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Document Control NR Clinical Department, ALARIS Medical Systems International. 2002
Welcome toALARIS AEP session
Welcome toALARIS AEP session
Kaare Jevnaker
Alaris Medical
Document Control NR Clinical Department, ALARIS Medical Systems International. 2002
Document Control NR Clinical Department, ALARIS Medical Systems International. 2002
Document Control NR Clinical Department, ALARIS Medical Systems International. 2002
Incidence of explicit recallIncidence of explicit recall
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)
Number of patientsNumber of patients
With kind permission from Dr Rolf Sandin, Kalmar, Sweden
Remember being awake and recall things that were said or done during operation
YearYear IncidenceIncidence
The first half is not relevant today because the anaesthesia technique has changes a lot.
Document Control NR Clinical Department, ALARIS Medical Systems International. 2002
Basic basic basic basic basic basicBasic 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.
Document Control NR Clinical Department, ALARIS Medical Systems International. 2002
Dimensions of AEP, EEG & ECG
2,5
100
1000
1
10
100
1000
AEP EEG ECG
No
rma
l Dim
en
sio
n S
ca
le in
uV
(L
og
ari
tmic
)
ECG signal has approx. 400 x amplitude than the AEP signals.EEG signal has approx. 40 x amplitude than the AEP signal
400 x
40 x
Document Control NR Clinical Department, ALARIS Medical Systems International. 2002
Extracting the evoked response Before A-Line it took too long to ”detect and present” (extract) this
weak signal, because it requires advanced signal processing
Extracting the evoked response Before 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
100 msclick
Document Control NR Clinical Department, ALARIS Medical Systems International. 2002
But, lets make this more visibleBut, lets make this more visible
Let’s see what happens when we send a click through the ear.
Document Control NR Clinical Department, ALARIS Medical Systems International. 2002
A deviation in the positioning of the electrodes up to 2 cm does not have significant influence on the ARX-index.
Document Control NR Clinical Department, ALARIS Medical Systems International. 2002
To Monitor
Some prefer to wait with the headphones until electrodes are connected
Document Control NR Clinical Department, ALARIS Medical Systems International. 2002
Position Middle offorehead
Left side offorehead
Mastoid
Type Positive Ref. NegativeNo. 1 2 3Color White Green Black
Position Middle offorehead
Left side offorehead
Mastoid
Type Positive Ref. NegativeNo. 1 2 3Color White Green Black
Position Middle offorehead
Left side offorehead
Mastoid
Type Positive Ref. NegativeNo. 1 2 3Color White Green Black
Document Control NR Clinical Department, ALARIS Medical Systems International. 2002
2
The auditory Pathway
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
0 2 4 6 8 10
0.1
0.2
0.3
0.4
0.5
0.6
5 10 15 20 25 30 35
6 7
IIIIII
IIIIIIIVIV VV
VIVI
NoNo
PoPo
NaNa
PaPa
NbNb
PP11
NN11
PP22
NN22
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
0 2 4 6 8 10
0.1
0.2
0.3
0.4
0.5
0.6
5 10 15 20 25 30 35
6 7
IIIIII
IIIIIIIVIV VV
VIVI
NoNo
PoPo
NaNa
PaPa
NbNb
PP11
NN11
PP22
NN22
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
0 2 4 6 8 10
0.1
0.2
0.3
0.4
0.5
0.6
5 10 15 20 25 30 35
6 7
IIIIII
IIIIIIIVIV VV
VIVI
NoNo
PoPo
NaNa
PaPa
NbNb
PP11
NN11
PP22
NN22
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
0 2 4 6 8 10
0.1
0.2
0.3
0.4
0.5
0.6
5 10 15 20 25 30 35
6 7
IIIIII
IIIIIIIVIV VV
VIVI
NoNo
PoPo
NaNa
PaPa
NbNb
PP11
NN11
PP22
NN22
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
0 2 4 6 8 10
0.1
0.2
0.3
0.4
0.5
0.6
5 10 15 20 25 30 35
6 7
IIIIII
IIIIIIIVIV VV
VIVI
NoNo
PoPo
NaNa
PaPa
NbNb
PP11
NN11
PP22
NN22
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
0 2 4 6 8 10
0.1
0.2
0.3
0.4
0.5
0.6
5 10 15 20 25 30 35
6 7
IIIIII
IIIIIIIVIV VV
VIVI
NoNo
PoPo
NaNa
PaPa
NbNb
PP11
NN11
