Risk factors for deterioration of renal function after coronary artery bypass grafting.

Abstract

Various definitions of impairment of renal function after coronary artery bypass grafting (CABG) are used in the literature. Depending on the definition, several risk factors are identified. We analysed our data to determine the risk factors for postoperative deterioration of the creatinine clearance of 10% or more.
All patients undergoing isolated coronary surgery in a single centre between January 1998 and December 2007 are included. Clinical data, including demographics and renal risk factors, were prospectively collected in our database. The most recent preoperative serum creatinine level and the maximum serum creatinine level within the first week postoperatively were used to calculate the creatinine clearance. A deterioration of 10% or more was considered to be an endpoint for this study.
In 10098 out of a total of 10626 patients, the preoperative as well as the postoperative creatinine clearance could be calculated. In 1053 patients, the deterioration of the creatinine clearance was 10% or more. We could identify the following risk factors: advanced age, diabetes, chronic obstructive pulmonary disease, peripheral vascular disease, emergency operation, previous cardiac surgery, low preoperative haemoglobin level, high preoperative C-reactive protein level, perioperative myocardial infarction, re-exploration and the number of blood transfusions.
Risk factors for the deterioration of renal function after revascularisation have been confirmed in this study. In addition, we found peripheral vascular disease, previous cardiac surgery, low preoperative haemoglobin, increased preoperative C-reactive protein level, perioperative myocardial infarction and the number of blood transfusions to be risk factors that have not been described earlier.

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Risk factors for deterioration of renal function after coronary artery
bypass grafting
Albert H.M. van Stratena, Mohamed A. Soliman Hamada,*, Andre ´ A.A.J. van Zundertb,c,
Elisabeth J. Martensd,e, Jacques P.A.M. Scho ¨nbergera, Andre M. de Wolff
aDepartment of Cardio-Thoracic Surgery, Catharina Hospital, Eindhoven, The Netherlands
bDepartment of Anesthesiology, Catharina Hospital — Brabant Medical School, Eindhoven, The Netherlands
cUniversity Hospital Ghent, Ghent, Belgium
dDepartment of Education and Research, Catharina Hospital, Eindhoven, The Netherlands
eCenter of Research on Psychology in Somatic Diseases, Department of Medical Psychology, Tilburg University, The Netherlands
fDepartment of Anesthesiology, The Feinberg School of Medicine, Northwestern University, Chicago, IL, USA
Received 16 April 2009; received in revised form 23 June 2009; accepted 29 June 2009; Available online 20 August 2009
Abstract
Objective: Various definitions of impairment of renal function after coronary artery bypass grafting (CABG) are used in the literature.
Dependingonthedefinition,severalriskfactorsareidentified.Weanalysedourdatatodeterminetheriskfactorsforpostoperativedeterioration
of the creatinine clearance of 10% or more. Methods: All patients undergoing isolated coronary surgery in a single centre between January 1998
and December 2007 are included. Clinical data, including demographics and renal risk factors, were prospectively collected in our database. The
most recent preoperative serum creatinine level and the maximum serum creatinine level within the first week postoperatively were used to
calculatethecreatinineclearance.Adeteriorationof10%ormorewasconsideredtobeanendpointforthisstudy.Results:In10 098outofatotal
of 10 626 patients, the preoperative as well as the postoperative creatinine clearance could be calculated. In 1053 patients, the deterioration of
the creatinine clearance was 10% or more. We could identify the following risk factors: advanced age, diabetes, chronic obstructive pulmonary
disease, peripheral vascular disease, emergency operation, previous cardiac surgery, low preoperative haemoglobin level, high preoperative C-
reactive protein level, perioperative myocardial infarction, re-exploration and the number of blood transfusions. Conclusions: Risk factors for
the deterioration of renal function after revascularisation have been confirmed in this study. In addition, we found peripheral vascular disease,
previous cardiac surgery, low preoperative haemoglobin, increased preoperative C-reactive protein level, perioperative myocardial infarction
and the number of blood transfusions to be risk factors that have not been described earlier.
