Accuracy of flow and sensors of indirect calorimetry for neonates and infants: Using mass spectrometry and a pneumotachogram

Summary 1. The accuracy of measurements of flow rate and concentrations of O2 and CO2 in expiratory gas by indirect calorimetry (IC) using paediatric and adult circuits were assessed by mass spectrometry and a pneumotachogram, which have been proven as the most reliable instruments for these purposes. 2. In the paediatric circuit, all measurements were demonstrated to be reliable: error rates for flow rate, O2 concentration and CO2 concentration were +3.13, +2.66 and −6.63%, respectively. All were within the 10%, which is acceptable as a biological error. 3. However, in the adult circuit of IC, all measurements were reliable except for measurements of CO2 concentration: error rates for flow rate, O2 concentration and CO2 concentration were +2.82, +1.64 and +11.42%, respectively. 4. A fluctuation phenomenon of expiratory gas concentration was observed only in IC. Mass spectrometry did not show this phenomenon. This phenomenon seems to be derived from the IC machine itself.