1、ICU SKILLS UPDATEFebruary/March 2007By Dianne BrownICU Skills UpdatelTheory and Hands On Practice1.Bispectral Index MonitoringBISPECTRAL INDEX MONITOTINGBISPECTRAL INDEX MONITORINGlThe bispectral index(BIS)is a fairly recent technology used to measure the effects of anesthetics and sedatives on the
2、brain and consciousnesslUses a complex mathematical algorithm based upon descriptive EEG parameters from the frontal cortex to suggest various levels of sedation BISPECTRAL INDEX MONITORINGlA sensor,placed on the patients forehead,sends raw EEG waveforms to the monitor,where they are analyzed and a
3、BIS index is calculatedlThis value ranges from 100(completely awake)to 0(isoelectric EEG)BISPECTRAL INDEX MONITORINGBISPECTRAL INDEX MONITORINGUnderstanding the relationship between BIS and EEGlWhen BIS monitoring is initiated,a sensor is placed across the patients forehead per manufacturers recomme
4、ndations to detect one channel of EEG activitylThe EEG signal is filtered and digitalizedlThe EEG state(frequency/amplitude)is calculated and associated with the level of sedation,arousal or anesthesiaUnderstanding the relationship between BIS and EEGlThe BIS value is a single number based on the pr
5、evious 15 seconds of EEG data and is updated frequentlylThe BIS monitor provides a single channel of an EEG tracing from the right or left frontal-temporal montage electrode placementICU Sedation:A Bipolar ChallengeOver-sedationlPatient unable to participate in carelDelayed weaningl Ventilator-assoc
6、iated pneumonialUnnecessary testing lICU and hospital length of staylCostsUnder-sedationlAnxiety,agitationlCost,nursing timelUse of neuromuscular blocking agentslRisk of recall/awareness of unpleasant eventslUnintended medical device removalPotential Indications for BIS MonitoringlUse with neuromusc
7、ular blockade:BIS monitoring may help to identify patients at risk of awareness,recall and pain when paralyzedlUse of BIS values to guide sedation and analgesialTitrating sedation/analgesia in patients receiving controlled ventilationlAvoiding extremes of under and over sedationlTitration of medicat
8、ions for medication-induced comaFactors affecting the BIS valuelSedation:decrease in BIS valuelAnalgesia:decrease in BIS valuelNeuromuscular blocking agents:decrease in BIS value related to attenuation of high-frequency muscle activity across the patients foreheadlPainful(noxious)stimulation:if anal
9、gesia inadequate,arousal response may be produced within cerebral cortexFactors affecting the BIS valuelSleep:BIS range is lower(20-70)during deep sleep,and BIS range is higher(75-92)during REM sleeplHypothermia:decrease in BIS valuelCerebral ischemia:decrease in BIS valuelNeurological states:decrea
10、se in BIS value depending of location of injury and degree to which overall cerebral metabolism is affectedFactors affecting the BIS valuelEncephalopathic states:severe anoxic/ischemia encephalopathy(decrease in BIS value)lHigh-frequency electrical artifact from patient care equipment,such as pacema
11、ker or muscle activity;rapid head or eye movement(increase in BIS value)Interpretation of BIS valuelBIS is interpreted over time,in response to stimulation and within the context of whether therapeutic endpoints and overall goals of therapy are metlDecisions to increase or decrease titration of seda
12、tive or analgesic should be based on clinical assessment/judgement,goals of therapy,and the BIS valueInterpretation of BIS valuelRelying on BIS alone for sedation/analgesia management is not recommendedlMovement such as in response to painful stimulation may occur with low BIS valuesBIS increases su
13、ddenly or is higher than expectedlIs the sedative sufficient?lHas the sedation been decreased?lIs there an increase in stimulation?lIs there any muscle shivering or pt motion?lIs the NMBA wearing off?BIS decreases suddenly or is lower than expectedlHas been a decrease in stimulation?lHas patient rec
14、ently received NMBA?lHas there been an increase in sedation?lIs the patient sleeping?lHas the pt recently received analgesic?lHas there been a sudden significant drop in BP?Current Status of the LiteraturelBIS scores do not provide a differential diagnosis.BIS scores can be affected by many cerebral
15、 events including sedation,sleep and cerebral ischemialBIS/EEG activity can also be affected by age,temperature,PaCO2,hyper/hypo-glycemia,electroyte imbalances,hepatic or renal function,endocrine disordersCurrent Status of the LiteraturelBIS scores can be affected by many forms of artifact:-Artifact
16、 occurs with excessive muscle activity movement,swallowing,blinking,shivering etc.-Artifact can also occur with concomitant use of other electrical devices and monitoring equipment-EEGCurrent Status of the LiteraturelNeuromuscular activity typically elevates BIS scores.Hence the effects of NMBAs or
17、their metabolites may cause lower BIS scores as a result of decreased muscle activity and not decreased LOClThe synergistic action of agents affecting muscle relaxation must be considered when interpreting scoresCurrent Status of the LiteraturelOverall conflicting research resultslMay predict recove
18、ry of consciousness related to sedation and possibly traumatic brain injurylSeveral studies have found variable correlations between BIS scores and sedation scoreslBIS monitoring may serve as an adjunct measure to subjective scales of sedation monitoring in ICU patients,particularly in patients who
19、are heavily sedated or chemically paralyzedClinical ApplicationslBIS is only one part of a multi-modal assessment strategylIt remains unclear as to what BIS actually measures:Awareness?Hypnosis with recall?Delirium?Extent of brain injury,brain function or generalized cerebral electrical activity?Cli
20、nical ApplicationslOnly use trended scoreslWhen interpreting results,consider multiple factors including measurements error as well as the special/individual circumstances of each patientWhat the numbers meanBIS NumberlWhat the numbers mean:0=no electrical brain activity 100=fully awakelFor moderate
21、 sedation,aim for range from 60-70,below 60 is associated with a low probability of explicit recalllFor deeper sedation,aim for range from 40-60.A patient with a BIS value of less than 45 is approaching a deep hypnotic stateBIS NumberlFor a patient receiving neuromuscular blockage,sedation,analgesia
22、 therapy,the medication should be titrated for a BIS value between 45 and 60SQI:Signal Quality IndexlWhat the numbers mean:0=poor quality 100=excellent qualitylAim for range from 80-100%EMG:Electromyographic ActivitylReflects the electrical power of muscle activity or artifactlWhat the numbers mean:
23、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 activitylAcceptable EMG is less than 55 dBlOptimal EMG is less than 30 dBElectrode PlacementlPrep skin with alcohol prio
24、r to electrode placementlElectrode should be changed every 24 hours,alternating temples dailylLook at electrode packaging for placement instructionsElectrode PlacementlTo ensure adequate placement and impedance,check on the screenResourceslGuidelines and Procedure available in AACN Procedural Manual for Critical Care,Procedure 86,page 699
