Research Article
Off-Pump vs On-Pump Complete Coronary Revascularization: Comparison of the Effects on the Renal Damage in Patients with Non- Dialysis Dependent Renal Dysfunction
Umit Arslan* and Bilgehan Erkut
Department of Cardiovascular Surgery, Atatürk University, Turkey
*Corresponding author: Umit Arslan, Department of Cardiovascular Surgery, Atatürk University, Erzurum, Turkey
Published: 06 Jun, 2018
Cite this article as: Arslan U, Erkut B. Off-Pump vs
On-Pump Complete Coronary
Revascularization: Comparison of
the Effects on the Renal Damage in
Patients with Non- Dialysis Dependent
Renal Dysfunction. Clin Surg. 2018; 3:
1977.
Abstract
Objective: We aimed to compare off-pump technique with on-pump technique on renal function in
patients with non-dialysis-dependent renal dysfunction who underwent CABG.
Introduction: Preoperative non-dialysis-dependent renal dysfunction is a predictor of renal failure
in patients undergoing CABG with CPB. Off-pump coronary revascularization has been shown to
be less deleterious than on-pump bypass in patients.
Methods: The 94 patients with renal dysfunction undergoing isolated coronary artery bypass
grafting were retrospectively analyzed. No patient was receiving dialysis. Patients were randomly
assigned to conventional revascularization with CPB and beating heart. Both groups were compared
in terms of renal dysfunction parameters and dialysis requirement. The logistic regression models
were constructed to identify risk factors associated with dialysis requirement.
Discussion: Renal dysfunction requiring dialysis developed in 9 patients in the on-pump group. The
measures analysis of variance was performed on the data that showed worsening of renal function in
the on-pump group compared with the off-pump group. CPB is significant as independent predictor
for the development of postoperative dialysis.
Conclusion: These results suggest that off-pump coronary revascularization offers a superior renal
protection and has a significantly lower risk for renal complications in patients with non-dialysisdependent
renal dysfunction when compared with conventional coronary revascularization with
CPB.
Keywords: On and off-pump coronary revascularization; Coronary artery bypass grafting;
Renal insufficiency; Requiring dialysis; Surgical complications
Introduction
Despite improvements in surgical techniques, postoperative renal dysfunction remains a serious
complication of coronary revascularization surgery and is associated with significant increases in
morbidity and mortality, whether it is dialysis-dependent or not. It has been reported that acute
renal failure requiring dialysis develops in 2% to 7% of cardiac surgery patients [1-6]. Although the
cause is multi factorial and depends on the patient’s clinical status, Cardiopulmonary Bypass (CPB)-
related events, hypotension, renal hypo perfusion, hypothermia, micro emboli events in the renal
vasculature, non-pulsatile flow, hemolysis, stimulation of the inflammatory response, and increased
levels of circulating catecholamines, cytokines, and free hemoglobin may contribute significantly
to this condition [7,8]. Furthermore, the use of aortic cross-clamping and cardioplegic arrest can
result in myocardial dysfunction, which can lead to renal perfusion defects and subsequent renal
impairment [9,10]. However, the explicit contribution of these factors still remains unclear and
needs to be fully elucidated.
These effects result in damage to glomerular as well as tubular structures that, in turn, can produce
renal dysfunction especially in the presence of additional risk factors. The renal risk associated with
CPB may be avoided by a new surgical technique, off-pump coronary revascularization, which is
performed on the beating heart and hence does not use CPB [11].
Off-pump coronary revascularization is known to eliminate
several CPB-linked non-physiological conditions. Due to the fact
that off-pump coronary revascularization eliminates the use of CPB
and cardioplegia, the CPB- and cardioplegia associated morbidity
and mortality risks are significantly reduced compared to patients
undergoing conventional on-pump coronary revascularization.
Recently, the benefits of off-pump coronary revascularization have
been well established, and several studies have revealed that off-pump
coronary revascularization has better outcomes in patients with renal
dysfunction than conventional on-pump coronary revascularization
[12-14]. However, studies conducted previously in this field have
provided conflicting evidence to support this hypothesis, and the data
on this topic remain contradictory [8,15-18].
This randomized study was to assess the impact of the off-pump
coronary revascularization technique on the incidence and severity of
renal dysfunction according to on-pump coronary revascularization
technique in patients with preoperative non–dialysis-dependent
renal insufficiency. The renal functions have been defined according
to the levels of serum blood urea nitrogen, creatinine clearance
and glomerular filtration rate called glomerular filtration markers.
Besides, independent risk factors associated with requiring dialysis
were identified.
Materials and Methods
This study was designed to compare the effect of off-pump and onpump
coronary artery bypass grafting (CABG) techniques on renal
function in patients with non–dialysis-dependent renal insufficiency.
