The impact of cardiac surgery on cognition

Copyright © 2008 John Wiley & Sons, Ltd.

T h e i m p a c t o f c a r d i a c s u r g e r y o n c o g n i t i o n

Kathryn Bruce,1,2 Julian A. Smith,1,*,† Gregory Yelland2 and Stephen Robinson2

1 Department of Surgery, Monash University, Clayton, Victoria, Australia2 School of Psychology, Psychiatry & Psychological Medicine, Monash University, Clayton, Victoria, Australia

* Correspondence to: Julian A. Smith, Southern Health, Level 5/Block E, Monash Medical Centre, 246 Clayton Road, Clayton Vic 3168, Australia.† E-mail: [email protected]

S t r e s s a n d H e a l t hStress and Health 24: 249–266 (2008)

Published online 17 July 2008 in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/smi.1204Received 16 November 2007; Accepted 27 February 2008

SummaryThis brief review focuses on coronary artery bypass grafting (CABG) and valve surgery and their post-operative effects on cognitive domains. Despite the substantial technical advances in cardiac surgery over the past few decades, the incidence of permanent cognitive impairment remains alarmingly high: 20–70 per cent of patients exhibit cognitive impairment during the fi rst week after surgery, with the incidence declining to 10–40 per cent after 6 weeks and remaining at this level thereafter. We fi nd that language, concentration and motor control are most consistently reported to be affected, while memory, attention and executive function are more variably affected. Valve surgery is generally associated with a worse outcome than CABG surgery. It remains unclear whether the use of the cardio-pulmonary bypass machine adversely affects cogni-tive outcome. There is an urgent need to identify the risk factors and surgical techniques that infl uence post-operative cognitive impairment, yet it is diffi cult to reach meaningful conclusions from the present data due to a lack of concordance in experimental design and data analysis. To address this challenge, future research will need to control for confounds such as mood state, post-operative pain, learning effects, and anaesthesia and will need to compare a wide range of cognitive domains and surgical procedures within large multi-centre studies. Copyright © 2008 John Wiley & Sons, Ltd.

Key Wordsanaesthesia; cognitive impairment; decline; neurological; neuropsychological; post-operative

severe neurological complications such as stroke, transient ischaemic attack, delirium and stupor/coma. Nonetheless, the incidence of mild or moderate post-operative cognitive impairment remains high (Borowisz, Goldsborough, Selnes, & McKhann, 1996; Collie, Darby, Falleti, Silbert, & Maruff, 2002; Newman et al., 2006; Symes, Maruff, Ajani, & Currie, 2000). It has been esti-mated that 20–70 per cent of all cardiac patients exhibit cognitive impairment during the fi rst week after surgery, with the incidence declining to 10–40 per cent after 6 weeks and remaining at this level thereafter (Table I).

Post-operative cognitive impairment slows recovery from surgery, increases length of stay in

Introduction

Advances in surgical technique, procedural conduct and post-operative care have steadily reduced the rates of morbidity and mortality fol-lowing cardiac surgery (Arrowsmith, Grocott, Reves, & Newman, 2000; Mahanna et al., 1996; Zamvar et al., 2002), as well as the frequency of

K. Bruce et al.

Copyright © 2008 John Wiley & Sons, Ltd. Stress and Health 24: 249–266 (2008)DOI: 10.1002/smi

250

intensive care and delays discharge from hospital, reduces compliance with post-operative cardiac rehabilitation programmes, with some patients requiring readmission (Lewis, Maruff, & Silbert, 2004). The cognitive domains affected after cardiac surgery include attention and concentra-tion, memory and learning, psychomotor perfor-mance, and language (Table I). Impairment in these domains can interfere with quality of life by reducing the effectiveness of the patient in their occupation or in social settings. It can render the patient more prone to accidents and less able to lead an independent life. The costs to the health-care sector are substantial. In Australia 32,815 patients per year undergo coronary artery bypass grafting (CABG) and valve surgery (Australian Institute of Health and Welfare, 2007), and approximately a third of these patients experience signifi cant cognitive impairment as a result of the surgery. If it is assumed that each of these affected patients incurs an additional AUD$5,000 of healthcare (the longer bed stays associated with post-operative delirium alone have been estimated to cost AUD$3,000 per patient (Franco et al., 2001), then the annual cost to the health-care sector will exceed AUD$50 million.

Surgical factors that infl uence post-operative cognitive impairment

This present review is concerned with two common forms of cardiac surgery: CABG and valve repair or replacement surgery. Heart trans-plantation surgery is not considered here, but it should be noted that many of the issues and cog-nitive outcomes associated with transplant surgery are common to those of CABG and valve surgery (for review see Cupples & Stilley, 2005). We have restricted this review to neuropsychological impairment following cardiac surgery and no dis-cussion will be made of the syndromes that may be associated with post-surgical cognitive (e.g. delirium).

CABG surgery is a procedure in which narrow-ings or blockages in coronary arteries supplying the heart muscle are bypassed with veins or arter-ies that have been harvested from the patients’ chest, leg, or arm. To obtain an unobstructed view of the heart, the surgeon makes a midline thoracic incision and retracts the ribs (i.e. ster-notomy). Valve repair/replacement surgery also involves a sternotomy; in this procedure the

chambers of the heart or the great vessels are opened in order to gain access to the mitral and aortic valves. Valve replacement surgery requires the heart to be arrested, with the patients’ blood temporarily diverted away from the heart and circulated around the body using a cardio-pulmo-nary bypass (CPB) or heart-lung machine. In CABG surgery the use of a CPB machine is optional. Surgery involving a CPB machine is referred to as ‘on-pump’ CABG, whereas surgery performed on the beating heart without using the CPB machine is known as ‘off-pump’ CABG. Much of the literature dealing with post-surgical cognitive impairment has been concerned with the extent to which surgical factors infl uence cog-nitive outcome. These factors include the use of the CPB machine, the nature of valve replacement surgery and the role of anaesthesia.

CPB machine

The CPB machine introduces particles (e.g. damaged platelets) and gaseous microemboli into the bloodstream. In addition, after restoration of the normal blood supply following CPB, clots formed during cannulation and clamping of the aorta may be freed into the bloodstream. These thrombi and emboli lodge in the small arteries of the brain and cause transient ischaemic attacks or ‘micro-strokes’ that can temporarily or perma-nently impair function in the region of brain sup-plied by that vessel. The CPB machine can also cause fl uctuations in blood pressure, blood pH, and temperature and can induce a systemic infl am-matory response (Arrowsmith et al., 2000; Browne, Halligan, Wade, & Taggart, 2003; Kapetanakis et al., 2004; Mills, 1993). All of these effects have the potential to impair brain function.

