Asian Cardiovasc Thorac Ann 2008;16:468-472
© 2008 Asia Publishing EXchange Ltd
Renal Outcome Following On- and Off-Pump Coronary Artery Bypass Graft Surgery
Joanna SM Ooi, MMed(Anaes),
Mohd R Abdul Rahman, MS1,
Shamsul A Shah, MPH2,
Mohd Z Dimon, MS1
Division of Cardiothoracic Anesthesia
1 Division of Cardiothoracic Surgery
2 Department of Community Health, Heart and Lung Center, Hospital University Kebangsaan Malaysia, Kuala Lumpur, Malaysia
For reprint information contact: Joanna SM Ooi , MMed(Anaes) Tel: 60 3 9145 5555 Ext. 5852 Fax: 60 3 9173 7826 Email: joanna{at}mail.hukm.ukm.my, Department of Anaesthesiology & Intensive Care, Faculty of Medicine, University Kebangsaan Malaysia, Jalan Yaacob Latif, Bandar Tun Razak, Cheras 56000, Kuala Lumpur, Malaysia.
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ABSTRACT
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A prospective study was carried out to compare the outcomes of patients with preexisting non-dialysis-dependent renal dysfunction who underwent coronary artery bypass grafting with or without cardiopulmonary bypass. Elective off-pump coronary artery bypass was performed in 29 patients with renal dysfunction. Their results were compared with those of a similar group of 35 patients who underwent the conventional on-pump coronary artery grafting. There was a significant deterioration in creatinine clearance in the on-pump group on days 1, 2, and 4 after surgery, while creatinine clearance in the off-pump group remained close to the baseline level. Both groups had improved to the preoperative creatinine clearance values on follow-up at 4 weeks. It was concluded that off-pump surgery provided better renal protection than the conventional on-pump technique in patients with preexisting non-dialysis-dependent renal dysfunction.
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INTRODUCTION
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Renal dysfunction is a well-recognized complication after coronary artery bypass grafting (CABG) and a risk factor for morbidity and mortality. It has been reported to occur after 8%–30% of cardiac operations performed under cardiopulmonary bypass (CPB) and is associated with mortality rates of 7%–38%. When acute renal failure after CPB requires dialysis, the mortality rate exceeds 60%.1–3 Inadequate or nonpulsatile renal perfusion, macro- and microembolic loads on the renal vasculature, and the inflammatory response to CPB have been implicated as potential etiologic factors for postoperative renal dysfunction.4 With the recent revival of CABG without CPB, known as off-pump coronary artery bypass (OPCAB), there has been speculation that this technique may reduce the perioperative renal insult.5 Although many studies have found that OPCAB minimizes renal injury in elective patients with normal or impaired preoperative renal function, others have failed to show such benefit.4,6–10 A recent randomized controlled study comparing CABG with and without CPB in patients with preoperative non-dialysis-dependent renal insufficiency showed that OPCAB is more renoprotective than on-pump CABG, and this is more pronounced in patients with diabetes, hypertension, and compromised left ventricular function.11 We compared the effects of OPCAB and the on-pump CABG technique on renal function in patients with preexisting renal dysfunction.
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PATIENTS AND METHODS
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This was a prospective clinical trial involving patients with preexisting non-dialysis-dependent renal dysfunction stage 2–4, based on National Kidney Foundation12 guidelines, who underwent elective CABG at our Heart and Lung Center between June 2006 and October 2007. All 64 patients included in this study had raised preoperative serum creatinine levels, defined as > 106 µmol·L–1 in males and > 80 µmol·L–1 in females, based on our laboratory values. Those who had concomitant surgical procedures with CABG were excluded from the study. All patients ceased antiplatelet (aspirin or clopidogrel) therapy at least 1 week prior to the surgery. The decision on the type of surgical technique (on-pump CABG or OPCAB) was determined by the surgeon, and informed consent was obtained from each patient. The preoperative characteristics of the 29 patients who underwent OPCAB and the 35 who had on-pump CABG are given in Table 1
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Anesthesia was induced in all patients with intravenous fentanyl 10 µg·kg–1 and midazolam 3 mg. Intubation was facilitated by rocuronium 0.6 mg·kg–1. The patients were ventilated with oxygen-air, approaching a fractional concentration of oxygen in inspired gas of 45%–50%, and maintained with sevoflurane to achieve a minimum alveolar concentration of 1.0. Standard monitoring was used, including electrocardiogram, pulse oximetry, capnometer, multigas analyzer, invasive blood pressure, central venous pressure, and intraoperative transesophageal echocardiography. In patients with poor left ventricular function (ejection fraction < 50%), a pulmonary artery catheter was inserted. Intravenous heparin 300 IU·kg –1 was given to patients in both groups to achieve an activated clotting time > 400 sec. In the on-pump group, cold blood St Thomas’ Hospital cardioplegic solution was used. Complete reversal to the baseline activated clotting time was achieved in the on-pump CABG group, whereas patients in the OPCAB group each received 1.5 mg·kg–1 protamine. An intracoronary shunt was used during anastomosis in the OPCAB group. In the on-pump group, the mean systemic pressure was maintained at 60–70 mm Hg with phenylephrine. In the OPCAB group, intravenous fluids, positioning, and phenylephrine were used to maintain mean pressure > 60 mm Hg at all times. At the end of the operation, patients in both groups were ventilated in the cardiac intensive care unit.
