160 / 208
Chapter 8
158
In children with tube leak and children on HFO and ECMO, measurement of expiratory VCO
2
is
inherently meaningless. In children with a supplied oxygen level of more than 60%, validation
is restricted by the limitations of IC, so other validation techniques (e.g. double-labelled water)
can be used to study this method in these children.
Although limited to a selected group of patients, clinical implementation of the ventilator-
derived method will provide a more reliable determination of REE. Continuous provision of
values will help to visualise the course of REE values during PICU stay and thereby allow early
detection of changes in REE, as can be expected in septic neonates, children with fever and
neonates after surgery (Chapter 1). In order to do so, VCO
2
values from the ventilator need to
be automatically registered by the patient data management system and recalculated into REE
based on the previously validated metabolic equation
13
. Measurements with more than 10%
fluctuation in VCO
2
will need to be discarded automatically. Based on the remaining steady-
state VCO
2
measurements, mean REE values can be provided to the attending clinicians to
guide nutritional therapy. Although repeated measurements of REE improved outcome in
geriatric patients following surgery
14
and showed a trend towards improved hospital mortality
inmechanically ventilated adults
15
, a single determination of REE is sufficient to guide nutrition
in the majority of critically ill children. Repeated measurements may be useful only in children
with suspected metabolic alterations or malnutrition
16
.
Use of REE to guide nutritional support
In contrast with the paediatric guidelines, results from recent large RCTs in the adult ICU
question the need for matching REE by the enteral route during the acute phase of critical
illness. No differences in mortality or other clinical outcome measures were found between
permissive underfeeding and planned delivery of a full amount of nonprotein calories in
critically ill adults
17,18
. Moreover, no faster recovery was observed in critically ill adults receiving
more than 30% of the caloric goal by the enteral route compared to adults receiving less than
30% during the first week of the adult version of the PEPaNIC trial (EPaNIC trial)
19
. Finally,
endogenous energy production during the acute phase of critical illness limits the use of
exogenous provided energy. The optimal amount of required energy to supplement this
endogenous production cannot be measured by IC.
Therefore, emphasis on measurement of REE to guide nutritional therapy is likely to shift to
subsequent phases of critical illness, aimed at restoration of lean body mass while synthesis
of excess fat mass should be avoided. This is already practiced in the NICU, where longitudinal
IC measurements are mainly used to guarantee appropriate growth for this population
20,21
.
However, these phases are characterised by weaning or even absence of ventilatory support
(Chapter 1), limiting the use of IC or ventilator-derived values. Moreover, independently of
the phase, application of IC in preterm infants is extremely challenging and therefore hardly
practiced outside research settings. In absence of REE measurements, early initiation of
nutrition is aspired in all preterm infants (Chapter 5), irrespective of severity of illness
22
.