title: The influence of body mass index on outcomes in patients undergoing cardiac surgery: does the obesity paradox really exist?
abstract: OBJECTIVE
  Obesity influences risk stratification in cardiac surgery in everyday practice. However, some studies have reported better outcomes in patients with a high body mass index (BMI): this is known as the obesity paradox. The aim of this study was to quantify the effect of diverse degrees of high BMI on clinical outcomes after cardiac surgery, and to assess the existence of an obesity paradox in our patients.
  
  
  METHODS
  A total of 2,499 consecutive patients requiring all types of cardiac surgery with cardiopulmonary bypass between January 2004 and February 2009 were prospectively studied at our institution. Patients were divided into four groups based on BMI: normal weight (18.5-24.9 kg∙m-2; n = 523; 21.4%), overweight (25-29.9 kg∙m-2; n = 1150; 47%), obese (≥ 30-≤ 34.9 kg∙m-2; n = 624; 25.5%) and morbidly obese (≥ 35kg∙m-2; n = 152; 6.2%). Follow-up was performed in 2,379 patients during the first year.
  
  
  RESULTS
  After adjusting for confounding factors, patients with higher BMI presented worse oxygenation and better nutritional status, reflected by lower PaO2/FiO2 at 24h and higher albumin levels 48 h after admission respectively. Obese patients showed a higher risk for Perioperative Myocardial Infarction (OR: 1.768; 95% CI: 1.035-3.022; p = 0.037) and septicaemia (OR: 1.489; 95% CI: 1.282-1.997; p = 0.005). In-hospital mortality was 4.8% (n = 118) and 1-year mortality was 10.1% (n = 252). No differences were found regarding in-hospital mortality between BMI groups. The overweight group showed better 1-year survival than normal weight patients (91.2% vs. 87.6%; Log Rank: p = 0.029. HR: 1.496; 95% CI: 1.062-2.108; p = 0.021).
  
  
  CONCLUSIONS
  In our population, obesity increases Perioperative Myocardial Infarction and septicaemia after cardiac surgery, but does not influence in-hospital mortality. Although we found better 1-year survival in overweight patients, our results do not support any protective effect of obesity in patients undergoing cardiac surgery.
authors.affiliation: Hospital Universitari de Bellvitge, Intensive Care Department, IDIBELL (Institut d'Investigació Biomèdica Bellvitge; Biomedical Investigation Institute of Bellvitge), C/Feixa Llarga s/n. 08907, L'Hospitalet de Llobregat, Barcelona, Spain.
authors.forename: Juan Carlos
authors.initials: JC
authors.lastname: Lopez-Delgado
authors.affiliation: Hospital Universitari de Bellvitge, Intensive Care Department, IDIBELL (Institut d'Investigació Biomèdica Bellvitge; Biomedical Investigation Institute of Bellvitge), C/Feixa Llarga s/n. 08907, L'Hospitalet de Llobregat, Barcelona, Spain.
authors.forename: Francisco
authors.initials: F
authors.lastname: Esteve
authors.affiliation: Hospital Universitari de Bellvitge, Intensive Care Department, IDIBELL (Institut d'Investigació Biomèdica Bellvitge; Biomedical Investigation Institute of Bellvitge), C/Feixa Llarga s/n. 08907, L'Hospitalet de Llobregat, Barcelona, Spain.
authors.forename: Rafael
authors.initials: R
authors.lastname: Manez
authors.affiliation: Hospital Universitari de Bellvitge, Intensive Care Department, IDIBELL (Institut d'Investigació Biomèdica Bellvitge; Biomedical Investigation Institute of Bellvitge), C/Feixa Llarga s/n. 08907, L'Hospitalet de Llobregat, Barcelona, Spain.
authors.forename: Herminia
authors.initials: H
authors.lastname: Torrado
authors.affiliation: Hospital Universitari de Bellvitge, Intensive Care Department, IDIBELL (Institut d'Investigació Biomèdica Bellvitge; Biomedical Investigation Institute of Bellvitge), C/Feixa Llarga s/n. 08907, L'Hospitalet de Llobregat, Barcelona, Spain.
authors.forename: Maria L
authors.initials: ML
authors.lastname: Carrio
authors.affiliation: Hospital Universitari de Bellvitge, Intensive Care Department, IDIBELL (Institut d'Investigació Biomèdica Bellvitge; Biomedical Investigation Institute of Bellvitge), C/Feixa Llarga s/n. 08907, L'Hospitalet de Llobregat, Barcelona, Spain.
authors.forename: David
authors.initials: D
authors.lastname: Rodríguez-Castro
authors.affiliation: Hospital Universitari de Bellvitge, Intensive Care Department, IDIBELL (Institut d'Investigació Biomèdica Bellvitge; Biomedical Investigation Institute of Bellvitge), C/Feixa Llarga s/n. 08907, L'Hospitalet de Llobregat, Barcelona, Spain.
authors.forename: Elisabet
authors.initials: E
authors.lastname: Farrero
authors.affiliation: Department Physiological Sciences II, University of Barcelona, Barcelona, Spain.
authors.forename: Casimiro
authors.initials: C
authors.lastname: Javierre
authors.affiliation: Department of Public Health, University of Barcelona, Barcelona, Spain.
authors.forename: Konstantina
authors.initials: K
authors.lastname: Skaltsa
authors.affiliation: Hospital Universitari de Bellvitge, Intensive Care Department, IDIBELL (Institut d'Investigació Biomèdica Bellvitge; Biomedical Investigation Institute of Bellvitge), C/Feixa Llarga s/n. 08907, L'Hospitalet de Llobregat, Barcelona, Spain.
authors.forename: Josep L
authors.initials: JL
authors.lastname: Ventura
mesh_terms: D000368:Aged; D015992:Body Mass Index; D006348:Cardiac Surgical Procedures; D005260:Female; D005500:Follow-Up Studies; D006331:Heart Diseases / Q000150:complications / Q000601:surgery*; D006801:Humans; D007431:Intraoperative Complications / Q000453:epidemiology*; D008297:Male; D008875:Middle Aged; D009765:Obesity / Q000150:complications*; D011183:Postoperative Complications / Q000453:epidemiology*; D012307:Risk Factors; D016019:Survival Analysis; D016896:Treatment Outcome