CARESCAPE Monitor Addendum for Surgical Pleth Index (SPI) measurement

Addendum for Surgical Pleth Index (SPI) measurement

•

The operator is responsible for checking the compatibility of the SpO2 module, sensor, and patient cable prior to use. Incompatible components can result in degraded performance and/or device malfunction.

•

CABLE/SENSOR AFTER CARE:

•



Do not immerse sensors or patient cables in water, solvents or cleaning solutions.



Do not reuse sensors intended for single patient use.



Do not sterilize sensors or patient cables by irradiation, steam, or ethylene oxide.



Clean the surface of the sensor before and after each patient use.



Allow sensor and cable to dry completely after cleaning. Moisture and dirt on the connector can affect the measurement accuracy.

Many factors may cause inaccurate readings and alarms, decreased perfusion, and/or low signal strength:

•

Physiological characteristics:



Cardiac arrest



Hypotension



Shock



Severe vasoconstriction



Hypothermia



Venous pulsations



Ventricular septal defects (VSDs)

•

Environmental conditions:



Excessive ambient light



Electrical interference



Electrosurgery



Defibrillation - May cause inaccurate reading for a short amount of time.



Excessive patient/sensor motion. In order to ensure reliable patient monitoring, the proper application of the sensor and the signal quality must be checked at regular intervals.

•

Sensor placement:



Incorrect sensor placement - prolonged monitoring or incorrect sensor application can cause skin irritation or impaired circulation. It is recommended that you check the sensor site every four hours (more frequently for poor perfusion). Refer to the instructions supplied with the sensor.



Sensor placement on the same extremity as a blood pressure cuff, arterial catheter or intravascular line; or arterial occlusion proximal to the sensor.



Poor sensor fit.



Do not allow tape to block the sensor light emitter and detector.

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Addendum for Surgical Pleth Index (SPI) measurement

CAUTIONS • •

The SPI measurement is to be used as an adjunct to other physiological parameters.

•

Any direct or indirect action of medication, treatment, stimuli or care that affects PR, amplitude of the plethysmogram (e.g. by vasoconstriction), or both, may also affect the SPI.

The SPI reflects autonomic nervous system and cardiovascular activity. Any medication, treatment, stimuli or action that affects either the autonomic nervous system or cardiovascular system or both, might also affect the SPI.

SPI measurement limitations Also see the “Practicalities “ section.

•

Only use SpO2 finger sensors, SPI has not been validated with ear sensors. The plethysmogram waveform is different when measured from the ear.

• • •

The SPI measurement is contraindicated if the patient has a cardiac pacemaker. The SPI values may be affected by anticholinergic agents. The SPI measurement option is only available in the OR software package.

Compatibility NOTE: Only use SpO2 finger sensors, SPI has not been validated with ear sensors. SPI measurement functions with E- and M-modules measuring GE Ohmeda pulse oximetry, and the following SpO2 finger sensors:

Sensor

Part number

OxyTip+ Finger sensor

OXY-F-UN, OXY-F4-N, OXY-F-DB

OxyTip+ Adult/Pediatric Adhesive sensor OXY-AP OxyTip+ Allfit Adhesive sensor

OXY-AF

OxyTip+ Sensitive Skin Multi-site sensor OXY-SE OxyTip+ Wrap Multi-site sensor

OXY-W-UN, OXY-W-DB

NOTE: The OxyTip+ Multi-site sensor OXY-SE and OXY-W-UN, OXY-W-DB are technologically equivalent. NOTE: OXY-W-DB, OXY-F4-N and OXY-F-DB are not compatible with E-modules.

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Addendum for Surgical Pleth Index (SPI) measurement

Points to note •

The SpO2 sensor should be attached to a finger. It is recommended to do this when the patient is still awake.

• •

Always refer to the instructions for use delivered with the sensor.