In this retrospective study, from May 2014 through June 2015, 94
consecutive patients with preoperative non–dialysis-dependent
renal insufficiency was performed primary, isolated, non emergent
coronary surgery. Patients were prospectively randomized on the
day before their operation into two groups by card allocation. Group
on the pump (n=48) had conventional myocardial revascularization
with CPB and cardioplegic arrest of the heart, whereas group off the
pump (n=46) had to beat heart revascularization. Each on-pump and
off-pump coronary revascularization was performed with the goal of
achieving complete surgical revascularization. Patients were assigned
to one of the surgical techniques according to clinical indications
as well as to the surgeon’s decision to use the off-pump or the
conventional on-pump approach.
The preoperative demographics, operative variables, operative
morbidity and mortality, short-term survival, cardiac-related event,
postoperative renal parameters, requiring dialysis and postoperative
data were compared between the 2 groups. The preoperative data
and values indicating the preoperative renal dysfunction were shown
in Table 1. Factors looked at were considered to be good predictors
of postoperative renal complications as postoperative Blood Urea
Nitrogen (BUN), creatinine, creatinine clearance, Glomerular
Filtration Rate (GFR) and requiring dialysis. After comparing renal
dysfunction associated with parameters and requiring dialysis
between groups, risk factors associated with requiring dialysis were
determined by logistic regression analysis.
In our study, data was collected from patients’ case notes in the
Medical Records Office. The data were prospectively collected and
recorded by clinical cardiology and cardiac surgeon. The study was
approved by the Erzurum Regional Training and Research Hospital
Ethics Committee. The local institutional review board approved
this study and waived the need for informed consent. The study is in
accordance with the declaration of Helsinki.
Data definition
BUN is an indication of renal kidney health. The reference range
of the BUN level is 10 mg/dL to 50 mg/dL. Individual laboratories may
have different reference ranges, since the procedure may vary. BUN
levels of >50 mg/dL or least a 20% increase without requiring dialysis
was considered renal dysfunction. The reference ranges of serum
creatinine in our laboratory were 0.4 mg/dl to 1.1 mg/dl. Creatinine
levels of >1.5 mg/dL or least a 20% increase without requiring
dialysis was considered renal dysfunction. Creatinine clearance
was calculated using the Cockcroft and Gault Formula: (140-age) x
kg/serum creatinine (mg/dL) x 72), and reference ranges of serum
creatinine clearance in our laboratory was 80-120 ml/min-1/1.48 m-2.
Creatinine clearance ≤ 60mL/dk/1.73 m-2 or decreases of 50% or
higher without requiring dialysis was considered renal dysfunction.
The GFR was measured with the MDRD equation (mL/min-1/1.73
m-2). The variables included were age, sex, height in centimeters, and
weight in kilograms for body surface area calculation, BUN, serum
creatinine, and serum albumin. The formula used is as follows.
170 x (Cr) -0.999x (Age) -0.716 x (BUN) -0.070 x (Alb)+0.318
for male patients 170 x (Cr) -0.999x (Age) -0.716 x (BUN) -0.070 x
(Alb)+0.318 x (0.762) for female patients. These stages are defined
by a GFR greater than or equal to 90 (stage 1), 60 to 89 (stage 2),
30 to 59 (stage 3), 15 to 29 (stage 4), and less than 15 (stage 5).
Generally, decreases of 50% or higher in the GFR was considered
renal dysfunction. These parameters were measured postoperatively
at day 7 and confirmed in at least two measurements.
Non-requiring dialysis renal dysfunction: BUN levels; 30 mg/dL
to 60 mg/dL, median GFR; stage I, creatinine levels; 1.3 mg/dL to 1.7
mg/dL, creatinine clearance; 40 mL/min to 70 mL/min.
Requiring dialysis
Acute renal dysfunction was classified on the basis of RIFLE
(Risk, injury, failure, loss, ESRD) criteria [19]. Postoperative dialysis
was indicated if they had diuretics-resistant oliguria associated with
volume overload or hyperkalemia. Postoperative renal failure was
defined as either a requirement of hemodialysis to support renal
function, an increase in serum creatinine greater than 1.5 mg/dl
postoperatively, or an occurrence of oliguria (< 0.5 ml/kg-1/min-1)
for more than 6 hr.
Postoperatively, all patients were admitted to the intensive care
unit (ICU), and received standardized treatment. Anesthesia was
maintained in all patients with propofol (100 mg/h) for no longer
than 24 hr postoperatively. When longer anesthesia was required,
propofol was switched to sufentanil (0.02 mg/h) and midazolam
(5 mg/h). The fluid substitution was adjusted to a central venous
pressure of 12 mmHg. The target level for the mean arterial pressure
was ≥ 70 mmHg. Crystalloid fluids and inotropes were administered
in the case of lower mean arterial pressure according to the specific
clinical situation. In the absence of hemorrhage, intravenous heparin
was applied for 2 hr and 500 mg of intravenous acetylsalicylic acid 4
hr after arrival on the ICU. In-hospital outcomes were collected from
the medical records. Post discharge outcomes were collected from the
medical records and telephone interviews. These data were complete
for all patients until discharge from hospital or death.
Exclusion criteria
Patients who underwent combined procedures were excluded.
