The authors reply
Although report by Bechard et al (1) concern that our finding was only found in this indirect lung injury subgroup, we offer a counter point to this concern: The presence of the obesity paradox in those with indirect lung injury only (e.g., sepsis or systemic inflammatory response syndrome from polytrauma or systemic vasculitis) may point to a pathobiologic, mechanistic link between increased adiposity, ARDS, and the systemic inflammatory response. In fact, Stapleton et al (5) evaluated biomarkers of systemic inflammatory response in 1,409 adult ARDS subjects and found lower levels of proinflammatory markers (interleukin-8 and tumor necrosis factor-α) as body mass index (BMI) increased, with lower levels of such markers correlating to reduced mortality. Further investigation is clearly needed to parse out this attenuated inflammatory response to critical illness. Such exploration is a future direction of this research team, because we believe that understanding these differences in pathobiology by weight category and mechanism of injury may be useful in adjusting our protocol-driven therapeutic strategies to better meet each patient’s specific premorbid and illness-focused characteristics.
Regarding our method of defining obesity utilizing Centers for Disease Control and Prevention–defined BMI z score cutoffs and excluding those less than 2 years old, we agree that our methodology is not perfect. Unfortunately, such issues plague all pediatric obesity research. This age-based exclusion criteria reduces the generalizability of our findings to our infant patients, but we chose to exclude those less than 2 years old for two reasons: 1) BMI is not a validated method in children less than 2 years old and 2) the inclusion of children less than 2 years old would introduce several confounders including impact of prematurity and intrauterine growth retardation, as well as the variation in dietary habits. This challenge of limiting confounders versus maximizing generalizability is an important one in our field, and we hope such discussions will drive the pediatric critical care community to work together and form a consensus of definitions regarding obesity and nutrition that would benefit all nutrition-based research.
Bechard et al (1) discuss the impact of premorbid conditions on outcome studies in pediatric critical care, and we completely agree that such factors, including past medical history and pre-illness nutritional status, are important. Unfortunately, we did not have an objective way to assess premorbid nutritional status in this cohort. Once again, the lack of objective pre-illness health status plagues all of pediatric critical care (and adult critical care, for that matter) and limits, not only studies of mortality and duration of hospitalization but also longer term outcomes such as post-ICU function and neurocognitive status.