Applied nutritional investigationAdequate feeding and the usefulness of the respiratory quotient in critically ill children
Introduction
Nutritional support is essential in the care of critically ill children because inadequate feeding can increase morbidity and mortality rates [1]. Critically ill children who receive adequate nutritional support have shown significant improvement in physiologic stability and outcome [2], [3]. Further, the goal of supporting critically ill children is not only to restore a normal functioning level but also to meet the requirements for growth and development. Thus clinicians in the pediatric intensive care unit (ICU) are challenged to provide adequate energy for optimal tissue synthesis and immune function and avoid complications of overfeeding.
The major problem in clinical practice is to define nutritional requirements for critically ill children because demands range widely, with altered metabolic states determined by a child's age, state of health, and nutritional status. Moreover, metabolic responses may greatly vary, depending on the nature of the injury and the variability of the individual response to the same type of injury [4], [5]. Because standard feeding protocols do not provide for interindividual differences in energy requirements and because the available prediction equations are inadequate for calculating energy needs in critically ill children, these children are more vulnerable to complications that arise from underfeeding or overfeeding.
Therefore, it is important to monitor whether children admitted to an ICU are adequately fed. Indirect calorimetry provides a method that can help in this matter. In studies in adults, feeding adequacy was determined by the ratio of energy intake (EI) to measured energy expenditure (MEE) plus 10% for activity [6]. A second parameter derived from indirect calorimetry is the respiratory quotient (RQ), which is the ratio of carbon dioxide produced to oxygen consumed. The role of the RQ as a marker of substrate use is controversial in critical illness because the body's ability to use nutrient substrates may be altered. Moreover, the clinical usefulness of the RQ as an indicator of underfeeding or overfeeding has been found to be limited in adult critically ill patients due to its low sensitivity and specificity [7]. McClave et al. [7] concluded that its clinical usefulness is restricted to a marker of test validity and a marker of respiratory tolerance of the nutritional support regimen. Previous studies among critically ill children using indirect calorimetry have not specified criteria for adequate feeding; the only criterion specified to define overfeeding is a measured RQ higher than 1.0 [4], [8].
We developed this study with two objectives: 1) to determine incidences of underfeeding and overfeeding in a heterogeneous cohort of children who had been admitted to the pediatric ICU of our level III children's hospital, based on the criterion used in adults, and 2) to evaluate whether the RQ could be used to monitor whether these children were adequately fed.
Section snippets
Subjects
Over a 1-y period (2001) children 18 y and younger who had been admitted to our level III multidisciplinary pediatric or surgical ICU with an expected stay of at least 48 h were studied repeatedly by indirect calorimetry during the first 14 d of admission. The institutional review board of the Erasmus MC (Rotterdam, The Netherlands) approved the study protocol, and written (parental) informed consent was obtained before subjects entered the study. Exclusion criteria for this study were
Clinical characteristics
One hundred twelve children were eligible for this study. However, 14 children were excluded from analysis because of invalid results (e.g., did not reach steady state) or incomplete nutritional data. Thus 98 children comprised the final study group, and their clinical characteristics at admission are presented in Table 1.
A total of 195 measurements, 83 in canopy mode and 112 in respiratory mode, were performed. In 49 children (50%), more than one valid indirect calorimetric measurement could
Discussion
In this study we analyzed relations between MEE, actual EI, and measured RQ in a mixed cohort of children who had been admitted to our ICU. On 21% and 79% of measurement days, EI was below and above MEE, respectively. By applying a classification used for adults [6], [7], children would have received adequate nutrition on only 10% of days, whereas children would have been underfed and overfed on 21% and 69% of days, respectively.
The large proportion of overfeeding noted in this study is
Acknowledgments
The authors thank Ada van den Bos, Annelies Bos, Marjan Maliepaard, Marianne Mourik, and Ineke van Vliet for help with data collection. They also thank Ko Hagoort (Erasmus MC, Rotterdam) for careful editing.
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This study was supported in part by Nutricia Nederland BV, Zoetermeer, The Netherlands.