PP22
NN22
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
0 2 4 6 8 10
0.1
0.2
0.3
0.4
0.5
0.6
5 10 15 20 25 30 35
6 7
IIIIII
IIIIIIIVIV VV
VIVI
NoNo
PoPo
NaNa
PaPa
NbNb
PP11
NN11
PP22
NN22
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
0 2 4 6 8 10
0.1
0.2
0.3
0.4
0.5
0.6
5 10 15 20 25 30 35
6 7
IIIIII
IIIIIIIVIV VV
VIVI
NoNo
PoPo
NaNa
PaPa
NbNb
PP11
NN11
PP22
NN22
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
0 2 4 6 8 10
0.1
0.2
0.3
0.4
0.5
0.6
5 10 15 20 25 30 35
6 7
IIIIII
IIIIIIIVIV VV
VIVI
NoNo
PoPo
NaNa
PaPa
NbNb
PP11
NN11
PP22
NN22
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
0 2 4 6 8 10
0.1
0.2
0.3
0.4
0.5
0.6
5 10 15 20 25 30 35
6 7
IIIIII
IIIIIIIVIV VV
VIVI
NoNo
PoPo
NaNa
PaPa
NbNb
PP11
NN11
PP22
NN22
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
0 2 4 6 8 10
0.1
0.2
0.3
0.4
0.5
0.6
5 10 15 20 25 30 35
6 7
IIIIII
IIIIIIIVIV VV
VIVI
NoNo
PoPo
NaNa
PaPa
NbNb
PP11
NN11
PP22
NN22
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
0 2 4 6 8 10
0.1
0.2
0.3
0.4
0.5
0.6
5 10 15 20 25 30 35
6 7
IIIIII
IIIIIIIVIV VV
VIVI
NoNo
PoPo
NaNa
PaPa
NbNb
PP11
NN11
PP22
NN22
Document Control NR Clinical Department, ALARIS Medical Systems International. 2002
Acoustic nerveand brainstem
Medial geniculate and
primary auditory cortex
Frontal cortex andassociation areas
1 2 5 10 20 50 100 200 500 1000 msms
IIIIII
IIIIIIIVIV VV
VIVIPoPo
NaNa
PaPa
NbNb
PP11
NN11
PP22
NN22
vv
Brain stemBrain stemresponseresponse
Early corticalEarly corticalresponseresponse
Late cortical Late cortical responseresponse
msms
IIIIII
IIIIIIIVIV VV
VIVI
No
PoPo
NaNa
PaPa
NbNb
PP11
NN11
PP22
NN22
vv
Brain stemBrain stemresponseresponse
Early corticalEarly corticalresponseresponse
Late cortical Late cortical responseresponse
Document Control NR Clinical Department, ALARIS Medical Systems International. 2002
What does the AEP Look Like?
+0.1µV
100 msec
Pa
Nb
Pa latency
Pa amplitude
Document Control NR Clinical Department, ALARIS Medical Systems International. 2002
Basic knowledgeBasic 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!
+0.1µV
100 msec
Pa
Nb
AEP
Document Control NR Clinical Department, ALARIS Medical Systems International. 2002
And, this is what happensAnd, this is what happens
Document Control NR Clinical Department, ALARIS Medical Systems International. 2002
Acoustic nerveand brainstem
Medial geniculate and
primary auditory cortex
Frontal cortex andassociation areas
1 2 5 10 20 50 100 200 500 1000 msms
IIIIII
IIIIIIIVIV VV
VIVIPoPo
NaNa
PaPa
NbNb
PP11
NN11
PP22
NN22
vv
Brain stemBrain stemresponseresponse
Early corticalEarly corticalresponseresponse
Late cortical Late cortical responseresponse
msms
IIIIII
IIIIIIIVIV VV
VIVI
No
PoPo
NaNa
PaPa
NbNb
PP11
NN11
PP22
NN22
vv
Brain stemBrain stemresponseresponse
Early corticalEarly corticalresponseresponse
Late cortical Late cortical responseresponse
Document Control NR Clinical Department, ALARIS Medical Systems International. 2002
1 2 5 10 20 50 100 200 500 1000 msms
IIIIII
IIIIIIIVIV VV
VIVIPoPo
NaNa
PaPa
NbNb
PP11
NN11
PP22
NN22
vv
Brain stemBrain stemresponseresponse
Early corticalEarly corticalresponseresponse
Late cortical Late cortical responseresponse
msms
IIIIII
IIIIIIIVIV VV
VIVI
No
PoPo
NaNa
PaPa
NbNb
PP11
NN11
PP22
NN22
vv
Brain stemBrain stemresponseresponse
Early corticalEarly corticalresponseresponse
Late cortical Late cortical responseresponse
Document Control NR Clinical Department, ALARIS Medical Systems International. 2002
1 2 5 10 20 50 100 200 500 1000 msms
IIIIII
IIIIIIIVIV VV
VIVIPoPo
NaNa
PaPa
NbNb
PP11
NN11
PP22
NN22
vv
Brain stemBrain stemresponseresponse
Early corticalEarly corticalresponseresponse
Late cortical Late cortical responseresponse
msms
IIIIII
IIIIIIIVIV VV
VIVI
No
PoPo
NaNa
PaPa
NbNb
PP11
NN11
PP22
NN22
vv
Brain stemBrain stemresponseresponse
Early corticalEarly corticalresponseresponse
Late cortical Late cortical responseresponse
Document Control NR Clinical Department, ALARIS Medical Systems International. 2002
