Comparison of the Q-NRG+ Indirect Calorimetry Device Versus the V(Max) Encore Device in Mechanically Ventilated Children

Indirect calorimetry allows accurate measurement of energy expenditure in this population but current technology is cumbersome and time-consuming, and has many limitations that exclude a majority of criticaly ill children. A new device was recently developed to address some of the limitations of IC devices and is widely endorsed for IC measurements in critically ill adults. The Q-NRG+ IC device incorporates an easier gas calibration technique to facilitate faster start up, and a micro-mixing chamber (2ml) allows rapid achievement of steady state gas exchange measurement. The device may address some of the current barriers for the use of indirect calorimetry in critically ill children. A device with short calibration time and reliable measurements could enhance the ability of clinicians to deliver individualized energy prescriptions for patients.

Description of Study Treatments

Following informed consent, the following steps will be followed for the study procedure:

1. The two testing indirect calorimetry devices will be tested in an alternating fashion for each enrolled patient, therefore it will be decided the V(max) will be tested first in the first enrolled patient then the Q-NRG+ second. Each enrolled patient subsequently will alternate in which device is tested first.
2. The first device will be connected to the patient, after calibration, and data collection will begin for a maximum duration of 30 minutes.
3. At the end of the first testing period, the first device will be disconnected and the second device will be connected to the study patient.
4. Data collection for the second device will then begin for a maximum duration of 30 minutes.
5. At the end of the testing period, the data collected for the V(max) device will be discussed with the parents and the clinical team. Data collected from the Q-NRG+ will not be shared with the clinical team or family as this device is still being investigated in the pediatric population.
6. The study will then conclude.

Definitions of Outcomes/Endpoints The primary variables to be collected are steady state measurements of VO2 and VCO2 from both indirect calorimetry devices. Steady state will be defined as a period of greater than five minutes with coefficient of variation of the VO2 and VCO2 measurements of less than 10%. If steady state is not achieved, energy calculations will not be included in data analysis. Secondary variables to be collected include total time to obtain indirect calorimetry measurement, from arrival at the bedside to completion of the study. Steady state conditions will be defined using existing institutional practice.

Data Collection Methods and Assessments Descriptive characteristics will also be collected for each patient including age, weight, height, diagnosis, severity of illness, length of ICU stay, vital signs, and ventilator settings. We will also collect endotracheal tube size, presence of cuff, leak percentage. We will also collect information about medications, including inotropes and vasopressors, sedation medications (as well as SBS score) and nutrition parameters. Markers of inflammation, WBC and CRP will be collected from the patient chart.

Statistical Analysis Descriptive statistics will be computed for measured REE, VO2 and VCO2 and Bland-Altman analysis will be utilized to quantify the mean bias and limits of agreement between devices. Acceptable limits of agreement between the devices will be +/- 20%. VO2, CO2 will be reported as means (SD). The time to steady state and total time of IC measurement will be compared using a T-test (if normally distributed) or Mann-Whitney U-test (if not normally distributed).