# 2009 European Association for Cardio-Thoracic Surgery. Published by Elsevier B.V. All rights reserved.
Keywords: Coronary artery bypass grafting; CABG; Database; Renal function
1. Introduction
Several risk factors for impairment of renal function after
coronary artery bypass grafting (CABG) have been identified,
of which female sex, age, diabetes mellitus, hypertension,
preoperative creatinine clearance (CrCl) <50 ml min?1,
impaired left ventricular function, need for intra-aortic
balloon pump (IABP) and re-exploration are most often
mentioned [1—4]. Several studies state that deterioration of
renal function occurs more often after conventional coronary
artery bypass operation with the use of extracorporeal
circulation (ECC) than after off-pump coronary artery bypass
(OPCAB) [5—9] although others could not confirm this
statement [3,4,10]. In addition, the use of aprotinin during
CABG has been identified as another important risk factor for
impairment of renal function [11,12]. Others could not
supportthisfinding[13,14].Variousdefinitionsofimpairment
of renal function after CABG are used in the literature. Some
authors use postoperative serum creatinine levels [5,6,10],
some with a cut-off value of 1.5 mg dl?1as an endpoint [6],
while others use CrCl as a postoperative marker for renal
function, with a cut-off point of 50 ml min?1as an endpoint
[4]. Sometimes, the postoperative CrCl is compared with the
preoperative value to indicate change in renal function
[4,15]. The Cockroft—Gault formula for CrCl [16] and the
modification of diet in renal disease (MDRD) formula for
estimated glomerular filtration rate (eGFR) [17] have been
usedtodeterminerenalfunction.Recently,thedeterioration
of renal function has been described as a predictor of poor
long-term survival [18]. We analysed our data to determine
risk factors for the deterioration of CrCl after CABG, adding
www.elsevier.com/locate/ejcts
European Journal of Cardio-thoracic Surgery 37 (2010) 106—111
* Corresponding author. Address: Department of Cardio-Thoracic Surgery,
Catharina Hospital, Michelangelolaan 2, Postbus 1350, 5602 ZA Eindhoven, The
Netherlands. Tel.: +31 40 239 86 80; fax: +31 40 244 02 68.
E-mail address: aasmsn@cze.nl (M.A. Soliman Hamad).
1010-7940/$ — see front matter # 2009 European Association for Cardio-Thoracic Surgery. Published by Elsevier B.V. All rights reserved.
doi:10.1016/j.ejcts.2009.06.048

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some variables which, to our knowledge, have not yet been
described as such.
2. Materials and methods
2.1. Patients
In this retrospective study, we analysed the data of all
patientsundergoingisolatedCABGwithorwithouttheuseof
ECC in a single centre (Catharina Hospital, Eindhoven, the
Netherlands) between January 1998 and December 2007.
Clinical data, including demographics and renal risk factors,
wereprospectively collectedinour database.Thestudy was
approved by the local Medical Ethics Review Committee.
2.2. Operative techniques
In CABG surgery, all patients received short-acting anaes-
thetic drugs to facilitate early extubation. Normothermic ECC
was performed using non-pulsatile flow. Cold crystalloid
cardioplegia (St Thomas’solution) or warm blood cardioplegia
was used to induce and maintain cardioplegic cardiac arrest,
accordingtothesurgeon’spreference.Allpatientsundergoing
CABG received a low dose of aprotinin (2 million kallikrein
inhibiting units) during ECC, administered to the prime
solution. The anaesthetic management in OPCAB surgery
was the same as in CABG surgery, but aprotinin was omitted.
2.3. Estimation of renal function
Creatinine clearance (CrCl) was determined using the
Cockroft—Gault formula [15], which is different for men:
[(140 ? age) ? weight/(serum
[(140 ? age) ? weight/(serum Cr ? 72)) ? 0.85]. The most
recent preoperative serum creatinine level and the maximum
serum creatinine within the first week postoperatively, or, if
sooner, before discharge, were used to calculate the CrCl and
the percentage change from the preoperative value. Patients
with preoperative CrCl below 15 ml min?1and those treated
with dialysis were excluded from this study. A deterioration of
10% or more was considered to be an endpoint for this study.
Cr ? 72)]andwomen:
2.4. Statistical analyses
Discrete variables were compared with the chi-square test
and are presented as percentages. Continuous variables were
compared with the Student’s unpaired t-test and univariate
logistic regression analyses wereperformedtoinvestigate the
impact ofbiomedical variables onrenal function. Ifsignificant
at p < 0.05, the variables were included into the multivariate
logisticregressionanalysesforrenalfunction.Ap-value<0.05
was used for all tests to indicate statistical significance. Odds
ratios(OR)witha confidenceinterval(CI)of95%withp-values
are reported. All statistical analyses were performed using
SPPS version 15.0 (SPSS Inc., Chicago, IL, USA).