•

If possible, do not place an NIBP cuff on the same arm as the SpO2 measurement sensor, as NIBP measurement may cause disturbances in the plethysmogram. The SPI is calculated from the plethysmogram (also used for the SpO2 measurement). The quality of the SPI depends on the quality of the plethysmogram.

SPI clinical implications SPI is a non-invasive parameter derived from plethysmogram, and it is suitable for use with adult patients. By observing the SPI value and the trend, the clinician can monitor an adult patient's responses to surgical stimuli and analgesic medications during general anesthesia.

Basics of SPI measurement SPI measurement description The SPI incorporates two dimensions of the plethysmogram, the pulse amplitude and pulse interval. Both of these parameters show a patient's hemodynamic responses to surgical stimuli and analgesic medications. These two parameters are available in the SpO2 measurement. The SPI algorithm uses these finger pulse wave characteristics to create a single numerical value that correlates with the level of sympathetic activation. This means that the SPI value may be used to monitor the patient's responses to surgical stimuli and analgesic medications during general anesthesia. The degree of responses depends on the levels of surgical stimulation and analgesic medications. The SPI algorithm uses pulse amplitude and the pulse interval values by normalizing the raw components (thereby considerably reducing the inter-patient variability) and then combining them in an optimal proportion.

Normalization Clinical indexes are calculated on-line, as the actual patient reactions are taking place. In SPI measurement, the normalization of the individual patient data is based on adaptive histogram transformation. Using this principle, regardless of the original value, a normalized value is produced and uniformly distributed between 0 and 100%. Normalization balances the responsiveness of the SPI, as well as discriminates typical high and low ranges for each patient. Normalization also addresses these factors: 

The normal heart rate range varies between individuals more than within a person



The plethysmographic pulse amplitude varies between patients and between sensor sites



The plethysmographic amplitude can be "too responsive" to stimuli



Some patients have reactive heart rates, while others have a reactive plethysmogram.

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Addendum for Surgical Pleth Index (SPI) measurement

Learning At the beginning of the measurement, and as needed later on, the algorithm starts to learn the patient's pulse rate and pulse amplitude. During this time of initialization, SPI numbers are shown in gray color and the message ‘Learning’ is displayed. Due to this learning process, the SPI readings may be less accurate during the first three minutes. Learning is marked in the trend as dashed vertical line in SPI color.

How to interpret the SPI values SPI in typical general anesthesia Waveform on the left: 1. Patient awake, SPI not valid 2. Intubation 3. Incision 4. Remifentanil up Waveform on the right: 5. Inadequate analgesia 6. Adequate analgesia 7. Patient awake, SPI not valid

When the SPI is high, surgical stimulation may be high or the level of analgetics is low. When the number is low, it may indicate that the level of stimulation has decreased or that the concentration of analgetics is adequate. Individual patients may show different base values and responsiveness to noxious stimuli as the individual sensitivity to both the stimulus and analgesic medication may vary.

Common surgical events Laryngoscopy and intubation Sudden reaction to laryngoscopy and intubation is common even in an anesthetized state. It is not necessarily a sign of inadequate anesthesia. The pulse wave's reaction is reflective in nature, and normally recovers quickly. The SPI, too, will react in relations to the pulse wave amplitude changes. Slow recovery of amplitude may indicate anesthesia that is too light, thus producing higher SPI values.

Skin incision Skin incision is one of the strongest intraoperative stimuli. Skin incision may cause significant reduction of the pulse wave amplitude.

Maintenance phase Changes in the intraoperative pulse wave amplitude will affect the SPI. If the intraoperative pulse wave amplitude:

•

Remains low or frequently changes, it can be an indication of light anesthesia. This low pulse wave amplitude can produce a higher SPI value.

•

Progressively, continuously decreases, it is usually due to discomfort, hypovolemia, hypothermia, or hyperventilation. This lowering pulse wave amplitude can produce a higher SPI value.

