Proefschrift Kerklaan

Use of indirect calorimetry to detect overfeeding

INTRODUCTION

Nutritional support affects outcome in critically ill children 1-3 . Undernutrition has long been the primary focus for nutritional research, but overfeeding is also prevalent in pediatric intensive care units (PICUs) 1,4-6 . Caloric overfeeding is associated with increased mortality in critical ill adults 7 . It may lead to liver dysfunction by increasing the risk for hepatobiliary complications, such as steatosis and cholestasis, and might increase the risk of infection secondary to hyperglycemia 8 . Overfeeding of glucose leads to lipogenesis with an increase in carbon dioxide 9 , resulting in a difficulty to wean from the ventilator 10,11 . Furthermore, overfeeding during critical illness might evoke a phenotype of autophagy deficiency as a potentially important contributor to mitochondrial, organ and skeletal muscle damage, particularly when amino acid enriched parenteral nutrition (PN) is provided 12,13 . Also in critically ill children, unintended consequences of overfeeding are likely to occur 14 . To prevent these detrimental effects, nutritional therapies are ideally guided by resting energy expenditure (REE) throughout the course of illness 15 . REE can be measured (mREE) by indirect calorimetry or predicted by use of equations, and might be affected by the type, severity and stage of disease 16-18 . Because there is a lack of studies using clinical endpoints to determine the optimal caloric intake in critically ill children, recommendations on minimum caloric intake are often based on equilibrating energy or protein balances 19,20 . So far, however, no clinical endpoint or (surrogate) marker has been studied to determine the optimal maximum caloric intake in this population. Overfeeding is arbitrarily defined as a ratio caloric intake/ REE >110% 7,21-23 or >120% 14,24-28 (see related studies in Table 1). As an alternative method the comparison of measured respiratory quotient (RQ) to the predicted RQ based on the macronutrient intake (RQ macr ) is suggested 29,30 . The measured RQ is derived from the ratio of CO 2 production over O 2 consumption and reflects the use of different substrates. An RQ value >1.0 indicates lipogenesis, and is frequently used to identify carbohydrate overfeeding 29 . RQ macr is the weighted average of the RQs of the different macronutrients administered, which can be obtained from the modified Lusk table. A difference >0.05 between RQ and RQ macr has been proposed to define overfeeding 29,30 . The aim of the present study was to compare different definitions of overfeeding in critically ill mechanically ventilated children based on measurements of mREE, RQ and caloric intake and to find an appropriate definition to study the effect of overfeeding on clinical endpoints in future trials.

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