Proefschrift Kerklaan

Introduction

Nutritional challenges in the paediatric intensive care unit Critical illness is characterised by anorexia and/or feeding intolerance. Critically ill children have limited macronutrient stores and higher energy requirements compared with adults. Without intervention, this results in substantial caloric and macronutrient deficits following paediatric intensive care unit (PICU) admittance, which have been associated with poor outcomes and impaired growth 1,2 . Therefore, current guidelines recommend to initiate nutritional support as soon as possible after admission 3,4 , as it is associated with improved recovery and outcome in critically ill children 2,5 . However, these international consensus-based guidelines mostly rely on expert opinion and studies in adults and noncritically ill children, as there is a scarcity of high- level evidence on all aspects of nutritional support in critically ill children 6 . These low-grade and inconclusive guidelines are likely to represent a barrier to implemen- tation 7,8 , allowing wide variations in nutritional practices between PICUs 9,10 . Several recent high-quality trials in critically ill adults have raised questions on the presumed benefits of full-replacement nutrition early during critical illness 11,12 . Also in critically ill children, the optimal route, amount, and timing of nutritional support are expected to be dependent on the phase of the stress response in critical illness. The stress response of critical illness The concept of stress was already introduced more than 300 years ago, to describe a regular occurring event that enables an organism to cope with daily changes in the environment 13 . However, excessive stress, as seen in critical illness, is a well-recognised precedent of harm 13 , and in order to survive it, a stress response is initiated. The teleological goal of this response is to provide effective supply of blood, energy and substrates to the injured site and vital tissues 14 . The neuro-endocrine, immunologic and metabolic responses to trauma or severe illness evolve over time 15,16 . This concept of different phases of stress response probably also applies to critically ill children. The following three phases of illness in critically ill children admitted to the PICU are proposed: the acute phase, the stable phase and the recovery phase, all characterised by specific neuro-endocrine, metabolic, and immunologic alterations (Table 1). We hypothesise that these phase-specific changes necessitate different macronutrient intakes.

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Table 1. Definitions of the three phases of the stress response in critically ill children Definition Acute phase

First phase after event, characterised by requirement of (escalating) vital organ support

Stable phase Stabilisation or weaning of vital organ support, whereas the different aspects of the stress response are not (completely) resolved Recovery phase Clinical mobilisation with normalisation of neuro-endocrine, immunologic and metabolic alterations

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