Serum creatinine levels were measured on the preoperative day, on postoperative days 1, 2, and 4, and on follow-up at 4 weeks. Estimation of the glomerular filtration rate was based on creatinine clearance (CrCl) calculated using the Cockroft-Gault equation: for men: CrCl = ([140 – age] x weight)/(serum Cr x 72); for women: CrCl = ([140 – age] x weight) x 0.85/[serum Cr x 72]. Units of weight are kg, age is in years, and serum Cr in mg·dL–1 (88.4 µmol·L–1 = 1 mg·dL–1).
Statistical analysis was performed using SPSS version 13.0 software (SPSS, Inc., Chicago, IL, USA). Student’s t test was used for continuous variables and the chi-squared test for categorical data. Univariate analysis of demographic variables between groups was made using Student’s t test. A p value < 0.05 was considered significant.
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RESULTS
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The operative details of both groups are given in Table 2. None of the patients in the OPCAB group required conversion to cardiopulmonary bypass. Table 3 gives serial CrCl results calculated from serum creatinine levels. There were no significant differences in mean CrCl between the 2 groups at each time point. However, there was a significant decrease in CrCl compared to the baseline level on days 1–4 in the on-pump CABG group (Figure 1). Additional postoperative data are given in Table 4. There was no mortality, and no patient developed postoperative stroke.
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Figure 1. Creatinine clearance before and after on-pump coronary artery bypass grafting (CABG) or off-pump coronary artery bypass (OPCAB) in patients with non-dialysis-dependent renal insufficiency. *p < 0.05 for the difference from baseline value.
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DISCUSSION
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The findings of this study show that renal function deteriorated significantly in the first 4 days after on-pump CABG. These changes were not seen in the OPCAB group. Thus our results confirm that OPCAB reduces the risk of renal impairment caused by CPB. A similar study by Sajja and colleagues11 concluded that OPCAB was more renoprotective in patients with non-dialysis-dependent renal insufficiency. Hirose and colleagues13 retrospectively analyzed a similar subgroup of patients and concluded that OPCAB was safe for patients with decreased renal function, and it helped to shorten the recovery period.
We noted that the time of worst deterioration in renal function occurred on days 2–4 after surgery, which is the critical period for patients’ recovery in general. Significant multiorgan dysfunction with deleterious effects associated with high mortality have been seen in patients who suffered significant renal impairment during this early postoperative period.1–3 Hence this subgroup of patients would probably benefit from the OPCAB technique. Although the mean arterial pressure during surgery and displacement of the heart in the OPCAB group were not documented, we managed to maintain arterial pressure above 60 mm Hg by various techniques including volume loading, the Trendelenburg position, requesting repositioning of the displaced heart, and administration of vasopressors. Our results also show significantly less postoperative bleeding in the OPCAB group due to the avoidance of dilutional anemia during CPB. These patients also demonstrated fewer postoperative complications and a significantly shorter hospital stay, which is also consistent with other similar studies.11,13,14 Although the duration of ventilation postoperatively was not significantly different between groups, a longer ventilation period was required in the on-pump CABG group, and 3 of these patients required reintubation. Some impairment of lung function may be due to the inflammatory response to CPB, causing acute lung injury, and also to impaired water clearance as a result of further deterioration in renal function, resulting in postoperative hypoxia secondary to pulmonary congestion. One patient in the on-pump group had to undergo dialysis postoperatively.
A limitation of this study was that it was a single-center series with a small sample size. Although it was a prospective study, we were unable to randomize the patients as the preferred surgical technique was determined by the surgeons. Continuing this clinical trial with the recruitment of more patients from multiple centers might further confirm our findings that OPCAB provides better renal protection than on-pump CABG in patients with preexisting non-dialysis-dependent renal dysfunction.
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REFERENCES
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Renal Outcome Following On- and Off-pump Coronary Artery Bypass Graft Surgery: Few Patients, Cautious Conclusions
Asian Cardiovasc Thorac Ann,
August 1, 2009;
17(4):
440 - 441.
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ABSTRACT
INTRODUCTION
