HHS Public Access Author manuscript Author Manuscript
J Cardiothorac Vasc Anesth. Author manuscript; available in PMC 2017 October 01. Published in final edited form as: J Cardiothorac Vasc Anesth. 2016 October ; 30(5): 1308–1316. doi:10.1053/j.jvca.2016.03.002.
Impact of body mass index on the outcomes in cardiac surgery Mei Gao, MD1,2, Jianzhong Sun, MD, PhD3, Nilas Young, MD4, Douglas Boyd, MD4, Zane Atkins, MD4, Zhongmin Li, PhD5, Qian Ding, MD3,6, James Diehl, MD7, and Hong Liu, MD2 1Department
of Anesthesiology, First Affiliated Hospital of Nanjing Medical University, Nanjing, Jiangsu, China
2Department
Author Manuscript
of Anesthesiology and Pain Medicine, University of California Davis Health System, Sacramento, CA
3Department
of Anesthesiology, Thomas Jefferson University and Hospitals, Philadelphia, PA
4Department
of Surgery University of California Davis Health System, Sacramento, CA
5Department
of Internal Medicine, University of California Davis Health System, Sacramento, CA
6Department
of Anesthesiology, The Fourth Military Medical University, Xian, China
7Division
of Cardiothoracic Surgery, Thomas Jefferson University and Hospitals, Philadelphia, PA
Abstract Author Manuscript
Objectives—Body mass index (BMI) is commonly used in obesity classification as a surrogate measure and obesity is associated with a cluster of risk factors for cardiovascular disease. The aim of this study was to investigate BMI on short-term outcomes after cardiac surgery. Design—A retrospective cohort study. Setting—University teaching hospital, two centers. Participants—The study consisted of 4,740 patients who underwent cardiac surgery of two hospitals from July 1, 2001 to June 30, 2013 in one hospital and from September 1, 2003 to August 31, 2014 in another hospital were included in this study. Interventions—No changes to standard practice were required.
Author Manuscript
Measurements and Main Results—They were assigned into six BMI groups as follows: Underweight BMI < 18.5 kg/m2), Normal weight (18.5 ≤ BMI < 25 kg/m2), Overweight (25 ≤ BMI < 30 kg/m2), Class I (30 ≤ BMI < 35 kg/m2), Class II (35 ≤ BMI < 40 kg/m2) and Class III obese (BMI ≥ 40 kg/m2). Short-term major postoperative complications (post-operative stroke, cardiac arrest, new atrial fibrillation/flutter, permanent rhythm device insertion, deep sternal infection, sepsis, prolonged ventilation, pneumonia, renal dialysis, renal failure, ICU readmission, total ICU hours and readmission in 30 days) and mortalities (in-hospital mortality, 30-day Correspondence to: Hong Liu, MD, Department of Anesthesiology and Pain Medicine, University of California Davis Health System, 4150 V Street, Suite 1200, Sacramento, CA 95817, Tel: 916-734-5031, Fax: 916-734-7980, [email protected]. Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Gao et al.
Page 2
Author Manuscript
mortality, operative mortality) were compared among various BMI groups after cardiac surgery. Age, gender, surgery type, family history of CAD, diabetes, hypertension, heart failure and lipid lowering medication were the risk factors for early outcomes. Multiple logistic regression analysis indicated that being Underweight or Class III obese may present with significant differences of some short-term outcomes, including deep sternal infection, prolonged ventilation, new atrial fibrillation/flutter and renal failure. However, being Overweight or Class I obese has a positive impact on discharge mortality and operative mortality. Conclusions—The results of this study demonstrated that extreme obesity and underweight were significantly associated with early major adverse clinical outcomes. However, there was an “obese paradox” in short-term mortality after cardiac surgery. Keywords
Author Manuscript
BMI; obese; outcome; cardiac surgery; mortality
Author Manuscript
Body mass index (BMI) is a person's weight in kilograms divided by the square of height in meters, which is commonly used in obesity classification as a surrogate measure. A BMI value of ≥30.0 kg/m2 defines obesity while a BMI value of 25.0–29.9 kg/m2 defines being overweight.1,2 Obesity is associated with a cluster of risk factors for cardiovascular disease, known as the metabolic syndrome, which include hypertension, dyslipidemia, insulin resistance, and diabetes mellitus.2,3 The prevalence of obesity worldwide, especially in developed countries, has reached epidemic proportions. It is expected that an increasing number of obese patients will require cardiac surgery.4 While not always accurate, BMI is still a useful measure of overall body habitus since it is highly correlated with body surface area (BSA);5 it is also commonly used in anthropometric measurements in most previous and new risk models for the Society of Thoracic Surgeons (STS).5-7 Several studies examine the effect of obesity on in-hospital mortality and long-term survival with variable conclusions. Some studies suggested that obesity did not increase morbidity or mortality, but actually had favorable outcomes after cardiac surgery;8-11 whereas other studies demonstrated that obesity was a predictor of either morbidity or mortality.12-17 Since the relation between BMI and surgical outcomes is complex, the aim of the present study was to evaluate the influence of BMI on early clinical outcomes in patients undergoing cardiac surgery.
