The impact of cardiac surgery on cognition
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Transcript of 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
Copyright © 2008 John Wiley & Sons, Ltd. Stress and Health 24: 249–266 (2008)DOI: 10.1002/smi
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.
Copyright © 2008 John Wiley & Sons, Ltd. Stress and Health 24: 249–266 (2008)DOI: 10.1002/smi
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%
The impact of cardiac surgery on cognition
Copyright © 2008 John Wiley & Sons, Ltd. Stress and Health 24: 249–266 (2008)DOI: 10.1002/smi
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.
Copyright © 2008 John Wiley & Sons, Ltd. Stress and Health 24: 249–266 (2008)DOI: 10.1002/smi
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
The impact of cardiac surgery on cognition
Copyright © 2008 John Wiley & Sons, Ltd. Stress and Health 24: 249–266 (2008)DOI: 10.1002/smi
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.
Copyright © 2008 John Wiley & Sons, Ltd. Stress and Health 24: 249–266 (2008)DOI: 10.1002/smi
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
The impact of cardiac surgery on cognition
Copyright © 2008 John Wiley & Sons, Ltd. Stress and Health 24: 249–266 (2008)DOI: 10.1002/smi
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.
Copyright © 2008 John Wiley & Sons, Ltd. Stress and Health 24: 249–266 (2008)DOI: 10.1002/smi
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
The impact of cardiac surgery on cognition
Copyright © 2008 John Wiley & Sons, Ltd. Stress and Health 24: 249–266 (2008)DOI: 10.1002/smi
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.
Copyright © 2008 John Wiley & Sons, Ltd. Stress and Health 24: 249–266 (2008)DOI: 10.1002/smi
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
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The impact of cardiac surgery on cognition
Copyright © 2008 John Wiley & Sons, Ltd. Stress and Health 24: 249–266 (2008)DOI: 10.1002/smi
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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.
The impact of cardiac surgery on cognition
Copyright © 2008 John Wiley & Sons, Ltd. Stress and Health 24: 249–266 (2008)DOI: 10.1002/smi
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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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