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Ann Thorac Surg 2009;87:540-546. doi:10.1016/j.athoracsur.2008.10.010
© 2009 The Society of Thoracic Surgeons
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Original Articles: Adult Cardiac

Is Cardiac Surgery Safe in Extremely Obese Patients (Body Mass Index 50 or Greater)?

Xiumei Sun, MDa,*, Peter C. Hill, MDa, Ammar S. Bafi, MDa, Jorge M. Garcia, MDa, Elizabeth Haile, MSb, Paul J. Corso, MDa, Steven W. Boyce, MDa

a Department of Surgery, Section of Cardiac Surgery, Washington Hospital Center, Washington, DC
b Medstar Research Institute, Hyattsville, Maryland

Accepted for publication October 8, 2008.

* Address correspondence to Dr Sun, Section of Cardiac Surgery, Department of Surgery, Washington Hospital Center, 110 Irving St NW, Room 1F-1223, Washington, DC 20010-2975 (Email: xiumei.sun{at}medstar.net).


   Abstract
Top
 Abstract
Introduction
 Patients and Methods
 Results
 Comment
 Acknowledgments
 References
 
Background: We investigated the impact of extreme obesity (body mass index [kg/m2] 50 or greater) on short-term clinical outcomes and report 1-year mortality.

Methods: Fifty-seven patients were found to have a body mass index of 50 or greater among 14,449 patients who underwent cardiac surgery between July 2000 and June 2007. Multivariable logistic regression analyses were used to assess the independent influence of extreme obesity on the major outcomes.

Results: Of the 57 patients, the mean age was 58 ± 11 years, mean body mass index was 55.1, and 63% of the patients were women. Forty patients underwent elective surgery. Forty-one patients had isolated coronary artery bypass graft surgery. The overall operative mortality was 9%; the mortality was 5% in isolated coronary artery bypass graft surgery and 5% in elective surgery. Fifteen patients had nonelective isolated coronary artery bypass graft surgery, and 2 patients had emergent active endocarditis surgery. Off-pump coronary artery bypass graft surgery was performed on 23 patients (23 of 41, 54%). After adjusting for known preoperative and operative risk factors through a multivariate logistic model, extreme obesity did not emerge as a significant risk factor for operative mortality (odds ratio, 1.75; p = 0.47) and other adverse outcomes (p > 0.05) after elective surgery; however, extreme obesity was marginally associated with increased mortality (odds ratio, 2.69; p = 0.05) and was a risk predictor for longer intensive care unit stays (odds ratio, 2.43; p = 0.01) in overall surgery. The 1-year survival rate was 82.5%.

Conclusions: Extreme obesity is not a contraindication to elective cardiac surgery. Studies stratifying the risk factors of mortality for nonelective surgery in extremely obese patients may be warranted.


   Introduction
Top
 Abstract
 Introduction
Patients and Methods
 Results
 Comment
 Acknowledgments
 References
 
Obesity has traditionally been considered a strong risk factor associated with increased cardiovascular disease and mortality. However, several large clinical studies have found that obese patients have equal or even better clinical outcomes than nonobese patients after coronary surgery [1–3]. Most studies estimated the impact of obesity with two categories: body mass index (BMI, kg/m2) 30 to 39 defined as obese and 40 or greater as severely obese. This severely obese group (BMI ≥ 40) includes a wide range of patient BMI values. Such wide variations in obesity may dilute or mask the influence of extreme obesity (BMI ≥ 50) on postoperative outcomes. Our study evaluated the clinical consequences of extremely obese patients undergoing cardiac surgery.


   Patients and Methods
Top
 Abstract
 Introduction
 Patients and Methods
Results
 Comment
 Acknowledgments
 References
 
Patient Population
All patients undergoing cardiac surgery from July 1, 2000, to June 30, 2007, were retrospectively reviewed through a computerized cardiac surgery database at the Washington Hospital Center in Washington, DC. Baseline demographics, procedure data, and perioperative outcomes were recorded and entered concurrently during hospitalization into the computerized database by a data-coordinating center as part of routine clinical practice. All data were defined according to The Society of Thoracic Surgeons national database (version 2.52). Guidelines and definitions are available at http://www.sts.org/sections/stsnationaldatabase/datamanagers. The Medstar Institutional Review Board approved the research protocol before the study and waived the requirement of informed consent as well as the requirement for signed Health Insurance Portability and Accountability Act authorization.

Operative mortality was identified as death occurring during hospital stay or within 30 days after surgery. Patients were contacted by telephone 30 days after hospital discharge as part of our routine clinical follow-up. One-year postoperative all-cause mortality was acquired from the US Social Security death index.

