Postoperative Complication in Overweight Patients Undergoing Coronary Artery Bypass Graft Surgery

Background: Obesity has a great impact on overall mortality and morbidity in cardiac surgery. The magnitude of obesity is defined by means of body mass index (BMI). At this study we aim to correlate between grade of BMI and postoperative complications in patients undergoing coronary revascularization. Methods: A prospective observational study was conducted in Ain Shams University hospitals and the National Heart Institute of Egypt. 98 patients with multi-vessel CAD and candidate for CABG were included in the study and divided into two groups Group I: 53 patients with BMI over 30. Group II: 45 patients with a BMI under 30. The primary endpoint was wound infection and mediastinitis. Secondary endpoints included mortality, prolonged ICU and hospital stay, stroke, renal and hepatic impairment. Results: As regard primary ending point, eight patients of Group I had their wounds infected which is significantly higher than the other group (p-value 0.034). The total ward stay in days was significantly higher in Group I (p-value 0.027). Conclusion: BMI more than 30 is associated with increased rates of wound complications either superficial or deep wound infections. Robust measures should be taken to prevent such grave complications.


Introduction
Obesity is without doubt a heavy burden both for patients and healthcare sys-World Journal of Cardiovascular Surgery tems alike; a burden which is greatly increased in cardiac surgery patients, especially those in need of coronary revascularization.
Body Mass Index (BMI) is the scale by which populations are classified according to their obesity. Patients with BMI ≥ 30 Kg/m 2 were classified as obese and those with BMI < 30 Kg/m 2 considered as non-obese [1] [2]. Controversies still exist between authors regarding whether a high BMI is associated with more complications or not in cardiac surgery. Among those who propose a significant increase of mortality and morbidity in obese patients is Engelman and colleagues [3]. While Reeves and his team showed some increase in rates of complications but neither reaching a statistical significance [4].
Wound complications either superficial or deep infections were among the first discussed in obese patients. This is also true for ICU stay, and ventilation hours which subsequently increase the total hospital stay for those patients. Simopoulos in his published manuscript, proved an association between high BMI and wound infection rates, which significantly affected the mortality in his series [5].
At this study, we aim to correlate between grade of BMI and postoperative complications in patients undergoing coronary revascularization.

Patients and Methods
After approval of Ain Shams University and National Heart Institute Ethical committee for the study proposal between October 2017 and June 2018, prospective observational study was conducted in Ain Shams University hospitals and National Heart Institute of Egypt. Ninety-eight patients with multi-vessel coronary artery disease and candidate for CABG were included in the study and divided into two groups Group I: 53 patients with BMI over 30. Group II: 45 patients with a BMI under 30.

Inclusion Criteria
All Patients presented with ischemic heart disease scheduled for elective CABG. Collected data were cross-clamp and total bypass times. The need for intra-aortic balloon pump and inotropic support were also recorded.

Exclusion Criteria
The primary endpoint was wound infection and mediastinitis. Secondary endpoints included mortality, prolonged ICU and hospital stay, stroke, renal and hepatic impairment.

Statistical Analysis
Data were expressed as mean ± standard deviation (SD) percentages (%) as indicated. For categorical variables, we used Chi-square test and Fisher. For numerical variables, we used student's t-test. P value ≤ 0.05 was considered a statistically significant result.

Sample Size
Sample size calculation was made based on the work of Ridderstolpe and colleagues showing a prevalence of all sternal wound infections of 10.6% of a study population of 2108 patients. Using Medcalc ® software with a type I error of 0.05, type II error of 0.1; the minimum sample size per group was 38 patients per group [6].

Results
There is a statistically insignificant difference between group I and group II as regard age and sex; however, the prevalence of CABG in male patients (62) is more than in female patients (36). The mean age in both groups was about the same (53.45 ± 6.6, 54.89 ± 6.13) as shown in Table 1. Group I had a higher prevalence of hypertension and DM rather than group II (58.5% versus 51.1%) (56.6% versus 46.7%) respectively with no significant difference, as shown in Table 2. Table 3 shows preoperative echocardiography characteristics, there is a statistically insignificant difference between group I (BMI > 30) and group II (BMI < 30)    Table 5). Table 6 shows a statistically insignificant difference between group I and group II as regard Inotropes and Intra-Aortic Balloon pump use (P > 0.05); however; group I had a higher prevalence of more than two Inotropes used than group II (3.8% versus 0.0%); in addition to that; group I had lower prevalence of   There is a statistically significant difference between group I and group II as regard ward stay in days (P < 0.05); where the group I had higher mean ward stay rather than group II (5.04 ± 2.65 versus 4.09 ± 1.33) ( Table 7).
There is a statistically significant difference between group I and group II regarding incidence of wound infection (P < 0.05); where the group I had a higher incidence of wound infection than group II (15.1% versus 2.2%). There is a statistically significant difference between group I and group II as regard incidence of mediastinitis (P < 0.05); group I had a higher incidence of mediastinitis than group II (9.8% versus 2.2%). Surprisingly; group I had a lower incidence of re-exploration than group II (2.0% versus 4.4%); as shown in Table 8.
There is a statistically insignificant difference between group I and group II regarding in-hospital mortality (P > 0.05); however; group I had higher hospital mortality than group II (3.8% versus 0.0%).
There is a statistically insignificant difference between group I and group II regarding incidence of Chest infection and Cerebrovascular Stroke (P > 0.05).

