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

Testing of a proprietary indirect calorimeter (MGM, Jr.) was performed by using nitrogen displacement and added carbon dioxide to simulate oxygen consumption (VO2), carbon dioxide production (VCO2), and the respiratory quotient (RQ; VCO2/VO2). Errors in measured VO2, VCO2, and RQ were less than or equal to 2.5% when VO2 and VCO2 were 4-43 mL/min and flow rate was 100-2000 mL/min. The relative error in predicted VO2 was increased as the inspired oxygen concentration (FiO2) was raised but the error was less than 4% when the value of FiO2 minus expired oxygen concentration (FeO2) was greater than or equal to 0.015 and the FiO2 was less than or equal to 0.6. Sixteen studies were performed on seven very-low-birth-weight (VLBW), mechanically ventilated infants aged less than or equal to 11 d. VO2 was 8.37 +/- 1.81 mL.kg-1.min-1, VCO2 was 8.15 +/- 2.03 mL.kg-1.min-1, and RQ was 0.969 +/- 0.061 (means +/- SD). The MGM, Jr. is accurate for studies of low-birth-weight infants on mechanical ventilators when VO2 and VCO2 are greater than or equal to 4 mL/min, flow rate is less than or equal to 3000 mL/min, and FiO2 is less than or equal to 0.6. Clinical testing resulted in values similar to previously published data but the variability was higher.