Proefschrift Kerklaan

Chapter 4

fact that a positive protein balance should be interpreted as an intermediate and not a clinical outcome measure 40 . Based on our data the upper limit of caloric intake was found to be 165% of the ratio caloric intake/mREE based on RQ-RQ macr, reflecting a caloric intake of 79 kcal/kg/day. This upper limit is more in line with the identified minimum intakes than the most frequently used limits of 110% and 120%. An age-dependent definition of overfeeding, however, might be necessary. In the single- center study by Jotterand Chaparro et al., it was shown that nitrogen balance was equilibrated with a caloric intake close to mREE in children younger than 3 years, and 122% of mREE in children older than 3 years 19 . Another reason to question the use of the ratio caloric intake/mREE to identify overfeeding throughout the course of PICU stay is the effect of the phase of critical illness. Several studies have shown that REE remains stable during the first week after admission 16,21,41 . This implies that, when using this ratio to guide nutritional therapy, the upper limit of caloric intake remains stable in this period as well, even if the patient is recovering, and extra energy is presumed necessary for tissue repair and growth. Furthermore, REE is measured in rest, whereas the patient in the recovery phase will be mobilizing. These patients have a higher energy need than patients who are not able to mobilize, but this increase in caloric requirements cannot be identified with current methods. So far, only one study, with a limited number of surgical infants, investigated the relation between caloric intake and the phases of the metabolic stress response using an RQ>1.0, reflecting lipogenesis, to define overfeeding 11 ; it was found that the rate of overfeeding was lower in the resolving stress group, defined by a C-reactive protein (CRP) level of 2 mg/dL or less, compared to the acute stress group (CRP >2 mg/dL) (33.4 vs 69.2%, p<0.001). Although inflammatory parameters such as a CRP level might be used to guide caloric intake, it is not clear how soon energy intake can be increased without the risk of overfeeding, because no single metabolic or hormonal markers or parameters have consistently shown to indicate the start of the anabolic phase. When the child is in the recovery phase and is able to mobilize, optimal caloric intake might be as high as the recommended intake for healthy children 24 or even higher to compensate for catch-up growth. The risk of overfeeding might also be affected by the nutritional status of the child. More attention is paid to nutritional support of malnourished children or children at nutritional risk 42 and absolute weight-based intake goals are lower for malnourished patients than nonmalnourished peers 25 . Also in our study, caloric intake was higher in children with an SD-score WFA<-2. Therefore nutritional goals are more easily reached in this population, but with a concomitant increased risk of overfeeding. Besides the increased caloric intake, malnourishment is likely to affect energy expenditure by an altered body composition. In a recent study, mREE in malnourished critically ill children was found to be 80% of predicted 43 , highlighting the need for measurement of energy requirements to identify overfeeding in

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