Desflurane
1.5%
Pa
Nb
3%
6%
The AEP during Anaesthesia
With kind permission from Dr Christine Thornton, Northwick Park, London, UK.
Document Control NR Clinical Department, ALARIS Medical Systems International. 2002
Pre-intubation
100ms
0.1µV+
Pa
Nb Post-intubation
Effect of intubation on the AEPEffect of intubation on the AEP
With kind permission from Dr Christine Thornton, Northwick Park, London, UK.
Document Control NR Clinical Department, ALARIS Medical Systems International. 2002
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
Document Control NR Clinical Department, ALARIS Medical Systems International. 2002
AEP signal processing?
How can it be so fast?
AEP signal processing?
How can it be so fast?
Document Control NR Clinical Department, ALARIS Medical Systems International. 2002
ALARIS AEP ™ signal processing v. 1.4
Bandpass filterEMG
65-85 Hz
Bandpass filterBurst Suppr.
1-35 Hz
Signal OK?
ARXMODEL
YesAAI
Calc.
BS%Calc.
EMGCalc.
MTA256
sweeps
MTA18
sweeps
Bandpass filterAEP
25-65 Hz
A/DConverter
900 xSec.
No
Reject
Reject
EEG + AEP + Artifact
AEP MTA256
AMP
A-line Electrodes
Signal OK?
No
Yes
Document Control NR Clinical Department, ALARIS Medical Systems International. 2002
12345678...........239...256
MTA 256sweeps
MTA 18sweeps
Moving time Averaging and ARX
ARX-model
257
Document Control NR Clinical Department, ALARIS Medical Systems International. 2002
Index calculation?
Document Control NR Clinical Department, ALARIS Medical Systems International. 2002
Index calculationIndex calculation
• So, then you have a real curve, the index is high
• And, an almost flat curve gives a low index
= 93
= 16
Document Control NR Clinical Department, ALARIS Medical Systems International. 2002
What it isWhat 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
Document Control NR Clinical Department, ALARIS Medical Systems International. 2002
0
10
20
30
40
50
60
70
80
90
100
1
80
16
0
24
0
31
9
39
8
47
7
55
7
63
6
71
6
79
5
87
4
95
4
10
33
111
2
119
1
12
70
13
50
14
29
15
08
15
88
Induction
EMG
Burst Suppression
Intubation
Start of surgery
Utter boredom
End of operation
Awake
A typical caseA typical case
Document Control NR Clinical Department, ALARIS Medical Systems International. 2002
Fentanyl 0,15 + Pentothal 250mg
Tracrium 15mg
Intubation. + Sevo FI 0,2 Moved Patient on table
Start surgery. Gyn. Lap. procedure . FI 1,0 + MAC 1,0
Induction started with normal dosesIndex dropped and NMB was given to prepare intubationIntubation too soon. Fentanyl had not reached peak effect. Penthotal dose was small for this patient. Gas conc. too lowTIVA with induction and Maintenance would have prevented thisPatient was not deep enough to be moved on table. Dose of gas too low.Patient still not deep enough and reacts. Remember: 50% sleep at 1 MAC
Document Control NR Clinical Department, ALARIS Medical Systems International. 2002
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
Document Control NR Clinical Department, ALARIS Medical Systems International. 2002
Document Control NR Clinical Department, ALARIS Medical Systems International. 2002
Document Control NR Clinical Department, ALARIS Medical Systems International. 2002
Document Control NR Clinical Department, ALARIS Medical Systems International. 2002
Document Control NR Clinical Department, ALARIS Medical Systems International. 2002
Document Control NR Clinical Department, ALARIS Medical Systems International. 2002
Document Control NR Clinical Department, ALARIS Medical Systems International. 2002
Document Control NR Clinical Department, ALARIS Medical Systems International. 2002
Document Control NR Clinical Department, ALARIS Medical Systems International. 2002
Document Control NR Clinical Department, ALARIS Medical Systems International. 2002
Document Control NR Clinical Department, ALARIS Medical Systems International. 2002
Document Control NR Clinical Department, ALARIS Medical Systems International. 2002