Methods Study design
Author Manuscript
This was a two-center study involving 6,515 patients who underwent cardiac surgery at two hospitals with the period spanning from July 1, 2001 to June 30, 2013 in one hospital and September 1, 2003 to August 31, 2014 in the other hospital. The institutional review board permissions of the two hospitals were granted for this retrospective study. Patients included in this study met the following criteria: CABG and/or valve surgery, CABG and/or valve surgery combined with other procedures. Patients excluded from this study met one of the following criteria: emergency surgery, off-pump or robotic surgery, surgery requiring deep hypothermic circulatory arrest or involving the thoracic aorta, and patients with incomplete J Cardiothorac Vasc Anesth. Author manuscript; available in PMC 2017 October 01.
Gao et al.
Page 3
Author Manuscript
data. A total of 4,740 patients met the inclusion criteria and were assigned into six classes according to their BMI: ‘Underweight’ (BMI < 18.5 kg/m2) (n = 62), ‘Normal’ (18.5 ≤ BMI < 25 kg/m2) (n = 1144), ‘Overweight’ (25 ≤ BMI < 30 kg/m2) (n = 1774), ‘Class I obese’ (30 ≤ BMI < 35 kg/m2) (n = 1044), ‘Class II obese’ (35 ≤ BMI < 40 kg/m2) (n =441) and ‘Class III obese’ (BMI ≥ 40 kg/m2) (n = 275).18 The study design is shown in Figure 1. Data collection The patient data from two hospitals were both collected and organized following the template of the Society of Thoracic Surgeons Adult Cardiac Surgery Database Data Specifications (Version 2.81, 2014) and the hospital medical records, including demographics, patient history, medical record information, preoperative risk factors, preoperative medications, intraoperative variables, postoperative events, in-hospital mortality, 30-day mortality and operative mortality.
Author Manuscript
Outcome definitions Primary outcomes were in-hospital mortality, 30-day mortality, operative mortality and life threatening cardiovascular events including post-operative stroke, cardiac arrest, new atrial fibrillation/flutter, and permanent rhythm device insertion. Secondary outcomes included deep sternal infection, sepsis, prolonged ventilation, pneumonia, renal dialysis, renal failure, ICU readmission, total ICU hours and readmission in 30 days.
Author Manuscript Author Manuscript
The definitions of all these outcomes are based on the STS Adult Cardiac Surgery Database Data Specifications. Primary outcome definitions are as follows: in-hospital mortality--death during the hospitalization in which surgery occurred; 30-day mortality--death at 30 days post-surgery (whether in hospital or not); operative mortality--including (1) all deaths, regardless of cause, occurring during the hospitalization in which the operation was performed, even if after 30 days (including patients transferred to other acute care facilities), and (2) all deaths, regardless of cause, occurring after discharge from the hospital, but before the end of the thirtieth postoperative day; stroke--a postoperative stroke and the type of stroke (i.e., any confirmed neurological deficit of abrupt onset caused by a disturbance in blood supply to the brain) that did not resolve within 24 hours; cardiac arrest-- indication of the patient acquiring acute cardiac arrest documented by one of the four diagnosis (ventricular fibrillation, rapid ventricular tachycardia with hemodynamic instability, asystole and implantable cardioverter defibrillator shocks); new atrial fibrillation/flutter (AF)-- the patient experienced AF requiring treatment excluding AF at the start of surgery; permanent device insertion-- indication of the development of new dysrhythmia requiring insertion of a permanent device. Secondary outcomes definitions are as follows: deep sternal infection indicates a deep sternal wound infection or mediastinitis within 30 days of the procedure or any time during the hospitalization for surgery, sepsis is evidence of serious infection accompanied by a deleterious systemic response, prolonged ventilation is described as the patient had prolonged post-operative pulmonary ventilation > 24.0 hours, pneumonia the patient had pneumonia according to the Center for Disease Control definition, renal-dialysis is defined as the patient having a new requirement for dialysis postoperatively which may include hemodialysis and peritoneal dialysis, renal failure defined as the patient had acute renal failure or worsening renal function resulting in one or both criteria (1. increase in
J Cardiothorac Vasc Anesth. Author manuscript; available in PMC 2017 October 01.
