Assessing energy expenditure: Accuracy of predictive equations versus indirect calorimetry in older hospitalized patients at the medical ward

Abstract

Background & aims: Indirect calorimetry (IC) is considered the gold standard to measure Resting Energy Expenditure (REE) in clinical practice. However, this method is more time-consuming than using estimates. Therefore, this study aimed to determine 1) the accuracy between estimated and measured energy requirement and 2) if certain patient characteristics were associated with discrepancies between measured and estimated energy requirement.

Methods: The patient's measured REE was assessed with IC. To determine Total Energy Expenditure (TEE), an individual level of activity was applied. The measured REE and TEE were compared with the Harris-Benedict (H-B) equation and measured TEE with two weight-based formulas. A variation of ±10 % was regarded as an acceptable value of variation. To explore whether specific variables were related to differences between measurements and estimates, the following variables were recorded: age, Body Mass Index (BMI), body temperature, heart rate, Mean Arterial Pressure (MAP), respiratory rate, p-C-Reactive Protein (p-CRP), B-Leucocytes, and p-Albumin.

Results: We included 110 patients (58 % women), mean age 81.5 (±7.6) years. The H-B equation most accurately predicted REE for n = 56 (51 %) and TEE for n = 57 (52 %). The H-B equation tended to underestimate REE n = 35 (32 %) rather than overestimate n = 18 (16 %). Underestimation by the H-B equation was significantly (p < 0.05) associated with having higher p-CRP, heart rate, body temperature, and B-Leucocytes. Including these variables with a significant association in a multiple linear regression model revealed that only 17 % (r² = 0.170) of the variation could be explained by these variables.

Conclusion: The H-B equation was most accurate at predicting energy expenditure, however, only in alignment with IC measurements in about half of the patients. Several infectious markers were associated with an increase in REE compared with estimated by the H-B equation.

Keywords: Energy requirement; Geriatrics; Indirect calorimetry.