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Depth of Anaesthesia Monitoring : What’s validated and What’s next?. British Journal of Anaesthesia 2006 R4 최 정 현. new surgical procedure increasing prevalence of day surgery ‘value for money’ influence the choice of drug and techniques for anesthesia
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Depth of Anaesthesia Monitoring: What’s validated and What’s next? British Journal of Anaesthesia 2006 R4 최 정 현
new surgical procedure • increasing prevalence of day surgery • ‘value for money’ influence the choice of drug and techniques for anesthesia • Anesthesia (balance) • Amount of anesthetic drug state of arousal • Equipment failure, error underdosing • Inappropriate titration excessive DoA(depth of anesthesia) compromise patient outcome
Patient movement to noxious stimulation : important sign of inadequate DoA but unreliable, suppressed by paralysis • Traditional clinical sign(HTN, tachycardia, lacrimation) unreliable • Reliable DoA monitor have been developed • Early : raw or summate EEG, lower esophageal contractility unreliable • Isolated forearm technique : not been widely adopted • Useful comparator in the evaluation of newer method • AEP(Auditory-evoked potential) : clear dose-response • Bispectral index (BIS) • Spectral entropy • Typically scaled from 100 (awake) to 0 (deep coma)
Do we need DoA monitors? • Patient experienced awareness traumatized, anxious • Incidence
Do we need DoA monitors? • Larger than adequate dose for avoiding awareness risk of hypotension, delay recovery time, increase other complications • Monk and collegues : • Significant independent predictors of mortality • Three variables • Patient co-morbidity • Cumulative deep hypnotic time (BIS<45) • Intraop sys. hypotension
What DoA monitoring technologies are available? • Spontaneous EEG & MLAEP (Mid-latency auditory-evoked response) information about the hypnotic state • Fast few years • EEG-derived SNAPTM Index • ARX-derived AER Index • AAI 1.5 : MLAEP derived
What DoA monitoring technologies are available? • Newly introduced • EEG-derived cerebral state index • AAI 1.6 : EEG, MLAEP derived • PSI (patient state analyser) : quantitative EEG-derived • More established monitors • BIS (Bispectral Index Monitor, Aspect Medical Inc.,Newton, MA, USA) • Narcotrend index (Narcotrend Monitor, Schiller AG, Baar,Switzerland) • M-entropy module (GE Healthcare Helsinki, Finland) :State and Response Entropy (SE and RE)
What DoA monitoring technologies are available? • Technical aspects • BIS
What does the DoA monitor do? • Three differnetDoA monitors • Uses completely different algorithms (details are not published) • Basic principles (1)BIS based on a large volume of clinical data integrates several disparate descriptors of the EEG single variable (2)Narcotrend index • EEG change during sleep Automatic classification (based on visual assessment:originally related to sleep classification) • Applied to EEG change during anesthesia (stage A~F) • Statistical analysis identify subsets of EEGs between stage A~F finally further refined to numerical index between 0~100 (3)M-Entrophy module EEG : non-linear dynamics quantify non-linear dynamics RE : calculated in 0 – 47 Hz, include EEG and EMG SE : 0 – 32 Hx , mainly include EEG
Validation of DoA monitoring • Recovery time • Ganand colleagues • multicentre, randomized trial • 302 pts : propofol-alfentanil-nitrous oxide • Routine traditional care(age, health status, BP, HR)vsBIS minitoring • BIS monitoring : reduction in propofol administration, earlier recovery • Several trials : no substantial effect • Important issue by this series of studies • Meaningful reduction in recovery time reduction in anesthetic drug administration • Short-acting drug (such as desflurane ) already rapid recovery time
Validation of DoA monitoring • Definitive studies • Several large-scale studies : whether DoA monitoring can reduce the risk of awareness • Ekman and colleagues • before-and-after comparison 4945 patients(BIS monitor) vs 7826 patients • significant 5-fold reduction in risk, 0.04% vs 0.18%, P=0.038. • Myles and co-workers • A randomized, double-blind, multicentre trial • in 2643 adult patients at high risk of awareness • BIS-guided anaesthesiavsroutine care • a blinded observer for awareness at 2–6 h, 24–36 h, and 30 days after surgery • 2 reports of awareness in the BIS-guided group • 11 reports in the routine care group • P=0.022. BIS-guided anaesthesia reduce the risk of awareness by 82%
DoA monitors : what’s next? • Future advaces in both anesthetic technology and pharmacology increase overall quality of anesthesia • DoA monitor : important role • Economic decision • Cost-benefit anaysis need to be done • Routine awareness monitoring (about £30 million : UK health care) vs • reduction in drug usage, recovery times, Cx, hopital day • Awareness still occur in pt with DoA monitoring failure of monitoring algorithm or artifact detetion some pt condition human error • Require further study
DoA monitors : what’s next? • Aim during anesthesia or sedation • Without risk of awarness, hemodynamic instability, respiratory depression • Achieve and maintain adequate DoA • Large inter-individual variability difficult to quantify clinical/phamacological effect • Recently Improved understanding of pharmacokinetics and pharmacodynamics TCI , end-tidal controlled inhaled administration • DoA monitor : future anesthetic advisory and feedback system total coverage of the dose-reponse relation • Such systems might help anaesthetist • Optimizing the titration of drug administration without overshoot • Controlling physiologic function • Guiding monitoring variables