ICU SKILLS UPDATE

February/March 2007

By Dianne Brown

ICU Skills Update

Theory and Hands On Practice

1. Bispectral Index Monitoring

BISPECTRAL INDEX MONITOTING

BISPECTRAL INDEX MONITORING

The bispectral index (BIS) is a fairly recent technology used to measure the effects of anesthetics and sedatives on the brain and consciousness

Uses a complex mathematical algorithm based upon descriptive EEG parameters from the frontal cortex to suggest various levels of sedation

BISPECTRAL INDEX MONITORING

A sensor, placed on the patient’s forehead, sends raw EEG waveforms to the monitor, where they are analyzed and a BIS index is calculated

This value ranges from 100 (completely awake) to 0 (isoelectric EEG)

BISPECTRAL INDEX MONITORING

BISPECTRAL INDEX MONITORING

Understanding the relationship between BIS and EEG

When BIS monitoring is initiated, a sensor is placed across the patient’s forehead per manufacturer’s recommendations to detect one channel of EEG activity

The EEG signal is filtered and digitalized The EEG state (frequency/amplitude) is

calculated and associated with the level of sedation, arousal or anesthesia

Understanding the relationship between BIS and EEG

The BIS value is a single number based on the previous 15 seconds of EEG data and is updated frequently

The BIS monitor provides a single channel of an EEG tracing from the right or left frontal-temporal montage electrode placement

ICU Sedation: A Bipolar Challenge

Over-sedation Patient unable to

participate in care Delayed weaning ↑Ventilator-associated

pneumonia ↑Unnecessary testing ↑ICU and hospital

length of stay ↑Costs

Under-sedation Anxiety, agitation ↑Cost, nursing time ↑Use of neuromuscular

blocking agents ↑Risk of

recall/awareness of unpleasant events

↑Unintended medical device removal

Potential Indications for BIS Monitoring

Use with neuromuscular blockade: BIS monitoring may help to identify patients at risk of awareness, recall and pain when paralyzed

Use of BIS values to guide sedation and analgesia Titrating sedation/analgesia in patients receiving

controlled ventilation Avoiding extremes of under and over sedation Titration of medications for medication-induced

coma

Factors affecting the BIS value

Sedation: decrease in BIS value Analgesia: decrease in BIS value Neuromuscular blocking agents: decrease in

BIS value related to attenuation of high-frequency muscle activity across the patient’s forehead

Painful (noxious) stimulation: if analgesia inadequate, arousal response may be produced within cerebral cortex

Factors affecting the BIS value

Sleep: BIS range is lower (20-70) during deep sleep, and BIS range is higher (75-92) during REM sleep

Hypothermia: decrease in BIS value Cerebral ischemia: decrease in BIS value Neurological states: decrease in BIS value

depending of location of injury and degree to which overall cerebral metabolism is affected

Factors affecting the BIS value

Encephalopathic states: severe anoxic/ischemia encephalopathy (decrease in BIS value)

High-frequency electrical artifact from patient care equipment, such as pacemaker or muscle activity; rapid head or eye movement (increase in BIS value)

Interpretation of BIS value

BIS is interpreted over time, in response to stimulation and within the context of whether therapeutic endpoints and overall goals of therapy are met

Decisions to increase or decrease titration of sedative or analgesic should be based on clinical assessment/judgement, goals of therapy, and the BIS value

Interpretation of BIS value

Relying on BIS alone for sedation/analgesia management is not recommended

Movement such as in response to painful stimulation may occur with low BIS values

BIS increases suddenly or is higher than expected

Is the sedative sufficient?

Has the sedation been decreased?

Is there an increase in stimulation?

Is there any muscle shivering or pt motion?

Is the NMBA wearing off?

BIS decreases suddenly or is lower than expected

Has been a decrease in stimulation?

Has patient recently received NMBA?

Has there been an increase in sedation?

Is the patient sleeping? Has the pt recently received

analgesic? Has there been a sudden

significant drop in BP?

Current Status of the Literature

BIS scores do not provide a differential diagnosis. BIS scores can be affected by many cerebral events including sedation, sleep and cerebral ischemia

BIS/EEG activity can also be affected by age, temperature, PaCO2, hyper/hypo-glycemia, electroyte imbalances, hepatic or renal function, endocrine disorders

Current Status of the Literature BIS scores can be affected by many forms of

artifact:

- Artifact occurs with excessive muscle activity – movement, swallowing, blinking, shivering etc.

- Artifact can also occur with concomitant use of other electrical devices and monitoring equipment - EEG

Current Status of the Literature

Neuromuscular activity typically elevates BIS scores. Hence the effects of NMBAs or their metabolites may cause lower BIS scores as a result of decreased muscle activity and not decreased LOC

The synergistic action of agents affecting muscle relaxation must be considered when interpreting scores

Current Status of the Literature

Overall conflicting research results May predict recovery of consciousness related to

sedation and possibly traumatic brain injury Several studies have found variable correlations

between BIS scores and sedation scores BIS monitoring may serve as an adjunct measure to

subjective scales of sedation monitoring in ICU patients, particularly in patients who are heavily sedated or chemically paralyzed

Clinical Applications

BIS is only one part of a multi-modal assessment strategy

It remains unclear as to what BIS actually measures: Awareness? Hypnosis with recall? Delirium? Extent of brain injury, brain function or generalized cerebral electrical activity?

Clinical Applications

Only use trended scoresWhen interpreting results, consider

multiple factors including measurements error as well as the special/individual circumstances of each patient

What the numbers mean

BIS Number

What the numbers mean:

0 = no electrical brain activity

100 = fully awake For moderate sedation, aim for range from 60-

70, below 60 is associated with a low probability of explicit recall

For deeper sedation, aim for range from 40-60. A patient with a BIS value of less than 45 is approaching a deep hypnotic state

BIS Number

For a patient receiving neuromuscular blockage, sedation, analgesia therapy, the medication should be titrated for a BIS value between 45 and 60

SQI: Signal Quality Index

What the numbers mean: 0 = poor quality

100 = excellent quality Aim for range from 80-100%

EMG: Electromyographic Activity

Reflects the electrical power of muscle activity or artifact

What the numbers mean: the higher the number, the greater the muscle activity

- if the EMG is high, can make the number artificially high (it incorrectly reads the increased muscle activity as increased EEG activity

Acceptable EMG is less than 55 dB Optimal EMG is less than 30 dB

Electrode Placement

Prep skin with alcohol prior to electrode placement

Electrode should be changed every 24 hours, alternating temples daily

Look at electrode packaging for placement instructions

Electrode Placement

To ensure adequate placement and impedance, check on the screen

Resources

Guidelines and Procedure available in AACN Procedural Manual for Critical Care, Procedure 86, page 699