Awareness Monitoring should not be routine. Jamie Sleigh

Awareness / Recall: Epidemiology Sweden: patients –0.18% (paralysed) vs 0.1% (not) Sandin Lancet ;707 Australia: patients –0.11% Myles, BJA 2000;84:6-10 USA: patients –0.13% Sebel et al, Anesth Analg Sep;99(3):833 = 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 Apr;48(4): If blinded, a routine GA  BIS 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 –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 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 = and

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$ (Cost of CPR > US$ )

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 6  g/min BIS EMG

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

Detection of awareness in surgical patients with EEG-based indices — bispectral index and patient state index. Schneider et al Br. J. Anaesth : 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 P k 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 THE TWIGHLIGHT ZONE

Low values of BIS in awake patients?

BIS goes down during recovery! BIS Time

The Bispectral Index Declines During Neuromuscular Block in Fully Awake Persons Anesth Analg 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) N2ON2O BIS

…and some effects both well and badly at the same time! TELL ME WHY! BIS 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 ROUSABILITY AWAKE COMA/ ANAESTHESIA SLOW-WAVE SLEEP 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)