However; group I had a lower incidence of Chest infection and Cerebrovascular
Stroke than group II (9.8% versus 11.1%) and (0.0% versus 2.2%) respectively. In addition to that; none of the studied patients, in both groups had a liver impairment or renal impairment.

Discussion
Classification of overweight patients varies greatly between a BMI of 25 up to 40.
Being of a BMI of 25 -29.9, i.e. below 30, makes the patient overweight but not obese. While a BMI 30 -34.9 is a class 1 obesity, 35 -39.9 is a class 2 and class 3 is equal or greater than 40. Obesity is associated with many systemic comorbidities namely systemic hypertension, diabetes mellitus, dyslipidemia and cardiovascular diseases. All these comorbidities significantly increase the burden of undergoing CABG in such patients [7].
Many authors advocate obesity might not be a direct cause of mortality in cardiac patients undergoing CABG. However, when it comes to early morbidity following surgery and total hospital stay, obesity may be a game changer [8].
In our study, we found that there is no difference between group (I) and group (II) in age, sex and other co-morbidities like diabetes and hypertension. On the contrary to our findings, many other studies associate younger age with revascularization, denoting a higher risk among obese patients than in non-obese individuals. This is also true when it comes to comorbidities like hypertension and diabetes mellitus [7] [9].
Our study included predominantly obese male patients in contrast to other studies. Females in our cohort accounted for 39% of our obese and 33% of nonobese patients. This may be attributed to social and genetic properties in our community, Egyptian females tend to have late menopause, this means prolonged hormonal protection against coronary artery diseases. This natural physiologic protection is potentiated by less prevalence of smoking among females [10].
We found that the prevalence of diabetes is high in both groups and account for 56% of our obese and 46% of nonobese. Hyperglycemia is almost always identified as a risk factor for surgical site infection (SSI) [7]. respectively. This finding conforms to that reported by Ridderstolpe and colleagues associating a high BMI (>30 kg/m 2 ) with a significant increase of risk of developing superficial and deep wound complications [10]. However, other studies found that there was no significant difference in wound infection rates that could be attributed to high BMI [7] [11].
Other post-operative morbidities e.g. chest infection, renal or hepatic affection along with new cerebrovascular strokes were not higher in obese patients. This is in concurrence with other studies [4] [8].
The study showed that the incidence of bleeding and reopening is higher in nonobese patients and other studies revealed the same result [2].
In our cohort, obese patients had a higher white blood cells count and more elevated serum cholesterol levels. This may be attributed to the link demonstrated by other studies between adipose tissue and obesity in one hand and in-duced inflammatory reactions with their adverse effects in the other hand [12].
The significant increase in total hospital, ward stays and rates of wound infection in obese patients in our study, conforms to many major studies [13]. Although development of medical care plans and marked improvement of health care services worldwide markedly reduced the impact of obesity on CABG patients; obesity still a major challenge [7]. The "less than optimum" surgical exposure of the field, the wide and deep field along with fatty lower limbs all add to the technical challenge. All these necessitate a gentle tissue handling, proper meticulous hemostasis and endoscopic graft harvesting during revascularization [17].

Limitations of the Study
The study has its limitations of small number of patients with the exclusion of poorly controlled diabetic individuals, in whom diabetes may greatly affect the outcome of the study. Also, the study lacks follow up data for those patients to assess mid and late-term results and outcome.

Conclusion
Obesity was associated with wound infection and mediastinitis more than non-obese patients. This led to prolonged ICU and in-hospital stay. Otherwise, it may not be associated with significant increase of mortality or other morbidities risks. Robust, specific antibiotic protocol must be started immediately post-operative to have an infection free wound.