Despite the strong a priori reasons for expecting the CPB machine to contribute to post-operative cognitive impairment, the available data are equiv-ocal. A study by Zamvar et al. (2002) showed that off-pump CABG patients were signifi cantly less cognitively impaired than on-pump CABG patients, both at 1 week and 10 weeks post- operatively. Ngaage (2003) obtained similar results, whereas Motallebzadeh, Bland, Markus, Kaski, and Jahan-giri (2007) demonstrated an improved cognitive outcome in off-pump CABG patients at discharge from hospital, but this difference was not evident at later time points, with on-pump CABG patients recovering to the level observed for off-pump patients. On the other hand, a number of studies

The impact of cardiac surgery on cognition


251

have reported similar levels of cognitive dysfunc-tion after on-pump or off-pump CABG (Kilo et al., 2001; Rankin, Kochamba, Boone, Petitti, & Buck-walter, 2003). Furthermore, on-pump CABG is associated with a similar incidence of post-opera-tive impairment to that found after other forms of major surgery that do not use a CPB machine (Moller et al., 1998).

It is possible that while the CPB machine does cause cognitive impairment, off-pump CABG may cause a similar degree of cognitive impair-ment due to factors specifi cally associated with off-pump surgery. Indeed, off-pump CABG is associated with less complete revascularization and graft patency, with a risk of embolism from manipulation of the aorta, and triggering of the infl ammatory response through sternotomy and heparin administration (Newman et al., 2006).

Valve repair/replacement surgery

It has been suggested that mitral and aortic valve surgery may lead to more neurological damage than on-pump CABG surgery due to the increased number of micro-embolic events that occur during valve surgery (Braekken, Reivang, Russell, Brucher, & Svennevig, 1998). Several studies have reported that valve repair/replacement surgery is associated with a greater incidence of cognitive impairment than that observed after on-pump CABG surgery. For instance, Ebert, Walzer, Huth, and Herrmann (2001) reported that the valve replacement patients exhibit more neuro-psychological defi cits and a slower recovery than patients who undergo CABG surgery. Andrew, Baker, Kneebone, and Knight (2001) found that 50 per cent of the valve surgery group and 50 per cent of the on-pump CABG group displayed cog-nitive impairment 7 days post-operatively, yet when retested at 6 months, the incidence of impairment had decreased to 27 per cent in the on-pump CABG group and remained signifi cantly higher at 40 per cent in the valve group. Similarly, both the CABG and valve groups displayed an equal degree of impairment on an auditory dis-crimination task at 7 days, but the CABG patients recovered to pre-operative levels 4 months after surgery whereas the valve patients showed a con-tinued impairment (Zimpfer et al., 2002). Zimpfer and colleagues were unable to obtain a compa-rable result using a brief neuropsychological test battery. That battery, however, consisted of only two tests, one of which (Mini-Mental State

Examination) has a poor sensitivity to changes in cognitive function (Newman, 1995). Lastly, Braekken et al. (1998) showed that 2 months after valve replacement, 23 per cent of patients exhibited post-operative cognitive impairment compared to 14 per cent of on-pump CABG patients.

While there are some inconsistencies in the out-comes of studies that have compared the inci-dence of cognitive decline following on-pump and valve surgery, there are two points of congruence: that cognitive impairment shortly after valve surgery is at best equivalent to that observed for on-pump CABG and that the long-term prospects for a return to normal levels of cognitive function are much worse for valve surgery.

Anaesthesia

Anaesthetic agents have a negative impact on cog-nitive function in the days immediately after surgery (Newman et al., 2006; Papaioannou, Fraidakis, Michaloudis, Balalis, & Askitopoulou, 2005; Rasmussen et al., 2003). Ritchie, Polge, de Roquefeuil, Djakovic, and Ledesert (1997) reviewed the effects of anaesthesia after various types of surgery and found that cognitive impair-ment is a common outcome of surgery and that the incidence of such impairment was highest fol-lowing cardiac surgery. Papaioannou et al. (2005) showed that cognitive function was impaired during the fi rst three post-operative days (patients were retested each day up to post-operative day three) and that this impairment was greater in patients who had received general anaesthesia. Estimates of the duration of post-operative impairment caused by anaesthesia range from 1 h to a week (Moller et al., 1998; Papaioannou et al., 2005; Rasmussen et al., 2003). These fi nd-ings show why it is necessary to include a surgical control group when investigating cognitive function after cardiac surgery. Data obtained from such control groups can indicate the extent to which defi cits seen in the early post-operative period are due to the residual effects of general anaesthesia rather than to cardiac surgery per se.

Post-operative pain and discomfort

A median sternotomy allows excellent exposure of the surgical fi eld, yet it can cause signifi cant

K. Bruce et al.


252

Tab

le I

. A

n ill

ustr

ativ

e sa

mpl

e of

stu

dies

rev

iew

ing

the

neur

opsy

chol

ogic

al t

ests

use

d, t

he m

etho

ds u

sed

to d

efi n

e co

gnit

ive

impa

irm

ent

and

the

cogn

itiv

e im

pair

men

t fo

und

in t

hose

stu

dies

.

Ref

eren

ceSu

rger

y (n

umbe

r of

pa

tien

ts)

T1*

ho

urs

(h)

days

(d

)

T2/

T3*

w

eek

(w)

mon

th

(m)

year

(y

)

Defi

nit

ion

of

decl

ine†

NP

test

sC

ore

batt

ery

used

Cha

nge

in i

ndiv

idua

l N

P te

sts

Ove

rall

prev

alen

ce o

f co

gnit

ive

impa

irm

ent

(%)

And

rew

et

al.

(200

1)O

n-pu

mp

CA

BG

(59)

va

lve(

50)

7 d

6 m

7 an

d de

fi cit

on

≥2

test

s

CV

LT

, Pu

rdue

Pe

gboa

rd,

CO

WA

T,

TM

T

A&

B,

Dig

it

Sym

bol,

Bos

ton

Nam

ing

Tes

t.

Yes

T1:

Dig

it S

ymbo

l↓(V

alve

&

CA

BG

), T

MT

B↓

(Val

ve &

CA

BG

),

CV

LT

↓ (V

alve

onl

y)T

2: T

MT

A↓(

Val

ve &

C

AB

G),

TM

T B

↓(V

alve

& C

AB

G),

D

igit

Sym

bol↓

(Val

ve

only

)

T1:

CA

BG

50

% V

alve

50

%T

2: C

AB

G

27%

Val

ve

40%

Bra

ekke

n et

al.

(199

8)O

n-pu

mp

CA

BG

(14)

va

lve

26)

3–5

d2

m1

CO

WA

T,

CV

LT

, G

roov

ed

pegb

oard

, T

MT

A

&B

, W

MS,

Se

rial

Dig

it

Lea

rnin

g, L

ette

r C

ance

llati

on T

est,

D

igit

Sym

bol,

Com

pute

rise

d R

eact

ion

Tim

e T

est,

Sta

te T

rait

A

nxie

ty

Inve

ntor

y.

