February/March 2007 By Dianne Brown ICU SKILLS UPDATE February/March 2007 By Dianne Brown

ICU Skills Update Theory and Hands On Practice 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 scores When 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