Welcome to ALARIS AEP session

1. Welcome toALARIS AEP session Kaare Jevnaker Alaris Medical

4. Incidence of explicit recall Remember being awake and recall things that were said or done during operation Year Incidence Number of patients Hutchinson 1960 1.2% 656 Harris 1971 1.6% 120 McKenna 1973 1.5% 200 Wilson 1975 0.8% 490 Flier 1986 1.4% 140 Liu 1991 0.2% (0.3) 1000 (684) Nordström 1997 0.2% (0.2) 1000 (1000) Ranta 1998 0.4 - 0.7% 2612 Myles 2000 0.11% 10811 Sandin 2000 0.15% (0.18) 11785 (7757) The first half is not relevant today because the anaesthesia technique has changes a lot. With kind permission from Dr Rolf Sandin, Kalmar, Sweden

5. Basic basic basic basic basic basic • The hearing is the last sense that leaves and the first that returns during anaesthesia. • AEP is just the brain response to a click stimuli through the hearing nerve • AEP is a very weak electrical signal wrapped in the EEG background actvity. • Let’s look at how tiny tiny this signal is.

6. 400 x 40 x ECG signal has approx. 400 x amplitude than the AEP signals. EEG signal has approx. 40 x amplitude than the AEP signal

7. Extracting the evoked responseBefore A-Line it took too long to ”detect and present” (extract) this weak signal, because it requires advanced signal processing 1 click 128 clicks 256 clicks 1024 clicks click 100 ms

8. But, lets make this more visible Let’s see what happens when we send a click through the ear.

9. Position of electrodes A deviation in the positioning of the electrodes up to 2 cm does not have significant influence on the ARX-index.

10. Place Headphones To Monitor Some prefer to wait with the headphones until electrodes are connected

12. The auditory Pathway 2

13. Frontal cortex and association areas Medial geniculate and primary auditory cortex Acoustic nerve and brainstem

14. What does the AEP Look Like? Pa Pa latency + 0.1µV Pa amplitude Nb 100 msec

15. Basic knowledge • The early cortical AEP waves called Pa and Nb, which occurs between 20 and 80 ms reflects the activity in the temporal lobe/primary auditory cortex ( the site of sound registration) • Changes in the latency of these waves ( in particular the Nb wave) are highly correlated with a transition from awake to loss of consciousness • Changes in the amplitude of these waves reflects the interplay of general anaesthetics,surgical stimulation and the obtunding of the latter by analgesics!

16. And, this is what happens

17. Frontal cortex and association areas Medial geniculate and primary auditory cortex Acoustic nerve and brainstem

20. Desflurane Pa 1.5% Nb 3% 6% The AEP during Anaesthesia With kind permission from Dr Christine Thornton, Northwick Park, London, UK.

21. Effect of intubation on the AEP Pa + 0.1µV Nb Post-intubation Pre-intubation 100ms With kind permission from Dr Christine Thornton, Northwick Park, London, UK.

22. Conclusions • Graded changes with depth of anaesthesia • Similar changes for different anaesthetics • Shows response to noxious stimulation • AEP indicates level of consciousness • Technology has been studied since early 1980’s

23. AEP signal processing?How can it be so fast?

24. A-line Electrodes Signal OK? AMP MTA256 sweeps AAI Calc. Bandpass filter AEP 25-65 Hz Yes ARX MODEL No MTA18 sweeps A/D Converter 900 x Sec. Reject Signal OK? EEG + AEP + Artifact Bandpass filter EMG 65-85 Hz EMG Calc. Yes No Bandpass filter Burst Suppr. 1-35 Hz AEP MTA256 BS% Calc. Reject ALARIS AEP ™signal processing v. 1.4

25. 1 2 3 4 5 6 7 8 . . . . . . . . . . . 239 . . . 256 257 Moving time Averaging and ARX ARX -model MTA 256 sweeps MTA 18 sweeps

26. Index calculation?

27. Index calculation • So, then you have a real curve, the index is high = 93 • And, an almost flat curve gives a low index = 16

28. What it is • AAI is typically higher than 60 when the patient is awake and decreases when the patient is anaesthetised; loss of consciousness typically occurs when the AAI is below 30

29. Induction Awake Burst Suppression Utter boredom EMG Start of surgery End of operation Intubation A typical case

30. Fentanyl 0,15 + Pentothal 250mg Intubation. + Sevo FI 0,2 Start surgery. Gyn. Lap. procedure . FI 1,0 + MAC 1,0 Moved Patient on table Tracrium 15mg Index dropped and NMB was given to prepare intubation TIVA with induction and Maintenance would have prevented this Patient still not deep enough and reacts. Remember: 50% sleep at 1 MAC Intubation too soon. Fentanyl had not reached peak effect. Induction started with normal doses Penthotal dose was small for this patient. Gas conc. too low Patient was not deep enough to be moved on table. Dose of gas too low.

31. Put in trocar (insertion tube for scope) FI 1,8 + MAC 1,4 Sevo stopped FI 0,7 + MAC 0,9 At MAC 1,4 the patient is deep enough and all problems stops

32. Start Up

46. Induction is given

47. EMG starts to drop