No

T1:

Val

ve o

nly:

Gro

oved

pe

gboa

rd↓,

Let

ter

Can

cella

tion

Tes

t↓,

Dig

it S

ymbo

l↓T

2: V

alve

: C

VL

T↑,

Sta

te

Tra

it A

nxie

ty

Inve

ntor

y↑ C

AB

G:

CV

LT

↑, W

MS↑

, D

igit

Sy

mbo

l↑

T1:

Val

ve

67%

T2:

Val

ve

23%

CA

BG

14

%

Di

Car

lo e

t al

. (2

001)

On-

pum

p C

AB

G(5

6)

valv

e(54

)N

il6

m1

MM

SE,

Ran

dt

Mem

ory

Tes

t,

Tok

en T

est,

C

onfr

onta

tion

an

d D

efi n

itio

nal

nam

ing,

Si

mila

riti

es &

D

iffe

renc

es.

No

T2:

MM

SE↓,

Ran

dt

Mem

ory

Tas

k↓,

Tok

en T

est↓

, C

onfr

onta

tion

N

amin

g↓

T2:

29%



253

Ebe

rt e

t al

. (2

001)

On-

pum

p C

AB

G(4

2)

valv

e(42

)2

d,

7 d

Nil

2M

MSE

, C

OW

AT

, Pi

ctur

e N

amin

g,

12 A

rith

met

ic

task

s, V

erba

l M

emor

y, C

lock

R

eadi

ng T

asks

.

No

T1:

CA

BG

& V

alve

: ↓

on a

ll te

sts

exce

pt

Nam

ing

but

Val

ve

had

sign

ifi ca

ntly

gr

eate

r de

clin

e th

an

CA

BG

on

CO

WA

T,

Ver

bal

Mem

ory

and

Ari

thm

etic

Tas

ks.

T2:

CA

BG

: ve

rbal

fl u

ency

↓, C

lock

re

adin

g↓,

Ari

thm

etic

↓ V

alve

: V

erba

l fl u

ency

↓, A

rith

met

ic↓,

V

erba

l le

arni

ng↓

T1:

Val

ve

71%

CA

BG

57

%T

2: V

alve

36

% C

AB

G

19%

Ham

mon

et

al.

(200

7)O

n-pu

mp

CA

BG

(81)

of

f-pu

mp

CA

BG

(26)

3–7

d3–

6 w

, 6

m3

WA

IS,

RA

VL

T,

TM

T A

&B

, G

roov

ed

Pegb

oard

, Fi

nger

T

appi

ng T

est,

D

igit

Sym

bol,

Let

ter

Can

cella

tion

T

ask,

Vis

ual

Rea

ctio

n T

ime

Tes

t

No

Dat

a on

sta

tist

ical

ly

diff

eren

t ch

ange

s in

pe

rfor

man

ce o

n in

divi

dual

tes

ts w

as

not

prov

ided

.

T3:

(6

m

only

): O

n-pu

mp:

26.

0 –4

4.4%

↓,

Off

-pum

p:

11.5

%–

38.4

%↓

Ho

et a

l. (2

004)

On-

pum

p C

AB

G

(939

)N

il6

m2,

3,6

Ble

ssed

Ori

enta

tion

-M

emor

y-C

once

ntra

tion

T

est,

Beh

avio

ural

D

ysco

ntro

l Sc

ale,

T

MT

A.

No

T2:

Beh

avio

ural

D

ysco

ntro

l↓,

Ble

ssed

O

rien

tati

on-M

emor

y-C

once

ntra

tion

Tes

t↓

T2:

≥0.

5SD

=

4.7%

↓ >

1SD

=

8.2%

↓ >2

0% =

36

.6%

↓H

ogue

et

al.

(200

3)O

n-ou

mp

CA

BG

(1

17)

Nil

4–6

w2

TM

T A

&B

, D

igit

Sy

mbo

l, D

igit

Sp

an,

Gro

oved

Pe

gboa

rd,

WM

S,

Ben

ton

Vis

ual

Form

D

iscr

imin

atio

n,

RA

VL

T.

Yes

T2:

TM

T A

&B

↓,

Ben

ton

Vis

ual

Form

D

iscr

imin

atio

n↓,

Gro

oved

peg

boar

d↓

T2:

Fem

ale

10.7

%↓

Mal

e 9.

9%↓

K. Bruce et al.


254

Ref

eren

ceSu

rger

y (n

umbe

r of

pa

tien

ts)

T1*

ho

urs

(h)

days

(d

)

T2/

T3*

w

eek

(w)

mon

th

(m)

year

(y

)

Defi

nit

ion

of

decl

ine†

NP

test

sC

ore

batt

ery

used

Cha

nge

in i

ndiv

idua

l N

P te

sts

Ove

rall

prev

alen

ce o

f co

gnit

ive

impa

irm

ent

(%)

Kei

zer

et a

l. (2

005)

CA

BG

(22

4)N

il3

m,

12 m

2,3,

7R

AV

LT

, St

ernb

erg

Let

ter

Can

cella

tion

Tes

t,

TM

T A

&B

, G

roov

ed

Pegb

oard

, St

roop

T

est,

Sym

bol

Dig

it M

odal

itie

s T

est,

Sel

f-or

deri

ng

Tas

ks.

No

Dat

a on

sta

tist

ical

ly

diff

eren

t ch

ange

s in

pe

rfor

man

ce o

n in

divi

dual

tes

ts w

as

not

prov

ided

.

T2:

(3

m)

>SD

=

10.5

%↓

>20%

=

31%

↓ R

CI

= 7.

7%↓

T3:

(12

m)

RC

I =

12.3

%↓

Kilo

et

al.

(200

1)O

n-pu

mp

CA

BG

(224

) O

ff-

Pum

p C

AB

G(8

4)

7 d

4 m

1M

MSE

, T

MT

A.

No

T1:

TM

T A

↔,

MM

SE↔

T2:

TM

T A

↔,

MM

SE↔

T1:

↔T

2:↔

Kne

ebon

e et

al.

(199

8)O

n-pu

mp

CA

BG

(74)

7 d

Nil

1,7

CV

LT

, Pu

rdue

Pe

gboa

rd,

CO

WA

T,

TM

T

A&

B,

Dig

it

Sym

bol,

Bos

ton

Nam

ing

Tes

t.

