TECHNICAL AND METHODOLOGIC CONSIDERATIONS FOR PERFORMANCE OF INDIRECTCALORIMETRY IN VENTILATED AND NONVENTILATED PRETERM INFANTS

Objective: To evaluate and refine indirect calorimetry measurement tec hniques so that accurate metabolic measurements can be performed in me chanically ventilated and convalescing preterm infants who require sup plemental oxygen, Design: Laboratory validation of an indirect calorim eter; clinical and laboratory assessments of technical problems in per forming metabolic measurements; and clinical indirect calorimetry stud ies in mechanically ventilated and nonventilated preterm infants, Sett ing: Neonatal intensive care unit (ICU) in a tertiary care university hospital. Patients: Level II and level III mechanically ventilated (n = 10) and nonventilated (n = 14) neonatal ICU patients who required FI O2 levels ranging from 0.21 to 0.42, Interventions: None, Measurements and Main Results: System calibration was assessed by combustion of 10 0% ethanol; the mean respiratory quotient was 0.667 +/- 0.001 (SEM). I n addition, oxygen consumption (VO2) and CO2 production (VCO2) were si mulated by CO2/nitrogen infusions within the range expected for 0.5- t o 7-kg infants. Mean relative errors were 0.6 +/- 0.3% and 1,8 +/- 0.3 % for expected VO2 and VCO2 values, respectively. In 27 mechanically v entilated patients with no audible endotracheal tube leak, measured en dotracheal tube leak ranged from 0.0% to 7.5%. Fluctuations in FIO2 du ring mechanical ventilation were monitored in 30-min studies, using wa ll-source (n = 27) or tank-source (n = 11) supplemental oxygen. Mean F IO2 variation was 0.00075 +/- 0.00013 vs. 0.00011 +/- 0.00001 using wa ll-source and tank-source oxygen, respectively, Some of the difficulti es of obtaining accurate measurements in supplemental hood oxygen stud ies were overcome by using tank-source vs, wall-source oxygen and a un ique hood design. Conclusions: Accurate indirect calorimetry studies c an be performed in both ventilated and nonventilated infants weighing as little as 500 g, providing that sufficient attention is paid to tec hnical and methodologic measurement details.