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Introduction
11
1
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.
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