Proefschrift Kerklaan

Introduction

Despite the improvement of neuro-endocrine, immunologic and metabolic status, clinical parameters, such as weight and functional status (measured with the Functional Status Scale in medical and cardiac critically ill children), are known to be worse at discharge 71,87 . Profound muscle weakness, due to muscle wasting and critical illness myopathy as observed with prolonged duration of the stable phase, contributes to morbidity and adverse outcome in the ICU and PICU 88,89 and may even cause long-term functional disability beyond hospital discharge 89 . Nutrient administration in the stable and recovery phase The focus of nutritional therapy during the stable and recovery phase should be aimed at restoration of lean body mass whereas synthesis of excess fat mass is to be avoided. To prevent muscle weakness, the duration of immobilisation should be reduced as much as possible 90 . A combination of optimal nutritional support and physical exercise/mobilisation appears to be a logical intervention, but no such studies have been performed in critically ill patients 91 . A recent systematic review and a single centre study in mechanically ventilated children, calculated a minimum intake of respectively 57 and 58 kcal/kg/day to achieve a positive nitrogenbalance 92,93 . Inboth studies, a protein intake of 1.5 g/kg/daywas required to equilibrate nitrogen balance, reflecting a protein-energy ratio of around 10 energy%protein. Since these two studies made no distinction between the phases of critical illness, it remains unclear if this minimal intake should already be provided in the acute phase or should be reserved for subsequent phases. Because nutritional intake during the stable and recovery phase is not only aimed at equilibrating nitrogen balance, but also at enabling recovery, growth and catch- up growth, caloric intake during these phases needs to be inclined from the above mentioned minimum intake 94,95 . Indeed, higher caloric and protein intake (with a sufficient protein-energy ratio) via the enteral route are associated with higher 60-day survival 2,96 , asking for a more aggressive feeding approach than in the acute phase. Energy expenditure throughout the course of critical illness Energy requirements for critically ill children vary between individuals and also between the phases of critical illness. REE is one component of total energy expenditure (TEE), the other components are physical activity, the thermic effect of food, and the energy cost of growth. Currently, optimal caloric intake in critically ill children is frequently defined as 90- 110% of REE 1,97-99 , with an intake below or above this range indicating underfeeding and overfeeding, respectively. In order to prevent the detrimental effects associated with these two types of malnutrition, REE is advised to guide nutritional therapy throughout the course of illness 2,4,100-102 . Ideally, REE should be measured using indirect calorimetry (IC). With IC, a metabolic monitor is attached to the ventilator circuit of the child to derive REE from minute- to-minute measurements of oxygen consumption (VO 2 ) and carbon dioxide production (VCO 2 ) 103 . Alternatively, a canopy mode can be used for spontaneously breathing children. The

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