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Eur J Cardiothorac Surg 2004;25:212-217
© 2004 Elsevier Science NL
im Biçerb
imekcahin enaya
a Department of Cardiovascular Surgery, Siyami Ersek Thoracic and Cardiovascular Surgery Center, Zaman Sok. Güngör Apt. 4/9, Dumlup
nar Mah., Kadköy, Istanbul, Turkey
b Department of Anesthesiology, Siyami Ersek Thoracic and Cardiovascular Surgery Center, Istanbul, Turkey
c Division of Infectious Disease, Siyami Ersek Thoracic and Cardiovascular Surgery Center, Istanbul, Turkey
Received 2 September 2003; received in revised form 6 November 2003; accepted 11 November 2003.
* Corresponding author. Tel.: +90-532-6400-397
e-mail: gokcenorhan{at}hotmail.com
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Abstract |
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 Top Abstract 1. Introduction2. Materials and methods3. Results4. DiscussionReferences |
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Key Words: Obesity • Body mass index • Coronary artery bypass surgery
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1. Introduction |
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TopAbstract1. Introduction2. Materials and methods3. Results4. DiscussionReferences |
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The effect of the body size on the coronary artery bypass grafting (CABG) operations outcome is less clear. It is on doubt that obesity itself is an independent risk factor that increases the mortality and morbidity. In the literature, obesity is associated with high mortality after CABG of obese patients; on the other hand, there are some publications that show no difference between obese and non-obese patients [1–6].
Several risk stratification systems are defined to evaluate the results of surgery in acquired heart disease. Parsonnet score, Higgins Cleveland score, and Euroscore are the most used risk stratification models. In Parsonnet and society of thoracic surgeons risk stratification obesity is defined as a risk factor; on the other hand, it is not mentioned in the other stratification systems [7–13].
It is necessary to define the term ‘obesity’. It can be defined by using body mass index (BMI), calculated by Quetelet's formula, which is best correlated with body fat content [14].
The effect of obesity on postoperative outcome is unclear. The goal of this study is to find out if there is an increase in mortality and morbidity of obese patients in comparison with normal weight and overweight patients.
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2. Materials and methods |
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TopAbstract1. Introduction2. Materials and methods3. Results4. DiscussionReferences |
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The study was performed with the approval of the Institutional Human Investigation Committee.
2.2. Data collection and definitions
The variables were collected prospectively. Preoperative, intraoperative variables and postoperative complications were entered into our cardiac surgery database. The pertinent information for this study included age, sex, BMI score, and preoperative medical history including New York Heart Association Class, history of angina pectoris, left main lesion status, urgency of the operation, previous myocardial infarction, diabetes mellitus, hypertension, renal failure, chronic pulmonary obstructive disease, low ejection fraction (EF <40%), and preoperative hospitalisation time. Intraoperatively cross-clamp time, cardiopulmonary bypass time, operation time and the number of the vessels bypassed were recorded. Postoperative details recorded, included the amount of the postoperative bleeding, blood or erythrocyte suspension used, fresh frozen plasma transfusion required, intraortic balloon pump (IABP) usage, inotropic drug need, entubation time, the occurrence of sternal dehiscens, deep and superficial surgical infections, and mediastinitis, the length of hospital and intensive care unit (ICU) stay and hospital mortality.
Urgent operation was defined as the operation that occurred within 24 h of coronary catheterisation because of unstable symptoms. Preoperative myocardial infarction was determined as a Q wave or non-Q wave myocardial infarction that occurred preoperatively and was documented by a rise in cardiac isoenzyme values or electrocardiographic changes. Diabetes mellitus (DM) was present in patients receiving insulin therapy or oral hypoglycaemic medications or regulated by diet. Blood creatinin levels higher than 1.5 mg/dl and urea levels higher than 50 mg/dl were defined as renal failure. Hypertension was determined by a documented history of hypertension necessitating medical treatment. EF<40%, determined with biplane cineangiography or preoperative echocardiography was named as poor ventricular function. Chronic obstructive pulmonary disease was determined in patients who underwent pulmonary functional tests and had a forced expiratory volume in 1 s or diffusion capacity less than 75% of that predicted. Haemodynamic instability was diagnosed in patients who required inotropic medications and IABP in the ICU. Postoperative stroke was defined as a persistent neurological deficit seen during the period from the time of operation to discharge. In the definition of infection the reproduction of pathogenous microorganisms in the wound species was taken as a criteria. Superficial infections were defined as those limited to subcutaneous and soft tissues without mediastinal involvement. Infections limited to the bone and cartilage with extensive necrosis of tissues were considered to be deep wound infections. Mediastinal involvement was considered to be mediastinitis. Hospitalisation time was measured by the cardiovascular ICU stay and total length of hospital stay. Operative mortality was defined as any death occurring during the hospital stay.
