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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
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%
awareness urban myths
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
advantages of bisguided anaesthesia
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)
bis rx of awareness
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%
slide7
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.
conclusions and comments
Conclusions and Comments
  • 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)
slide9
BUT…
  • 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)
slide13

People lose responsiveness at different BIS

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

slide14

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%.”
slide15

“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

slide18
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
BIS tracks (some) drug effects badlyN2O Increases BIS (Rampil Anesthesiology. Sept;1998)

BIS

N2O

and some effects both well and badly at the same time tell me why

BIS

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

End Tidal Desflurane

BIS

End Tidal Desflurane

slide22

BIS =

CORTICAL ACTIVITY

ACTIVITY 

AROUSAL

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

causes of decreased cortical activity
Causes of Decreased Cortical activity
  • Sleep
  • Sedative Drugs
  • Metabolic
    • Hypothermia
    • Uraemia
    • Acidosis
  • Illnesses
    • Any CNS disease
    • Sepsis
slide24

AWAKE

SLOW-WAVE

SLEEP

CORTICAL ACTIVITY

ROUSABILITY

COMA/

ANAESTHESIA

REM SLEEP/

DELIRIUM

conclusions
CONCLUSIONS
  • 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.
advice to would be eeg manufacturers
Advice to would-be EEG manufacturers
  • 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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