Exclusion criteria were patients with mechanical complications
of myocardial infarction such as ventricular septum defect,
papillary muscle rupture, mitral valve regurgitation, and patients
with cardiogenic shock persisting for a length of 24 hr. Besides,
it included impaired left ventricular function as assessed by
angiography (ejection fraction < 30%), patients with requiring
chronic dialysis patients, oliguria and anuria, high serum creatinine
level (≥ 2.5 mg/dl), emergency surgery or reoperation, respiratory
impairment, and coagulopathy. All patients in both groups received
600 mg of N-acetylcysteine orally once daily immediately before
revascularization and for the first 5 postoperative days. None of the
patients received amino glycosides or non steroidal anti-inflammatory
agent's perioperatively.
Anesthesia
Anesthetic technique was standardized for all patients and
consisted of intravenous anesthesia with propofol infusion at 3 mg/
kg per hour combined with remifentanil infusion at 0.5 mg/kg to 1
mg/kg per minute. Neuromuscular blockade was achieved by using
0.1 mg/kg to 0.15 mg/kg pancuronium bromide or vecuronium,
and the lungs were ventilated to normocapnia with air and oxygen
(45% to 50%) without positive end-expiratory pressure. Off-pump
surgery was performed at a mean arterial pressure between 70 mmHg
and 100 mmHg. Deviations beyond this range were corrected with
phenylephrine or nitroglycerine. If necessary, esmolol hydrochloride
(11 mg/kg) was used to maintain a heart rate less than 70 beats per
minute.
Surgical techniques
All patients underwent surgical revascularization through a
median sternotomy. Conduits were harvested and prepared. The
arterial conduits (internal mammalian artery) were harvested with
pedicle preparation technique using surgical electrocautery for left
anterior descending artery anastomosis. Saphenous vein grafts were
harvested with the open method using fine scissors, and they were
used generally other cardiac coronary anastomosis. Two surgeons
completed all procedures. The daily operation schedule, which
established the order of all surgical procedures and scheduled the
surgeons to these procedures, assigned patients to one of the two
surgeons and by this means to either the off-pump or on-pump
technique. A deep posterior pericardiotomy was carried out to
allow for rigorous exposure of the heart without hemodynamic
compromise. In both groups, a minimal dose of catecholamines was
used to maintain a cardiac index of greater than 2.0 L/min-1/m-2
and systolic blood pressure of greater than 80mmHg after surgery.
Intravenous diltiazem and nitroglycerin were administered routinely
in the ICU.
Conventional CABG
Before CPB was initiated, heparin sodium was administered at an
initial dose of 300 IU/kg. Additional heparin was administered if the
ACT became less than 500s. CPB was instituted by using ascending
aortic cannulation and a two-stage venous cannulation in the right
atrium. The aorta was cross-clamped, and myocardial protection
was achieved with intermittent antegrade and retrograde blood
cardioplegia. A standard circuit was used, including a Bard tubing
set, which included a 40-m filter, a roller pump, and a hollow fiber
membrane oxygenator. During CPB, the hematocrit was maintained
between 18% and 25%, perfusion flows were kept between 2.2 and 2.8
L/min-1/m-2, and mean arterial pressure was maintained between
50 mmHg and 70 mmHg. A 1000-mL cold cardioplegic solution
(Custodiol®, Alsbach-Hahnlein, Germany) was infused through the
aortic root to achieve cardioplegia during aortic cross-clamping. The
non pulsatile flow was used. Antegrade and/or retrograde cold blood
cardioplegia was used to induce cardiac arrest, which was maintained
by serial administration of additional aliquots at 15-min intervals.
The systemic temperature was maintained between 30°C and 34°C.
Once all distal anastomoses were completed, the aortic cross-clamp
was removed and the proximal anastomosis performed with partial
clamping. The distal anastomoses were constructed with running
sutures of 7-0 or 8-0 polypropylene, and the proximal anastomoses
were connected to the ascending aorta with 5-0 or 6-0 polypropylene
sutures during a single cross clamping period. After the patient
was weaned from CPB and decannulated, heparin was completely
neutralized using protamine (1/1.5 rate; Valeant, Eschborn,
Germany). Epicardial pacemaker wires were inserted on the surface
of the right ventricle for the heart rate manipulations, then the heart
was filled with volume adequately and the table broke for variable
"head down" Trendelenburg position manipulations.
Off- pump beating-heart technique
After cardiac stabilization, the operation was continued with
the assisted beating heart. The temperature of patients was kept
approximately 36°C without cooling (normothermic). After
mediastinal entry, deep pericardial sutures were placed to lift the
myocardial apex and facilitate exposure to the posterior and lateral
aspects of the myocardium. The distal anastomoses were constructed
before the proximal anastomoses. The left anterior descending
artery was re-vascularized first with the internal mammalian artery,
followed by the circumflex and right coronary arteries. Stabilization
during distal anastomosis was performed using the Octopus®
stabilizing system (Medtronic Inc, Minneapolis, MN, USA), and
if found necessary by the surgeon, Starfish heart suction stabilizer
of the same manufacturer was used for additional traction and
stabilization, prominently for the exposure of the circumflex region.