BMI was calculated by standard formulas: BMI=weight/height2 (kg/m2) [14].
The patients were divided into three groups according to the BMI score classification, which is accepted by the WHO and other international leader committees [15,16]
2.3. Surgical and perfusion technique
Operations were performed by eight different surgery teams. CABG under standard cardiopulmonary bypass protocols of our institution was applied to all patients and done by our hospital's eight different staff surgery teams, thus minimizing intersurgeon variability. Cardiopulmonary bypass was performed using an extracorporeal circuit consisting of a membrane oxygenator and a centrifugal pump. Arterial blood flow was determined to be 2.5–3 l/min m2, and mean arterial pressure was maintained at 40–80 mmHg.
According to the standard cardiopulmonary bypass protocols of our institution, haemodilution with 1700 cm3 priming solution was applied to the patients. In almost all patients cardioplegia techniques consisted of systemic hypothermia (28–32 °C) and intermittent cold blood cardioplegia. Proximal anastomoses were done during a single cross-clamp period or during reperfusion with a partial occluding clamp.
2.4. Sample size determination
At the beginning of the study we assumed that the mortality rate would be 3% in obese population, and the minimal difference we wish to detect significance is taken as 1.5%. Depending upon the existing literature, the power of the study was taken as 90% and 
value as 5%. Under this assumption a sample size of 1069 will be appropriate for the study.
2.5. Statistical analysis
Statistical analysis was performed with the Statistical Package for the Social Sciences for windows (SSPS PC, version 10.0, Chicago, IL). Continuous variables are expressed as mean±standard error and categorical data as proportions (%). Statistical comparison performed by one-way ANOVA followed by posthoc Tukey test was used for multiple comparison in the analysis of variances. Categorical variables were analysed by 
2 test.
Multivariate logistic regression analysis was performed to evaluate independent risk factors for operative mortality and morbidity. The adjusted odds ratios for mortality and morbidity for each of the identified risk factors were then calculated.
P<0.05 was considered significant.
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3. Results |
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TopAbstract1. Introduction2. Materials and methods3. Results4. DiscussionReferences |
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The frequency of BMI values among patients undergoing CABG occurred in a near-normal distribution, with most patients clustered around the median BMI, between 24 and 28 kg/m2. The median BMI value was found to be 26 and mean value as 26.76±3.47 kg/m2.
The majority of the obese group was diabetic patients (38.58%). The mean age of the obese group was relatively lower than the other two groups. The obese patients mostly suffered from severe coronary heart disease at an early age. Elective surgical operations were usually preferred in the obese patient group. There was no significant difference between these three groups about preoperative demographic values except these specialties (Table 1).
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The overall hospital mortality rate in CABG operations on cardiopulmonary bypass was 2.1%. Mortality rate in the normal weight group was 1.87%, in the overweight group it was 1.80% and in the obese group it was 2.75%. In the obese group the rate of mortality seemed to be higher but the difference was not statistically significant (Table 2). We believe that this difference in mortality is not clinically important.
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The clinical outcome demonstrated significantly higher superficial wound infection rate in the patients, who were obese and females. Diabetes mellitus, and female gender were strongly associated with deep wound infections.
The significant multivariate predictors of long hospital stay were diabetes mellitus and the existence of previous myocardial infarction. Also, age over 65 years, cardiopulmonary bypass time over 120 min and the existence of renal pathology were determined as predictors for the overall hospital mortality rate (Table 3).
