Determinants of energy expenditure in ventilated preterm infants.

The purpose of this study was to determine oxygen consumption (VO2), carbon dioxide production (VCO2), and energy expenditure (EE) in a group of preterm ventilated infants during the first 3 weeks of life, and to determine the major factors that influence EE. Thirty-eight indirect calorimetry studies were performed in 18 ventilated infants with mean gestational age of 27.9 +/- 0.6 (SEM) weeks. The relationship of demographic factors, nutrient intake, and severity of illness assessments of EE were determined by regression analysis. Repeated measure analysis was performed for the effect of multiple studies in the same patient. Although VO2, VCO2, and EE all tended to increase over the first 3 weeks of life, there was a wide range of values. EE was best predicted by nonprotein calorie intake and postnatal age, while there was no correlation with birthweight, weight at the time of study, gestational age, protein intake, or severity of illness. Multiple regression analyses demonstrated a strong interaction between PNA and EI. In this population EE is best predicted by PNA and EI. The interactive effect between PNA and EI on EE is probably explained by the clinical practice of daily increments in substrate intake in these patients.

Fatal meconium aspiration in spite of appropriate perinatal airway management: pulmonary and placental evidence of prenatal disease.

OBJECTIVE: Our purpose was to summarize eight cases of fatal meconium aspiration syndrome where pathologic review showed evidence of chronic prenatal disease and to compare these findings with those of a group of control infants and fetuses who died of other causes. STUDY DESIGN: A 15-year retrospective chart review identified the infants who died of meconium aspiration within 48 hours of life and who also had autopsies performed. Neonatal pulmonary and available placental pathologic findings are described from these study infants and are compared with published norms and with autopsy results from a group of control infants and fetuses. RESULTS: Seven of the eight study infants underwent suctioning of the trachea immediately after birth. In all eight cases the neonatal lungs demonstrated histologic evidence of significant hypoxic changes of a chronic nature with onset before birth. The available placentas showed variable but significant abnormalities that support a case for subacute or chronic in utero compromise. CONCLUSIONS: As in other reports, there is evidence that meconium aspiration may be a prenatal rather than a postnatal disease. However, this is the first study that presents evidence on the basis of both pulmonary and placental pathologic findings and reinforces the importance of placental examinations in complicated pregnancies.

Technical and methodologic considerations for performance of indirect calorimetry in ventilated and nonventilated preterm infants.

OBJECTIVE: To evaluate and refine indirect calorimetry measurement techniques so that accurate metabolic measurements can be performed in mechanically ventilated and convalescing preterm infants who require supplemental oxygen. DESIGN: Laboratory validation of an indirect calorimeter; clinical and laboratory assessments of technical problems in performing metabolic measurements; and clinical indirect calorimetry studies in mechanically ventilated and nonventilated preterm infants. SETTING: 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 FIO2 levels ranging from 0.21 to 0.42. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: System calibration was assessed by combustion of 100% ethanol; the mean respiratory quotient was 0.667 +/- 0.001 (SEM). In addition, oxygen consumption (Vo2) and CO2 production (Vco2) were simulated by CO2/nitrogen infusions within the range expected for 0.5- to 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 ventilated patients with no audible endotracheal tube leak, measured endotracheal tube leak ranged from 0.0% to 7.5%. Fluctuations in FIO2 during mechanical ventilation were monitored in 30-min studies, using wall-source (n = 27) or tank-source (n = 11) supplemental oxygen. Mean FIO2 variation was 0.00075 +/- 0.00013 vs. 0.00011 +/- 0.00001 using wall-source and tank-source oxygen, respectively. Some of the difficulties of obtaining accurate measurements in supplemental hood oxygen studies were overcome by using tank-source vs. wall-source oxygen and a unique hood design. CONCLUSIONS: Accurate indirect calorimetry studies can be performed in both ventilated and nonventilated infants weighing as little as 500 g, providing that sufficient attention is paid to technical and methodologic measurement details.