Yes

T1:

RC

I m

etho

d: P

urdu

e Pe

gboa

rd↓,

TM

T B

↓,

Dig

it S

ymbo

l↓,

Bos

ton

Nam

ing

Tes

t↓

T1:

RC

I 36

%

SD 0

%

Lew

is e

t al

. (2

006)

On-

pum

p C

AB

G(2

04)

1 w

Nil

2W

LT

, T

MT

A&

B,

Dig

it S

ymbo

l, C

OW

AT

, G

roov

ed

Pegb

oard

No

T1:

CE

RA

D↓,

TM

T

A&

B↓,

CO

WA

T↓,

G

roov

ed P

egbo

ard↓

T1:

2 t

ests

=

13.3

%↓

7 te

sts

= 49

.4%

↓ A

djus

ted

for

cont

rols

=

8%–

17.5

%↓

Mill

ar e

t al

. (2

001)

On-

pum

p C

AB

G(2

0)6

d6

m1

Stro

op T

est,

Bec

k D

epre

ssio

n In

vent

ory.

No

Pre-

exis

ting

cog

niti

ve

impa

irm

ent

and

depr

essi

on s

igni

fi can

t fa

ctor

s in

dec

line.

T1:

14%

↓T

2: 2

%↓

inde

pend

ent

of

depr

essi

on

and

exis

ting

im

pair

men

t

Tab

le I

. C

onti

nued



255

Mot

alle

bzad

eh e

t al

. (2

007)

On-

pum

p C

AB

G(1

04)

off-

pum

p C

AB

G(1

08)

7 d

6 w

, 6

m6

MC

G C

ompl

ex

Figu

re T

est,

G

roov

ed

Pegb

oard

, R

AV

LT

, L

ette

r C

ance

llati

on T

est,

Sy

mbo

l D

igit

M

odal

itie

s T

est,

V

erba

l Fl

uenc

y T

est

Yes

Dat

a on

sta

tist

ical

ly

diff

eren

t ch

ange

s in

pe

rfor

man

ce o

n in

divi

dual

tes

ts w

as

not

prov

ided

.

T1:

(1

w):

On-

pum

p↓ v

s of

f-pu

mp

T2:

(6

w):

↔T

3 :

(6 m

) :

↔

New

man

et

al.

(200

1)O

n-pu

mp

CA

BG

(261

)7

d6

w ,

6

m,

5 y

2R

andt

Mem

ory,

D

igit

Spa

n,

Ben

ton

Rev

ised

V

isua

l R

eten

tion

, D

igit

Sym

bol

Subs

titu

tion

, T

MT

B.

No

Dat

a on

sta

tist

ical

ly

diff

eren

t ch

ange

s in

pe

rfor

man

ce o

n in

divi

dual

tes

ts w

as

not

prov

ided

.

T1:

(1

w):

53

%T

2: (

6 w

):

36%

T3:

(6

m):

24

%T

4: (

5 y)

: 42

.5%

O’B

rien

et

al.

(199

2)O

n-pu

mp

CA

BG

(16)

va

lve(

4)10

d24

– 40 d

Oth

er‡

Dig

it S

pan,

CPT

, C

VL

T,

Vis

ual

Rep

rodu

ctio

n an

d L

ogic

al M

emor

y su

btes

ts o

f W

MS,

PE

RT

.

No

T1:

CV

LT

↓, C

PT↓,

T2:

CV

LT

↓T

1: ↓

T2:

↔

Ran

kin

et a

l. (2

003)

On-

pum

p C

AB

G

off-

pum

p C

AB

G

(34

tota

l)

Nil

10 w

5 an

d 6

Bos

ton

Nam

ing

Tes

t, C

OW

AT

, R

ey &

Tay

lor

Com

plex

Fig

ure

Tes

ts,

Judg

emen

t of

Lin

e O

rien

tati

on,

Dig

it

Span

, T

MT

A&

B,

Stro

op T

est,

C

VL

T,

Gro

oved

Pe

gboa

rd,

Ruf

f Fi

gura

l Fl

uenc

y,

MM

SE.

Yes

CFT

↑ (b

oth

on-

and

off-

pum

p)N

o si

gnifi

cant

de

clin

e in

of

f- o

r on

-pu

mp

CA

BG

Ras

mus

sen

et a

l. (2

004)

On-

pum

p C

AB

G

(253

6)7

d3

m5

Vis

ual

Ver

bal

Lea

rnin

g T

est,

C

once

pt S

hift

ing

Tes

t, S

troo

p T

est,

L

ette

r D

igit

C

odin

g T

est.

No

Dat

a on

sta

tist

ical

ly

diff

eren

t ch

ange

s in

pe

rfor

man

ce o

n in

divi

dual

tes

ts w

as

not

prov

ided

.

T1:

19.

7%↓.

T2:

14.

3%↓,

K. Bruce et al.


256

Ray

mon

d et

al.

(200

6)O

n-pu

mp

CA

BG

(74)

2 w

Nil

2,3,

7,8

Mic

roC

og

Ass

essm

ent

of

Cog

niti

ve

Func

tion

No

T1:

SR

B:

Info

rmat

ion

proc

essi

ng s

peed

↓,

Gen

eral

Cog

niti

ve

Func

tion

ing↓

All

met

hods

: A

tten

tion

/m

enta

l co

ntro

l↓

T1:

>1S

D =

3.

6%↓,

65

.5%

↑ >2

0% =

5.

5%↓,

69

.1%

↑ R

CI

= 16

.4%

↓,

<7%

↑ SR

B

= 32

.7%

↓,

<7%

↑R

osen

gart

et

al.

(200

6)O

n-pu

mp

CA

BG

(35)

3

w4

m1,

4,7

Dig

it S

pan,

Gro

oved

pe

gboa

rd,

Dig

it

Sym

bol,

TM

T

A&

B,

Stro

op

Tes

t, C

OW

AT

, V

isua

l N

amin

g of

th

e M

ulti

lingu

al

Aph

asia

Exa

m,

Hop

kins

Ver

bal

Lea

rnin

g T

est.

No

T1:

RC

I: V

isua

l N

amin

g of

the

Mul

tilin

gual

A

phas

ia E

xam

↓

T1:

↔T

2:↔

Seln

es e

t al

. (2

005)

On-

pum

p C

AB

G(1

40)

Nil

12, 36

m5

RA

VL

T,

RC

FT,

Bos

ton

Nam

ing

Tes

t, M

MSE

, T

MT

A&

B,

Wri

tten

Alp

habe

t,

Gro

oved

Pe

gboa

rd.

No

T2:

RA

VL

TI↑

T3:

RA

VL

TI↑

T2:

(12

m)

↔T

3: (

3 y)

↔

Silb

ert

et a

l. (2

001)

On-

pum

p C

AB

G(3

0)18

h,

5 d

Nil

2W

MS,

TM

T A

&B

, D

igit

Spa

n,

CO

WA

T.

Yes

Dat

a on

sta

tist

ical

ly

diff

eren

t ch

ange

s in

pe

rfor

man

ce o

n in

divi

dual

tes

ts w

as

not

prov

ided

.

T1:

18

hrs

30%

, 5

days

10%

Tab

le I

. C

onti

nued



257

Van

Dijk

et

al.