Body Mass Index Category
According to the definition of the Centers for Disease Control and Prevention [4], BMI is categorized into five groups: BMI less than 19 lean, 19 to 24 normal, 25 to 29 overweight, 30 to 39 obese, and 40 or greater severely obese. Because our particular interest was in the surgical outcomes of extremely obese patients, we subcategorized the severely obese group (BMI ≥ 40) into two groups, BMI 40 to 49 severely obese, and BMI 50 or greater extremely obese.

Statistics
Data are expressed as percentages, mean value ± standard deviation, and median (minimum, maximum). The univariate analysis was conducted to compare the perioperative variables in extremely obese patients with normal BMI category using {chi}2 test, Fisher's exact test, or Wilcoxon two-sided test, as appropriate.

Multivariable logistic regression models were constructed to evaluate the impact of extreme obesity and other BMI groups, compared with normal BMI, on operative mortality and each of the other major outcomes. Stepwise logistic regression was used to select variables to be included in the final logistic regression models. Confounding variables included in the stepwise logistic models were age, female sex, race, diabetes, hypertension, family history of coronary artery disease, history of myocardial infarction (MI), recent MI (within 24 hours), left main disease, preoperative cardiac shock, cardiovascular disease history, preoperative angina, hypercholesterolemia, ejection fraction less than 0.35, intraaortic balloon pump, previous stroke, carotid artery disease, peripheral vascular disease, renal failure, hemodialysis, current smoker, chronic obstructive pulmonary disease, redo coronary artery bypass graft surgery (CABG), elective surgery (versus nonelective surgery), on-pump CABG (versus off-pump), isolated CABG (versus other cardiac surgery), and preoperative use of β-blockers, calcium-channel blockers, angiotensin-converter enzyme inhibitors, and lipid-lowering drugs. The resultant odds ratios are presented with 95% confidence intervals. The relationship between extreme obesity and mortality was explored for overall cardiac surgery, and elective surgery.

All statistical analysis was performed with SAS for Windows Version 9.1 (SPSS Inc, Chicago, IL). Probability values of less than 0.05 were considered significant.


   Results
Top
 Abstract
 Introduction
 Patients and Methods
 Results
Comment
 Acknowledgments
 References
 
A total of 14,449 patients had cardiac surgery during the study interval. Fifty-seven patients (0.4%) were identified as having a BMI of 50 or greater. Of these, 41 patients with a BMI of 50 or greater underwent isolated CABG surgery.

Procedures performed on patients with a BMI of 50 or greater are presented in Table 1. Seventeen patients (33%) underwent nonelective surgery, 15 of these had isolated CABG; the remaining 2 each had endocarditis and both underwent mitral and aortic valve replacement.


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  		Table 1 Procedures Performed in 57 Patients With Body Mass Index of 50 or Greater
 
Among 41 isolated CABG patients, 75.6% (31 patients) had three or more grafts, and 90% (37 patients) had left internal mammary artery revascularization. More than one-half (23 patients) of these patients (56%) underwent off-pump surgery. Nonelective CABG was performed in 37% (15 patients) of these patients; 53.3% (8 patients) of them had off-pump CABG.

Comparison of preoperative characteristics with the normal BMI group is presented in Table 2. The extremely obese group was predominantly composed of female patients (61%). The mean BMI was 55.1 kg/m2 (range, 50 to 68.4 kg/m2); the mean weight was 143.4 kg (range, 82.7 to 230 kg); mean height was 160 cm (range, 118 to 183 cm). By comparison with normal BMI patients, patients with a BMI of 50 or greater were significantly younger and shorter, more likely to be African American (52%), and associated with a higher prevalence of diabetes and hypertension. On further review of the preoperative morbidities of isolated CABG surgery (41 patients), a marginally higher prevalence of hypercholesterolemia (p = 0.06), history of family cardiovascular disease (p = 0.06), and peripheral vascular disease (p = 0.06) were noted. The usage of calcium channel-blockers (p = 0.01) was significantly increased, as well as angiotensin-converter enzyme inhibitors and angiotensin II receptor blockers (p = 0.05) in this group.


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  		Table 2 Characteristics Comparing Normal Body Mass Index With Other Body Mass Index Categories: All Surgery a
 
Univariate analysis (Table 3) revealed that the extremely obese patients had a similar incidence of major adverse clinical outcomes compared with patients with normal BMI (p > 0.05) in all surgery. In the subanalyses, the mortality in patients with extreme obesity was also not significantly different from normal BMI patients undergoing elective cardiac surgery (5% versus 4%; p = 0.66) and isolated CABG surgery (5% versus 3%; p = 0.17).


