monitoring / tiva / awareness

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Monitoring in TIVAThis can be done by: Clinical Monitoring Special Monitoring

Clinical MonitoringStandard ASA recommended monitoring plus as per requirement of surgery/ individual patient. MONITORS-ECG , PULSE OXYMETRY, MONITORSNIBP, ETCO2, TEMP SUBJECTIVE METHOD: 1}AUTONOMIC RESPONSE-hemodynamic changes, lacrimation, RESPONSEsweating, pupillary dilatation 2}ISOLATED FOREARM TECHNIQUETECHNIQUE-

Short Coming of Clinical MonitoringClinical assessment of anaesthetic depth has become more challenging because IV anaesthetic techniques involve combination of hypnotics, Opioids, muscle relaxants and adjuvant drugs. The interaction between these drugs result in additive, supra additive, infra-additive, or even infraantagonist effects making clinical monitoring alone unreliable leading to the chances of Awareness or Delayed awakening

Special MonitoringTwo simple noninvasive monitor to measure depth on anaesthesia could be: EEG & DERIVED INDICES 1. Bispectral index(BIS) 2.Entropy 3.Patient State Index (PSI) 4.Narcotrend 5.Cerebral State Index 5.Cerebral 6.SNAP index EVOKED POTENTIALS. 1.MLAEP- AEP index 1.MLAEP-

Definitions of Awareness and MemoryAwareness Postoperative recall of events occurring during general anesthesia . Amnesic wakefulness Responsiveness during general anesthesia without postoperative recall Dreaming Any experience (excluding awareness) that patients are able to recall postoperatively that they think occurred during general anesthesia and that they believe is dreaming. Explicit memory Conscious recollection of previous experiences ( awareness is evidence of explicit memory) Implicit memory Changes in performance or behavior that are produced by previous experiences but without any conscious recollection of those experiences ( unconscious memory formation during general anesthesia).

High Risk Patient Characteristics Substance use or abuse Limited hemodynamic reserve ASA IV V Previous episode of intraoperative awareness Chronic pain patients Younger age Tobacco smoking

High Risk Anesthetic TechniquesReduced anesthetic doses in presence of paralysis Total intravenous anesthesia Nitrous oxide-opioid anesthesia oxideRapid sequence induction

TIVA and AwarenessTIVA independent high risk for awareness TIVA recipe: Propofol/opioid +/- ketamine +/ Ketamine is controversial since Ketamine (as well as Etomidate) enhance both SSEP s and MEP s

Wake up test (rarely done anymore!) BIS monitoring Small bolus (eg, 1-2mg) of Midazolam 1intraop (too much will affect monitoring!!)

SEA # 32

Reducing risk of awareness

Pre operative amnestics Deeper anesthesia during intubation Appropriate use of narcotics to prevent pain separate recall of events from pain Less profound muscle relaxation Appropriate considerations for substance-tolerant patients substanceMaintain accuracy of anesthesia delivery systems Brain monitoring Better OR decorum less talking and loud music at times of expected light anesthesia Post op review and counseling Informed consent?10

EEG monitoring limitations: Insensitive to nitrous oxide, ketamine, xenon Sensitive to Beta- blockers, muscle relaxants Hypothermia, hypoglycemia can affect the reading 5-10% of normal population has congenitally low-voltage EEG Subject to artifact from other electrical equipment in the OR.

Practical Problems with EEG/BIS/EntropyAlgorithmic Artifacts (diathermy, eyeeyemovements etc ) EMG and Burst Suppression

Inherent Prediction of movement /MAC Other drugs atropine Disease CNS Systemic

Awake (E) (E DrowsySpindle

Light GA Deeper GA (H) (H BurstBurst suppression

EEG analysis3 predominant methods time domain analysis methods: analyse the methods: time, changes in the EEG signal in respect to time, frequency domain analysis methods: analyse methods: the changes in the EEG potentials in respect to frequency bispectral analysis methods: analyse EEG methods: amplitude, signal in respect to its amplitude, its frequency and its correlation between phase angle and the frequency range of the included waves.

Bispectral Index (BIS)

Bispectral IndexBIS is a proprietary that converts a single channel of frontal EEG into an index of hypnotic level (BIS). To compute the BIS, several variables derived from the EEG time domain (burst-suppression analysis), frequency domain (burst(power spectrum, bispectrum: inter-frequency phase bispectrum: interrelationships) are combined into a single index of hypnotic level. A multivariate logistic regression was used in offline analysis and identified those features of the EEG recordings that best correlated with clinical depth of sedation/anaesthesia, and these were then fitted to a model. The resulting algorithm generates the BIS. BIS model accounts for the nonlinear stages of EEG activity by allowing different parameters to dominate the resulting BIS as the EEG changes its character with increasing plasma concentrations of various anaesthetics, resulting in a linear decrease in BIS. It is suggested that routine intraoperative events (e.g., administration of depolarizing muscle relaxants, activation of electromagnetic equipment or devices, patient warming or planned hypothermia)may interfere with BIS functioning.