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4. Discussion |
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TopAbstract1. Introduction2. Materials and methods3. Results4. DiscussionReferences |
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In the obese patient group, the age of CABG operation is found to be earlier. Also in obese patients the incidence of DM is found to be higher. The less significant number of emergency operations instead of elective in obese patients may be explained by the more detailed preoperative evaluation of obese patients by the surgery team. The amount of bleeding was not different in our study between these three groups. Although Birkmeyer et al.'s and some other studies associated obesity with reduced risk of bleeding state postoperatively, the same studies demonstrate that obesity has no effect on bleeding [1–5,17–19].
There is no difference between groups about the amount of red cell transfusion used, but in obese patients, the need for fresh frozen plasma was lower. This result may be explained by less fluid escaping from intravascular space to interstitial space and less haemodilution with prime volume used, so this might have decreased the need for colloidal fluid postoperatively at ICU. Because the cardiopulmonary bypass circuit volume is the same for every patient, the haemodilution in patients during cardiopulmonary bypass is different. As defined in the literature, patients with low BMI have remarkable haemodilution and fall in the oncotic pressure. Thus fluid extravasation postoperatively is higher in low BMI patients [17]. This result may prolong the need for mechanic ventilation in patients with low BMI. On the other hand the anaesthetic drugs that are revealed from the fat tissue, or low vital capacity in patients with a high BMI score, may prolong the need for mechanic ventilation. We did not find any difference between the entubation periods.
Although there is no difference between the three groups in aspects of the cross-clamp and bypass time, the operation times were longer but not statistically significant in the obese group. This may be a result of prolonged duration of sternotomy, cannulation, and bleeding control in this group.
The IABP and inotropic drug usage and postoperative duration of ICU stay were not different between the three groups.
Despite the usage of prophylactic antibiotics and the increased surgical experiences, sternal wound infections still remain an important problem because of the associated high mortality and morbidity. In this study surgical sternum infections are grouped into three: superficial (cutanenous–subcutaneous infections), deep tissue infections and mediastinitis. According to this, superficial infections were more common in all the groups. This result was also demonstrated by some other studies [2–5,20–22]. Moulton et al. [1] showed obesity as a risk factor for superficial infections but not for mediastinitis. The decreased microcirculation of fat tissue or the elevated number of diabetic patients in the obese group may be associated with decreased perfusion. Also, in obese patients, the prolonged operation time, causing a more open surgical area to the external conditions may be a reason for the higher incidence of superficial infections. These patients have to be hospitalised until the end of their treatment for surgical infections, which prolongs the duration of hospital stay. Except the existence of diabetes mellitus and previous myocardial infarction, we could not determine any factor that prolongs the staying time in hospital. But still the surgery teams, due to possible complications that are kept in mind, hospitalise obese patients longer.
The atrial arrhythmias, which cause haemodynamic instability, can also prolong the duration of hospital stay and affect the patient's comfort. Although there are some publications saying atrial arrhythmias are seen in high BMI score patients, in our study no significant difference was determined [1–4,17].
Obesity was not evaluated as a risk factor that affects hospital mortality, and postoperative morbidity. Also in a study by the NNECDSG research group, Moulton et al. did not show obesity as a risk factor for mortality. Kuduvalli et al. defined that obese patients are not associated with an increased risk of in-hospital mortality; in contrast there is a significant increased risk of morbidity and postoperative length of stay in obese patients compared to non-obese patients [23]. In the study of Brandt et al. it was evaluated that severe obesity does not adversely affect preoperative mortality and morbidity in patients undergoing CABG [24].
Our data showed that the common factors that increase the mortality after CABG in overall patients were age over 65 years, prolonged cardiopulmonary bypass time and renal pathology but not obesity. According to these, it may be truly said that obese patients can safely undergo CABG operation.
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Acknowledgments |
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References |
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TopAbstract1. Introduction2. Materials and methods3. Results4. DiscussionReferences |
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This article has been cited by other articles:
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  J. Nakano, H. Okabayashi, M. Hanyu, Y. Soga, T. Nomoto, Y. Arai, T. Matsuo, M. Kai, and M. Kawatou Risk factors for wound infection after off-pump coronary artery bypass grafting: Should bilateral internal thoracic arteries be harvested in patients with diabetes? J. Thorac. Cardiovasc. Surg., March 1, 2008; 135(3): 540 - 545. [Abstract] [Full Text] [PDF]
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