(200

2)O

n-pu

mp

CA

BG

(139

) of

f-pu

mp

CA

BG

(142

)

Nil

3, 12

m5

RA

VL

T,

Gro

oved

pe

gboa

rd,

TM

T

A&

B,

Ster

bery

M

emor

y C

ompa

riso

n, L

ine

Ori

enta

tion

Tes

t,

Stro

op T

est,

CPT

, Se

lf-o

rder

ing

task

s,

Vis

uosp

atia

l W

orki

ng

Mem

ory,

Dig

it

Sym

bol.

Yes

Dat

a on

sta

tist

ical

ly

diff

eren

t ch

ange

s in

pe

rfor

man

ce o

n in

divi

dual

tes

ts w

as

not

prov

ided

.

T1:

On-

pum

p 29

.2%

Off

-pu

mp

21.1

%T

2: O

n-pu

mp

33.6

% O

ff-

pum

p 30

.8%

Vin

gerh

oets

et

al.

(199

7)O

n-Pu

mp

CA

BG

(87)

va

lve(

18)

7–8

d6

m1

RC

FT,

RA

VL

T,

TM

T A

&B

, Pu

rdue

Peg

boar

d,

Dig

its

Tes

t an

d T

aps

Tes

t, S

troo

p C

olou

red-

Wor

d T

est,

Dot

C

ance

llati

on T

est,

L

ine

Bis

ecti

on

Tes

t, C

OW

AT

, T

oken

Tes

t.

Yes

, te

sts

used

but

no

m

enti

on

of

Con

sens

us

T1:

Lin

e B

isec

tion

↓,

RA

VL

T↓,

Tap

s T

est↓

, C

OW

AT

↑, T

MT

A↑,

T

oken

Tes

t↑T

2: C

FT↑,

TM

T A

↑,

CO

WA

T↑,

Str

oop

Tes

t↑

T1:

45%

T2:

12%

Zam

var

et a

l. (2

002)

On-

pum

p C

AB

G(3

0)

off-

pum

p C

AB

G(3

0)

7 d

10 w

2R

AV

LT

, T

MT

A

&B

, D

igit

Sy

mbo

l, D

igit

Sp

an,

Gro

oved

Pe

gboa

rd,

CO

WA

T.

Yes

T1:

On-

pum

p: G

roov

ed

pegb

oard

↓, D

igit

Sy

mbo

l↓T

2: O

n-pu

mp:

TM

T B

↓,

Gro

oved

peg

boar

d↓,

Dig

it S

ymbo

l↓

T1:

On-

pum

p 66

% O

ff-

Pum

p 27

%T

2: O

n-Pu

mp

40%

Off

-Pu

mp

10%

Zim

pfer

et

al.

(200

2)O

n-pu

mp

CA

BG

(30)

va

lve(

30)

7 d

4 m

1T

MT

A,

MM

SE.

No

T1:

TM

T A

↔,

MM

SE↔

T2:

TM

T A

↔,

MM

SE↔

T1:

↔

T2:

↔

† Defi

nit

ion

of D

eclin

e: 1

= 1

SD f

rom

ind

ivid

ual

base

line

perf

orm

ance

; 2

= 1S

D d

eclin

e of

20%

or

mor

e te

sts;

3 =

20%

dec

line

on 2

0% o

r m

ore

test

s, 4

= c

ompo

site

sco

re;

5 =

Rel

iabl

e C

hang

e In

dex;

6 =

Sta

ndar

d R

egre

ssio

n B

ased

, ‡ U

sed

t-te

sts

rela

tive

to

cont

rol

not

1SD

cha

nge

* T1,

sho

rt-t

erm

fol

low

-up

sess

ion;

T2,

ong

-ter

m f

ollo

w-u

p se

ssio

nC

ore

batt

ery:

Rey

Aud

itor

y V

erba

l L

earn

ing

Tas

k (R

AV

LT

), T

rail

Mak

ing

Tes

ts A

& B

, G

roov

ed P

egbo

ard

↔ N

o si

gnifi

cant

cha

nge,

↑Si

gnifi

cant

im

prov

emen

t fo

und

on t

est,

↓Si

gnifi

cant

dec

line

foun

d on

tes

t

K. Bruce et al.


258

pain and distress to the patient in the weeks after surgery (Mossad, Serkey, Longworth, Cosgrove, & Gordon, 1997; Stahle et al., 1997). Since per-formance on most neuropsychological tests is suboptimal if the subject is distracted or lacking in motivation, there is a high probability that some of the ‘cognitive impairment’ reported after cardiac surgery is due to an inability to fully con-centrate on the cognitive tasks. Furthermore, a number of cognitive tests (e.g. Rey Complex Figure Test, Grooved Pegboard) involve drawing or fi ne movement control. The present authors have observed that such tasks can be diffi cult to complete in the weeks immediately following a median sternotomy. Thus, if performance on these tests is worse than it was prior to surgery, it may be due to physical impairment rather than to cognitive impairment. Indeed, there is clear evidence that pain can disrupt attention and memory (Dick & Rashiq, 2007), reduce mental fl exibility (Karp et al., 2006), and increase emo-tional distress (which in turn negatively effects cognitive function) (Iezzi, Archibald, Barnett, Klinck, & Duckworth, 1999). It is the view of the present authors that pain and physical restriction following cardiac surgery has contributed to an overestimation of the extent of cognitive impair-ment that exists immediately after surgery. In addition, the majority of patients receive analge-sics post-operatively (generally opiates), which may also have adverse effects on their cognitive performance (Johnson et al., 2002; Wang, Sands, Vaurio, Mullen, & Leung, 2007). It is possible, therefore, that much of the ‘recovery’ in cognitive performance seen in the weeks and months after surgery is largely due to a reduction in pain and physical restriction and to withdrawal of analge-sia. This speculation needs to be confi rmed, but it raises the concern that any genuine cognitive impairment that exists a week after surgery has little prospect of recovery.

Neuropsychological testing following cardiac surgery

While there are a great many neuropsychological tests to choose from, studies of cardiac surgery are limited by practical considerations. Neuro-psychologists are generally not available at the bedside, so testing is often conducted by the surgeon or a nurse, which requires the battery of tests to be brief and basic. Furthermore, the tests

must be easy to conduct at the bedside and should display minimal practice effects (i.e. availability of alternate forms for repeat testing or choice of tests with no inherent learning), and they should have no linguistic or cultural bias. While these features represent the optimal properties for a test battery, researchers have not always operated within these constraints when constructing bat-teries of tests that are sensitive to performance in a range of cognitive domains (Table II).