Gao et al.
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Author Manuscript
serum creatinine level 3.0 × greater than baseline, or serum creatinine level ≥ 4 mg/dL, acute rise must be at least 0.5 mg/dl and 2. a new requirement for dialysis postoperatively), ICU readmission represents whether the patient spent time in an intensive care unit (ICU) after having been transferred to a step-down unit, total ICU hours is the summation of initial ICU hours and additional ICU hours, readmission in 30 days indicates whether the patient was readmitted to an acute care facility as an inpatient within 30 days from the date of initial surgery for any reason. Statistical analysis
Author Manuscript
SAS version 9.4 for Windows (SAS Inc., Cary, NC) was used for statistical analysis. BMI group categorical variables were compared by using the χ2 test and presented as numbers and percentages. Continuous variables were compared by using t-test analysis and presented as mean±SD. Univariate and multivariate logistic regressions were performed to assess associations of demographic, preoperative risk factors and clinical outcome variables. Parsimonious multivariate logistic regression and multivariable general linear analysis adjusted with patient demographic and clinical risk factors were performed to investigate the impact of BMI on short-term outcomes (categorical and continuous variables, respectively). To achieve model parsimony and stability, the backward selection procedure was applied with the drop-out criterion p>0.05 from risk factors on the basis of variables collected in the database, forced inclusion of BMI, surgery type, age, gender and status. The results are reported as numbers with percentages, mean±SD and odds ratios (OR) with 95% confidence intervals (CI). All reported p values are 2-tailed, and p values
J Cardiothorac Vasc Anesth. Author manuscript; available in PMC 2017 October 01. Published in final edited form as: J Cardiothorac Vasc Anesth. 2016 October ; 30(5): 1308–1316. doi:10.1053/j.jvca.2016.03.002.
Impact of body mass index on the outcomes in cardiac surgery Mei Gao, MD1,2, Jianzhong Sun, MD, PhD3, Nilas Young, MD4, Douglas Boyd, MD4, Zane Atkins, MD4, Zhongmin Li, PhD5, Qian Ding, MD3,6, James Diehl, MD7, and Hong Liu, MD2 1Department
of Anesthesiology, First Affiliated Hospital of Nanjing Medical University, Nanjing, Jiangsu, China
2Department
Author Manuscript
of Anesthesiology and Pain Medicine, University of California Davis Health System, Sacramento, CA
3Department
of Anesthesiology, Thomas Jefferson University and Hospitals, Philadelphia, PA
4Department
of Surgery University of California Davis Health System, Sacramento, CA
5Department
of Internal Medicine, University of California Davis Health System, Sacramento, CA
6Department
of Anesthesiology, The Fourth Military Medical University, Xian, China
7Division
of Cardiothoracic Surgery, Thomas Jefferson University and Hospitals, Philadelphia, PA
Abstract Author Manuscript
Objectives—Body mass index (BMI) is commonly used in obesity classification as a surrogate measure and obesity is associated with a cluster of risk factors for cardiovascular disease. The aim of this study was to investigate BMI on short-term outcomes after cardiac surgery. Design—A retrospective cohort study. Setting—University teaching hospital, two centers. Participants—The study consisted of 4,740 patients who underwent cardiac surgery of two hospitals from July 1, 2001 to June 30, 2013 in one hospital and from September 1, 2003 to August 31, 2014 in another hospital were included in this study. Interventions—No changes to standard practice were required.
