Comparative characteristics of some methods for estimating energy expenditure in critically ill mechanically ventilated patients

Abstract

Aim: To compare the energy expenditure (EE) assessed by ventilator-derived carbon dioxide production (EE–VCO2-ventilator) and the energy expenditure calculated from six predictive equations with the gold standard energy expenditure measured with indirect calorimetry (IC) in mechanically ventilated patients. Materials and methods: This is a prospective, non-randomized, one-month study which included six mechanically ventilated patients with FiO2 <60% and PEEP <10 mbar. Thirty-minute measurements were taken using a Cosmed Q-NRG+ metabolic monitor. The average ventilator-derived VCO2 from the Drager Evita Infinity V500 respirator (VʹCO2, ml/min) was calculated for the same period. The IC-measured EE (MEE-IC) was compared with EE–VCO2-ventilator by a formula proposed in ESPEN (8.19×VCO2) and with six predictive equations. Results: Mean MEE-IC was 1650±365 kcal. Mean measured EE–VCO2-ventilator was 1669±340 kcal. A statistically nonsignificant difference was found between the two measurements (p=0.84, correlation coefficient 0.98). Of the predictive equations we compared, the best correlation to the reference method was the Penn State 3 with mean EE of 1679±356 (p=0.81, correlation coefficient of 0.78). Conclusions: In critically ill mechanically ventilated patients, the assessment of EE based on a ventilator-derived VCO2 is an alternative to IC and is more accurate than most predictive equations.