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Use of indirect calorimetry to detect overfeeding
73
4
METHODS
Neonates and children up to the age of 18 years admitted to our level III multidisciplinary PICU
were consecutively included in the study when they met the criteria for indirect calorimetric
measurements: mechanical ventilation with a Servo ventilator (Siemens-Elema, Solna,
Sweden); FiO
2
<0.6, tube leakage <10% and hemodynamic stable condition (blood pressure
and heart rate within 2 standard deviation (SD) of age-related values).
The institutional review board of the Erasmus MC approved the study protocol, and written
parental informed consent was obtained before children entered the study. Data, including
age, sex, weight, primary diagnosis, surgical status, days on mechanical ventilation, length of
ICU stay, route of nutritional support, and energy and macronutrient intake were recorded. The
severity of illness on admission was assessed by the Pediatric Risk of Mortality score (PRISM)
31
.
Nutritional status on admission was defined by weight for age (WFA) SD-scores using Dutch
Growth Standards
32
; children were categorized as underweight if their WFA SD-score was <-2.
Indirect calorimetrymeasurementswereperformedas soonaspossibleafter admission.Oxygen
consumption (VO
2
) and carbon dioxide production (VCO
2
), standardized for temperature,
barometric pressure, and humidity were measured for at least 2 hours using the Deltatrac®
(Datex Division Instrumentarium, Helsinki, Finland) metabolic monitor. Measured REE (mREE)
was calculated with the modified Weir formula
33
. The properties of the Deltatrac® metabolic
monitor have been described previously
34
. The RQ was calculated from the measured VO
2
and
VCO
2
levels
24
.
Children were fed enterally and/or parenterally according to the local feeding protocol
25
and
the judgement of the attending physician. A glucose infusion was provided during the first 12
to 24 hours after admission aimed at a carbohydrate intake of 4 to 6mg/kg/min (children<30kg)
or 2 to 4 mg/kg/min (>30kg)
35,36
. Enteral nutrition (EN), consisting of human milk or standard
formula, was started as soon as possible in all patients, either continuously or intermittently
through a postpyloric or nasogastric tube. PN was started within 48 hours after admission in
case of insufficient EN, either by peripheral infusion or by central venous access. Fluid and
electrolyte intakes were adjusted to individual requirements.
Energy goals for EN were based on the body weight-based Schofield equation
37
on the first day
of admission and on the Recommended Dietary Allowances for the subsequent length of stay
(Dietary Reference Intake: energy, protein and digestible carbohydrates, 2001, Health Council
of the Netherlands: The Hague). Parenteral energy goals were based on the weight-based
guidelines of the European Society of Paediatric Gastroenterology, Hepatology and Nutrition
(ESPGHAN) throughout PICU stay
38
. Actual total daily intake of energy, carbohydrate, protein
and fat were derived from patient records on the day of calorimetry.