The authors reply
One concern raised by Zamberlan et al (5) is the adequacy of the definition of obesity and other weight categories. This is indeed an issue that plagues both pediatric clinical care and research. Body mass index (BMI) z scores are currently the most validated tool for assessment of appropriate growth for children above 2 years old through adulthood. BMI z scores are utilized by both the Center for Disease Control (CDC) and the World Health Organization (WHO) to define weight categories. The WHO and CDC definitions are comparable for children over 5 years old, but significant variance in weight category classification occurs for children less than 5 years old, as previously reported by our group (6). For our article, we presented CDC-defined BMI categories because our cohort demographics are most comparable to that utilized for CDC data. To respond to the specific concerns by Zamberlan et al (5), we completed an additional analysis of our data using WHO definitions. This analysis reveals the same finding that the obese have reduced mortality risk from ARDS caused by indirect lung injury compared to their normal weight counterparts, whereas no difference is noted between those with direct lung injury ARDS (Table 1). Zamberlan et al (5) also appropriately state that weight alone cannot be used to define obesity and other weight categories. Currently, BMI-based categorization is the best available option since it accounts for height and gender and is less affected by rapid physique changes that occur during puberty. This is an important consideration since studies using BMI have found an association between obesity and reduced mortality (1–3), while those unable to add the impact of height have shown no difference in outcome by weight category (7). Given that over 20% of hospitalized children are obese and that obesity is independently associated with mortality and other outcomes, it is imperative that the pediatric critical care community reach consensus to operationalize definitions of obesity and nutrition to advance this field.
An additional concern appropriately raised by Zamberlan et al (5) is the accuracy of ARDS diagnosis in obese children. Both the 1994 American-European Consensus Conference definition and the newer Pediatric Acute Lung Injury Consensus Conference definition of pediatric ARDS require the presence of new pulmonary infiltrates on chest radiograph. Obese individuals have greater chest wall mass and increased risk of development of atelectasis, which make reading of chest radiographs difficult and may lead to over diagnosis of mild ARDS in overweight and obese children. We agree that this is a concern and further investigations should subanalyze those of moderate and severe ARDS to test the impact of this potential misdiagnosis.