The obesity paradox is still there: a risk analysis of over 15 000 cardiosurgical patients based on body mass index.

OBJECTIVES: Obesity is an ever-growing problem in contemporary cardiac surgery. Although it accounts for many perioperative comorbidities, it has not been shown to increase mortality. Body mass index (BMI) is therefore not considered in the European System for Cardiac Operative Risk Evaluation (EuroSCORE). We sought to confirm whether this holds true for our own single-centre patient population.
METHODS: Data from 15 314 consecutive patients receiving major cardiac surgery at our institution were analysed. Gender, age, BMI, EuroSCORE, urgency, redo status and all-cause in-hospital mortality were derived from our database. Mortality was grouped into 4 BMI categories. We created a logistic regression model to identify predictors of mortality.
RESULTS: There were 11 034 males and 4280 females. Categorical mortality was 8.79% (underweight), 7.04% (normal weight), 5.16% (overweight), 6.30% (obese), rendering an inverse J-shaped pattern known as obesity paradox. Univariable regression detected significant predictors of mortality: rising age, female gender, urgent procedures, redo surgery ( P  < 0.001). BMI was no predictor ( P  = 0.575) but became significant with the multivariable analysis ( P  = 0.004). Its effect on mortality was exclusively indirect, being mediated through age ( P  < 0.001). Receiver-operating characteristics curve analysis also confirmed that BMI did not qualify as a risk factor. However, the overweight category was a predictor of lower mortality.
CONCLUSIONS: Our findings from >15 000 patients confirm the obesity paradox showing the least mortality in the overweight group. They support the current EuroSCORE model in that BMI is no independent predictor of early mortality. However, such patients still carry the risk of comorbidities. Likewise, special care is required with underweight patients who show the highest in-hospital mortality.