Accuracy of an indirect calorimeter for mechanically ventilated infants and children: the influence of low rates of gas exchange and varying FIO2.
OBJECTIVE
To test the accuracy and validity of the Deltatrac II MBM-200 metabolic monitor for use in mechanically ventilated infants and children in the pediatric intensive care unit.


METHODS
Laboratory validation of an indirect calorimeter with a ventilated lung model. The influence of low tidal volumes and low levels of oxygen consumption (V(O2)) and carbon dioxide production (V(CO2)) in combination with different levels of inspired oxygen concentrations (F(IO2)) was investigated.


METHODS
University research laboratory.


METHODS
Low tidal volumes were provided with two intermittent flow types of ventilators, a Servo 300 and a Servo 900C.


METHODS
A butane flame with a V(O2) approximating 20 mL/min and 40 mL/min was ventilated. To investigate the effect of different levels of F(IO2) on the accuracy of V(O2), V(CO2), and respiratory quotient (RQ), measurements were performed at F(IO2) target values of 0.25, 0.40, and 0.60.


RESULTS
No significant differences were found between the ventilators regarding V(O2), V(CO2), and RQ measurements. The mean deviation of V(O2) increased significantly with increasing F(IO2) to -7.98% with a V(O2) of 21.0 mL/min and to -8.46% with a V(O2) of 38.9 mL/min (F(IO2), 0.558) with a variability (2 SD) of +/- 4.86% and +/- 6.82%, respectively. The mean deviation and variability of V(CO2) in all tests remained within 8%. The mean deviation of RQ increased significantly with increasing F(IO2) to 5.5% with a V(O2) of 21.0 mL/min and to 5.69% with a V(O2) of 38.9 mL/min (F(IO2), 0.558) with a variability (2 SD) of +/- 5.62% and +/- 5.76%, respectively. The minute to minute delivered F(IO2) fluctuated significantly when increasing the level of F(IO2).


CONCLUSIONS
The Deltatrac II MBM-200 metabolic monitor appears accurate for low levels of V(O2) and V(CO2) during mechanical ventilation with F(IO2) levels up to 0.390. With increasing F(IO2) to 0.558, the increase in deviation of V(O2) for single measurements can be of clinical relevance for mechanically ventilated infants and children. The increased fluctuation of delivered F(IO2) on higher levels of F(IO2) is likely the cause of the inaccuracy.
Joosten
K F
KF
Department of Pediatrics, Erasmus University Rotterdam, The Netherlands. joosten@alkg.azr.nl
Jacobs
F I
FI
van Klaarwater
E
E
Baartmans
M G
MG
Hop
W C
WC
Meriläinen
P T
PT
Hazelzet
J A
JA
D002153:Calorimetry, Indirect; D002648:Child; D006801:Humans; D011659:Pulmonary Gas Exchange; D015203:Reproducibility of Results; D012121:Respiration, Artificial