3. Results
Between January 1998 and December 2007, a total of
10 626 patients underwent isolated CABG surgery with or
without ECC. Preoperative CrCl was not calculated in 432
patients due to emergency situation or missing records of
patient’sweight. PostoperativeCrCl wasnotcalculated in277
patients due to mortality before renal function could be
determined.Completedata wereobtainedin10 098patients.
Mean preoperative CrCl was 74.5 ? 24.4 ml min?1(range: 7—
308) (Fig. 1)and themean postoperativeCrClwas 79.2 ? 28.4
(Fig.2).DistributionofchangesinCrClisshowninFig.3.Eighty
patients required some form of renal replacement therapy
(continuous haemofiltration or dialysis). Deterioration of the
CrCl of 10% or more was found in 1053 patients.
Patients’ preoperative and perioperative demographic
and clinical characteristics stratified by the degree of
deterioration of CrCl are presented in Table 1.
A.H.M. van Straten et al./European Journal of Cardio-thoracic Surgery 37 (2010) 106—111
107
Fig. 2. Distribution of postoperative creatinine clearance (ml min?1).
Fig. 1. Distribution of preoperative creatinine clearance (ml min?1).

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Patients with a deterioration of CrCl of more than 10%
were older, more often had diabetes, a body mass index (BMI)
of more than 35 kg m?2, chronic obstructive pulmonary
disease (COPD), hypertension, peripheral vascular disease
(PVD), a left ventricular ejection fraction (EF) of less than
35%, an emergency operation, previous cardiac surgery and
more preoperative myocardial infarctions. The preoperative
haemoglobin (Hb) level as well as the preoperative CrCl was
lower whereas the preoperative C-reactive protein (CRP)
level was higher. Off-pump CABG was performed less often,
whereas the duration of ECC was longer. Complications such
as the need for intra-aortic balloon pump support, perio-
perative infarction and re-exploration for any cause were
more frequent. The number of red blood cell (RBC) units
transfused was higher.
3.1. Univariate analyses
Results of univariate logistic regression analyses to
identify risk factors for deterioration in CrCl of 10% or more
are shown in Table 2.
Preoperative significant risk factors were: advanced age,
diabetes,BMI>35 kg m?2,COPD,hypertension,PVD,number
of preoperative myocardial infarctions, EF <35%, emergency
operation, previous cardiac surgery, lower preoperative Hb
A.H.M. van Straten et al./European Journal of Cardio-thoracic Surgery 37 (2010) 106—111
108
Table 1
Demographic characteristics stratified by deterioration of creatinine clear-
ance.
Deterioration of creatinine
clearance
p-value
<10%, n = 9045
?10%, n = 1053
799 (75.9)
67.8 ? 9.4)
288 (27.4)
44 (4.3)
5 (0.5)
172 (16.3)
494 (46.9)
151 (14.3)
2.5 ? 1.3
71 (7.2)
139 (13.2)
0.53 ? 0.63
134 (12.7)
13.3 ? 1.6
16.4 ? 28.9
69.6 ? 27.9
70 (6.6)
455 (43.2)
478 (45.4)
63.7 ? 38.9
3.4 ? 1.2
91 (8.6)
90 (8.5)
162 (15.4)
3.25 ? 6.2
Male gender
Age
Diabetes
BMI >35 kg m?2
BMI <20 kg m?2
COPD
Hypertension
PVD
CCS class
EF <35%
Emergency
Number of preop MI
Redo
Preop Hb (g dl?1)
Preop CRP (mg l?1)
Preop CrCl (ml min?1)
OPCAB
Crystalloid cardioplegia
Blood cardioplegia
ECC-time
Number of grafts
IABP
Periop MI
Re-exploration
Number of RBC units
6998 (77.4)
64.2 ? 9.5
1839 (20.3)
192 (2.1)
44 (0.5)
1088 (12.0)
3711 (41.0)
1004 (11.1)
2.6 ? 1.2
265 (3.0)
227 (2.5)
0.48 ? 0.60
468 (5.2)
13.9 ? 1.3
10.4 ? 15.9
75.1 ? 23.9
825 (9.1)
3772 (41.7)
4090 (45.2)
57.0 ? 33.2
3.4 ? 1.1
111 (1.2)
196 (2.2)
374 (4.1)
0.75 ? 2.3
0.146
<0.0001
<0.0001
<0.0001
0.599
<0.0001
<0.0001
0.001
0.397
<0.0001
<0.0001
0.005
<0.0001
<0.0001
<0.0001
<0.0001
0.004
0.346
0.346
<0.0001
0.894
<0.0001
<0.0001
<0.0001
<0.0001
Results in numbers (percentage) of mean ? standard deviation.