BIS Range Guidelines

Titration of sedatives to BIS ranges should be dependent upon the individual goals for sedation that have been established for each patient. These goals and associated BIS ranges may vary over time, in the context of patient status and treatment plan.

Bispectral Index (BIS)Proprietary algorithm converts a single channel of frontal EEG into an index of hypnotic level BIS values scaled from 0-100 Specific range of 40-60 = low probability of consciousness under GA

Entropy

ENTROPYBased on acquisition and processing of raw EEG and FEMG signals describes the irregularity, complexity, or unpredictability characteristics of a signal. EEG recordings change from irregular to more regular patterns when anaesthesia deepens.

Entropy Describes

the irregularity, complexity or unpredictable characteristics of a signal Single sine wave represents a completely predictable signal (entropy = 0) Noise represents entropy = 1 State entropy: cortical state (hypnosis) Response entropy: EMG activity from inadequate analgesia

Entropy and Anaesthesia Awake brain = High Entropy =>Freedom Boiling

Brain

there are many available microstates energy spreads out easily spatial coherence or decoherence? accurate & fast cortical information processing

Comatose brain = Low Entropy =>Prison Frozen

Brain

few microstates slow inaccurate information processing

ENTROPY AND ANAESTHESIADeep GA Awake 0.90(0.03)

0.74(0.02)

Loss-of-Consciousness

0.69(0.06)Increasing Anaesthetic Effect

EEG & Power Spectrum - Alert Patient

Spectral Entropy = 0.9

EEG & Power Spectrum - Anaesthetised

Spectral Entropy = 0.4

State/ Response entropyState entropy (SE) is an index ranging from 0 to 91 (awake)-(awake)-- the frequency range from 0.8 to 32 Hz, reflecting the cortical state of the patient. Response entropy (RE) is an index ranging from 0 to 100 (awake)--a frequency range from 0.8 to 47 Hz, (awake)--a containing the higher EMG-dominated frequencies, and EMGwill thus also respond to the increased EMG activity resulting from inadequate analgesia. Vakkuri A et al have been reported that entropy monitoring assists better titration of propofol especially during the last part of the procedures, as indicated by higher entropy values, decreased consumption of propofol, and shorter recovery times in the entropy group.

The PSI monitor is based on a quantitative analysis of the , , , and frequency bands as revealed by fast Fourier transformation, recorded from anterior and posterior scalp sites, as input to a multivariate algorithm that quantifies the most probable level of hypnosis. 4-channel EEG Patient State Analyzer: self-norming technique selfvalues: 0 to 100 faster emergence and recovery from propofol-alfentanilpropofol-alfentanilnitrous oxide anesthesia, with modest decrease in the amount of propofol delivered. useful in assessing patients receiving a combination of propofol and sufentanil. the influence of muscle activity: uncertain. less interference with the PSI readings during electrocautery use

PSI(PATIENT STATE INDEX)

PSI VALUES

AUDITORY EVOKED POTENTIALS

The AEP is defined as the passage of electrical activity from the cochlea to the cortex, which produces a waveform consisting of 15 waves. The waveform can be divided into three parts: Brainstem Auditory Evoked Potential (BAEP) from brainstem, Middle Latency Auditory Evoked Potential (MLAEP) from medial geniculate body and the primary auditory cortex and Long Latency Auditory Evoked Potential (LLAEP) from frontal cortex and association areas. Measures the brain s reaction to acoustic stimuli. Hearing,a natural choice for measuring patient consciousness under anaesthetic The brainstem response is relatively insensitive to anaesthetics, whereas early cortical responses (MLAEPs), change predictably with increasing concentrations of both volatile and intravenous anaesthetics

AEP monitoringFrom a mathematical analysis of the AEP waveform, the device generates an AEP index {from 0-100} or A-line ARX Index(AAI){0 0A60 range } ReRe-usable headphones/earphones deliver the active stimulation, costcost-effective disposable surface electrodes are used to measure the AEP. The AAI index is calculated in the 20 80 ms window of the AEP and latency and amplitude changes in the AEP are weighted equally. The typical AEP response to increasing anaesthetic concentrations is increased latency and decreased amplitude of the various wavef