Mechanically Ventilated, Cardiothoracic Surgical Patients Have Significantly Different Energy Requirements Comparing Indirect Calorimetry and the Penn State Equations

Background: Nutrition equations have been validated with indirect calorimetry for determining energy needs in intensive care unit (ICU) populations. This study tested the hypothesis that mechanically ventilated cardiothoracic surgical patients would have significantly different energy requirements when determined by indirect calorimetry vs the Penn State equations.

Materials and methods: This single-center, retrospective cohort analysis of consecutive cardiothoracic surgical patients adhered to a prospectively designed protocol for indirect calorimetry energy measurements. Energy needs were estimated by Penn State equations 2010 and 2003b and then indirect calorimetry.

Results: Analyzed patients (n = 71) had a mean ± SD difference of 556 ± 543 calories/d between indirect calorimetry and Penn State formulae, as well as a mean ± SD percentage caloric difference of 32% ± 31% (95% confidence interval [CI], -20 to 87) with a range of 1311 calories (minimum difference, -379; maximum difference, 933). There was a 10% or greater difference in resting metabolic rate between indirect calorimetry and the Penn State equations in 89% of patients (95% CI, 79%-95%). Based on Lin's concordance correlation of 0.20 (95% CI, 0.09-0.32), the strength of agreement between the resting metabolic rates determined by indirect calorimetry compared with the Penn State equations was poor within this patient sample. Indirect calorimetry performance showed a 10% increase in caloric need in 77% of patients and was associated with a nutrition prescription change in 66%.

Conclusions: Mechanically ventilated cardiothoracic surgical ICU patients appear to have higher energy requirements by indirect calorimetry than those determined by Penn State equations. Future studies targeting indirect calorimetry in relation to clinical outcomes are needed.