Introducing a new generation indirect calorimeter for estimating energy requirements in adult intensive care unit patients: feasibility, practical considerations, and comparison with a mathematical equation

Abstract

Purpose: Indirect calorimetry (IC) is increasingly advocated for individualizing nutritional therapy in critically ill adult patients, but questions remain regarding its practical implementation.

Materials and methods: During 12 weeks, we prospectively assessed utility and practical aspects of IC use. Adult medico-surgical intensive care unit (ICU) patients were daily screened for malnutrition. Indirect calorimetry was planned in subjects considered unable to meet energy requirements on day 3 after admission. Measured energy expenditure (MEE) was compared with calculated (resting/total) energy expenditure.

Results: A total of 940 evaluations were performed in 266 patients (age, 63±16 years; 59% males; Acute Physiology and Chronic Health Evaluation II score, 14±8). A total of 230 patients (86.5%) were at risk for malnutrition, and in 118 of them, IC was indicated. Practical considerations precluded measurements in 72 cases (61%). Forty-six calorimetric evaluations revealed an MEE of 1649±544 kcal per 24 hours that poorly correlated with calculated resting energy expenditure (r2=0.19) and calculated total energy expenditure (r2=0.20). Indirect calorimetry measurements were not time-consuming.

Conclusions: Indirect calorimetry was indicated in half but effectively performed in only 20% of a representative intensive care unit population at risk for malnutrition. Correlation between MEE and CEE was poor.

Clinical relevancy statement: Indirect calorimetry is increasingly advocated for individualizing nutritional therapy in critically ill adult patients. Practical feasibility is tested in this study. Large differences between measured and calculated energy expenditure are observed. Together with patients' characteristics, feasibility results can guide clinicians or institutes in using IC in their daily clinical practice.

Keywords: Critically ill; Energy requirements; Indirect calorimetry; Nutrition.