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Addendum for Surgical Pleth Index (SPI) measurement

Changes in the pulse wave amplitude and their effect on SPI should always be considered together with other parameters in order to diagnose the real cause of any changes. When the nociceptive level is stable and low for a long time, such as during epidural anesthesia, the relative nature of histogram transformation may cause the SPI to remain in the mid-range.

The end of anesthesia Vasoconstriction is the expected reaction during this phase. As the patient awakens, the SPI is no longer valid since the parameter is indicated for anesthetized patients. As the level of surgical stimulation decreases, the SPI also decreases. The waking of the patient can be seen in the SPI values as well as in the Entropy values.

Sensor removal If the SpO2 sensor is off of the patient for more than five minutes, the SPI measurement will start the learning process as if the case was just beginning. This is similar to ending a case situation. If the sensor's location is changed, the pulse amplitude may abruptly change. This may cause a large and persistent change in the SPI values. To facilitate the learning of new values in this case, the SPI tries to identify these types of changes by seeking periods with unavailable data that are followed by a change in the pulse amplitude. The history data is compressed down to a 15-minute span. This is similar to what occurs to the SPI when the patient falls asleep.

AoA split screen The AoA (Adequacy of Anesthesia) split screen includes a view combining the SPI and State Entropy values in an x-y graph. This part of the AoA split screen is referred to as BalView. Note that you need an Entropy module for this view. The graph visualizes the combined effects of anesthetic and analgesic medications administered during general anesthesia. For more information on the BalView, see the “Tips on making your assessment with the BalView “ section. The current SPI and SE values will appear as a dot, and there is a trace to show the trend for the last minute.

SE

SPI The AoA Split Screen shows:

•

The last minute SPI and SE (State Entropy, requires the E-ENTROPY module) values as a trend line

• • •

The current SPI and SE values as an SPI+SE dot The SPI numeric value and minitrend It can also contain selected Entropy values and minitrend (with Entropy module), and NMT parameter window (with NMT module).

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Addendum for Surgical Pleth Index (SPI) measurement

Equipment to patient connections 3

2 4

1

(1)

Compatible module with SpO2 measurement capability; see the “Compatibility “ section.

(2)

SpO2 cable and a compatible SpO2 finger sensor

(3)

Emitter

(4)

Detector

Preparing the patient 1.

Connect the SpO2 adapter cable to the module connector.

2.

Clean the surface of reusable sensors.

3.

Prepare the application site. This may include: 

Clipping long fingernails.



Removing artificial finger nails.



Removing nail polish.

4.

Attach the sensor carefully to the patient, and secure and check adequate finger perfusion.

5.

Stabilize the adapter cable to minimize sensor movement by attaching it to the patient’s wrist or bed clothes.

SPI measurement on the monitor screen For information on how to configure the monitor screen and options below, see the relevant chapters in the user’s manual. SPI does not have a menu of its own. You can configure SPI data to be shown: 

As numeric data and microtrend in a parameter window (select SPI from the list of parameters). The trend length is the same as that of Entropy, and it is set through the Entropy menu.



As numeric data together with the SE number and BalView in a parameter window (select SE & SPI from the list of parameters).



As a minitrend.

In addition, you can select the AoA split screen, see previous page, and configure SPI data to graphic trends, numeric trends and snapshots.

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Addendum for Surgical Pleth Index (SPI) measurement

Stopping the measurement 1.

Remove the sensor from the patient.

2.

Disconnect the sensor from the patient interface cable.

3.

Discard the sensor (if not reusable).

