The Dose-Response Relationship Between Body Mass Index and Mortality in Subjects Admitted to the ICU With and Without Mechanical Ventilation

BACKGROUND: Obesity has been associated with increased mortality in the general population, whereas a paradoxical relationship between higher body mass index and lower mortality has been referred to as the obesity paradox in critically ill patients. However, it remains unknown whether a particular subgroup is most affected. The aim of the present study is to elucidate whether obesity is associated with lower mortality in the ICU population by comparing subjects with and without mechanical ventilation. METHODS: A total of 334,238 subjects from a nationwide database who were discharged between July 2010 and March 2012 and who were admitted to general ICUs during their hospitalization were included in this study. The primary outcome was in-hospital mortality. RESULTS: Of all subjects evaluated, 23.3% were started on mechanical ventilation within the first 2 d after ICU admission. Compared with the non-ventilated group, the ventilated group was more likely to have sepsis, pneumonia, or coma. The ventilated group underwent more procedures within the first 2 d after ICU admission compared with the non-ventilated group. A restricted cubic spline function showed lower mortality in subjects with a higher body mass index among the ventilated group, whereas mortality was increased with increasing body mass index in the non-ventilated group. CONCLUSIONS: This study shows that a high body mass index is associated with low mortality in the mechanically ventilated group, whereas the non-ventilated group showed a reverse J-shaped association. There was a higher mortality rate in underweight subjects in both groups.