awareness monitoring should not be routine. jamie sleigh
TRANSCRIPT
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Awareness Monitoring should
not be routine.
Jamie Sleigh
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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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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 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 RCT Myles, 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
• 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…
• 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)
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There are cracks in the edifice
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A man’s gotta know his limitations.
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59yr NIDDM, Desflurane 2%, Remi 6g/min
BISEMG
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People lose responsiveness at different BIS 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 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
THETWIGHLIGHT
ZONE
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Low values of BIS in awake patients?
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BIS goes down during recovery! B
IS
Time
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The Bispectral Index Declines During
Neuromuscular Block in Fully Awake Persons Anesth 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.”
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BIS tracks (some) drug effects well
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BIS tracks (some) drug effects badly N2O Increases BIS (Rampil Anesthesiology. Sept;1998)
N2O
BIS
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…and some effects
both well and badly at the same
time!
TELL ME WHY!
BIS
BIS
End Tidal Desflurane
End Tidal Desflurane
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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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CORTICAL ACTIVITY
RO
US
AB
ILIT
Y
AWAKE
COMA/ANAESTHESIA
SLOW-WAVESLEEP
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
doesn’t.• Relate the number to real cortical neurophysiology.• Have a belt and braces (IFT)