Studies of post-operative cognitive impairment vary tremendously in terms of patient variables, surgical technique and assessment procedure. These variables make it diffi cult to directly compare individual studies or to derive meaning-ful trends. Differences in patient variables include age, education and severity of illness (Mahanna et al., 1996). Variables related to surgery include differences in the type of surgical technique and differences in the type and duration of anaesthe-sia used (Swearer, 2001). The third source of variation relates to differences in neuropsycho-logical assessment procedure such as the choice of tests, the criteria used for detecting and quan-tifying impairment, and the timing of post- operative cognitive testing (Kneebone, Andrew, Baker, & Knight, 1998; Murkin, 2001; Murkin, Newman, Stump, & Blumenthal, 1995; Raymond, Hinton-Bayre, Radel, Ray, & Marsh, 2006; Wu, Hsu, Richman, & Raja, 2004). The present review is primarily concerned with issues relating to differences in neuropsychological assessment protocols.

The fi eld is characterized by a lack of consensus or consistency concerning which tests to use, which cognitive domains to examine, what post-operative intervals to use when testing patients and even what constitutes cognitive impairment (Arrowsmith et al., 2000; Lewis et al., 2004). Furthermore, some studies that have utilized tests that while being quick and easy to perform (e.g. MMSE), are of limited use because they are rela-tively insensitive to cognitive change (Newman, 1995).

A consensus for assessment of cognitive function following cardiac surgery

In 1995 a ‘Statement of Consensus’ made recom-mendations about the design of neuropsycholog-ical test batteries used to assess cognitive impairment after cardiac surgery (Murkin et al., 1995). The consensus was drafted by researchers



259

Tab

le I

I. S

umm

ary

of c

ogni

tive

dom

ains

ass

esse

d in

car

diac

sur

gery

stu

dies

and

the

mea

sure

s us

ed t

o as

sess

the

m.

Cog

niti

ve

dom

ain

Des

crip

tion

of

cogn

itiv

e do

mai

nM

easu

res

used

to

asse

ss c

ogni

tive

im

pair

men

t fo

llow

ing

card

iac

surg

ery

Att

enti

on a

nd

conc

entr

atio

nT

he m

enta

l pr

oces

ses

of c

once

ntra

ting

eff

ort

on

a st

imul

us o

f a

men

tal

even

t. I

nvol

ves

a ra

nge

of p

heno

men

a in

clud

ing:

aro

usal

and

al

ertn

ess,

foc

usse

d, s

elec

tive

and

shi

ftin

g at

tent

ion,

and

con

scio

usne

ss a

nd a

war

enes

s.

Con

cept

Shi

ftin

g T

ask

Con

tinu

ous

perf

orm

ance

Tes

t (C

PT)

Dig

it-S

ymbo

l su

btes

t of

the

WA

ISD

ot C

ance

llati

on T

est

Lin

e B

isec

tion

Tes

tSe

lf-o

rder

ing

Tas

ksSt

ernb

erg

Let

ter

Can

cella

tion

Tes

tSt

roop

Tes

tSy

mbo

l D

igit

Mod

alit

ies

Tes

t*T

rail

Mak

ing

Tes

t (A

& B

) (T

MT

)W

ritt

en A

lpha

bet

Con

stru

ctio

nal

perf

orm

ance

The

set

of

proc

esse

s th

at f

acili

tate

the

co

mbi

ning

of

plan

ning

and

org

aniz

atio

nal

skill

s w

ith

perc

eptu

al a

bilit

ies

and

spat

ial

awar

enes

s.

Ben

ton

Vis

ual

Ret

enti

on T

est

Blo

ck D

esig

n su

btes

t of

the

WA

ISM

edic

al C

olle

ge o

f G

eorg

ia C

ompl

ex F

igur

es (

MC

G)

Rey

Com

plex

Fig

ure

Tas

k (R

CFT

)E

xecu

tive

fu

ncti

onT

he r

ange

of

com

plex

men

tal

proc

esse

s in

volv

ed

in t

he p

lann

ing,

org

aniz

ing

and

sequ

enci

ng o

f ta

sks,

and

the

con

trol

ling

and

regu

lati

on o

f be

havi

our.

Inc

lude

s th

e pr

oces

ses

requ

ired

for

go

al-d

irec

ted

beha

viou

r, a

nd f

or a

ntic

ipat

ion

and

adap

tati

on t

o ne

w s

itua

tion

s.

Beh

avio

ural

Dys

cont

rol

Scal

eC

once

pt S

hift

ing

Tas

kSt

roop

Tes

t*T

rail

Mak

ing

Tes

t (A

& B

) (T

MT

)

Gen

eral

co

gnit

ion

The

col

lect

ion

of m

enta

l fu

ncti

ons

and

acti

viti

es

acro

ss t

he f

ull

rang

e of

cog

niti

ve d

omai

ns.

Ble

ssed

Ori

enta

tion

-Mem

ory-

Con

cent

rati

on T

est

Mic

roC

og A

sses

smen

t of

Cog

niti

ve F

unct

ion

Min

i-M

enta

l St

ate

Exa

min

atio

n (M

MSE

)W

echs

ler

Adu

lt I

ntel

ligen

ce S

cale

Lan

guag

eT

he p

rodu

ctio

n an

d co

mpr

ehen

sion

of

lang

uage

at

the

lev

el o

f in

divi

dual

wor

ds,

sent

ence

s,

pass

ages

or

conv

ersa

tion

.

Bos

ton

Nam

ing

Tes

tC

ontr

olle

d O

ral

Wor

d A

ssoc

iati

on T

ask

(CO

WA

T)

Pict

ure

Nam

ing

*Rey

Aud

itor

y V

erba

l L

earn

ing

Tes

t (i

mm

edia

te a

nd r

ecen

t m

emor

y)(R

AV

LT

)T

oken

Tes

tV

erba

l Fl

uenc

y T

est

Vis

ual

Nam

ing

subt

est

of t

he M

ulti

lingu

al A

phas

ia E

xam

inat

ion

Voc

abul

ary

Info

rmat

ion,

Com

preh

ensi

on,

and

Sim

ilari

ties

sub

scal

es o

f th

e W

AIS

K. Bruce et al.


260

Cog

niti

ve

dom

ain

Des

crip

tion

of

cogn

itiv

e do

mai

nM

easu

res

used

to

asse

ss c

ogni

tive

im

pair

men

t fo

llow

ing

card

iac

surg

ery

Mem

ory

&

lear

ning

Men

tal

proc

esse

s in

volv

ed i

n th

e ac

quis

itio

n,

enco

ding

, st

orin

g an

d re

trie

val

of k

now

ledg

e.A

rith

met

ic T

asks

Ben

ton

Vis

ual

Ret

enti

on T

est

Cal

ifor

nian

Ver

bal

Lea

rnin

g T

est

(CV

LT

)D

igit

Spa

n, V

isua

l R

epro

duct

ion

and

Log

ical

Mem

ory

subt

ests

of

the

Wes

chle

r M

emor

y Sc

ale

(WM

S)L

ette

r D

igit

Cod

ing

Tes

tPi

ctur

e N

amin

gPu

blic

Eve

nts

Rec

all

Tes

t (P

ER

T)

