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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 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
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” • 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 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 • 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)
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 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%.”
“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
BIS goes down during recovery! BIS Time
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 badlyN2O Increases BIS (Rampil Anesthesiology. Sept;1998) BIS N2O
BIS …and some effects both well and badly at the same time!TELL ME WHY! End Tidal Desflurane BIS End Tidal Desflurane
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 • Sleep • Sedative Drugs • Metabolic • Hypothermia • Uraemia • Acidosis • Illnesses • Any CNS disease • Sepsis
AWAKE SLOW-WAVE SLEEP CORTICAL ACTIVITY ROUSABILITY COMA/ ANAESTHESIA 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)