Application of indirect calorimetry in monitoring the feeding of small premature infants

Background: We investigated the practical use of indirect calorimetry for t he individual nutritional support of preterm infants in order to answer the question whether it is possible to reliably calculate energy expenditure, fat and carbohydrate oxidation in preterm infants individually by using the results of a timed B-hour-measurement of oxygen consumption and carbon dio xide production. Patients: Measurements were performed in 20 preterm infants (gestational ag e 30.2+/-9.6 weeks, birth weight 1.09 +/- 0.07; mean +/- SEM) at a mean pos tnatal age of 25 +/- 4 days and with a body weight of 1.35 +/- 0.06 kg. Methods: Carbon dioxide production (24h-VCO2), oxygen consumption (24 h-VO2 ) and respiratory quotient (24h-RQ) were measured by indirect calorimetry f or 24 hours using the Deltatrac(R) II metabolic monitor (Datex, Helsinki, F inland). Additionally, 6 h-VCO2, 6 h-VO2 and 6h-RQ were determined by measu rement over 6 hours. The patients' energy expenditure, fat and carbohydrate oxidation were calculated from VCO2 and VO2 measured over a 24 hour- and 6 hour-period with or without consideration of urinary nitrogen excretion (N -U). Results: If N-U was not included in the calculation of energy expenditure, the values differed by maximally 1.1% from the calculations including N-U. The correlations between the 24h-RQ and the calculated 24h-fat or 24h-carbo hydrate oxidation values were statistically significant (r = - 0.99; p = 0. 0001 and r = 0.773; p = 0.0002 respectively). However, in individual patien ts, it was not possible to predict 24 h energy expenditure, fat and carbohy drate oxidation of preterm infants using values determined by 6 h indirect calorimetry. Conclusion: The determination of the urine-nitrogen excretion is not necess ary for calculation of energy expenditure of preterm infants. It is possibl e to estimate fat and carbohydrate oxidation of preterm infants by the meas ured 24 h-RQ, but 6 h indirect calorimetry is not accurate enough for calcu lating the individual nutritional needs of preterm infants in clinical prac tice. Indirect calorimetry over 24 h may be helpful in the management of se lected patients with nutritional problems.