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  		Table 3 Clinical Outcomes by Body Mass Index Category in All Surgery a
 
Table 4 depicts the multivariable risk factors for operative mortality in overall surgery and in elective surgery. The adjusted odds ratios for other major outcomes are presented in Table 5. In multivariate analysis, with adjustment by normal BMI and other confounding factors, extreme obesity did not emerge as a risk predictor for operative mortality (odds ratio, 1.75; 95% confidence interval, 0.38 to 8.09; p = 0.47; Table 4) and for other adverse outcomes compared with normal BMI after elective surgery (p > 0.05; Table 5). Extreme obesity was marginally associated with increased operative mortality and was a risk factor of longer postoperative intensive care unit stays (p = 0.03) in overall surgery (p = 0.05). A strong association was observed between extreme obesity and decreased requirement of red blood cell products in overall (p < 0.01) and in elective surgery (p < 0.01).


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  		Table 4 Multiple Logistic Regression With Operative Mortality as an Outcome
 

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  		Table 5 Impact of Extreme Obesity on Major Outcomes Other Than Mortality
 
Operative mortality is characterized in Table 6. All 5 patients were female. Two patients had endocarditis, underwent emergent mitral and aortic valve replacement surgery, and died of postoperative endocarditis. Another nonemergent mitral and aortic valve replacement patient died of postoperative multiple organ failure. The death of both isolated CABG patients was related to cardiac dysfunction. The mortality in overall surgery was 8.7%; 5% in isolated CABG surgery, 5% in elective surgery, 17.6% in all nonelective surgery, and 6.7% in nonelective isolated CABG surgery.


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  		Table 6 Characteristics of Mortality in Patients With Body Mass Index of 50 or Greater
 
Using the US Social Security Death Index, the overall survival after 1 year was found to be 82.5% (47 of 57 patients). Five patients died between 30 days and 6 months after surgery. Of the 5 patients, 80% had isolated CABG surgery (Table 6).


   Comment
Top
 Abstract
 Introduction
 Patients and Methods
 Results
 Comment
Acknowledgments
 References
 
The relationship between obesity and short-term mortality after CABG surgery has remained controversial [1–3, 5, 6]. Recently, two large-scale studies [5, 6] demonstrated severe obesity (BMI ≥ 35) was associated with higher operative mortality compared with normal and overweight patients. In our study, extreme obesity (BMI ≥ 50) was not associated with increased mortality after elective cardiac surgery.

Villavicencio and associates [7] conducted an analysis of 57 patients with a BMI of 50 or greater and found the operative mortality was 7%, a mortality of 15% in emergent or urgent surgery, and a mortality of 15% in nonisolated CABG surgery. Our study observed similar results. Although the mortality in nonelective surgery in this group of patients was higher than expected in patients after regular cardiac surgery, it still compares favorably with the results previously published [8–10]. Mortality for nonelective CABG has remained from 9% to 17% [8, 9], or even higher in patients with left main coronary disease [10].

The impact of BMI on the outcomes of endocarditis surgery has been rarely reported. In our study, 2 patients had emergent valve surgery for active endocarditis, and died of refractory sepsis in the intensive care unit. Both patients had multiple preoperative hospital admissions owing to pulmonary edema, intractable heart failure, central nervous system syndrome, syncope, annular abscess, and severe mitral insufficiency. Villavicencio and colleagues [7] found that the incidence of endocarditis was 9% in 57 patients with a BMI of 50 or greater who underwent cardiac surgery at the Mayo Clinic, which was significantly higher than in normal patients or those in other obese categories (p < 0.001); the operative mortality was 22%. A mortality rate of 36% was reported for endocarditis patients who underwent emergent or urgent surgery [11]. Studies have reported that no patients with preoperatively complicated septic shock survived after emergent surgery [12, 13]. In our study the number of patients with endocarditis was too small to enable formal analysis and meaningful conclusions, but the combination of an increased preoperative incidence, disease nature, and high operative mortality in this extremely obese group underscores the critical need for baseline risk stratification to avoid devastating complications.

Most of the previous studies have been conducted focusing on the comparisons of short-term outcomes between obese and nonobese patients after cardiac surgery [1–3, 5]. The impact of obesity on long-term outcome has rarely been reported. Our study found that the 1-year mortality differed from the operative mortality in surgery distribution. Extreme obesity did not affect operative mortality of elective isolated CABG, but mortality from CABG surgery accounted for 80% of the 1-year mortality. Schwann and associates [14] found better short-term outcomes in obese patients but worse long-term outcomes after coronary surgery. In our study, extremely obese patients had a higher prevalence of diabetes, hypertension, and hypercholesterolemia. These comorbidities may play a critical role in predisposing obese patients to long-term adverse outcomes.

