Validation of ventilator-derived VCO2 measurements to determine energy expenditure in ventilated critically ill children

Abstract

Indirect calorimetry (IC) is considered the gold standard to determine resting energy expenditure (REE) but its availability in PICUs worldwide is limited. Ventilator-derived VCO2 could potentially improve the possibility of performing REE measurements. We investigated whether ventilator-derived VCO2 values are comparable to IC-derived VCO2 values and can clinically be used in clinical practice to determine REE. VCO2-values were simultaneously collected in mechanically ventilated children from IC (Deltatrac®) and Servo-I® ventilator on a minute base over at least 10min period of steady state. REE was calculated using the modified Weir formula (for IC) or REE=5.5*VCO2 (L/min)*1440 (for the Servo-I values) and compared with frequently used predictive equations by Schofield and the WHO to calculate REE. Measurements were performed in 41 children; median age 2 years. The mean relative difference between VCO2 measured by IC and Servo-I® was 15.6% (p=0.002), and limits of agreement in the Bland-Altman analysis were wide. Comparable measurements, defined as a difference ≤10% between IC and Servo-I® VCO2 values, were seen in 18 (44%) children, but this proportion was 70% in children ≥15kg. In this group, REE could be accurately predicted using Servo-I® derived VCO2 values and this method was superior to the use of predictive equations. The Servo-I® derived VCO2 values were not sufficiently accurate for the large proportion of children weighing <15kg. In children ≥15kg, VCO2 measurements of the Servo-I® seem sufficiently accurate for use in clinical practice and may be used to determine energy expenditure in the future.