BMI: body mass index; COPD: chronic obstructive pulmonary disease; PVD:
peripheral vascular disease; CCS class: Canadian Cardiovascular Society Func-
tional Classification of Angina; EF: left ventricular ejection fraction; preop MI:
preoperative myocardial infarction; Redo: previous cardiac surgery; preop Hb:
preoperative hemoglobin level; preop CRP: preoperative C-reactive protein
level; preop CrCl: preoperative creatinine clearance; OPCAB: off-pump cor-
onary artery bypass grafting; ECC-time: duration of extra-corporeal circula-
tion; IABP: intra-aortic balloon pump support; periop MI: perioperative
myocardial infarction; RBC: red blood cell.
Fig. 3. Percentage change in creatinine clearance.
Table 2
Univariate logistic regression analysis for deterioration of creatinine clearance
of more than 10%.
Risk factorOdds ratio (95% CI)p-value
Preoperative risk factors
Male gender
Age*
Diabetes
BMI >35 kg m?2
BMI <20 kg m?2
COPD
Hypertension
PVD
CCS class*
Number of preop MI*
EF <35%
Emergency
Redo
Preop Hb (g dl?1)*
Preop CRP (mg l?1)*
Preop CrCl (ml min?1)*
0.92 (0.79—1.06)
1.044 (1.036—1.051)
1.47 (1.27—1.70)
2.02 (1.44—2.82)
0.98 (0.38—2.47)
1.42 (1.19—1.70)
1.27 (1.11—1.41)
1.34 (1.11—1.61)
0.978 (0.929—1.030)
1.157 (1.046—1.280)
2.48 (1.89—3.26)
5.90 (4.73—7.37)
2.67 (2.18—3.27)
0.753 (0.719—0.788)
1.013 (1.009—1.016)
0.990 (0.987—0.993)
0.275
<0.0001
<0.0001
<0.0001
0.965
<0.0001
<0.0001
0.002
0.397
0.005
<0.0001
<0.0001
<0.0001
<0.0001
<0.0001
<0.0001
Peri- and postoperative risk factors
OPCAB
Crystalloid cardioplegia
ECC-time*
Number of grafts*
IABP
Periop MI
Re-exploration
No of blood transfusions*
0.71 (0.55—0.91)
1.03 (0.90—1.18)
1.005 (1.003—1.007)
0.996 (0.941—1.054)
7.61 (5.72—10.12)
4.21 (3.25—5.46)
4.21 (3.46—5.13)
1.196 (1.173—1.220)
0.008
0.648
<0.0001
0.894
<0.0001
<0.0001
<0.0001
<0.0001
CI: confidence interval; BMI: body mass index; COPD: chronic obstructive
pulmonary disease; PVD: peripheral vascular disease; CCS class: Canadian
Cardiovascular Society Functional Classification of Angina; preop MI: preo-
perative myocardial infarction; EF: ejection fraction; Redo: previous cardiac
surgery; preop Hb: preoperativehemoglobin level; preop CRP: preoperativeC-
reactive protein level; preop CrCl: preoperative creatinine clearance; OPCAB:
off-pump coronary artery bypass; ECC: extra-corporeal circulation; IABP:
intra-aortic balloon pump; periop MI: perioperative myocardial infarction.
*Entered as a continuous variable.

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level, higher CRP and lower preoperative CrCl. On the other
hand, sex, BMI of <20 kg m?2and functional angina class
(CCS) were not identified as risk factors. Significant peri- and
postoperative risk factors were CABG versus OPCAB, duration
of ECC, the need for IABP, perioperative myocardial
infarction, re-exploration for any cause as well as the
number of perioperative RBC unit transfusions. The type of
cardioplegia and the number of grafts were not identified as
risk factors.
3.2. Multivariate analyses
All statistically significant preoperative risk factors
identified with univariate regression analyses were entered
into a multivariate logistic regression analysis. Results of
these analyses are shown in Table 3.