Silicon suture applied proximally and distally to the site selected
for the anastomosis and a surgical blower humidifier (Visu-Flow,
Research Medical, Midvale, UT, USA) were used for visualization
of the surgical field. Systolic arterial pressures were maintained at
a minimum of 70 mmHg during distal anastomoses using venous
volume regulation, rate control, inotropic agents, or vasoconstrictors.
Distal anastomoses were made with running sutures of 7-0 or 8-0
polypropylene. Intracoronary shunts were not used routinely during
the distal anastomoses. In compliance with international experience,
ischemia or hypotension was addressed by volume, heart rate,
inotrope or beta-blocker-based manipulations and short release of
too vigorous exposure and torsion. After each distal anastomoses,
perfusion was maintained with warm blood through the pump by
using anastomosed saphenous veins. Proximal anastomoses were
performed with a side-biting aortic clamp, with systemic pressures
that were dictated by individual surgeon preference. These patients
received heparin sodium (150 IU/kg) before the anastomosis and
the elite-activated clotting time was maintained at more than 300 s.
Normothermia was maintained by using warm intravenous fluids, a
heating mattress, and a humidified airway, in addition to maintaining
a warm operating theater. Postoperatively, whole blood or packed red
blood cells were transfused to all patients whose hemoglobin value
was less than 9 mg/dL.
Statistical analysis
Values of continuous variables are expressed as mean ± standard
deviation (SD). Student’s t-test and Mann-Whitney test were used to
analyze continuous variables. The categorical or dichotomous data
were presented in percentages (%) and compared by the Chi-square
or Fisher's exact test, and p values of 0.05 or less were considered
significant.
A univariate logistic regression analysis was performed to identify
significant predictors associated with preoperative factors. Besides,
the multivariable logistic regression analysis was used to identify
independent risk factors for requiring dialysis. The results of the
logistic regression analysis were presented as Odds Ratios (OR) and
95% Confidence Intervals (CI). Statistically, significant differences
were noted for each analysis, with statistical significance based on a
p value of <0.05. Statistical analysis was performed with SPSS version
11.5 J (SPSS, Inc, Chicago, IL).
Table 1
Results
The study consisted of 49 men and 45 women. The mean age was
49 ± 3.1 years for the off-pump group and 51 ± 2.5 years for the onpump group. Pre- and intra operative demographics characteristics of
the 46 patients operated by the off-pump and the 48 patients operated
by the on-pump technique are shown in Table 1 and 2, respectively.
There were no major differences between patients with regard to
gender, age, severity of coronary disease, prevalence of diabetes,
hypertension, hypercholesterolaemia, ejection fraction, New York
Heart Association functional class, and surgical data such as number
of distal anastomoses, and there was no statistically significant
difference in preoperative serum creatinine, BUN, creatinine
clearance, and GFR levels between the two groups. Conversion from
off-pump to on-pump did not occur for any patients. All patients had
an uneventful operation and postoperative stay.
Five patients in the on-pump group and 4 in the off-pump group
were unstable, in-hospital patients treated with inotropic treatment
and Intra-aortic balloon pump (IABP). The severity of coronary
heart disease did not differ between both cohorts as indicated by
similar rates of left main, two- and three-vessel diseases. There was
no statistically significant difference in the index of completeness of
revascularization (Table 1).
Preoperative furosemide usage and total requirements of
intravenous catecholamines and trinitrate during the first 48 hr after
surgery didn't found significant differences (Table 1 and 2).
The cross-clamp time in the on-pump group was 56 ± 12 minutes
and the perfusion time was 73 ± 13 minutes. Operation time was
shorten in an off-pump group than the on-pump group (Table 2).
This different was significant statistically (p=0.012).
Preoperative renal function parameters are shown in Table 1;
there was no significant difference between groups. Although there
were renal function disorders in both groups, none of them had
no indication of dialysis (Table 1). Postoperative data showed that
impaired renal function parameters were less in the off-pump group.
The increase in postoperative creatinine and BUN levels compared to
the preoperative value was markedly higher in the on-pump group
(p=0.006 and p=0.007). The decreases in the GFR and the creatinine
clearance levels were higher in the on-pump group as opposed to
the off-pump group (p=0.002, p=0.004) at postoperative days 7
(Table 3). Nine patients in the on-pump group had required dialysis,
whereas only 1 patients in the off-pump group had required dialysis
(p=0.0001). Consequently, it was deduced that renal dysfunction
was higher in the on-pump group than in the off-pump group after
cardiac surgery.
