Obesity in critically ill children associated with increased mortality

1. After controlling for demographic characteristics, comorbidities and severity of illness, being overweight or obese were both associated with increased pediatric intensive care unit (PICU) mortality in the United States.

2. Including height in mortality analysis resulted in different conclusions than in prior studies. When height data was accounted for, the lowest mortality occurred in critically ill children at normal weight levels. This differs from previous studies when height has not be included in the analysis and the lowest mortality in critically ill children was found to occur in those who were mildly to moderately obese.

Evidence Rating Level: 2 (Good)

Study Rundown: In critically ill adults, some data suggests that obesity may be a protective factor. However, in children, this relationship is unknown and studies that currently exist on this topic have reported inconsistent results. Existing studies do not consider weight-for-height/body mass index (BMI) as a variable when addressing PICU mortality. The current study sought to address this gap and to demonstrate whether height data was a necessary measure to properly identify obesity in critically ill children. Using data from a national PICU database from January 2009 to March 2013, researchers found that, after controlling for confounding, overweight and obese BMI status were both associated with increased PICU mortality. These findings were based on weight-for-height/BMI classifications to provide an accurate assessment of body habitus, as opposed to weight-for-age, which has been used in previous studies. Limitations in this study included the inability to determine how weight and height were measured across institutions, and the exclusion of patients with underlying syndromes that affect weight. Despite these limitations, data suggest that the obese or overweight, critically ill child has a higher mortality risk than those with a normal weight-for-height/BMI.

Click to read the study, published today in Pediatrics

Relevant Reading: Extremes of weight centile are associated with increased risk of mortality in pediatric intensive care

In-Depth [retrospective cohort]: This study included 127 607 patients from the Virtual PICU Systems (VPS) database. Using weight-for-gender and age, a z score was calculated according to the World Health Organization (WHO, for children under 2 years of age) and Center for Disease Control (for children above 2 years of age) growth curves. This z score represented one standard deviation away from the United States population mean. A separate z score was calculated using height-for-age, gender, and WHO growth curves. The z scores from both of these groups were combined and patients were then classified into 9 different z score groups. Overall mortality in PICU database was 2.48%. After controlling for age group, hospital, demography characteristics, being moderately underweight or being in any of the overweight categories (including obese) all had a significant independent associations with PICU mortality (p < 0.012). After stratifying data based off of height-for-age, the nadir of mortality shifted and spanned to include more groups. Height data inclusion results in modification of results: analysis without height was found to overestimate the number of overweight and obese children, and overestimate the number of underweight children. If it was not included, it could have been falsely concluded that mildly to moderately overweight status indicates a protective benefit.

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