Transcript ALARIS Medical Systems

Welcome to
ALARIS AEP session
Kaare Jevnaker
Alaris Medical
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Incidence of explicit recall
Remember being awake and recall things that were said or done during operation
Hutchinson
Harris
McKenna
Wilson
Flier
Liu
(684)
Nordström
Ranta
Myles
Sandin
Year
Incidence
1960
1971
1973
1975
1986
1.2%
1.6%
1.5%
0.8%
1.4%
1991
1997
1998
2000
2000
Number of patients
656
120
200
490
140
0.2% (0.3)
0.2% (0.2)
0.4 - 0.7%
0.11%
0.15% (0.18)
1000
1000 (1000)
2612
10811
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
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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.
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Normal Dimension Scale in uV
(Logaritmic)
Dimensions of AEP, EEG & ECG
1000
1000
400 x
100
100
40 x
10
2,5
1
AEP
EEG
ECG signal has approx. 400 x amplitude than the AEP signals.
EEG signal has approx. 40 x amplitude than the AEP signal
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ECG
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
click
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100 ms
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But, lets make this more visible
Let’s see what happens when we send a
click through the ear.
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A deviation in the positioning of the electrodes up to 2 cm does not have
significant influence on the ARX-index.
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To Monitor
Some prefer to wait with the
headphones until electrodes are
connected
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Position
Type
No.
Color
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Middle of
forehead
Positive
1
White
Left side of
forehead
Ref.
2
Green
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Mastoid
Negative
3
Black
The
auditory
Pathway
2
0.8
0.8
0.8
IV V
III
I
0.6
0.6
0.6
0.6
0.6
0.6
P22
P
Pa
Pa
0.5
0.5
0.5
II
P11
P
0.4
0.4
0.4
0.4
0.4
0.4
VI
0.3
0.3
0.3
Po
0.2
0.2
0.2
0.2
0.2
0.2
0.1
0.1
0.1
5555
6666
10
10
10
10
No
7777
15
15
15
15
20
20
20
20
25
25
25
25
30
30
30
30
000
000
35
35
35
35
222
Na
Na
-0.6
-0.6
-0.6
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666
Nb
Nb
-0.4
-0.4
-0.4
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444
-0.2
-0.2
N22
N
N11
888
10
10
10
Frontal cortex and
association areas
Medial geniculate and
primary auditory cortex
IV V
P1
III
I
P2
Pa
II
VI
Po
Acoustic nerve
and brainstem
No
v
Na
Nb
N2
N1
Brain stem
response
1
2
5
Early cortical
response
10
20
Late cortical
response
50 100 200 500 1000
ms
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What does the AEP Look Like?
+
Pa latency
Pa
0.1µV
Pa amplitude
Nb
100 msec
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+
Pa
0.1µV
Basic knowledge
AEP
Nb
•
•
•
100 msec
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!
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And, this is what happens
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Frontal cortex and
association areas
Medial geniculate and
primary auditory cortex
IV V
P1
III
I
P2
Pa
II
VI
Po
Acoustic nerve
and brainstem
No
v
Na
Nb
N2
N1
Brain stem
response
1
2
5
Early cortical
response
10
20
Late cortical
response
50 100 200 500 1000
ms
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IV V
P1
III
I
P2
Pa
II
VI
Po
No
v
Na
Nb
N2
N1
Brain stem
response
1
2
Early cortical
response
5
10
20
Late cortical
response
50 100 200 500 1000
ms
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IV V
P1
III
I
P2
Pa
II
VI
Po
No
v
Na
Nb
N2
N1
Brain stem
response
1
2
Early cortical
response
5
10
20
Late cortical
response
50 100 200 500 1000
ms
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The AEP during Anaesthesia
Desflurane
Pa
1.5%
Nb
3%
6%
With kind permission from Dr Christine Thornton, Northwick Park, London, UK.
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Effect of intubation on the AEP
Pa
+
0.1µV
Nb
100ms
Post-intubation
Pre-intubation
With kind permission from Dr Christine Thornton, Northwick Park, London, UK.
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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
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AEP signal processing?
How can it be so fast?
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ALARIS AEP ™ signal processing v. 1.4
A-line Electrodes
Signal OK?
AMP
Bandpass filter
AEP
25-65 Hz
A/D
Converter
MTA256
sweeps
ARX
MODEL
MTA18
sweeps
900 x
Sec.
AAI
Calc.
Yes
No
Reject
Signal OK?
Yes
EEG + AEP + Artifact
Bandpass filter
EMG
65-85 Hz
EMG
Calc.
Bandpass filter
Burst Suppr.
1-35 Hz
BS%
Calc.
No
Reject
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AEP MTA256
Moving time Averaging and ARX
1
2
3
4
5
6
7
8
.
.
.
.
.
.
.
.
.
.
.
239
.
.
.
256
MTA 256
sweeps
ARX
-model
MTA 18
sweeps
257
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Index calculation?
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Index calculation
• So, then you have a real curve, the index is high
= 93
• And, an almost flat curve gives a low index
= 16
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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
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A typical case
Induction
Awake
100
90
Burst
Suppression
80
70
Utter boredom
60
EMG
50
Start of
Intubation surgery
40
End of
operation
30
20
10
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1588
1508
1429
1350
1270
1191
1112
1033
954
874
795
716
636
557
477
398
319
240
160
80
1
0
Fentanyl 0,15 +
Pentothal 250mg
Tracrium
15mg
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Intubation. +
Sevo FI 0,2
Moved Patient on table
Start surgery. Gyn. Lap.
procedure . FI 1,0 + MAC 1,0
Index
TIVA
Intubation
with
dropped
still
too
induction
notsoon.
and
deep
NMB
Fentanyl
enough
and
Maintenance
was
had
Induction
started
with
normal
Penthotal
Patient
was
dose
was
small
for and
to
this
bereacts.
given
would
Remember:
notClinical
reached
to
have
prepare
prevented
50%
peak
intubation
sleep
effect.
this
at
1 MAC
doses
patient.
moved
on
Gas
table.
conc.
Dose
too
low
of
gas
too
Department,
ALARIS
Medical
Systems
International.
2002 low.
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
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Induction is given
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EMG starts to drop
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Burst Suppression appears
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Starting to wake up
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Observe Alarm and EMG
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Operation over
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Exit
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Check and transfer DATA
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A 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
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