By using stepwise logistic regression analysis 12 variables were
identified as independent predictors of postoperative requiring
dialysis, and was presented in Table 4. The use of cardiopulmonary
bypass and increasing age were a significant factor on the univariate
logistic regression analysis (OR: 2.91, 95% CI: 1.65-4.11, p=0.0001 and
OR: 0.71, 95% CI: 0.55-1.16, p=0.002, respectively). Besides, operating
time (OR: 1.09, 95% CI: 0.98-2.44, p=0.038), hypertension (OR: 2.52,
95% CI: 1.26-5.18, p=0.008), diabetes (OR: 2.90, 95% CI: 2.05-3.15,
p=0.001), smoking (OR: 1.99, 95% CI: 1.02-3.18, p=0.022), multiple
vessels disease (OR: 1.45, 95% CI: 0.17-3.10, p=0.040), preoperative
IABP (OR: 5.9, 95% CI: 4.66-12.01, p=0.011), preoperative left
ventricle ejection fraction (LVEF) < 40 (OR: 4.66, 95% CI: 2.01-9.62,
p=0.002), preoperative increased creatinine and BUN levels (OR:
0.85, 95% CI: 0.66-1.98, p=0.001), preoperative deceased creatinine
clearance and GFR levels (OR: 0.91, 95% CI: 0.73-2.02, p=0.0001),
and having had a previous myocardial infarction (OR: 0.41, 95%
CI: 0.35-1.06, p=0.025)also showed a significant association with
requiring dialysis.
A multivariate ordered logistic regression analysis (with
propensity adjustment) was performed to compare the occurrence
of requiring dialysis between patients having on-pump and patients
having off-pump. The most significant contributor toward the
occurrence of post-operative dialysis was the use of cardiopulmonary
bypass with OR: 2.51, 95% CI: 1.33-3.77, p=0.0001. Besides, diabetes
mellitus and hypertension (OR: 3.10, 95% CI: 2.66-3.49, p=0.001
and (OR: 2.52, 95% CI: 1.51-4.90, p=0.008, respectively) significantly
increased the risk of requiring dialysis. Other independent predictors
of postoperative dialysis were ejection fraction <40%, multiple vessels
disease, the excess of preoperative creatinine and BUN levels, the lack
of preoperative of creatinine clearance and GFR rates, and age >70
were determined to be among other risk factors. These variables are
summarized in Table 5, with their regression coefficient, adjusted
odds ratios, and p values.
The postoperative clinical data are given in Table 6. There was
no significant difference between the two groups with respect to
complications, such as lung infections, stroke, or transient ischemic
attacks. The incidence of low-output syndrome, perioperative
myocardial infarction, stroke, and mediastinitis, superficial would
complication, and atrial fibrillation was similar in two groups.
Patients in the on-pump group showed a higher requirement
blood transfusion. Blood loss was higher in the on-pump group
than in the off-pump group. In the off-pump group, postoperative
bleeding >1000 mL, surgical revision for bleeding, chest tube drainage
and blood transfusion amount less than the on-pump group. This
difference was statistically significant (Table 6). Nosocomial infection
and multiple organ dysfunctions were more frequently observed in
the on-pump group (p=0.048 and p=0.033). The incidence of inhospital
mortality following isolated off-pump patients was 4.3%,
compared to 12.5% for patients with on-pump (p=0.003). Mean
follow-up ranged from 6 to 24 months. No significant difference in
long-term survival at 2 years was absorbed between the two groups
of hospital survivors.
There was an important difference between the groups in terms
of durations of ICU and hospital stay. Patients in the on-pump group
had a significantly longer ICU stay as well as total hospital stay as
those undergoing off-pump surgery (p=0.005 and p=0.006). Because
ICU and hospital stay, postoperative bleeding and surgical revision
and nosocomial infections were less in patients off-pump than
patients on-pump, the hospital costs were significantly lower for offpump
(p=0.001) (Table 6).
Table 2
Table 3
Table 4
Table 4
Results of Univariate Logistic Regression Analysis for Risk Factors Associated with requiring dialysis.
Discussion
Renal dysfunction is a well-recognized complication following
CABG and has been associated with increased morbidity, mortality,
intensive care unit stay, and hospital fees particularly [10,20]. A
significant proportion of conventional CABG had a degree of renal
dysfunction develop postoperatively [21,22]. Besides, preoperative
renal dysfunction is a predictor of renal failure in patients undergoing
conventional CABG. Coronary revascularization without CPB
has been shown to minimize renal injury in patients with normal
preoperative renal function who undergo elective procedures, but
the effect of coronary revascularization without CPB in patients
with preoperative non-dialysis-dependent renal insufficiency is still
controversial, and it has been shown in many studies that preoperative
non-dialysis-dependent renal dysfunction have a further deterioration
in renal function leading to postoperative renal injury [4,5,17,23-25].
Kidney parenchyma is more sensitive for postoperative renal failure
after cardiac surgery, and it can occur as a result of the drop in renal
perfusion pressure during CPB or during mechanical lifting of the
heart in off-pump surgery.
We investigated the results of patients with non-dialysis renal
dysfunction after on-pump and off-pump coronary surgery and risk
factors that may cause postoperative dialysis in this study. Both effects
of surgical intervention associated with coronary surgery and risk
factors requiring dialysis are important determinants of postoperative
renal dysfunction. This concept is the basis of our study. Display of
renal tubular damage is used many parameters by some authors over
the years such as creatinine clearance, fractional excretion of sodium,
micro albuminuria, free hemoglobin, free water clearance and
N-acetyl-glucosaminidase activity in patients undergoing off-pump
as compared with conventional CABG patients [10,16]. This study
examined serum creatinine, blood urea nitrogen concentration and
serum creatinine clearance and GFR levels in both groups.