Practicalities Tips on making your assessment with the BalView The BalView plots SPI and SE values on an x-y graph. It can be divided into four areas:

2

3

1

4

SE

SPI

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Addendum for Surgical Pleth Index (SPI) measurement

Use the following guide to help interpret the BalView: BalView Your assessment includes:

What it may indicate

Evaluate your patient, surgical situation and assess:

area 1

SPI

and SE

SPI: a low stress response, adequate analgesia SE: deep anesthesia, adequate anesthesia

• Other parameters

2

SPI

and SE

SPI: a low level of surgical stress SE: waking to awake

• Anesthetics • Other parameters

3

SPI

and SE

SPI: a high stress response SE: waking to awake

• Analgetics • Anesthetics • Other parameters

4

SPI

and SE

SPI: a high stress response SE: deep anesthesia, adequate anesthesia

• Analgetics • Other parameters

SPI and NIBP measurement There is no way for the monitor to identify which limb has the NIBP cuff placed on it. NIBP cuff inflation causes temporary blood flow occlusion distal to the measurement site. If an SpO2 sensor is located distally to the NIBP cuff, this inflation will also cause a temporary interruption to blood flow at the SpO2 sensor site. SpO2, SPI, and plethysmogram measurements will be temporarily interrupted. To avoid this situation, it is suggested that you obtain NIBP measurements from another limb. When the first NIBP measurement is made during a case, the monitor always performs a safety check. This means that the ‘NIBP cuff inflated’ message will appear on the monitor screen. After the first NIBP measurement, the SPI algorithm checks for any disturbances in the plethysmogram during subsequent NIBP cuff inflations. If there are no variances detected, the ‘NIBP cuff inflated’ message will appear only once. However, if there are any simultaneous disturbances in the plethysmogram during NIBP inflation, the message will reappear. Situations that produce external artifact or sensor movement may cause the message to appear. The message will occur until there are no changes in the plethysmogram during NIBP cuff inflation. If, for any reason, the plethysmogram signal is disturbed during NIBP inflation (either coincidentally or because of same-limb measurement), the message will appear.

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Physiological and technical issues affecting SPI There are widely known physiological and technical limitations of pulse oximetry, and some of those that may affect the interpretation of the SPI are mentioned below.

Physiological issues

• •

•

Vasoconstriction and low amplitude states Low perfusion states: 

Cold extremities (hypothermia)



Blood loss (hypovolemia) or



Low blood pressure (hypotension)

Venous congestion or pulsation

Technical issues

•

Artifact 

Any type of patient or clinician induced motion. This includes flexion, clenching, shivering, kicking, sensor/cable movement, or patient repositioning, etc.

•

Electrosurgery, magnetic resonance imaging (MRI), or pulsatile interference from external devices

•

Sensor selection/application 

Patient's weight, sensor type (durable or adhesive), site location, sensor placement/ displacement, finger circulation (sensor not too tight), correct sensor fit

Calculations Adaptive histogram transformation (scale of 0 to 100) from the pulse interval and plethysmogram’s pulse amplitude (PGA) = 100 - 0.3 * Pulse interval (with normalization) - 0.7 * PGA (with normalization) = SPI The SPI algorithm is published: Huiku M, Uutela K, van Gils M, Korhonen I, Kymäläinen M, Meriläinen P, Paloheimo M, Rantanen M, Takala P, Viertiö-Oja H, Yli-Hankala A. Assessment of surgical stress during general anaesthesia. (Br J Anaesth 2007; 98: 447-55).

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Addendum for Surgical Pleth Index (SPI) measurement

Basic troubleshooting Problem

What to do

AoA Split Screen is not shown

• Configure the AoA Split Screen to the screen. • Make sure that both Entropy and SPI are being measured.

BalView dot is missing in the AoA Split Screen

• Make sure that both Entropy and SPI are being measured.

SPI color is gray

• Wait until the message ‘Learning’ disappears. • Wait for the NIBP measurement to finish. • Try to ensure an as artifact-free plethysmogram as possible.

SPI measurement is not available

• Check that SPI is licensed in your configuration. • Configure SPI into a digit field. • Check the connections and compatibility.

SPI values seem incorrect

• Check the sensor contact and position on the finger. • Check the compatibility of the sensor and module. • Assess the patient. Check that the plethysmogram is as artifact-free as possible.

