In vitro validation of indirect calorimetry device developed for the ICALIC project against mass spectrometry

Accurate evaluation of the energy needs is required to optimize nutrition support of critically ill patients. Recent evaluations of indirect calorimeters revealed significant differences among the devices available on the market. A new indirect calorimeter (Q-NRG^®, Cosmed, Roma, Italy) has been developed by a group of investigators supporting the international calorimetry study initiative (ICALIC) to achieve ultimate accuracy for measuring energy expenditure while being easy to use, and affordable. This study aims to validate the precision and the accuracy of the Q-NRG^® in the in-vitro setting, within the clinically relevant range for adults on mechanical ventilation in the ICU. Mass spectrometry is the reference method for the gas composition analysis to evaluate the analytic performances of the Q-NRG^®.

The accuracy and precision of the O₂ and CO₂ measurements by the Q-NRG were evaluated by comparing the measurements of known O₂ and CO₂ gas mixtures with the measurements by the mass spectrometer (Extrel, USA). The accuracy and precision of the Q-NRG^® for measurements of VO₂ (oxygen consumption) and VCO₂ (CO₂ production) at clinically relevant ranges (150, 250 and 400 ml/min STPD) were evaluated by measuring simulated gas exchange under mechanically ventilated setting at different FiO₂ settings (21-80%), in comparison to the reference measurements by the mass spectrometer-based mixing chamber system.

The measurements of gas mixtures of predefined O₂ and CO₂ concentrations by the Q-NRG^® were within 2% accuracy versus the mass spectrometer measurements in Passing Bablok regression analysis. In a mechanically ventilated setting of FiO₂ from 21 up to 70%, the Q-NRG^® measurements of simulated VO₂ and VCO₂ were within 5% difference of the reference mass spectrometer measurements.

In vitro evaluation confirms that the accuracy of the Q-NRG^® indirect calorimeter is within 5% at oxygen enrichment to 70%; i.e. maximum expected for clinical use. Further recommendations for the clinical use of the Q-NRG^® by will be released once the ongoing multi-center study is completed.