Conclusions : Obesity is associated with lower risks after cardiac surgery , with consistent effects noted in multiple analyses attempting to address residual confounding and reverse causation
Background : In an apparent paradox , morbidity and mortality are lower in obese patients undergoing cardiac surgery  , although the nature of this association is unclear .
We sought to determine whether the obesity paradox observed in cardiac surgery is attributable to reverse epidemiology , bias , or confounding .
The Influence of Body Mass Index on Outcomes in Patients Undergoing Cardiac Surgery: Does the Obesity Paradox Really Exist?
Purpose 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 prospect ively 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 ( 25–29.9kg∙m−2 ; n = 1150 ; 47 % ) , obese ( ≥30–≤34.9kg∙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 48h after admission respectively . Obese patients showed a higher risk for Perioperative Myocardial Infa rct ion ( 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 Infa rct ion 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
Conclusions : Obesity is associated with lower risks after cardiac surgery , with consistent effects noted in multiple analyses attempting to address residual confounding and reverse causation
Background : In an apparent paradox , morbidity and mortality are lower in obese patients undergoing cardiac surgery  , although the nature of this association is unclear .
We sought to determine whether the obesity paradox observed in cardiac surgery is attributable to reverse epidemiology , bias , or confounding .