Technical and clinical testing of a computerized indirect calorimeter for use in mechanically ventilated neonates

Abstract

Testing of a proprietary indirect calorimeter (MGM, Jr.) was performed by using nitrogen displacement and added carbon dioxide to simulate oxygen consumption (V̇O2), carbon dioxide production (V̇CO2), and the respiratory quotient (RQ; V̇CO2/V̇O2). Errors in measured V̇O2, V̇CO2, and RQ were ≤ 2.5% when V̇O2 and V̇CO2 were 4-43 mL/min and flow rate was 100-2000 mL/min. The relative error in predicted V̇O2 was increased as the inspired oxygen concentration (FiO2) was raised but the error was < 4% when the value of FiO2 minus expired oxygen concentration (FeO2) was ≥ 0.015 and the FiO2 was ≤ 0.6. Sixteen studies were performed on seven very-low-birth-weight (VLBW), mechanically ventilated infants aged ≤ 11 d. V̇O2 was 8.37 ± 1.81 mL·kg-1·min-1, V̇CO2 was 8.15 ± 2.03 mL·kg-1·min-1, and RQ was 0.969 ± 0.061 (x̄ ± SD). The MGM, Jr. is accurate for studies of low-birth-weight infants on mechanical ventilators when V̇O2 and V̇CO2 are ≥ 4 mL/min, flow rate is ≤ 3000 mL/min, and FiO2 is ≤ 0.6. Clinical testing resulted in values similar to previously published data but the variability was higher.