Independent preoperative risk factors were advanced
age,diabetes,PVD,emergency
cardiac surgery, lower Hb level, higher CRP level and
lower preoperative CrCl. Peri- and postoperative risk
factors were added to the multivariate model when
identified to be significant using the univariate logistic
regression analyses. The following factors were identified
as independent risk factors (Table 4): advanced age,
diabetes, COPD, PVD, emergency operations, previous
cardiac surgery, lower preoperative Hb level, higher
preoperative CRP level, perioperative myocardial infarc-
tion, re-exploration for any cause and the number of RBC
unit transfusions.
operation,previous
4. Discussion
In this retrospective single-centre study of more than
10 000 patients, we found several independent risk
factors for the deterioration of renal function after CABG.
Some of them are in agreement with the previously
reported findings whereas others are not. This might be
explained by the different definitions of deterioration of
renal function.
4.1. Definition of the study endpoint
The need for dialysis [14,20], a postoperative creatinine
level of >2.1 mg dl?1[19] or a postoperative CrCl less than
50 ml min?1[4] are examples of study endpoints commonly
used.However,inpatientswithpreoperativeimpairedrenal
function, only a small extra damage is needed to reach the
study endpoint. Patients with preoperative normal renal
function may experience severe damage of the kidneys
beforetheyreachthestudyendpoint.Consequently,inallof
these studies, the preoperative renal function, whether
definedbythecreatininelevelorCrCl,hasbeenidentifiedas
a risk factor for reaching the study endpoint. In studying
renal impact factors, changes in renal function not reaching
the previously described endpoints might be important as
well.
Creatinine clearance (CrCl) calculated by the Cockroft—
Gault formula has been described as a better indicator for
renal function than serum creatinine level in patients
undergoing CABG [21]. Therefore, we defined renal impair-
mentasa10%ormoredeteriorationofthepreoperativeCrCl.
Thus, we were able to describe risk factors for minor changes
in renal function. Even minor deterioration of renal function
inpatientswithalreadyimpairedrenalfunctionmightleadto
clinical problems [18]. The clinical significance of the 10%
deterioration in renal function is possibly only obvious in
patients with preoperative renal impairment. Furthermore,
it seems reasonable to assume that the same risk factors may
also play a role in more pronounced deterioration of renal
function.
A.H.M. van Straten et al./European Journal of Cardio-thoracic Surgery 37 (2010) 106—111
109
Table 3
Multivariate analysis of preoperative risk factors.
Preoperative risk factorsOdds ratio (95% CI)p-value
Age*
Diabetes
BMI >35 kg m?2
COPD
Hypertension
PVD
Number of preop MI*
EF <35%
Emergency
Redo
Preop Hb (g dl?1)*
Preop CRP (mg l?1)*
Preop CrCl (ml min?1)*
1.044 (1.029—1.060)
1.59 (1.28—1.98)
1.62 (0.94—2.79)
1.28 (0.99—2.79)
1.19 (0.97—1.45)
1.33 (1.03—1.74)
1.159 (0.991—1.356)
1.53 (0.96—2.45)
4.57 (2.44—8.57)
2.51 (1.76—3.58)
0.858 (0.799—0.921)
1.007 (1.003—1.012)
0.999 (0.993—1.004)
<0.0001
<0.0001
0.079
0.056
0.083
0.029
0.065
0.070
<0.0001
<0.0001
<0.0001
0.001
<0.0001
CI: confidence interval BMI: body mass index; COPD: chronic obstructive
pulmonary disease; PVD: peripheral vascular disease; EF: left ventricular
ejection fraction; Redo: previous cardiac surgery; preop Hb: preoperative
hemoglobin level; preop CRP: preoperative C-reactive protein level; preop
CrCl: preoperative creatinine clearance.
*Entered as a continuous variable.
Table 4
Multivariate logistic regression analyses including peri- and postoperative risk
factors.