In our study, extremely obese patients (58 ± 11 years) were 10 years younger than nonobese patients (68 ± 10 years) at the time of cardiac surgery. We noted a consistent trend toward younger age for cardiac surgery as BMI increased. Yap and coworkers [15] found obesity to be most prevalent in the age of 35 to 54 years, and obese patients were 1.4 times more likely to undergo CABG or valve surgery.

Female sex predominated the operative mortality in our study (100% female). Although women have been identified as experiencing greater mortality and morbidities after isolated CABG, valve, and combination surgery of valve and CABG [16–18], we cannot appreciate a similar observation in our study owing to the small sample size. All 5 of these patients underwent nonelective and redo surgery, which highly indicated the possibility of preoperative critical conditions or surgical reluctance.

Previous studies have demonstrated a prominent association between obesity and a number of adverse outcomes, such as atrial fibrillation, prolonged mechanical ventilation, longer intensive care unit stay, and sternal infection [1–3]. We were only able to identify a significant association between extreme obesity and longer intensive care unit stay. We found extremely obese patients had a decreased requirement for blood products transfusion. This is consistent with previous reports [1, 5, 14]. One of the possibilities for this finding is that extreme obesity is associated with a lower degree of hemodilution caused by the relatively fixed size of the bypass circuit. This may also decrease cardiopulmonary bypass–generated coagulopathy that reduces the rate of postoperative bleeding [14]. In our study, another explanation might be the more frequent use of off-pump CABG surgery.

A significant concern remains regarding the formidable surgical challenge of performing cardiac surgery on these extremely obese patients. In our hospital, an average of 50% of CABG surgery was performed by off-pump technique in the last 5 years. In this group of patients, 56% underwent off-pump CABG. The proportions of internal mammary artery (IMA) usage and grafts received per patient are highly comparable with other studies conducted on general isolated CABG patients, in which the use of the IMA graft was 83% and 93% in men, and 76% and 92% in women [19, 20]. The favorable result of CABG surgery in this group of patients is particularly noteworthy because of the dominant constitution of female patients (61%). Prior studies indicated that women have better outcomes with off-pump CABG than with on-pump CABG [16, 19, 20].

As regards the interpretation of our results, several study limitations need addressing. First, this study may include all the limitations inherent in any retrospective single-institution analysis, and underestimate the true effect of extreme obesity on combined outcomes from multiple centers. Second, the relatively small sample size limits powerful statistical conclusions. Additionally, extremely obese patients undergoing elective surgery were discretely selected, suggesting selection bias. With the exception of nonelective surgery, our current results are most likely attributable to improved diagnostics, case ascertainment, and intent references.

In summary, we found that extreme obesity promoted the need for surgical intervention 10 years earlier than normal weight. Cardiac surgery does not seem contraindicated among extremely obese patients. This group of patients could especially benefit from elective off-pump CABG surgery with lower operative mortality and other postoperative complications. Extreme obesity was not associated with increased risk of operative mortality in elective surgery.


   Acknowledgments
Top
 Abstract
 Introduction
 Patients and Methods
 Results
 Comment
 Acknowledgments
References
 
We thank Nancy J. Kershner, MedStar Research Institute, for editing the manuscript.


   References
Top
 Abstract
 Introduction
 Patients and Methods
 Results
 Comment
 Acknowledgments
 References
 

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  4. www.cdc.gov/NCHS.
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  8. Haan CK, O'Brien S, Edwards FH, Peterson ED, Ferguson TB. Trends in emergency coronary artery bypass grafting after percutaneous coronary intervention: 1994–2003 Ann Thorac Surg 2006;81:1658-1665.[Abstract/Free Full Text]
  9. Wasvary H, Shannon F, Bassett J, O'Neill W. Timing of coronary artery bypass grafting after acute myocardial infarction Am Surg 1997;63:710-715.[Medline]
  10. Hata M, Shiono M, Sezai A, et al. Outcome of emergency conventional coronary surgery for acute coronary syndrome due to left main coronary disease Ann Thorac Cardiovasc Surg 2006;12:28-31.[Medline]
  11. Revilla A, Lopez J, Vulacosta I, et al. Clinical and prognostic profile of patients with infective endocarditis who need urgent surgery Eur Heart J 2007;28:65-71.[Abstract/Free Full Text]
  12. Vistarini N, d'Alessandro C, Aubert S, et al. Surgery for infective endocarditis on mitral annulus calcification J Heart Valve Dis 2007;16:611-616.[Medline]
  13. Eicher JC, De Nadai L, Soto FX, et al. Bacterial endocarditis complicating mitral annular calcification: a clinical and echocardiographic study J Heart Valve Dis 2004;13:217-227.[Medline]
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  15. Yap CH, Mohajeri M, Yii M. Obesity and early complications after cardiac surgery Med J Aust 2007;186:350-354.[Medline]
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