The potential reduction of renal risk and its association with
morbidity and mortality may have a significant role in the choice of
operative technique. The on-pump and off-pump techniques after
cardiac surgery were compared in terms of creation of renal damage
over the years, and morbidity and mortality rate were examined
[16,26-28]. Although it has been reported that off-pump may
minimize renal injury in elective patients with normal and impaired
preoperative renal function and in high-risk patients [14,16,27,29,30],
other studies have failed to show such benefit [15,17,31,32]. Metaanalysis
of the literature has shown that off-pump surgery may result
in improved short-term and midterm outcomes, and glomerular
filtration was significantly worse with off-pump than with offpump.
Off-pump reduced the likelihood of acute renal failure in
patients with preoperative non dialysis-dependent renal insufficiency
[14,16,33]. In contrast, another studies [26,28] observed no difference
in glomerular or tubular function between off-pump and on-pump
techniques, and no difference in the requirement for dialysis between
on-pump and off-pump was detected in patients with preoperative
non dialysis-dependent renal insufficiency.
Previous retrospective analyses have failed to demonstrate a
significant renoprotective benefit from using off-pump techniques,
although the studies by Gamoso [17] and Zamvar [31] had relatively
small numbers of off pump patients in them. The study reported
by Wallace and colleagues [34] in Ohio was of comparable size to
our study and indicated rates of acute renal failure of 12% and 6%,
respectively, for on-pump and off-pump surgery. However, the
on-pump group had a higher percentage of high-risk patients,
such as diabetics, patients with poor left ventricular function, and
reoperations [34]. In our study, there was no significant difference
between the risk factors of the on-pump and off-pump.
The cause of renal dysfunction after the cardiac operation is
multifactorial and usually attributed to several factors, such as the use
of CPB, perioperative cardiovascular compromise, or toxic insults to
the kidneys [35-37]. Free plasma hemoglobin, elastase, and endothelin,
and free radicals including superoxide, hydrogen peroxide, and
the hydroxyl radicals can be generated during CPB and can induce
injury in the renal brush-border membrane [36]. Nonpulsatile flow,
renal hypoperfusion, hypothermia, and duration of CPB are also
thought to have adverse effects on renal function [36,38,39]. There
is no uniting mechanism explaining renal failure associated with
cardiac surgery [24,40-42]. Previous work has used algorithms to
stratify individual risk and has described clinical variables as exerting
their effects in four areas. First, there are factors relating to occult
renal ischemia caused largely by arteriosclerosis and exacerbated by
perioperative reduction of cardiac output, hypotension, and resultant
hypoperfusion. Second, the kidneys may be damaged by exogenous
nephrotoxins such as amino glycoside antibiotics, diuretics, or
radiologic contrast media. Third, endogenous nephrotoxins may
be released (eg, myoglobin, free radicals, or pro inflammatory
cytokines such as interleukin-8, interleukin-1, and tumor necrosis
factor). Last, there may be a background of reduced renal reserve as
assessed by preoperative estimates of creatinine clearance. The effect,
in turn, can produce renal dysfunction, especially in the presence of
additional risk factors like pre-existing renal dysfunction, diabetes,
and hypertension [43]. Avoiding CPB is beneficial even in patients
with an existing preoperative renal insufficiency undergoing CABG
as confirmed in this study [14,22]. This benefit may be due to the
avoidance of non-pulsatile flow, renal hypoperfusion, hypothermia,
and prolonged duration of CPB for all of them thought to have adverse
effects on renal function in patients undergoing off-pump coronary
artery bypass grafting. With the resurgence of interest in CABG
without the use of CPB, there were a few observational comparative
studies published on CABG with or without using CPB in patients
with preoperative non–dialysis-dependent renal insufficiency. All
these studies showed that off-pump reduces in-hospital morbidity
and the likelihood of renal failure in patients with preoperative non–
dialysis-dependent renal insufficiency [14,16,27,29,30]. Yet other
nonrandomized studies failed to show the renoprotective effect of the
off-pump technique in non-dialysis-dependent renal insufficiency
[15,17,31,32] as previously mentioned above.
The off-pump technique for coronary revascularization was
popularized in the early 1990s and led to an investigation as
to whether the avoidance of CPB altogether would minimize
postoperative renal injury and/or insufficiency. Use of beating heart
techniques means the maintenance of pulsatile flow and no exposure
to an extracorporeal circuit, with an anticipated reduction in the
inflammatory cytokine response that this would entail. It also means
normothermia and a decreased requirement for vasoconstrictor
administration to maintain target mean arterial pressures [17,42].
Off-pump CABG surgery eliminates several of the physiologic
perturbations associated with CPB that have been implicated in the
development of postoperative renal dysfunction. Off-pump may,
therefore, be the preferred technique for patients with multiple
preoperative risk factors for renal dysfunction. In the present study,
we used beating heart operations in elective patients who needed
myocardial revascularization to clarify the impact of this procedure
on renal function as part of a prospective randomized study. In several
previous studies, lower prevalence of postoperative complications
(eg, cerebral deficits [stroke or postoperative delirium] or renal
insufficiency), and a lower mortality rate have been documented for
patients undergoing beating heart surgery as compared with patients
undergoing conventional CABG [22,44-47].
