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Awareness Monitoring should not be routine. Jamie Sleigh. Awareness / Recall: Epidemiology. Sweden: 11785 patients 0.18% (paralysed) vs 0.1% (not) Sandin Lancet 2000 55;707 Australia : 10811 patients 0.11% Myles, BJA 2000;84:6-10 USA: 19575 patients

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Awareness recall epidemiology l.jpg
Awareness / Recall: Epidemiology

  • Sweden: 11785 patients

    • 0.18% (paralysed) vs 0.1% (not) Sandin Lancet 2000 55;707

  • Australia: 10811 patients

    • 0.11% Myles, BJA 2000;84:6-10

  • USA: 19575 patients

    • 0.13%Sebel et al,Anesth Analg. 2004 Sep;99(3):833

      = 26000 cases/yr in USA

      =20/yr Waikato

  • High-risk patients having relaxant GA with incidence as high as 1%


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Awareness: Urban Myths

  • High on patient concerns (The attitude of the general public towards preoperative assessment and risks associated with general anesthesia. Matthey P,Can J Anaesth. 2001 Apr;48(4):333-9.

  • If blinded, a routine GA  BIS 40-60 only half the time….

  • Clinical judgement is useless…

  • Midazolam is useless…

  • Need to ask 3 days later?!!

  • ½ post intubation

  • Painful/distressing awareness 1/5, Anaesth 2003;58:962



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Advantages of BISguided anaesthesia

  • BIS  Drug Dosage (19%) , &

    •  PONV(32%)

    • ?NOToverall cost (Liu, A 2004)

  • BIS and desflurane – 2.7% vs 3.6%

    • Wake up 7 vs 9 min!

    • Discharged 127 vs 195 min!

  • Propofol dose  40% if use BIS (Gurses A+A 2004)


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BIS “Rx of Awareness”

  • Reduction in the incidence of awareness using BIS monitoring.Ekman et al, AAS Jan 2004

    • 4945 pts + muscle relaxation: BIS 40-60.

    • Historical control 7826 pts

  • Awareness BISguided = 0.04%

    • 2 patients during induction – BIS>60 >10min

    • 8-20% patients have BIS >60 for 4min

      vs

  • Awareness MISguided = 0.18%


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Bispectral index monitoring to prevent awareness during anaesthesia: the B-Aware RCTMyles,Lancet 2004

  • 2503 high-risk patients recruited

  • Patients interviewed at 3 intervals: 6 h, at 36 h and 30 days

  • Awareness Rate:

    • BIS=2 (0.17%)vs

    • Routine=11 (0.91%)

  • Odds Ratio 0.18 (NNT is 138)

  • Episodes awareness in BIS group when: BIS = 55-59 and 79-82.


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Conclusions and Comments anaesthesia: the B-Aware RCT

  • BIS monitoring   risk of awareness by 82% in high-risk adults having relaxant GA.

  • Cost = US$ 16 per surgical procedure, (NNT of 138), i.e. to prevent one case of awareness in a high-risk population is about US$ 2208.

  • (Cost of CPR > US$ 500 000)


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BUT… anaesthesia: the B-Aware RCT

  • No difference in painful awareness (if 2 patients removed from routine group)

  • 36 ”possible awareness” episodes reported (20 BIS & 16 routine ) and when included no difference between groups

  • Same incidence of intra-operative dreaming, (62 BIS and 83 routine)


There are cracks in the edifice l.jpg
There are cracks in the edifice anaesthesia: the B-Aware RCT


A man s gotta know his limitations l.jpg
A man’s gotta know his limitations. anaesthesia: the B-Aware RCT


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59yr NIDDM, Desflurane 2%, Remi 6 anaesthesia: the B-Aware RCTg/min

BIS

EMG


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People lose responsiveness at different BIS anaesthesia: the B-Aware RCT

values.Kuizenga et al Anesthesiology. 2001;95:607-15, Br J Anaesth. 2001 Mar;86(3):354-60.


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Detection of awareness in surgical patients with EEG-based indices — bispectral index and patient state index.Schneider et al Br. J. Anaesth. 2003 91: 329

  • “Despite significant differences between mean valuesat responsiveness and non-responsiveness for BIS and PSI, neithermeasure may be sufficient to detect awareness in an individualpatient, reflected by a Pk less than below 70%.”


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“Wide variation in the awake values and considerable overlap between consciousness and unconsciousness... further improvement is required”AAI vs BIS during propofol-remifentanil anaesthesia. Kreuer Br J Anaesth 2003; 91: 336

THE

TWIGHLIGHT

ZONE


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Low values of BIS in awake patients? overlap between consciousness and unconsciousness... further improvement is required”


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BIS goes down during recovery! overlap between consciousness and unconsciousness... further improvement is required”

BIS

Time


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The Bispectral Index Declines During Neuromuscular Block in Fully Awake PersonsAnesth Analg. 2003 Aug;97(2):488-91,Messner M, et al

  • “There were no significant changes in the raw EEG ….

  • recorded EEG parameters (power, median frequency) remained stable in a range compatible with the awake state.

  • The suppression ratio was zero at all times.”



Bis tracks some drug effects badly n2o increases bis rampil anesthesiology sept 1998 l.jpg
BIS tracks (some) drug effects badly Fully Awake PersonsN2O Increases BIS (Rampil Anesthesiology. Sept;1998)

BIS

N2O


And some effects both well and badly at the same time tell me why l.jpg

BIS Fully Awake Persons

…and some effects both well and badly at the same time!TELL ME WHY!

End Tidal Desflurane

BIS

End Tidal Desflurane


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BIS = Fully Awake Persons

CORTICAL ACTIVITY

ACTIVITY 

AROUSAL

BIS vs Brain MetabolismQuantitative EEG Correlations with Brain Glucose Metabolic Rate during Anesthesia in Volunteers Alkire, Anesthesiology 1998


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Causes of Decreased Cortical activity Fully Awake Persons

  • Sleep

  • Sedative Drugs

  • Metabolic

    • Hypothermia

    • Uraemia

    • Acidosis

  • Illnesses

    • Any CNS disease

    • Sepsis


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AWAKE Fully Awake Persons

SLOW-WAVE

SLEEP

CORTICAL ACTIVITY

ROUSABILITY

COMA/

ANAESTHESIA

REM SLEEP/

DELIRIUM


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CONCLUSIONS Fully Awake Persons

  • Recall is uncomfortably common...

  • It is negligent not to use EEG monitoring for sick/weird patients

  • EEG is unnecessary for non-paralysed patients

  • Look at the frigging RAW EEG waveform!!!!

  • Isolated forearm is the proper test for awareness.


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Advice to would-be EEG manufacturers Fully Awake Persons

  • Have a narrow range of values at LOC

  • Have a simple, transparent, algorithm

  • Have a fast response

  • Have a clear EEG trace

  • Have a stable number, if the patient is stable

  • Market on which drugs it works, & on which it doesn’t.

  • Relate the number to real cortical neurophysiology.

  • Have a belt and braces (IFT)


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