External Validation with Accuracy Confounders of VCO(2)-Derived Predicted Energy Expenditure Compared to Resting Energy Expenditure Measured by Indirect Calorimetry in Mechanically Ventilated Children

Optimal energy provision, guided by measured resting energy expenditure (REE) and determined by indirect calorimetry (IC), is fundamental in Intensive Care Units (ICU). Because IC availability is limited, methods to predict REE based on carbon dioxide production (VCO(2)) measurements (REE(VCO2)) alone have been proposed as a surrogate for REE measured by IC (REE(IC)). The study aimed at externally and internally validating the accuracy of the REE(VCO2) as an alternative to REE(IC) in mechanically ventilated children. A ventilator’s integrated gas exchange module (E-COVX) was used to prospectively measure REE(IC) and predict REE(VCO2) on 107 mechanically ventilated children during the first 24 h of admission. The accuracy of the REE(VCO2) compared to REE(IC) was assessed through the calculation of bias and precision, paired median differences, linear regression, and ROC analysis. Accuracy within ±10% of the REE(IC) was deemed acceptable for the REE(VCO2) equation. The calculated REE(VCO2) based on respiratory quotient (RQ) 0.89 resulted in a mean bias of −72.7 kcal/day (95% limits of agreement −321.7 to 176.3 kcal/day) and a high coefficient of variation (174.7%), while 51.4% of the calculations fell outside the ±10% accuracy rate. REE(VCO2) derived from RQ 0.80 or 0.85 did not improve accuracy. Only measured RQ (Beta 0.73, p < 0.001) and no-recorded neuromuscular blocking agents (Beta −0.13, p = 0.044) were independently associated with the REE(VCO2)−REE(IC) difference. Among the recorded anthropometric, metabolic, nutrition, or clinical variables, only measured RQ was a strong predictor of REE(VCO2) inaccuracy (p < 0.001). Cutoffs of RQ = 0.80 predicted 89% of underestimated REE(IC) (sensitivity 0.99; specificity 0.89) and RQ = 0.82 predicted 56% of overestimated REE(IC) (sensitivity of 0.99; specificity 0.56). REE(VCO2) cannot be recommended as an alternative to REE(IC) in mechanically ventilated children, regardless of the metabolic, anthropometric, or clinical status at the time of the evaluation.