In most previous studies investigating the efficacy of off-pump
in patients with renal dysfunction, the number of grafts in off-pump
was significantly less than that of conventional CABG [4,13,14,48].
Sabik and associates [27] have reported increased occurrence of
incomplete revascularization in off-pump that could be harmful to
late results. In this study, the number of grafts was similar between
groups and complete revascularization carried out and there was no
different statistically both groups. However, off-pump techniques
are more technically demanding, there has been previous concern
over anastomotic quality, and the contortion of the heart for the
lateral and posterior vessels may cause outflow tract obstruction and
low cardiac output [49]. Off-pump contributes superior functional
renal preventing that higher mean arterial pressures are usually
maintained during off-pump surgery and may have a renoprotective
effect. We mention that systolic arterial pressures were maintained at
a minimum of 70 mmHg during distal anastomoses when performing
off-pump, especially in the circumflex territory. Besides, Starfish
(Medronic Inc) or the Guidant Vortex Vacuum Assist ensure that
higher systemic pressures are maintained when stabilizers are used
to facilitate suturing. In a comparable manner, the beneficial effect
on functional renal outcome seen with off-pump may be a reflection
of the maintenance of higher systemic blood pressures during offpump
[50,51]. In our study, the difference in terms of complete
revascularization could not be determined. In addition, hemodynamic
problems not encountered to on-pump from off-pump turn during
operation.
The patient’s age is one of the most reported preoperative risk
factors for postoperative renal requiring dialysis [17,23,24,52]. This
finding was confirmed in this series as an age of 70 years or older
and has been found to be significantly associated with postoperative
renal failure. The effect of diabetes mellitus on postoperative renal
failure may be the result of renal parenchymal disease, such as
glomerulonephritis or glomerulosclerosis [22]. In our study, diabetes
was found to be a risk factor relation to requiring dialysis.
The prominent finding in our study is that off-pump surgery
preserves renal function. Also, off-pump seems to reduce postoperative
bleeding, nosocomial infection, multiorgan dysfunction, ICU and
hospital stay, hospital charges, and mortality [53-60]. The incidence
of respiratory failure and postoperative bleeding tended to be
more frequent in patients with renal dysfunction than those with
normal renal function although there was no significant difference
[61]. Tabata et al. [61] suggest that off-pump does not reduce the
requirement of blood transfusion in patients with renal dysfunction.
The current study also showed a significantly higher blood loss and
transfusion requirement in the off-pump group. Furthermore, these
losses concur with other recently published data [62,63]. With regard
to the clinical outcomes, the off-pump group had a significantly
shorter duration of ICU and hospital stay and hospital charges
compared with the on-pump group. These results are in keeping
with those from a previous multicenter trial in which early clinical
outcomes were compared between off-pump and on-pump CABG in
a randomized fashion [64].
Postoperative renal dysfunction in patients undergoing CABG
has been associated with high morbidity and mortality [10,65-67].
Operative mortalities of conventional CABG have been reported to
range from 5.9% to 14.3% in patients with chronic dialysis [68-70]
and from 7.0% to 11.0% in patients with non-dialysis-dependent
renal dysfunction [4-6,13,14,25]. However, our results agree with the
findings of Ascione’s research group [58]. In their study, they have
clearly proven a benefit on cardiac outcome after off-pump surgery.
Some studies have reported better outcomes, however, they are much
smaller studies [12,48]. Operative mortalities of off-pump have been
recently reported to range from 0% to 6.7% in patients with chronic
dialysis [12,13,48] and to range from 5.9% to 6.3% in patients with
non dialysis-dependent renal dysfunction [4,14]. In this study, the
in-hospital mortality rate was 12.5% in patients with the on-pump
group. These patients had unstable angina and severe diffuse triplevessel
disease associated with diabetes, mediastinitis, peripheral
vascular disease, and low ejection fraction.
Although serum creatinine and blood urea nitrogen are the most
widely used assay to measure the presence and progression of kidney
disease, equations based on serum creatinine level, age, sex, and other
variables are more sensitive at predicting changes in renal function
[71]. Recently some parameters were developed such as creatinine
clearance and GFR to assess renal function [72], and are widely
used today. Loganathan show that there were no major differences
in any of the renal function associated parameters such as creatinine
and blood urea nitrogen blood levels between their off-pump and
on-pump groups [8]. In contrast to our study, other studies have
suggested serum creatinine levels be a compelling parameter for
renal dysfunction after cardiac surgery [32] as agree with our study.
Postoperatively, especially serum creatinine and urea levels revealed
a significant increase in the classical CABG group compared to the
off-pump group. Further, this study showed a significant rise in
serum creatinine and BUN levels at postoperative day 7 in the onpump
group compared with the off-pump group and a statistically
significant fall in GFR and creatinine clearance in the on-pump
group compared with the off-pump group. The decrease in creatinine
clearance and glomerular filtration rate was more in on-pump groups
compared to off-pump. The increases in serum creatinine and BUN
level significantly less in patient's off-pump postoperatively in 7 days.