• SPI only works with fully anesthetized patients. • Anticholinergic agents may increase SPI values. SPI values shown as ---

• Check the connections and compatibility. • Wait for the measurement to start. • If possible, do not place the NIBP cuff on the same arm.

SpO2 signal is poor

• Assess the patient and the measurement site.

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SPI related messages NOTE: The SPI messages are shown in the SE & SPI parameter window only if no Entropy messages are active at the same time. The background color of the SE value in the SE & SPI parameter window changes to cyan when there is an active SE alarm. For a graphic presentation of a generic layout, see the “Monitoring basics” chapter in the user’s manual. This will help you identify where on screen the following messages appear. The table below lists the messages in alphabetical order. In this table, the message location is indicated with the following: alarm = alarm area; param. = parameter window; wavef. = waveform area. Message

Location

Priority and Explanation escalation

What to do

Incompatible module • param.

info, 0 s

The module cannot be used for • SPI measurement.

Change the module.

Incompatible probe

• param.

info, 0 s

The module/sensor • combination is not compatible.

Check the compatibility and change module or sensor.

Irregular pulse

• param.

info, 0 s

Patient is having a cardiac arrhythmia. NOTE: Since arrhythmias may affect pulse rate and amplitude, the SPI calculation is disabled.

• Check the patient status.

Learning

• param.

info, 0 s

SPI is being initialized.

• When the measurement is started for the first time, the initialization will take at least 3 minutes.

NIBP cuff inflated

Noise

• param.

• param.

info, 0 s

info, 0 s

There may be some disturbances in the plethysmogram.

• See ”SPI and NIBP

SpO2 signal or amplitude is poor.

• Check the patient’s

Artifacts are disturbing the measurement.

No SpO2 signal

• param.

info, 0 s

There is no SpO2 sensor. The sensor or cable is faulty. The cable or sensor is not properly connected.

measurement .”

hemodynamic stability.

• Check the sensor contact and make sure nothing is pulling and/or rubbing against the sensor and that there is no constriction at the sensor site.

• Place the sensor on the patient’s finger.

• Replace the sensor or cable.

• Check all connections. Place SpO2 probe on • alarm finger for SPI measurement

info, 0 s

The SPI measurement is available for the new case.

• Attach the sensor on patient’s finger.

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Addendum for Surgical Pleth Index (SPI) measurement

Advanced troubleshooting If you feel that a reading is not correct, first confirm the clinical status of the patient and consult the ”Basic troubleshooting ” and “SPI related messages ” sections above.

• • • •

Check your sensor and the sensor site. Assess the trends and values of other monitored parameters, especially blood pressure, body temperature, capnogram. Confirm the use of anesthetics and other drugs. Assess for the possibility of clinical stimulation arising from a non-nociceptive origin (for example: severe hypovolemia or hypothermia may cause SPI responses similar to, but not originating from, nociception. They are not related to inadequate analgesia.)

After your assessment is complete, consider the appropriate interventions. These may include pharmacological or non-pharmacological interventions such as intravenous fluid administration, patient/sensor temperature factors, etc. Factors that affect the hemodynamic stability of the anesthetized patient may affect the SPI, as well. In some special situations, the SPI may not correctly indicate the nociceptionantinociception balance. These situations can be:

• • •

Severe arrhythmia affecting pulse interval or pulse amplitude Medications directly affecting both the autonomic nervous system and the hemodynamic system A paradoxical response to treatment, for example in elderly patients.

Technical specifications SPI microtrend length is user-selectable.

Measurement method The SPI measurement is derived from the plethysmographic pulse amplitude and interval from the finger.

Performance SPI has no measurement unit. Measurement range

0 to 100

Display resolution Display resolution

1 digit

SPI default settings The following table lists the SPI profile settings and the setting descriptions. Setting

Description

OR

Color

Select the color for displayed numerics, trends and messages

Violet

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