Awareness Monitoring should not be routine.

1
Awareness Monitoring should not be routine.

• Jamie Sleigh

2
Awareness / Recall Epidemiology

• Sweden 11785 patients
• 0.18 (paralysed) vs 0.1 (not) Sandin Lancet
  2000 55707
• Australia 10811 patients
• 0.11 Myles, BJA 2000846-10
• USA 19575 patients
• 0.13 Sebel et al, Anesth Analg. 2004
  Sep99(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 Apr48(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
  200358962

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Is this incidence acceptable?
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Advantages of BISguided anaesthesia

• BIS ? ? Drug Dosage (19) ,
• ? PONV(32)
• ?NOT overall 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 AA 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 BISgt60 gt10min
• 8-20 patients have BIS gt60 for 4min
• vs
• Awareness MISguided 0.18

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Bispectral index monitoring to prevent awareness
during anaesthesia the B-Aware RCT Myles,
Lancet 2004

• 2503 high-risk patients recruited
• Patients interviewed at 3 intervals 6 h, at 36 h
  and 30 days
• Awareness Rate
• BIS2 (0.17) vs
• Routine11 (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

• 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 gt US 500 000)

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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)

10
There are cracks in the edifice
11
A mans gotta know his limitations.
12
59yr NIDDM, Desflurane 2, Remi 6?g/min
BIS EMG
13
People lose responsiveness at different BIS
values.Kuizenga et al Anesthesiology.
200195607-15, Br J Anaesth. 2001
Mar86(3)354-60.
14
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
  values at responsiveness and non-responsiveness
  for BIS and PSI, neither measure may be
  sufficient to detect awareness in an individual
  patient, 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?
17
BIS goes down during recovery!
BIS
Time
18
The Bispectral Index Declines During
Neuromuscular Block in Fully Awake Persons Anesth
Analg. 2003 Aug97(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.

19
BIS tracks (some) drug effects well
20
BIS tracks (some) drug effects badly N2O
Increases BIS (Rampil Anesthesiology. Sept1998)
BIS
N2O
21
and some effects both well and badly at the
same time!TELL ME WHY!
BIS
End Tidal Desflurane
BIS
End Tidal Desflurane
22
BIS vs Brain Metabolism Quantitative EEG
Correlations with Brain Glucose Metabolic Rate
during Anesthesia in Volunteers Alkire,
Anesthesiology 1998
BIS CORTICAL ACTIVITY ACTIVITY ? AROUSAL
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Causes of Decreased Cortical activity

• Sleep
• Sedative Drugs
• Metabolic
• Hypothermia
• Uraemia
• Acidosis
• Illnesses
• Any CNS disease
• Sepsis

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AWAKE
SLOW-WAVE SLEEP
CORTICAL ACTIVITY
ROUSABILITY
COMA/ ANAESTHESIA
REM SLEEP/ DELIRIUM
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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.

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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
  doesnt.
• Relate the number to real cortical
  neurophysiology.
• Have a belt and braces (IFT)