Author Manuscript
Measurements and Main Results—They were assigned into six BMI groups as follows: Underweight BMI < 18.5 kg/m2), Normal weight (18.5 ≤ BMI < 25 kg/m2), Overweight (25 ≤ BMI < 30 kg/m2), Class I (30 ≤ BMI < 35 kg/m2), Class II (35 ≤ BMI < 40 kg/m2) and Class III obese (BMI ≥ 40 kg/m2). Short-term major postoperative complications (post-operative stroke, cardiac arrest, new atrial fibrillation/flutter, permanent rhythm device insertion, deep sternal infection, sepsis, prolonged ventilation, pneumonia, renal dialysis, renal failure, ICU readmission, total ICU hours and readmission in 30 days) and mortalities (in-hospital mortality, 30-day Correspondence to: Hong Liu, MD, Department of Anesthesiology and Pain Medicine, University of California Davis Health System, 4150 V Street, Suite 1200, Sacramento, CA 95817, Tel: 916-734-5031, Fax: 916-734-7980, [email protected]. Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Gao et al.
Page 2
Author Manuscript
mortality, operative mortality) were compared among various BMI groups after cardiac surgery. Age, gender, surgery type, family history of CAD, diabetes, hypertension, heart failure and lipid lowering medication were the risk factors for early outcomes. Multiple logistic regression analysis indicated that being Underweight or Class III obese may present with significant differences of some short-term outcomes, including deep sternal infection, prolonged ventilation, new atrial fibrillation/flutter and renal failure. However, being Overweight or Class I obese has a positive impact on discharge mortality and operative mortality. Conclusions—The results of this study demonstrated that extreme obesity and underweight were significantly associated with early major adverse clinical outcomes. However, there was an “obese paradox” in short-term mortality after cardiac surgery. Keywords
Author Manuscript
BMI; obese; outcome; cardiac surgery; mortality
Author Manuscript
Body mass index (BMI) is a person's weight in kilograms divided by the square of height in meters, which is commonly used in obesity classification as a surrogate measure. A BMI value of ≥30.0 kg/m2 defines obesity while a BMI value of 25.0–29.9 kg/m2 defines being overweight.1,2 Obesity is associated with a cluster of risk factors for cardiovascular disease, known as the metabolic syndrome, which include hypertension, dyslipidemia, insulin resistance, and diabetes mellitus.2,3 The prevalence of obesity worldwide, especially in developed countries, has reached epidemic proportions. It is expected that an increasing number of obese patients will require cardiac surgery.4 While not always accurate, BMI is still a useful measure of overall body habitus since it is highly correlated with body surface area (BSA);5 it is also commonly used in anthropometric measurements in most previous and new risk models for the Society of Thoracic Surgeons (STS).5-7 Several studies examine the effect of obesity on in-hospital mortality and long-term survival with variable conclusions. Some studies suggested that obesity did not increase morbidity or mortality, but actually had favorable outcomes after cardiac surgery;8-11 whereas other studies demonstrated that obesity was a predictor of either morbidity or mortality.12-17 Since the relation between BMI and surgical outcomes is complex, the aim of the present study was to evaluate the influence of BMI on early clinical outcomes in patients undergoing cardiac surgery.
Methods Study design
Author Manuscript
This was a two-center study involving 6,515 patients who underwent cardiac surgery at two hospitals with the period spanning from July 1, 2001 to June 30, 2013 in one hospital and September 1, 2003 to August 31, 2014 in the other hospital. The institutional review board permissions of the two hospitals were granted for this retrospective study. Patients included in this study met the following criteria: CABG and/or valve surgery, CABG and/or valve surgery combined with other procedures. Patients excluded from this study met one of the following criteria: emergency surgery, off-pump or robotic surgery, surgery requiring deep hypothermic circulatory arrest or involving the thoracic aorta, and patients with incomplete J Cardiothorac Vasc Anesth. Author manuscript; available in PMC 2017 October 01.
Gao et al.
Page 3
Author Manuscript
data. A total of 4,740 patients met the inclusion criteria and were assigned into six classes according to their BMI: ‘Underweight’ (BMI < 18.5 kg/m2) (n = 62), ‘Normal’ (18.5 ≤ BMI < 25 kg/m2) (n = 1144), ‘Overweight’ (25 ≤ BMI < 30 kg/m2) (n = 1774), ‘Class I obese’ (30 ≤ BMI < 35 kg/m2) (n = 1044), ‘Class II obese’ (35 ≤ BMI < 40 kg/m2) (n =441) and ‘Class III obese’ (BMI ≥ 40 kg/m2) (n = 275).18 The study design is shown in Figure 1. Data collection The patient data from two hospitals were both collected and organized following the template of the Society of Thoracic Surgeons Adult Cardiac Surgery Database Data Specifications (Version 2.81, 2014) and the hospital medical records, including demographics, patient history, medical record information, preoperative risk factors, preoperative medications, intraoperative variables, postoperative events, in-hospital mortality, 30-day mortality and operative mortality.
