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

Background & aims: 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. Methods: VCO2-values were simultaneously collected in mechanically ventilated children from IC (Deltatrac®) and Servo-I® ventilator on a minute base over at least 10 min 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. Results: 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 ≥15 kg. 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 <15 kg. Conclusions: In children ≥15 kg, 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.

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