In the present study, marked decreases in the creatinine clearance
and GRF values were found early after operation in on-pump groups,
which is in accordance with previous studies in which renal function
was evaluated in patients undergoing CPB.
In agreement with previous reports [36,75], this study found a
marked improvement in creatinine clearance, a reliable indicator
of glomerular filtration rate, during CPB in the on-pump group.
Nevertheless, at 24 hr and 48 hr postoperatively the creatinine
clearance values decreased significantly in the on-pump group,
reaching levels markedly lower than preoperative levels. Conversely,
in the off-pump group rising in creatinine clearance was less.
Functional alteration of the glomerular and tubular parts of the
nephron can be evaluated further by assessing micro albuminuria and
NAG activity, respectively. More recently, urinary NAG activity has
emerged as the most widely assayed urinary enzyme for detection of
renal damage because of its stability in urine, its relative molecular
mass which precludes filtration by the glomerulus, and its presence
in high activity in the tubular lysosomes. The marked increases in
urinary albumin-to-creatinine ratio and NAG activity levels in the
current study confirm the potential deleterious effect of the CPB on
renal function. Randomized controlled trials in this area have looked
beyond serum urea, creatinine, creatinine clearance, and GFR to
more sensitive biochemical markers of renal function. These have
been associated with decreases in measured creatinine clearance and
GFR have been demonstrated to occur with both on the pump and
off-pump surgery. But, this decrease was statistically more in onpump
patients.
In the present study, non similar to a previous one [64], the
prevalence of postoperative renal failure, defined as either requiring
hemodialysis, an increase in serum creatinine and BUN, or decrease
in GFR and creatinine clearance did not differ between the groups.
Ascione et al. [14] demonstrated higher postoperative serum
creatinine and urea levels in patients with preoperative non-dialysisdependent
renal insufficiency undergoing on-pump CABG with a
significant difference at 12 hr postoperatively as compared with those
undergoing OPCAB surgery. Hayashida et al. [7] found a significantly
less increase in creatinine levels and a greater creatinine clearance in
off-pump patients as compared with the CABG group. In contrast to
these findings, in a recent study by Gamoso et al. [17] including 690
patients, no significant reduction of perioperative renal dysfunction
in off-pump patients could be found.
In our study, logistic regression model analysis showed the use of
CPB is significantly associated with adverse renal outcome. In addition,
the effects of the presence of diabetes mellitus, age >70, hypertension,
multiple vessels disease, preoperative increased creatinine and BUN
levels, preoperative decreased creatinine clearance and GFR levels and
preoperative LVEF <40 had independent predictors for postoperative
renal failure requiring. Some parameters as congestive heart failure,
preoperative cardiogenic shock, urgent operations, increasing body
mass index, peripheral vascular disease, intraoperative low cardiac
output, high transfusion requirement, the use of non-left internal
mammary arterial conduits and persistent low cardiac output states
has found associated with postoperative dialysis-requiring in reported
other series [22,42,50] in addition to the findings of our study.
Table 5
Table 5
Multivariate Logistic Regression Analysis for Risk Factors Associated with requiring dialysis.
Table 6
Limitations of the Study
First, there are only a limited number of large comparative
studies between on-pump and off-pump focusing on renal outcome
and matched for number of coronary grafts.
Furthermore, this study is retrospective, observational and
limited to a single institution. All data were entered into the database
as part of patient management. One of the important limitations of
this study is that we did not investigate late outcomes. Several studies
have revealed poor late outcomes of conventional CABG in patients
with renal dysfunction. 5-year actuarial survival rates of dialysis
patients have been reported to range from 32.0% to 55.8% [2,3,69].
Using the levels of serum creatinine, BUN, creatinine clearance
and GFR as the sole marker of renal function can be also a limitation.
Although measurements of patients’ urinary microalbumin, retinalbinding
protein, or n-acetyl glucosaminidase might give a more
detailed picture of renal insult, in a study of this size it is largely
unrealistic.
Conclusion
To the best of our knowledge, there has been no randomized study
published comparing the effect of off-pump and on-pump CABG
in patients with non–dialysis dependent renal insufficiency defined
by GFR as well as serum creatinine, blood urea nitrogen, creatinine
clearance and requiring dialysis. These findings suggest that the offpump
technique is more renoprotective in patients with non–dialysis
dependent renal insufficiency.
Multivariate stepwise logistic regression confirmed the use
of CPB as an independent risk factor for the development of
requiring dialysis. In summary, the off-pump technique preserved
the glomerular filtration rate and prevented an increase in
creatinine concentration during the early postoperative period.
The technique also resulted in shorter ICU stay and mortality and
fewer complications and requirement for transfusion. The results
suggested that off-pump ensures an earlier patient recovery and gives
superior renal protection than conventional CABG in patients with
non-dialysis renal dysfunction. Although baseline measurements
of parameters of glomerular and tubular damage were the same in
both groups, disorder for these parameters was less in the off-pump
patients in the postoperative period in 7 days.
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