title: Can calculation of energy expenditure based on CO2measurements replace indirect calorimetry?
abstract: Methods to calculate energy expenditure (EE) based on CO2measurements (EEVCO2) have been proposed as a surrogate to indirect calorimetry. This study aimed at evaluating whether EEVCO2could be considered as an alternative to EE measured by indirect calorimetry.
  
  
  
  Indirect calorimetry measurements conducted for clinical purposes on 278 mechanically ventilated ICU patients were retrospectively analyzed. EEVCO2was calculated by a converted Weir's equation using CO2consumption (VCO2) measured by indirect calorimetry and assumed respiratory quotients (RQ): 0.85 (EEVCO2_0.85) and food quotient (FQ; EEVCO2_FQ). Mean calculated EEVCO2and measured EE were compared by paired t test. Accuracy of EEVCO2was evaluated according to the clinically relevant standard of 5% accuracy rate to the measured EE, and the more general standard of 10% accuracy rate. The effects of the timing of measurement (before or after the 7th ICU day) and energy provision rates (<90 or ≥90% of EE) on 5% accuracy rates were also analyzed (chi-square tests).
  
  
  
  Mean biases for EEVCO2_0.85 and EEVCO2_FQ were -21 and -48 kcal/d (p = 0.04 and 0.00, respectively), and 10% accuracy rates were 77.7 and 77.3%, respectively. However, 5% accuracy rates were 46.0 and 46.4%, respectively. Accuracy rates were not affected by the timing of the measurement, or the energy provision rates at the time of measurements.
  
  
  
  Calculated EE based on CO2measurement was not sufficiently accurate to consider the results as an alternative to measured EE by indirect calorimetry. Therefore, EE measured by indirect calorimetry remains as the gold standard to guide nutrition therapy.
authors.affiliation: Clinical Nutrition, Geneva University Hospital, Rue Gabrielle-Perret-Gentil 4, 1211, Geneva 14, Switzerland. Oshima.Taku@hcuge.ch.
authors.forename: Taku
authors.identifier: 0000-0002-3868-8272
authors.initials: T
authors.lastname: Oshima
authors.affiliation: Clinical Nutrition, Geneva University Hospital, Rue Gabrielle-Perret-Gentil 4, 1211, Geneva 14, Switzerland.
authors.forename: Séverine
authors.initials: S
authors.lastname: Graf
authors.affiliation: Adult Intensive Care, Geneva Universtiy Hospital, Rue Gabrielle-Perret-Gentil 4, Geneva 14, 1211, Switzerland.
authors.forename: Claudia-Paula
authors.initials: CP
authors.lastname: Heidegger
authors.affiliation: Clinical Nutrition, Geneva University Hospital, Rue Gabrielle-Perret-Gentil 4, 1211, Geneva 14, Switzerland.
authors.forename: Laurence
authors.initials: L
authors.lastname: Genton
authors.affiliation: Adult Intensive Care, Geneva Universtiy Hospital, Rue Gabrielle-Perret-Gentil 4, Geneva 14, 1211, Switzerland.
authors.forename: Jérôme
authors.initials: J
authors.lastname: Pugin
authors.affiliation: Clinical Nutrition, Geneva University Hospital, Rue Gabrielle-Perret-Gentil 4, 1211, Geneva 14, Switzerland.
authors.forename: Claude
authors.initials: C
authors.lastname: Pichard
mesh_terms: D000328:Adult; D000368:Aged; D002153:Calorimetry, Indirect / Q000379:methods*; D002245:Carbon Dioxide / Q000032:analysis* / Q000097:blood; D004734:Energy Metabolism / Q000502:physiology*; D005260:Female; D006801:Humans; D007362:Intensive Care Units / Q000458:organization & administration; D008297:Male; D008875:Middle Aged; D011659:Pulmonary Gas Exchange / Q000502:physiology; D012189:Retrospective Studies; D013557:Switzerland
chemical_list: D002245:Carbon Dioxide
keywords: Accuracy; Critical care; Energy expenditure; Indirect calorimetry