Welcome to ALARIS AEP session

Document Control NR Clinical Department, ALARIS Medical Systems International. 2002

Welcome toALARIS AEP session

Welcome toALARIS AEP session

Kaare Jevnaker

Alaris Medical


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.


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.


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


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


But, lets make this more visibleBut, lets make this more visible

Let’s see what happens when we send a click through the ear.


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


To Monitor

Some prefer to wait with the headphones until electrodes are connected


Position Middle offorehead

Left side offorehead

Mastoid

Type Positive Ref. NegativeNo. 1 2 3Color White Green Black



Mastoid




Mastoid



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


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





What does the AEP Look Like?

+0.1µV

100 msec

Pa

Nb

Pa latency

Pa amplitude


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


And, this is what happensAnd, this is what happens


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




msms

IIIIII

IIIIIIIVIV VV

VIVI

No

PoPo

NaNa

PaPa

NbNb

PP11

NN11

PP22

NN22

vv





1 2 5 10 20 50 100 200 500 1000 msms

IIIIII

IIIIIIIVIV VV

VIVIPoPo

NaNa

PaPa

NbNb

PP11

NN11

PP22

NN22

vv




msms

IIIIII

IIIIIIIVIV VV

VIVI

No

PoPo

NaNa

PaPa

NbNb

PP11

NN11

PP22

NN22

vv





Desflurane

1.5%

Pa

Nb

3%

6%

The AEP during Anaesthesia

With kind permission from Dr Christine Thornton, Northwick Park, London, UK.


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.


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


AEP signal processing?

How can it be so fast?

AEP signal processing?

How can it be so fast?


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


12345678...........239...256

MTA 256sweeps

MTA 18sweeps

Moving time Averaging and ARX

ARX-model

257


Index calculation?


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


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


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


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


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


Induction is givenInduction is given


EMG starts to dropEMG starts to drop


Burst Suppression appearsBurst Suppression appears


Starting to wake upStarting to wake up


Observe Alarm and EMGObserve Alarm and EMG


Operation overOperation over


ExitExit


Check and transfer DATACheck and transfer DATA


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

Welcome to ALARIS AEP session

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