Document Control NR Clinical Department, ALARIS Medical Systems International. 2002
Document Control NR Clinical Department, ALARIS Medical Systems International. 2002
Document Control NR Clinical Department, ALARIS Medical Systems International. 2002
Induction is givenInduction is given
Document Control NR Clinical Department, ALARIS Medical Systems International. 2002
EMG starts to dropEMG starts to drop
Document Control NR Clinical Department, ALARIS Medical Systems International. 2002
Document Control NR Clinical Department, ALARIS Medical Systems International. 2002
Document Control NR Clinical Department, ALARIS Medical Systems International. 2002
Document Control NR Clinical Department, ALARIS Medical Systems International. 2002
Burst Suppression appearsBurst Suppression appears
Document Control NR Clinical Department, ALARIS Medical Systems International. 2002
Document Control NR Clinical Department, ALARIS Medical Systems International. 2002
Document Control NR Clinical Department, ALARIS Medical Systems International. 2002
Document Control NR Clinical Department, ALARIS Medical Systems International. 2002
Document Control NR Clinical Department, ALARIS Medical Systems International. 2002
Document Control NR Clinical Department, ALARIS Medical Systems International. 2002
Document Control NR Clinical Department, ALARIS Medical Systems International. 2002
Document Control NR Clinical Department, ALARIS Medical Systems International. 2002
Document Control NR Clinical Department, ALARIS Medical Systems International. 2002
Starting to wake upStarting to wake up
Document Control NR Clinical Department, ALARIS Medical Systems International. 2002
Document Control NR Clinical Department, ALARIS Medical Systems International. 2002
Observe Alarm and EMGObserve Alarm and EMG
Document Control NR Clinical Department, ALARIS Medical Systems International. 2002
Document Control NR Clinical Department, ALARIS Medical Systems International. 2002
Document Control NR Clinical Department, ALARIS Medical Systems International. 2002
Document Control NR Clinical Department, ALARIS Medical Systems International. 2002
Document Control NR Clinical Department, ALARIS Medical Systems International. 2002
Document Control NR Clinical Department, ALARIS Medical Systems International. 2002
Operation overOperation over
Document Control NR Clinical Department, ALARIS Medical Systems International. 2002
ExitExit
Document Control NR Clinical Department, ALARIS Medical Systems International. 2002
Document Control NR Clinical Department, ALARIS Medical Systems International. 2002
Check and transfer DATACheck and transfer DATA
Document Control NR Clinical Department, ALARIS Medical Systems International. 2002
Document Control NR Clinical Department, ALARIS Medical Systems International. 2002
Document Control NR Clinical Department, ALARIS Medical Systems International. 2002
Document Control NR Clinical Department, ALARIS Medical Systems International. 2002
Document Control NR Clinical Department, ALARIS Medical Systems International. 2002
Document Control NR Clinical Department, ALARIS Medical Systems International. 2002
Document Control NR Clinical Department, ALARIS Medical Systems International. 2002
Document Control NR Clinical Department, ALARIS Medical Systems International. 2002
Document Control NR Clinical Department, ALARIS Medical Systems International. 2002
Document Control NR Clinical Department, ALARIS Medical Systems International. 2002
A good caseA good case
• Just to illustrate how important it is.• Customer couldn’t understand why the index was
high?• Complained that “something was wrong”• All details captured by our man• After downloading and descriptions the clinicians
agreed the anaesthesia was not optimal.• They could actually see things they never seen
before
Document Control NR Clinical Department, ALARIS Medical Systems International. 2002
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