Depth of Anaesthesia Monitoring : What’s validated and What’s next?

1. Depth of Anaesthesia Monitoring: What’s validated and What’s next? British Journal of Anaesthesia 2006 R4 최 정 현

2. 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

3. 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)

4. Do we need DoA monitors? • Patient experienced awareness  traumatized, anxious • Incidence

5. 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

6. 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

7. 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)

8. What DoA monitoring technologies are available? • Technical aspects • BIS

9. Narcotrend M-entropy module

10. 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

11. 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

12. 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%

13. 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

14. 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