Ran

dt M

emor

y T

est

*Rey

Aud

itor

y V

erba

l L

earn

ing

Tes

t (i

mm

edia

te a

nd r

ecen

t m

emor

y)(R

AV

LT

)R

ey C

ompl

ex F

igur

e T

est

(im

med

iate

and

rec

ent

mem

ory)

(R

CFT

)Se

rial

Dig

it L

earn

ing

Sym

bol

Dig

it M

odal

itie

s T

est

(im

med

iate

and

rec

ent

mem

ory)

Ver

bal

Mem

ory

Vis

uosp

atia

l W

orki

ng-M

emor

yV

isua

l V

erba

l L

earn

ing

Tes

tW

ord

Lea

rnin

g T

ask

(WL

T)

Mot

or s

kills

&

perf

orm

ance

The

pro

cess

es s

uppo

rtin

g m

otor

coo

rdin

atio

n an

d th

e sp

eed

of m

otor

fun

ctio

n.Fi

nger

Tap

ping

Tes

t*G

roov

ed P

egbo

ard

Purd

ue P

egbo

ard

Dex

teri

ty T

est

Rea

ctio

n ti

me

The

tim

e re

quir

ed t

o re

spon

d to

the

pre

senc

e of

a

stim

ulus

. R

eact

ion

Tim

e su

btes

t of

Mic

roC

og A

sses

smen

t of

Cog

niti

ve F

unct

ioni

ngSi

mpl

e R

eact

ionT

ime

Tes

tV

isua

l R

eact

ion

Tim

e T

est

Vis

uosp

atia

l fu

ncti

on &

V

isua

l pe

rcep

tion

The

men

tal

proc

esse

s in

volv

ed i

n th

e se

lect

ion,

or

gani

zati

on a

nd i

nter

pret

atio

n of

vis

ual

sens

ory

inpu

ts a

nd t

he s

pati

al r

elat

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261

with expertise in a range of disciplines including cognitive psychology and neuropsychology, epi-demiology, and biostatistics. It noted a need to include a baseline and control group for com-parison post-operatively, issues to consider when selecting an appropriate test, the optimal time to perform post-operative assessment, the impor-tance of including a mood state assessment, and advice regarding practice effects (which occur when the patient improves his or her outcome on a measure because of learning through practice).

After addressing the points mentioned earlier, the authors of the consensus recommended a core battery of four tests that could be used on its own or with other measures. The four core tests are the Rey Auditory Verbal Learning Task (RAVLT) (verbal memory), the Grooved Pegboard (motor skills) and the Trail Making Tests (TMTs) A & B (attention and concentration, and executive function, respectively). They were chosen because they can be standardized against a large bank of normative data, are easy to administer, have alternative forms available for repeat testing ses-sions and are known to be sensitive to cognitive changes following cardiac surgery (Murkin et al., 1995). These core tests have since been included in some research studies, either as the entire battery or as part of a larger battery (Table I).

There has not been widespread adherence to the consensus, however, and during the past decade, the majority of studies have not used the core test battery (Table I). While almost all of the studies reviewed (Table I) have used at least one of the tests from the recommended core battery, this is probably due to chance rather than design. Most of these papers did not cite Murkin et al. (1995) and instead stated that tests were chosen because of their ease of administration, reliability, suitability for the cognitive domains to be assessed or the availability of parallel forms. The lack of adherence may refl ect problems with the original proposals set out in the consensus. For instance, the consensus states the need for a baseline assess-ment, but some researchers have criticized this because there is a lack of comparative data from normal control groups of patients (Newman et al., 2006). The consensus also states the need for a control group, but there is no recommendation regarding which group to use (e.g. an age-matched group, a coronary artery disease-matched group, or a surgical control group) (Newman et al., 2006). The choice of control group will be dis-cussed in a later section.

Determining the incidence of post-operative cognitive impairment

The variability between studies regarding esti-mates of incidence of cognitive impairment after cardiac surgery is partly due to the variety of approaches used to defi ne post-operative cogni-tive change. Some approaches depend on the availability of pre-surgical test results, whereas others compare performance against population norms or the performance of a control group. Defi nitions of impairment have included:

• One standard deviation (SD) decline from the pre-operative test score on each test (Ebert et al., 2001; Keizer et al., 2005; Millar, Asbury, & Murray, 2001; Newman et al., 2001; O’Brien et al., 1992; Rosengart et al., 2006; Vinger-hoets, Van Nooten, Vermassen, De Soete, & Jannes, 1997).

• One SD from the pre-operative group mean on a specifi ed number of measures (i.e. usually ≥20 per cent or ≥2 tests) (Ho et al., 2004; Hogue et al., 2003; Silbert et al., 2001; Zamvar et al., 2002).

• 20 per cent decline from pre-operative test results on 20 per cent or more tests (Ho et al., 2004; Keizer et al., 2005; Van Dijk et al., 2002).

• One SD below published normative means for each test (Rosengart et al., 2006).

• Z-score: the mean difference between patient and control group is calculated and the z-score is determined by subtracting from it the mean learning effect in the control group and then dividing by the SD measured in the control group. Z-scores can be calculated for each test or each cognitive domain being assessed. Decline is defi ned by a cut-off value (e.g. Z ≥1.96) that can differ between studies (Ras-mussen, Siersma, & Ispocd, 2004; Selnes et al., 2005).

• Composite score: a combined score containing results from all or only some of the tests in the battery (Ho et al., 2004; McKhann et al., 1997; Motallebzadeh et al., 2007).

• Reliable Change Index (RCI): specifi es the degree of change from pre- to post-operative test results that is required to achieve a decline in performance that is statistically reliable after practice effects have been removed (Andrew, Baker, Kneebone, & Knight, 1998; Keith, Puente, Malcolmson, Tartt, & Coleman, 2002; Keizer et al., 2005; Kneebone et al.,

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1998; Raymond et al., 2006; Rosengart et al., 2006).

• Standardised Regression-based technique (SRB), a modifi ed z-score procedure that takes into account the change from baseline and the infl uence of any demographic variables chosen (Raymond et al., 2006).

This lack of concordance has itself contributed to the large variance in estimates of the incidence of cognitive impairment following cardiac surgery (Table I). Of the methods detailed earlier, the RCI and the SRBs are the most rigorous (Andrew et al., 1998; Keizer et al., 2005; Rosengart et al., 2006), as they account for the measurement error and practice effects that are a feature of repeated-measures tests (Jacobson & Truax, 1991; Knee-bone et al., 1998; Raymond et al., 2006). In a study by Kneebone et al. (1998) it was found that the incidence of cognitive impairment changed greatly with the defi nition of impairment that was used. For example, on one test no patients were classifi ed as showing post-operative decline using the SD method, whereas the RCI method demon-strated that 36 per cent of patients were impaired. In another study, the SRB and the RCI classifi ed more patients as being impaired than did the SD or the 20 per cent method on all tests except reac-tion time (Raymond et al., 2006). This lack of a difference on reaction times is to be expected. Since reaction time relies on the motor refl ex and does not involve practice effects, techniques that correct for practice effects should not yield different results from those that do not correct for practice effects.