Author Manuscript
Outcome definitions Primary outcomes were in-hospital mortality, 30-day mortality, operative mortality and life threatening cardiovascular events including post-operative stroke, cardiac arrest, new atrial fibrillation/flutter, and permanent rhythm device insertion. Secondary outcomes included deep sternal infection, sepsis, prolonged ventilation, pneumonia, renal dialysis, renal failure, ICU readmission, total ICU hours and readmission in 30 days.
Author Manuscript Author Manuscript
The definitions of all these outcomes are based on the STS Adult Cardiac Surgery Database Data Specifications. Primary outcome definitions are as follows: in-hospital mortality--death during the hospitalization in which surgery occurred; 30-day mortality--death at 30 days post-surgery (whether in hospital or not); operative mortality--including (1) all deaths, regardless of cause, occurring during the hospitalization in which the operation was performed, even if after 30 days (including patients transferred to other acute care facilities), and (2) all deaths, regardless of cause, occurring after discharge from the hospital, but before the end of the thirtieth postoperative day; stroke--a postoperative stroke and the type of stroke (i.e., any confirmed neurological deficit of abrupt onset caused by a disturbance in blood supply to the brain) that did not resolve within 24 hours; cardiac arrest-- indication of the patient acquiring acute cardiac arrest documented by one of the four diagnosis (ventricular fibrillation, rapid ventricular tachycardia with hemodynamic instability, asystole and implantable cardioverter defibrillator shocks); new atrial fibrillation/flutter (AF)-- the patient experienced AF requiring treatment excluding AF at the start of surgery; permanent device insertion-- indication of the development of new dysrhythmia requiring insertion of a permanent device. Secondary outcomes definitions are as follows: deep sternal infection indicates a deep sternal wound infection or mediastinitis within 30 days of the procedure or any time during the hospitalization for surgery, sepsis is evidence of serious infection accompanied by a deleterious systemic response, prolonged ventilation is described as the patient had prolonged post-operative pulmonary ventilation > 24.0 hours, pneumonia the patient had pneumonia according to the Center for Disease Control definition, renal-dialysis is defined as the patient having a new requirement for dialysis postoperatively which may include hemodialysis and peritoneal dialysis, renal failure defined as the patient had acute renal failure or worsening renal function resulting in one or both criteria (1. increase in
J Cardiothorac Vasc Anesth. Author manuscript; available in PMC 2017 October 01.
Gao et al.
Page 4
Author Manuscript
serum creatinine level 3.0 × greater than baseline, or serum creatinine level ≥ 4 mg/dL, acute rise must be at least 0.5 mg/dl and 2. a new requirement for dialysis postoperatively), ICU readmission represents whether the patient spent time in an intensive care unit (ICU) after having been transferred to a step-down unit, total ICU hours is the summation of initial ICU hours and additional ICU hours, readmission in 30 days indicates whether the patient was readmitted to an acute care facility as an inpatient within 30 days from the date of initial surgery for any reason. Statistical analysis
Author Manuscript
SAS version 9.4 for Windows (SAS Inc., Cary, NC) was used for statistical analysis. BMI group categorical variables were compared by using the χ2 test and presented as numbers and percentages. Continuous variables were compared by using t-test analysis and presented as mean±SD. Univariate and multivariate logistic regressions were performed to assess associations of demographic, preoperative risk factors and clinical outcome variables. Parsimonious multivariate logistic regression and multivariable general linear analysis adjusted with patient demographic and clinical risk factors were performed to investigate the impact of BMI on short-term outcomes (categorical and continuous variables, respectively). To achieve model parsimony and stability, the backward selection procedure was applied with the drop-out criterion p>0.05 from risk factors on the basis of variables collected in the database, forced inclusion of BMI, surgery type, age, gender and status. The results are reported as numbers with percentages, mean±SD and odds ratios (OR) with 95% confidence intervals (CI). All reported p values are 2-tailed, and p values
