4 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 consciousnessUses a complex mathematical algorithm based upon descriptive EEG parameters from the frontal cortex to suggest various levels of sedation
5 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 calculatedThis value ranges from 100 (completely awake) to 0 (isoelectric EEG)
9 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 activityThe EEG signal is filtered and digitalizedThe EEG state (frequency/amplitude) is calculated and associated with the level of sedation, arousal or anesthesia
10 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 frequentlyThe BIS monitor provides a single channel of an EEG tracing from the right or left frontal-temporal montage electrode placement
11 ICU Sedation: A Bipolar Challenge Over-sedationPatient unable to participate in careDelayed weaning↑Ventilator-associated pneumonia↑Unnecessary testing↑ICU and hospital length of stay↑CostsUnder-sedationAnxiety, agitation↑Cost, nursing time↑Use of neuromuscular blocking agents↑Risk of recall/awareness of unpleasant events↑Unintended medical device removal
12 Potential Indications for BIS Monitoring Use with neuromuscular blockade: BIS monitoring may help to identify patients at risk of awareness, recall and pain when paralyzedUse of BIS values to guide sedation and analgesiaTitrating sedation/analgesia in patients receiving controlled ventilationAvoiding extremes of under and over sedationTitration of medications for medication-induced coma
13 Factors affecting the BIS value Sedation: decrease in BIS valueAnalgesia: decrease in BIS valueNeuromuscular blocking agents: decrease in BIS value related to attenuation of high-frequency muscle activity across the patient’s foreheadPainful (noxious) stimulation: if analgesia inadequate, arousal response may be produced within cerebral cortex
14 Factors affecting the BIS value Sleep: BIS range is lower (20-70) during deep sleep, and BIS range is higher (75-92) during REM sleepHypothermia: decrease in BIS valueCerebral ischemia: decrease in BIS valueNeurological states: decrease in BIS value depending of location of injury and degree to which overall cerebral metabolism is affected
15 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)
16 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 metDecisions to increase or decrease titration of sedative or analgesic should be based on clinical assessment/judgement, goals of therapy, and the BIS value
17 Interpretation of BIS value Relying on BIS alone for sedation/analgesia management is not recommendedMovement such as in response to painful stimulation may occur with low BIS values
18 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?
19 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?
20 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 ischemiaBIS/EEG activity can also be affected by age, temperature, PaCO2, hyper/hypo-glycemia, electroyte imbalances, hepatic or renal function, endocrine disorders
21 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
22 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 LOCThe synergistic action of agents affecting muscle relaxation must be considered when interpreting scores
23 Current Status of the Literature Overall conflicting research resultsMay predict recovery of consciousness related to sedation and possibly traumatic brain injurySeveral studies have found variable correlations between BIS scores and sedation scoresBIS 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
24 Clinical Applications BIS is only one part of a multi-modal assessment strategyIt remains unclear as to what BIS actually measures: Awareness? Hypnosis with recall? Delirium? Extent of brain injury, brain function or generalized cerebral electrical activity?
25 Clinical Applications Only use trended scoresWhen interpreting results, consider multiple factors including measurements error as well as the special/individual circumstances of each patient
27 BIS Number What the numbers mean: 0 = no electrical brain activity 100 = fully awakeFor moderate sedation, aim for range from 60-70, below 60 is associated with a low probability of explicit recallFor deeper sedation, aim for range from A patient with a BIS value of less than 45 is approaching a deep hypnotic state
28 BIS NumberFor a patient receiving neuromuscular blockage, sedation, analgesia therapy, the medication should be titrated for a BIS value between 45 and 60
29 SQI: Signal Quality Index What the numbers mean: 0 = poor quality100 = excellent qualityAim for range from %
30 EMG: Electromyographic Activity Reflects the electrical power of muscle activity or artifactWhat 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 activityAcceptable EMG is less than 55 dBOptimal EMG is less than 30 dB
31 Electrode PlacementPrep skin with alcohol prior to electrode placementElectrode should be changed every 24 hours, alternating temples dailyLook at electrode packaging for placement instructions
32 Electrode PlacementTo ensure adequate placement and impedance, check on the screen
33 ResourcesGuidelines and Procedure available in AACN Procedural Manual for Critical Care, Procedure 86, page 699
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