Despite all of the limitations mentioned earlier, some trends have emerged from the studies we have reviewed (Table I). For instance, tests that have most commonly detected a defi cit include the Boston naming test, the visual naming test, the verbal fl uency test and the verbal learning test. Since all of these tests measure language profi -ciency, it appears that language is a domain that is frequently affected by cardiac surgery. Other tests that often detect post-operative impairment are the RAVLT, Digit Symbol and TMT. These tests are sensitive to impairments in several domains (Table II), but their area of commonality is concentration, making it more likely that this domain is affected. The grooved pegboard test, a measure of motor control, also features promi-nently among tests that have revealed impair-ment. This is noteworthy because movement is a domain that has been neglected by many studies.

Thus, language, concentration and motor control are the three domains most widely reported to be affected by cardiac surgery. It is likely, however, that other domains such as memory, attention and executive function are more frequently involved than the current data indicate, limita-tions being the lower proportion of studies that have investigated these domains and a lack of consistency in the tests used to assess these domains.

Future directions

The present review has highlighted the need for a more uniform approach to data analysis and for standardised defi nitions of cognitive impairment. New statistical methods that could aid in this regard are the reliable change index and the stan-dard regression-based method. A disadvantage of the reliable change index is that it requires an age-matched control group so that practice effects can be controlled for when examining data from repeated tests. The standard regression-based method does not require a control group if all of the tests used in the battery have test-retest reliability data available. This method also has the advantage of controlling for demographic variables such as age and education levels. None-theless, as noted earlier in this review, general anaesthesia and surgical trauma contribute to the cognitive impairment that is apparent during the fi rst week after surgery, independently of cardiac surgery. Therefore, the optimal experimental design would be to include a surgical control group and then use a battery of tests with good test-retest reliability so that the standard regres-sion-based method can be employed.

One domain that deserves more attention is executive function. Executive function is immensely important for daily function, as it underlies our ability to reason, to set goals, make corrective feedback and adapt to situations, and to develop strategies for problem solving. In the sample of 25 papers reviewed (Table I), the only tests of executive function used were the Trial Making Test and the Stroop test, and since these tests are also used to assess attention and concen-tration, it is diffi cult to ascertain the extent to which executive function was affected. To over-come the uncertainty in this area, future studies might include other measures of executive func-tion, such as the Wisconsin Card Sorting Test or the Category Test.



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Other aspects of cognitive function that have been overlooked are reaction time and response time. Reaction time is a measure of speed of refl ex reaction to a situation, while response time is a measure of the time taken to make a considered response to a situation. Both reaction time and response time are essential for the performance of everyday functions such as driving. However, only 1 of the 25 studies surveyed included a measure of reaction time and none examined response time. Such tests are readily available as quick, computer-based tests and could easily be included in future studies of cardiac surgery. It needs to be acknowl-edged, however, that one of the diffi culties facing researchers is that the individual examination of a large range of domains requires the use of a large number of tests, which takes time and can be impractical at the bedside. A way to circumvent this problem would be to screen patients with a single test that is sensitive to impairment in a wide range of domains or to defi cits in the processes that underlie general cognitive function (e.g. Subtle Cognitive Impairment Test (SCIT); Yelland, Rob-inson, Friedman, & Hutchison, 2004). Patients who are found to display such defi cits could then be tested on a battery of tests to determine the domains affected.

Another area requiring closer attention is the existence of pre-operative mood states such as depression and anxiety, since these are known to impair cognitive function (Lezak, 1995; Spernak, Moore, & Hamm, 2007). Andrew et al. (2001) revealed a signifi cant increase in the levels of anxiety after cardiac surgery. They showed that pre-operative mood was a strong predictor of post-operative mood, and that the majority of patients reporting elevated levels of depression, stress and anxiety had these symptoms pre- operatively. There are two important issues involved here. One is that mood disorders can confound measures of cognitive impairment (Ilsey, Moffoot, & O’Carroll, 1995; Murphy, Robbins, & Sahakian, 2003) and therefore they need to be controlled for. The second is the pos-sibility that pre-surgical anxiety or depression can affect the likelihood of post-surgical cognitive impairment (Andrew et al., 2001). This relation-ship might be amenable to pre-surgical interven-tion and may represent one way of lowering the incidence of post-surgical cognitive impairment. The consensus document suggested that a measure of mood state be included in assessment batteries (Murkin et al., 1995). However, only two of the 25 papers reviewed in Table I included an emo-

tional state assessment. Future studies could include a tool such as the Depression, Anxiety and Stress Scale, which is simple to conduct and would help to control for the confounding infl u-ence of abnormal mood states.

One of the promising new directions is the use of robot-assisted surgery for CABG. Robotic surgery requires the CPB machine but does not require median sternotomy, as access to the thorax is made via a keyhole incision. Robotic surgery results in less physical trauma and faster recovery (Childress, 2007; D’Attellis et al., 2002; Donias, Karamanoukian, D’Ancona, & Hoover, 2003; Jones, Krueger, Howell, Meinecke, & Dunn, 2005; Rayman, 2004; Reger & Janhke, 2003), but it is not yet known whether robotic surgery pro-vides cognitive benefi ts. Interestingly, robotic surgery offers the opportunity to investigate whether the pain and physical restriction caused by median sternotomy contributes to an overesti-mation of cognitive impairment in the weeks immediately after on-pump CABG surgery.

Despite the substantial technical advances in cardiac surgery over the past few decades, the incidence of permanent cognitive impairment remains alarmingly high. This brief review has shown that 10–40 per cent of patients who undergo cardiac surgery experience permanent defi cits in memory, attention and/or language, and the incidence of impairment may be found to be much higher than this once other areas of cognition such as response time and executive function have been considered. Valve surgery is generally associated with a worse outcome than CABG surgery, and it remains unclear whether the use of the CPB machine adversely affects cog-nitive outcome in patients undergoing CABG or valve surgery. There is an urgent need to identify the risk factors and surgical techniques that infl u-ence post-operative cognitive impairment, yet it is diffi cult to reach meaningful conclusions from the present data due to the widespread lack of concordance in experimental design and data analysis. To address this challenge, future research will need to control for confounds such as mood state, post-operative pain, learning effects, and anaesthesia and will need to compare a wide range of cognitive domains and surgical proce-dures within large multi-centre studies.

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The impact of cardiac surgery on cognition

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