcare representative for
a complete list of SPI-supporting components.
Integrated information in the BalView
SPI index and
trend active during
1 Huiku, M., et al. Assessment of surgical stress during general anaesthesia. British
Journal of Anaesthesia 98, 447-455 (2007).
In the AoA (Adequacy of Anesthesia) split screen,
you will find the BalView, which balances SPI and
State Entropy™ values on an x-y graph. This view is
a tool for visualizing the effects of anesthetic and
analgesic pharmaceuticals administered during
general anesthesia: The current, combined values are
expressed as a dot, and a trace shows the trend for
the last minute.
This AoA split screen view incorporates values and
trends obtained from the SPI, Entropy (State Entropy,
Response Entropy and Burst Suppression Ratio)
and Neuromuscular Transmission (NMT) modules,
providing a holistic view of the patient’s response to
anesthesia. The monitor must have active SPI, Entropy
and NMT measurements for the BalView to function.