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 – 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

• 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

Is this incidence acceptable?

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)

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%

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.

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)

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)

There are cracks in the edifice

A man’s gotta know his limitations.

59yr NIDDM, Desflurane 2%, Remi 6g/min

BISEMG

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

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%.”

“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

Low values of BIS in awake patients?

BIS goes down during recovery! B

IS

Time

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.”

BIS tracks (some) drug effects well

BIS tracks (some) drug effects badly N2O Increases BIS (Rampil Anesthesiology. Sept;1998)

N2O

BIS

…and some effects

both well and badly at the same

time!

TELL ME WHY!

BIS

BIS

End Tidal Desflurane

End Tidal Desflurane

BIS vs Brain Metabolism

Quantitative EEG Correlations with Brain Glucose Metabolic Rate during Anesthesia in Volunteers Alkire, Anesthesiology 1998

BIS = CORTICAL ACTIVITY

ACTIVITY AROUSAL

Causes of Decreased Cortical activity

• Sleep

• Sedative Drugs

• Metabolic– Hypothermia– Uraemia – Acidosis

• Illnesses– Any CNS disease– Sepsis

CORTICAL ACTIVITY

RO

US

AB

ILIT

Y

AWAKE

COMA/ANAESTHESIA

SLOW-WAVESLEEP

REM SLEEP/DELIRIUM

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

• 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)