Odds ratio (95% CI)p-value
Preoperative risk factors
Age*
Diabetes
BMI >35 kg m?2
COPD
Hypertension
PVD
Number of preop MI*
EF <35%
Emergency
Redo
Preop Hb (g dl?1)*
Preop CRP (mg l?1)*
Preop CrCl (ml min?1)*
1.048 (1.032—1.065)
1.70 (1.36—2.13)
1.60 (0.92—2.79)
1.36 (1.04—1.78)
1.22 (0.99—1.50)
1.35 (1.03—1.78)
1.162 (0.989—1.366)
1.53 (0.94—2.51)
2.19 (1.061—4.53)
2.05 (1.39—3.02)
0.887 (0.824—0.954)
1.008 (1.003—1.012)
1.002 (0.996—1.008)
<0.0001
<0.0001
0.095
0.024
0.059
0.028
0.067
0.086
0.034
<0.0001
0.001
0.001
0.499
Peri- and postoperative risk factors
OPCAB
ECC-time*
IABP
Periop MI
Re-exploration
No of RBC units*
1.04 (0.70—1.57)
1.000 (0.997—1.003)
1.77 (0.88—3.57)
2.83 (1.82—4.39)
2.49 (1.69—3.65)
1.152 (1.107—1.199)
0.817
0.879
0.105
<0.0001
<0.0001
<0.0001
BMI: body mass index; CI: confidence interval; COPD: chronic obstructive
pulmonary disease; ECC-time: duration of extra-corporeal circulation; EF:
ejection fraction; IABP: intra-aortic balloon pump support; OPCAB: off-pump
coronary artery bypass grafting; PVD: peripheral vascular disease; preop MI:
preoperative myocardial infarction; Redo: previous cardiac surgery; preop Hb:
preoperative haemoglobin level; preop CRP: preoperative C-reactive protein
level; preop CrCl: preoperative creatinine clearance; periop MI: perioperative
myocardial infarction; RBC: red blood cells.
*Entered as a continuous variable.

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4.2. Risk factors
In agreement with others, we found several independent
preoperative risk factors: age used as a continuous variable
[4,15,19,20], diabetes [15,20], COPD [20], emergency
operations [20] and re-exploration for any cause [4]. Other
independent risk factors, which, to our knowledge, have not
been described, were PVD, previous cardiac surgery, the
preoperative Hb and CRP levels, perioperative myocardial
infarction and the number of blood transfusions. Risk factors
described by others that could not be confirmed in this study
were EF [6,15], preoperative CrCl [4,6,15,19], preoperative
angina class [19], BMI <20 kg m?2[4], the need for IABP [4],
duration of ECC [19], the number of grafts [6] and female sex
[4]. In contrast with other investigators [5—8], OPCAB was
notsuperiortoCABGinpreservingrenal functioninourstudy.
This is in agreement with the findings of others [3,4,10]. The
use of aprotinin could have even exaggerated the negative
effect of ECC on postoperative renal function [11]. As stated
earlier, discrepancies in identified risk factors might at least
partly be explained by different definitions of renal
dysfunction. Already impaired renal function is mentioned
in most studies [4,6,15,19] as a risk factor for developing
renal insufficiency after cardiac surgery. This seems logical
when renal insufficiency is defined as the need for dialysis or
a CrCl of less than 50 ml min?1. In our study, using a 10% or
more deterioration of the preoperative CrCl as an endpoint,
we could not identify the preoperative CrCl as an indepen-
dent risk factor. We also noticed an improvement in the mean
valueofCrClincomparison with thepreoperativevalue. Only
10.4% of the whole patient population had postoperative
deterioration of CrCl. In the rest of the patients, CrCl either
deteriorated with <10% or even improved postoperatively.
This can possibly explained by haemodilution that is usually
observed in the perioperative period [9]. Some of the risk
factors that were identified in this study, for example,
diabetes and peripheral vascular disease, cannot be cor-
rected preoperatively. These risk factors can be used for risk
stratification and informing the patients. Others, such as
preoperative Hb and CRP level and the number of blood
transfusions, can be corrected. Further studies are needed to
investigate whether measures to correct preoperative Hb
and CRP level and avoidance ofblood transfusions will lead to
better preservation of renal function.
5. Conclusions
In this retrospective single-centre study of more than
10 000 patients, we could identify the following risk factors
for a deterioration of 10% or more of the preoperative CrCl:
advanced age, diabetes, COPD, peripheral vascular disease,
emergency operation, previous cardiac surgery, low pre-
operative Hb, high preoperative CRP, perioperative myocar-
dial infarction, re-exploration and the number of blood
transfusions.
5.1. Limitations of the study
This study had a retrospective design. Some patients
were lost to follow up and some data were unobtainable,
making results less accurate. The use of intra-operative
and postoperative medications that can affect the renal
function such as diuretics and inotropic support was not
registered.
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